Local- and regional-scale impacts of the ∼74 ka Toba supervolcanic eruption on hominin populations and habitats in India

Quaternary International 258 (2012) 100e118

Contents lists available at SciVerse ScienceDirect

Quaternary International journal homepage: www.elsevier.com/locate/quaint

Local- and regional-scale impacts of the w74 ka Toba supervolcanic eruption on hominin populations and habitats in India Sacha C. Jones McDonald Institute for Archaeological Research, University of Cambridge, Downing Street, Cambridge, Cambridgeshire CB2 3ER, United Kingdom

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 22 September 2011

The Toba supervolcanic eruption of w74,000 years ago is argued to have devastated Homo sapiens populations, causing a human population bottleneck. Through a combination of rapid global climatic deterioration and ecological disruption following the widespread ash-fall, this dramatic eruption, the largest in at least the last 2 million years, is hypothesized to have shaped the genetic structure and diversity of human populations today. Past assessments of Toba’s human impacts, however, have been predominantly theoretical. Using archaeological and geological evidence from sites in India, this study addresses Toba’s local-scale impacts on hominin technology, behavior, demography and habitats in two valleys in India (the Jurreru and Middle Son valleys). Using paleoclimatological and volcanological data, regional-scale impacts throughout India are inferred. A refugia hypothesis is presented that argues for variation in the scale of Toba’s impact throughout India, driven by regional differences in monsoonal dynamics, geography and topography. Areas of north-west India, the Indo-Gangetic Plain and parts of the Deccan to the east of the Western Ghats are argued to have been the most affected, whereas areas of southern and eastern India may have preserved the largest refugia for hominin populations. Ó 2011 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction Volcanic supereruptions are among Earth’s greatest natural hazards. Supervolcanoes such as Toba (Sumatra) and Yellowstone (USA) are often discussed, and both their violent past and the potential future threat they pose are sensationally described in the media (e.g. Horizon’s “Supervolcanoes”, broadcast by the BBC in 2000, and Supervolcano by the BBC in 2005). These popular portrayals, however, frequently offer an account of the most extreme outcome of a supervolcanic event. Views in the academic literature are more varied, particularly regarding the possible impacts of the w74 ka Toba supereruption on both climate and human evolution. Some argue for sudden climatic deterioration after the Toba eruption (Rampino and Self,1992, 1993a,1993b) and human population extinctions that resulted in a drastic decrease in the overall population size of Homo sapiens (Ambrose, 1998, 2003b; Rampino and Ambrose, 2000). Other more conservative interpretations argue that there is no strong evidence to support either an extreme climatic perturbation (Oppenheimer, 2002) or a dramatic human population crash (Lahr and Foley, 1998; Gathorne-Hardy and Harcourt-Smith, 2003; Petraglia et al., 2007). The w74 ka Toba supereruption was, however,

E-mail address: [email protected]. 1040-6182/$ e see front matter Ó 2011 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2011.09.017

the largest eruption of the Quaternary period and one of the largest known explosive eruptions to have ever occurred on Earth (Chesner and Rose, 1991), producing more than 2800 km3 of ejecta (Rose and Chesner, 1987). The sheer magnitude of this event should not be understated. Until recently, discussions of the relationship between Toba and H. sapiens populations have been predominantly theoretical. Ambrose (1998) and Rampino and Ambrose (2000) argued for causal associations between the Toba eruption and the following aspects of the Upper Pleistocene record; (1) a demographic bottleneck event occurring amongst H. sapiens 100e50 ka, inferred from mitochondrial DNA mismatch distributions (Harpending et al., 1993); (2) a comparable genetic bottleneck in the eastern African Chimpanzee, Pan troglodytes schweinfurthii (Rogers and Jorde, 1995; but see; Goldberg and Ruvolo, 1997; Gagneux et al., 1999; Stone et al., 2002); (3) climate change coincident with the eruption as suggested by paleoclimatic reconstructions (Rampino and Self, 1992, 1993a; Zielinski et al., 1996b); (4) low population densities in northern and southern Africa during the early part of the last glacial period, revealed by patterns of occupation in the African archaeological record (Ambrose, 1998). This evidence, however, could be interpreted as purely circumstantial; distinguishing cause from coincidence is notoriously difficult in the case of volcanic eruptions and their impacts (e.g. Torrence and Grattan, 2002b, p. 2; Grattan et al.,

S.C. Jones / Quaternary International 258 (2012) 100e118

2007). Without being able to precisely pinpoint the timing of the Toba event in the genetic and African archaeological records, and hence being unable to assess its direct impact on human populations, alternative interpretations can be offered to explain demographic patterns during the Upper Pleistocene. For example, fluctuations in population density, as seen in the African archaeological record (Ambrose, 1998), as well as the Upper Pleistocene genetic bottleneck (Harpending et al., 1993), may instead be due to the onset of Marine Isotope Stage 4 (MIS 4) and the global cooling that persisted throughout this period (w74e59 ka). Paleoclimatic data collected from ice and marine cores has been used to examine Toba’s impact on global climate (e.g. Zielinski et al., 1996a, b; Huang et al., 2001; Schulz et al., 2002), and predictive models have explored the climatic effects of Toba and supereruptions in general (e.g. Bekki et al., 1996; Jones et al., 2007; Robock et al., 2009; Timmreck et al., 2010). Pleistocene and extant Southeast Asian faunal records have been investigated to assess the extent of Toba’s impact on regional animal populations (Gathorne-Hardy and Harcourt-Smith, 2003; Louys, 2007). Several recent studies have focused on evidence from peninsular India, an area blanketed by distal Toba ash-fall (Fig. 1). Ash layers of the w74 ka Youngest Toba Tuff (YTT) form an isochronous marker horizon in numerous river valleys throughout the Indian subcontinent (Acharyya and Basu, 1993; Shane et al., 1995; Westgate et al., 1998). In some of these valleys, stone artifacts are preserved in contexts located

101

stratigraphically beneath and above the YTT layer (Jones, 2007a). Analyses have been conducted of lithic assemblages and sediments from contexts that pre-date and post-date YTT at sites in two Indian river valleys (Middle Son and Jurreru), separated by w1100 km. Data from both valleys have been compared in order to reconstruct the impacts of the Toba ash-fall on hominin lithic technology, behavior and habitats (Jones, 2007b, 2010). Other studies have discussed Toba’s impacts on the Jurreru valley exclusively (Petraglia et al., 2007; Haslam et al., 2010a), as well as on the Middle Son (Jones and Pal, 2005, 2009) and both the Middle Son and Narmada valleys (Williams et al., 2009). These studies highlight the ongoing controversy surrounding the extent of Toba’s human and environmental impacts in India (e.g. Haslam and Petraglia, 2010; Williams et al., 2010). Some argue for widespread human devastation postToba (Ambrose, 1998; Williams et al., 2009), while others argue for a minimal impact on humans (Petraglia et al., 2007). An alternative argument has been proposed that posits considerable spatial variability across India in hominin and habitat responses to the eruption (Jones, 2010). This paper expands upon this argument significantly, where, through a synthesis of all current evidence, the principal aim is to put forward the most parsimonious local- and regional-scale models of Toba’s impacts on Indian habitats and hominin demography. Three main objectives are pursued here: first, to synthesize pre-existing data from paleoclimatological and volcanological

Fig. 1. All terrestrial sites and marine cores (black circles) preserving distal YTT. Numbered locations indicate terrestrial sites preserving YTT; (1) Tejpur, Narmada valley; (2) Bori, Kukdi valley; (3) Morgaon, Karha valley; (4) Gandhigram Place, Purna valley; (5) Hindri valley; (6) Jwalapuram, Jurreru valley; (7) Sagileru valley; (8) Manneru valley; (9) Gundlakamma valley; (10) Krishna valley; (11e14) Devakachar, Hirapur, Guruwara, Pawlaghat in the Narmada valley; (15e18) Ghoghara, Ramnagar, Nakjhar and Khuteli in the Middle Son valley; (19) Pampa valley; (20) Damkelar, Indravati valley; (21) Hathipatharkhal, Nagavali valley; (22e23) Goguparu and Kareni, Vansadhara valley; (24e27) Sonepur, Pitamohul, Krushnamohanpur and Kumbia in the Mahanadi valley; (28) Samal, Brahmani valley; (29) Barakar; (30) Bogra, Bangladesh; (31) Padang Terap; (32) Kota Tampan; (33) Kapong Temong; (34) Ampang; (35) Serdang. See Jones (2007a) for further details on terrestrial YTT sites in India.

102

S.C. Jones / Quaternary International 258 (2012) 100e118

studies in order to predict the larger regional-scale environmental consequences of both climate change and the distal Toba ash-fall on environments throughout India. The second objective is to assess Toba’s local-scale impacts on hominin populations and habitats in more detail and on a much smaller geographic scale, by drawing on published data from both the Jurreru and Middle Son valleys. The aim of local-scale assessment is to use high resolution archaeological, paleoenvironmental, geological and geographical data from specific areas to make robust conclusions about local impacts. The concept of local- and regional-scale impacts of the eruption has been discussed, where the Toba event has also been contextualized within what is known about the Indian hominin paleontological, genetic and archaeological records (Jones, 2007a). The final objective is to interpret the local- and regional-scale evidence in order to, for the first time, discuss the pan-Indian paleoanthropological consequences of the Toba eruption and put forward two types of model. First, to posit areas of India that may have acted as refugia for hominin populations after Toba. Second, to propose a series of demographic scenarios which hypothesize the spatio-temporal movements of different hominin species and populations of H. sapiens from MIS 6 onwards. Lying approximately at the transition between MIS 5a and MIS 4, both models predict how the Toba eruption may have disrupted the course of evolutionary events in the Subcontinent. Species and population histories in India are modeled over this long time-frame (MIS 6 to MIS 3) given that Toba is frequently included in discussions of the wider spatio-temporal patterns of hominin dispersals into India during the Upper Pleistocene (e.g. Oppenheimer, 2003, 2009). The timing of the dispersal of H. sapiens into the subcontinent has been a matter of considerable debate over the last few years (Mellars, 2006a, 2006b; Petraglia et al., 2007, 2010), especially regarding the question of whether H. sapiens inhabited India before or after the Toba eruption. Answering this question is essential in order to ascertain who was affected by the eruption. Unfortunately, hominin fossil evidence from India is exceptionally limited, while genetic data from extant human populations can only provide us with an incomplete picture of India’s phylogeographic patterns. The demographic models presented here, therefore, constitute a first attempt at establishing testable hypotheses with respect to Upper Pleistocene population dynamics in India that will hopefully assist future research into this controversial topic. 2. A regional-scale approach: evidence from paleoclimatological, palaeoenvironmental and volcanological studies 2.1. Paleoclimatic and paleoenvironmental context The Indian subcontinent comprises a diverse range of habitats and microclimates created by varying regional topographies and influences of the Asian monsoon system. Accompanying such variable climates and topographies are differences in the type and extent of vegetation coverage. The Thar Desert occupies a significant proportion of north-west India and represents the most arid region of the subcontinent. Other areas, such as the Western Ghats and Sri Lanka preserve tropical evergreen forests, which receive very high amounts of rainfall during the summer monsoon and experience relatively short dry seasons (Spate and Learmonth, 1967, p. 79). Similar areas of evergreen forest were once also confined to littoral areas in the north-east, including Bengal and Orissa. The Indian environment is dominated by the dynamics of the Asian monsoon; the wet summer south-west monsoon brings huge quantities of moisture from the Indian Ocean to the subcontinent, and the cold and dry winter north-east monsoon directs winds from central Asia into the subcontinent (Webster, 1987, p. 4). Past

variations in this system would have dramatically affected Indian ecosystems. Paleoclimatic cycles recorded in marine cores from the Arabian Sea, Bay of Bengal and South China Sea can be correlated directly with high latitude ice and marine core records (Schulz et al., 1998, 2002; Lee et al., 1999; Huang et al., 1999, 2001; Song et al., 2000; Leuschner and Sirocko, 2000; Kudrass et al., 2001; von Rad et al., 2002). Dansgaard-Oeschger (D-O) interstadial events, first observed in the Greenland ice cores, are also visible at lower latitudes and into the Southern Hemisphere (e.g. Blunier and Brook, 2001; Cruz et al., 2005). Assuming the sulphate peak in the GISP 2 core has been correctly associated with the Toba eruption (Zielinski et al., 1996b), this establishes that the eruption occurred in between D-O 19 and 20. Several recent models and timescales for the timing of D-O events 19 and 20 are available (e.g. Jouzel et al., 2007; Capron et al., 2010; Landais et al., 2010). By correlating ice core records from Greenland (NorthGRIP) and Antarctica (EDML), Capron et al. (2010) provide dates of w74.6 ka for D-O 20 and w70.8 ka for D-O 19. While D-O 19 represents a particularly high temperature increase climatically, it may also have been a period of relative aridity when compared to other D-O events (Flückiger et al., 2004). This is suggested by lower levels of methane (CH4) production during D-O 19, where increased CH4 emissions are associated with more expansive wetland areas. CH4 production is expected to be high during monsoonal periods and therefore this evidence is suggestive of relatively depressed monsoons during D-O 19 when compared to D-O 20. The Jiyuan loess profile in China shows an increase in winter monsoon intensity after D-O 20, w71.8 ka (Huang et al., 2001). An increase in loess deposition is also recorded in Pakistan, w74 ka (Dennell et al., 1992). Evidence from the South China Sea shows a temperature decrease of w1
C after Toba that lasted for w1000 years. This corresponds to a decrease of 6e16
C at high latitudes, suggesting that extreme changes in temperature were confined to relatively high latitudes (Huang et al., 2001, 2002)). Kudrass et al. (2001) find no significant drop in sea surface temperatures in the northern Bay of Bengal after Toba, and Schulz et al. (1998), 2002), on the basis of marine core evidence from the Arabian Sea, argue against a volcanic winter and weakened summer monsoonal conditions post-Toba. Increased aridity in India post-Toba is suggested by enhanced levels of salinity recorded in northern Bay of Bengal marine cores, resulting from reduced freshwater input from rivers (Kudrass et al., 2001). A post-Toba decline in total organic carbon in the northern Arabian Sea also supports increased aridity, caused by a weakened south-west monsoon (von Rad et al., 2002). During MIS 4, marine core evidence indicates decreased precipitation, cooler conditions and lowered sea levels in western (Prabhu et al., 2004) and northwestern (van Campo et al., 1982) parts of India. An expansion of grasslands, suggestive of a weakened monsoon (Juyal et al., 2004), and a lengthy arid phase commencing w73 ka (Pandarinath et al., 1999), are also recorded in north-western India. The Thar Desert and surrounding regions of north-west India were particularly vulnerable to changes in climate and monsoonal dynamics, with increased aridity and decreased fluvial output during glacial periods (e.g. Chamyal et al., 2003; Jain and Tandon, 2003). The tropical evergreen ecosystems of the Western Ghats (a region that receives heavy summer monsoonal rains) may have also suffered environmental degradation post-Toba and during MIS 4. The Western Ghats form a geographic barrier that creates a west to east gradient of decreasing precipitation (Barboni and Bonnefille, 2001), suggesting that areas to the east of the Ghats would have been worse-affected by lower rainfall. While habitats in western parts of India would have become increasingly arid and uninhabitable during glacial periods, it has been argued that eastern and central regions of India may have been unaffected. Stronger north-east monsoons would have made the latter areas the most favorable for hominin

S.C. Jones / Quaternary International 258 (2012) 100e118

occupation, with no depletion of fresh water or food sources (Korisettar, 2007). In contrast with conditions during MIS 4, an increasing number of studies are pointing to a period w50e30 ka (i.e. falling within MIS 3) where the south-west monsoon was strong, marking a return to more humid and wet conditions. This has been noted w50 ka (Pandarinath et al., 1999), and w50e30 ka in north-west India (Juyal et al., 2004) and the southern Gangetic plain (Singh et al., 1999; Tewari et al., 2002; Srivastava et al., 2003), and w40e20 ka in the Nilgiri Hills in southern India (Rajagopalan et al., 1997). The evidence reviewed here suggests that three major consequences of the Toba eruption should be considered; (1) the impact of the huge quantities of sulphate aerosols, which would have persisted in the atmosphere for some time after the eruption; (2) the disturbance of the Asian monsoon system and increased strength of the winter monsoon; (3) the impact of the YTT ash-fall on environments. All three factors may have led to an increase in the albedo effect. An increase in snow and ice coverage at high latitudes and on the Tibetan plateau would have enhanced albedo (Colin et al., 1998), as might the light-colored ash (Jones et al., 2007) and sulphate aerosols. Interactions between these three factors may have induced various feedback mechanisms leading to an overall deterioration in conditions. It is plausible that deforestation in southern Asia, caused by the ash-fall, as well as increased aridity, also contributed to changes in surface albedo. Gupta et al. (2005) have modeled the effects of deforestation on the Indian climate, arguing that 100% deforestation would result in an increase in rainfall of 5 mm/day in southern India but a decrease of 2 mm/ day in northern India or 4 mm in north-east India. Establishing the rapidity of climatic deterioration as well as the speed of recovery is essential when considering the impacts of paleoclimatic and hence paleoenvironmental change on hominins and their habitats. Unfortunately, marine core records do not possess the required decadal, much less annual, resolution generally necessary to detect a volcanic winter or other relatively short-scale perturbations. The paleoclimatic records do, however, suggest that the w1000-year stadial during which the Toba eruption occurred was followed by D-O 19. During this interstadial, an expansion of both viable habitats and hominin populations in India could have occurred and the signature of this may be detectable in the archaeological record. Yet, high amplitude climatic fluctuations had already been occurring for some time before the Toba eruption, as represented, for example, by the stadial in between D-O 20 and 21 and throughout the preceding sub-stages of MIS 5. Even during MIS 5e, broadly coincidental with the last interglacial, high amplitude temperature oscillations occurred every 70e750 years (Dansgaard et al., 1993). It could be argued that hominin species had already developed the capacities to adapt to ongoing climatic variability long before Toba. In this way, hominins may have been selected for their ability to adapt to these fluctuating conditions (e.g. via variability selection [Potts, 1998]). 2.2. Evidence from volcanological studies: potential impacts of distal Toba volcanic ash-fall on ecosystems A number of studies have focused on the impacts of natural disasters in general (McGuire et al., 2000; Torrence and Grattan, 2002a) and volcanic eruptions in particular (Sheets and Grayson, 1979; McCoy and Heiken, 2000; Grattan and Torrence, 2007a) on past human societies and environments, and the role they played in past cultural change. Several critical variables should be considered when assessing the impacts of volcanism; magnitude, duration, frequency, perception (e.g. Blong, 1982) and vulnerability (Torrence and Grattan, 2002b, p. 9). For example, it is argued that the more vulnerable the group, the greater the disaster and hence the higher

103

the probability that cultural change will occur (Torrence and Grattan, 2002b, p. 7). Few studies have specifically addressed the potentially hazardous consequences of the Toba ash-fall for Indian ecosystems. Studies of the impacts of distal ash-falls are rare when compared to the proximal impacts of eruptions (e.g. Rose et al., 2003); however, information can be gleaned from a large corpus of studies that have focused on the impacts of other prehistoric as well as historic volcanic eruptions. Several of these have utilized an archaeological approach in concert with information from other disciplines such as geology, zoology and botany. These studies have provided useful reconstructions of both the short- and long-term impacts of eruptions on past societies (e.g. Sheets, 1980; Torrence et al., 2000; Torrence, 2002). Other studies have focused on more recent volcanic eruptions, such as Parícutin (e.g. Rees,1979), Mount St. Helens (e.g. Mack,1981; Antos and Zobel, 1986; Halpern et al., 1990; Zobel and Antos, 1997; Dale et al., 2005b), Hudson (Inbar et al., 1995), Pinatubo (Newhall and Punongbayan, 1996) and Chaitén (Martin et al., 2009). These have provided highly valuable empirical data on the direct impacts of ashfall on ecosystems as well as details, such as characteristics and speed, of the recovery period. Furthermore, a line of research that has grown over the last few years, particularly with the establishment of the International Volcanic Health Hazard Network (IVHHN) in 2003, tackles the effects of respirable volcanic ash and gases on human health (e.g. Horwell and Baxter, 2006). A small number of studies have also focused on the impact of volcanic ash on animal health, particularly that of grazing species (e.g. Cronin et al., 1998, 2000). The Toba eruption, via the injection of large amounts of volcanic gases and ash into the atmosphere, could have played a significant role in altering global temperature, lowering the amount of light reaching the Earth’s surface and weakening the strength of the summer monsoon for a certain period of time. These can all be considered abiotic impacts at the primary level, which would have indirectly affected biotic factors. The ash-fall over the Indian subcontinent would have caused additional abiotic changes to water sources, soil chemistry and landscape physiography and, in turn, these may have had secondary biotic impacts on vegetation, animals and hominins. The effects of tephra on vegetation can be highly variable depending, for example, on the depth of the ash, the compaction of the ash, its effects on soil fertility, rates of ash redeposition (Dale et al., 2005a) and vegetation type (Rees, 1979; Mack, 1981; del Moral and Grishin, 1999; Eastwood et al., 2002). Acid rain may have additional detrimental consequences; however, emission of large quantities of CO2 during eruptions can result in a short-term net increase in atmospheric CO2, enhancing plant growth and reproduction (Dale et al., 2005a). Some studies have described deleterious effects of tephra on vegetation (Baillie and Munro, 1988; Yadav, 1992; Boyd et al., 2005). Others have shown resilience of vegetation after ash-falls (Charman et al., 1995; Wilmhurst and McGlone, 1996; Eastwood et al., 2002; Hall, 2003; Jago and Boyd, 2005); these studies recommend against the often automatic assumption that ash-falls have a negative impact on vegetation cover. Rees (1979) studied the physiographic effects of ash following the Parícutin eruption (1943, Mexico), where ash was still mobile in the environment, particularly on plains, even thirty years after the eruption. Several variables governed the amount and distribution of ash-fall: distance from the volcano, wind direction, eruption intensity and frequency (the eruption lasted for several years), particle size and slope gradient. The movement of ash following deposition was also recorded; the unconsolidated ash was easily eroded, transported and redeposited, these processes being enhanced during the rainy season. Less vigorous erosional processes took place for years afterwards via mechanisms such as soil creep, landslides, sheet

104

S.C. Jones / Quaternary International 258 (2012) 100e118

flow, wind deflation, and splash, rill and channel erosion (Rees, 1979). Therefore, mobilization and repeated remobilization of ash can continue to occur over a substantial period of time after the initial ash-fall, which could have implications for the longevity of impact on vegetation. After the 1991 Hudson eruption, repeated ash remobilization by strong winds (“ash storms”) resulted in long-term environmental impacts, indicating that repeated reworking of ash can be as hazardous as the initial ash-fall for several years after the eruption (Wilson et al., 2011). In some cases, however, erosion and redeposition of tephra can assist the survival of plants (del Moral and Grishin, 1999), introducing organic material for plant growth (Rees, 1979). The deposition of distal volcanic ash in lacustrine habitats can change the structure and drainage of lake basins (e.g. Kataoka et al., 2009; Manville et al., 2009) and alter the biological and physical processes occurring within a lake. Changes can be caused by increased turbidity (Riedel et al., 2001), a decrease in pH as a result of acidic aerosol deposition, and lake productivity can even increase following injection of the large amounts of silica in volcanic ash (Telford et al., 2004). Even small amounts of tephra, however, can have severe environmental consequences for lacustrine ecosystems (Riedel et al., 2001). Reduced vegetation coverage following an ashfall can lead to an increase in erosional processes, resulting in an influx of sedimentary material into lakes (Hardardóttir et al., 2001, p. 226). Acidic aerosols and resultant acid rain, derived from the injection of large quantities of volcanic gases into the atmosphere, present a well-known threat to ecosystems (Grattan, 2006). In addition to acidic aerosols, leaching of various metal species into soils and aquatic habitats can result from ash deposition, leading to contamination of soils, vegetation (a particular hazard for grazing animals) and sources of drinking water. The impact of leaching on the environment depends on the quantity of water coming into contact with the ash; the greater the volume of water (e.g. during the monsoon season), the lower the concentration of leachates. Grain size is also a factor because ash of smaller particle size can produce greater amounts of leachate, suggesting that the associated hazardous effects may be greater in areas of distal ash-fall (Witham et al., 2005). Documented effects of tephra on animals are variable. Some studies have shown no substantial effects of tephra-fall on animal growth or mortality (Edwards, 2005), or have shown variable effects according to animal size (Dale et al., 2005b). Other studies illustrate that ash-fall can have fatal consequences for insects (Edwards, 2005), fish (Thorarinsson, 1979) or grazing animals (Rees, 1979). One of the most catastrophic accounts of the impact of volcanic ash on animals is provided by evidence from the “Ashfall fossil beds” in Nebraska, dated to w10 Ma (Voorhies and Thomasson, 1979). Numerous small- to large-sized animals are preserved in a w2 m-thick distal rhyolitic ash-fall (Rose et al., 2003). This high mortality rate could have been caused by the inhalation of large amounts of ash (Voorhies, 1992). Fluorine poisoning, caused by animals grazing on vegetation covered in fluorine-laden tephra, is another contributing factor (Thorarinsson, 1979; Cronin et al., 2000). Fluorine poisoning of water sources is also known and presents a particular hazard to sources of drinking water and thus to animal and human health (e.g. Witham et al., 2005). As with metal leachates, fluorine, which adheres to ash particles, can be deposited in higher concentrations where ash particles are smaller (due to greater surface areas for adsorption) and hence fluorosis may present a greater hazard in more distal areas of ash-fall. In addition, fluorine poisoning is known to be greater in areas where ash coverage is too thin to prevent animals from grazing (Thorarinsson, 1979). The potential human health hazards associated with volcanic eruptions have been reviewed by Baxter (2005) and Horwell and Baxter (2006). The main health risks posed to humans are related

to the direct impacts of volcanic ash and gas inhalation on the respiratory system, the abrasion of skin or eyes by tephra, or exposure to high levels of fluorine in sources of drinking water. These health risks vary between eruptions from different volcanoes as well as those from the same source (e.g. Hansell, 2003; Horwell, 2007). Eruption duration is also a critical variable in assessing the potential human health risk, as is the frequency of ash remobilization events. 3. Assessing the impact of the w74 ka Toba eruption at the local-scale: Toba ash deposits and cultural and environmental change in the Jurreru and Middle Son valleys The Jurreru valley in Andhra Pradesh, southern India, and the Middle Son valley in Madhya Pradesh, north-central India (Fig. 2) are two areas that have produced some of the strongest evidence for archaeology-YTT associations in India. This section is informed by fieldwork and analyses carried out by the author in both valleys between 2003 and 2005. Fieldwork in the Jurreru valley was conducted as part of a large international team of researchers. Some of this data is published elsewhere (Petraglia et al., 2007; Jones and Pal, 2009; Jones, 2010) and is available in Jones (2007b). For this reason, a summary of the data is provided below rather than a detailed account; instead, greater emphasis is placed on the discussion of Toba’s local impacts. Materials and methods for the analysis of both the lithic artifacts and sediments, as well as the location of samples, can be found in the aforementioned sources. 3.1. The Jurreru valley: evidence and interpretation The presence of volcanic ash in the Jurreru river valley (15
19.330 N; 78
8.020 E), in the Erramala Hills region of Kurnool District, Andhra Pradesh, was first documented by Rao and Rao (1992). Detailed archaeological and geological investigations were conducted in the valley in 2003 and 2004, after which the ash was geochemically identified as YTT (Petraglia et al., 2007, 2009; Jones, 2007b). Extensive YTT deposits are exposed in numerous quarries throughout the valley following intensive mining of the ash by local villagers. These ash exposures range in thickness from 0.15 to 2.55 m, covering a minimum area of 0.64 km2 (Petraglia et al., 2007). Initial surveys revealed the existence of artifacts ranging from the Lower Paleolithic to Historic periods and excavations at several locations resulted in the recovery of pre- and post-Toba artifacts in stratified contexts. An OSL date of 77  6 ka (JLP3A-200) for a sample taken from 1.8 m beneath the YTT at locality 3, and w0.3 m beneath a discrete excavated artifact horizon, provides a lower age limit for these preToba artifacts. At the same locality, a sample from w1.1 m above the ash, a context which contains post-Toba artifacts, has been OSLdated to 74  7 ka (JLP3-380) (Petraglia et al., 2007). Additional post-Toba artifact-bearing contexts are OSL-dated to 38  3 ka (JLP21B-30; locality 21) and more than 34  3 ka (JLP20B-60; locality 20) (Petraglia et al., 2009). These artifacts are characteristically Middle Paleolithic and are argued to share affinities with the African Middle Stone Age (Petraglia et al., 2007). A total of 221 stone artifacts were retrieved from beneath the ash at locality 3 and the Dry Well, and 312 artifacts were excavated from post-Toba contexts at localities 3, 21 and 17 (Fig. 2b). A further 575 lithics were recovered from locality 20. Detailed attribute analysis of these artifacts revealed only minor changes in lithic technology following the Toba eruption (Petraglia et al., 2007). As a whole, flakes became smaller and higher quality materials began to be used more frequently. Methods of blank selection for retouch altered; finer materials and

S.C. Jones / Quaternary International 258 (2012) 100e118

105

Fig. 2. (a) Digital elevation model showing the location and currently known extent of YTT deposits in the Jurreru valley; (b) location of archaeological sites and YTT deposits in the Jurreru valley; (c) digital elevation model showing the location of four alluvial sections in the Middle Son valley that preserve YTT; (d) map of India showing the location of the Jurreru and Middle Son valleys (after Jones, 2010: Fig. 1).

larger flakes were selected for retouch pre-Toba but not post-Toba. Methods of retouching were also different post-Toba; more flakes were retouched on their distal ends, yet retouch on either of the lateral margins and only the ventral surface were more common pre-Toba. There were several aspects of lithic technology that did not change post-Toba, and overall there is stronger evidence for technological continuity following the eruption. For example, a comparison of flake characteristics shows no significant changes in reduction intensity or retouch intensity, the shape of flakes produced did not change, nor did the frequency of blade production, which remained rare post-eruption (Jones, 2007b). An analysis of additional lithic artifacts recovered during excavations in the valley in 2008 and 2009 further support cultural continuity in the area post-Toba (Haslam et al., 2010a) with the same population inhabiting the valley before and after the eruption (Haslam et al., 2010b). Samples of tephra and sediments were collected from four excavated ash sites and were subjected to a range of sedimentological analyses. These samples were taken from pre-, within- and post-YTT contexts. The results and interpretations of the data are discussed in detail in Jones (2010) in accordance with seven separate phases of palaeoenvironmental change. Discussion here will focus

on the nature and extent of palaeoenvironmental, and hominin behavioral and demographic changes in the valley before the Toba eruption, whilst ash was being deposited and redeposited, and during the period after which local habitats had recovered. Before the Toba ash-fall, a lacustrine or paludal (swamp-like) environment dominated the centre of a densely vegetated valley. The paleolake or paleoswamp was a fairly low energy and shallow water environment, as suggested by the sedimentological characteristics of deposits underneath the ash and by a substantial presence of plant life within the paleolake. The latter is indicated by abundant fossilized plant remains preserved within the ash. The area occupied by the paleolake fluctuated over time, probably according to the climatic fluctuations of the Upper Pleistocene. For example, fluctuations associated with the end of MIS 5, such as the various interstadial and stadial periods, would have affected the relative strength of the monsoon and thus both the amount of rainfall in the valley and the spatial extent of the paleolake. During a phase when the paleolake had retreated slightly, dated to w77 ka, there is firm evidence that hominin groups were occupying the valley, their artifacts being concentrated at the lake’s edge. Hominins used local sources of lithic materials readily available in

106

S.C. Jones / Quaternary International 258 (2012) 100e118

the adjacent northern and southern hill-slopes of the valley (limestone and quartzite). Although higher quality (finer-grained stone) materials (e.g. chert and chalcedony) were infrequently used, these were preferentially retouched, probably as a means to resharpen the edges and extend use-life; something which may hint at the perceived value of these materials. Retouch of specific flake sizes and shapes, and the use of distinctive retouch methods, may be argued to have been guided by functional requirements, such as those related to particular subsistence practices. Alternatively, these traits could have been dictated by the tool-making habits and preferences of the hominin communities that made them. Given that retouch methods and products show no standardization in form, it is more plausible that these artifacts were manufactured in response to the ecological constraints of the environment, rather than according to any group- or population-defined technical or stylistic stricture. The technology of the pre-Toba hominins falls within that of Middle Paleolithic prepared-core technologies. Radial flaking is present, flakes show different forms of preparation, and scraper technologies, albeit unstandardized, exist. Burins, microliths and blades are present, but are rare. The presence of a utilized piece of hematite indicates that ochre was used by these pre-Toba hominin groups, for either symbolic or functional reasons. The distal w74 ka ash-fall covered the Jurreru valley and all surrounding regions in w5 cm of primary Toba ash (Petraglia et al., 2007, 2009; Jones, 2010). This ash settled through the shallow paleolake, ultimately resting on the lake bottom and capturing within it organic material as it descended through the water. In aquatic environments, both acidic aerosols and heavy metal and fluorine leachates contained in volcanic glass can result in water toxicity (Witham et al., 2005); however, these effects may have been rather limited in India given the vast distance (w2670 km) between Toba and the Jurreru valley. Indeed, there is evidence to suggest that the input of silica into the paleolake might have been beneficial by increasing its productivity (Telford et al., 2004). Some time after the initial ash-fall, the first ash redeposition event occurred. Ash from the surrounding hill-slopes and northern and southern plateaus was redeposited by wind (Jones, 2010) into the Jurreru valley and into the paleolake, burying large quantities of plant material. After this redeposition event, the paleolake desiccated following a temporary interruption of the water supply into the valley, in concordance with an extended arid period. Wetter conditions eventually returned to the valley, possibly caused by a monsoonal episode, and accompanying winds caused the remobilization of ash in the landscape and its further redeposition into the paleolake that had by now re-filled with water. Four further cycles of aridity followed by wetter episodes occurred, accompanied by four major episodes of ash remobilization and redeposition into an aquatic medium, via aeolian processes rather than fluvial. During the course of these redeposition events, the hydrology and geomorphology of the valley was constantly changing, where any water-filled depressions in the valley were plugged by ash. The paleolake disappeared and it is unlikely that lacustrine or paludal conditions returned to the Jurreru valley. There is no evidence, currently, to suggest that hominins inhabited the valley during the ash redeposition events. The presence of vast quantities of fossilized plant material in the ash suggests that vegetation in the paleolake, as well as terrestrial plants growing in the vicinity, were destroyed by both the ash-fall and the lengthy period of ash redeposition. The latter is argued to have lasted for several years, possibly accompanying each monsoon season. Paleoclimatic data discussed above suggests that Toba had an impact on Asian monsoonal dynamics, resulting in a depressed south-west summer monsoon and enhanced north-east winter monsoon. In addition, the relatively predictable pattern of monsoonal cycles that exists today may not have been the case during glacial periods, and

the YTT eruption could have further disrupted their pattern, with possible repeated failures of the annual summer monsoon. The north-east monsoon, however, brings rainfall to south-eastern areas of India. It is argued here that relatively strong post-Toba winter monsoons brought substantial rainfall to parts of present-day Andhra Pradesh, including the Jurreru valley. In this respect, the winter monsoonal rains and winds could have been responsible for the ash redeposition events in the Jurreru valley, bringing ash from the plateaus, hills and plains to the north-east. There appears to have been a substantial period of time in between each redeposition event; there was enough time for the paleolake to desiccate and for subsequent regeneration of life on the surface of the ash before successive redeposition episodes. Excavations of the 2.5 m-thick ash layer revealed traces of plant growth, animal burrows (e.g. insects, crustaceans), insect tracks and possible microbial activity on the desiccated surfaces of the ash, in between ash redeposition events. It is unlikely that the valley was habitable during this period, following vegetation destruction and influx of ash into the paleolake. Ingestion of ash-laden vegetation can also prove toxic or even fatal for grazing mammals (e.g. Cronin et al., 1998). These changes could have been sufficient to disrupt the local food chain and render the valley unattractive for hominin occupation. Archaeological evidence, however, suggests that the valley did not remain uninhabited for a substantial period of time. Hominin groups reoccupied the area during a period of landscape instability and ash remobilization, marked by a small number of unabraded artifacts in the upper levels of a post-Toba ashy silt deposit at excavated locality 3. Analyses reveal the gradual input of increasing sediment into the valley, and correspondingly less ash, the former acting as a substrate upon which vegetation could grow. Hominin groups were probably attracted to the valley by the return of vegetation and the animals that would have accompanied this. Hominins occupied the valley in greater numbers during this period, when wetter conditions had clearly returned to the valley. It has been argued that this phase is associated with Dansgaard-Oeschger (D-O) interstadial 19 (Jones, 2010). Hominins appear to have returned to exactly the same areas that they occupied prior to the eruption, regardless of these dramatic landscape changes. The lithic technology they utilized, however, did display some changes. The greater exploitation of finer-grained raw materials could be due to greater exposure of these sources following post-ash-fall vegetation clearance. In fact, the varied range of lithic material sources in this geologically diverse area must have been a significant attraction for hominins, ensuring their continued return to the valley, even so soon after the eruption. The preferential retouch of flakes made from lower quality materials was likely caused by changes in subsistence behavior and functional requirements, or by a change in habitual group preferences and behavior. The latter could have been a result of various demographic processes, such as local group extinctions, genetic drift, or a loss of vertical transmission. The lack of blank selection, a practice that existed pre-Toba, as well as different retouch methods and the manufacture of smaller blanks, were changes that were plausibly driven by adaptations to a different environment post-Toba. These aspects of hominin behavior may have altered after the eruption because of a combination of changes in subsistence practices and demographic structure compared to the pre-Toba population. The landscape of the Jurreru valley changed considerably following the ash-fall; vegetation cover likely shifted towards a dominance of less ash-sensitive plants or those that were relatively tolerant of more arid and cooler conditions. A change in the fauna occupying the valley probably coincided with this vegetation shift. Methods of hunting and gathering could have similarly shifted in accordance with a change in resource base. Therefore,

S.C. Jones / Quaternary International 258 (2012) 100e118

a degree of behavioral adaptation of pre-Toba populations took place in order to survive the post-Toba conditions of the area; however, population structure also changed. Post-Toba changes in technology and behavior are too small to suggest large-scale population extinction in the area. Instead, localized extinctions of small enclaves within the wider population are posited as a more likely scenario. While cultural drift may have occurred through a loss of vertical transmission, post-Toba cultural changes were more plausibly caused by the reoccupation of the valley by different groups from the same population with slightly different technologies. Although the Jurreru valley would have been temporarily uninhabitable for hominins during the ash-fall and the subsequent redeposition events, it is proposed that several areas surrounding the valley could have acted as refugia for hominins. Areas of highly variable topography, such as the hill ranges of the Eastern Ghats, would have been less vulnerable to the effects of the ash-fall on vegetation. The ash would have been relatively rapidly redeposited into areas of topographic depression, such as the Jurreru or nearby Sagileru valley, where ash is also documented (Acharyya and Basu, 1993). Other less topographically variable areas, such as the Nandyal valley plain to the east of the Jurreru, would probably have been even more susceptible to prolonged damage caused by the ash. Plains could have become ash playas for decades after the initial ash-fall, as was the case in areas of Mexico after the Parícutin eruption (Rees, 1979). In contrast, subsisting in the hill ranges should not have been problematic provided that hominins possessed adequate water supplies via hill streams or springs to supply small mobile hominin groups and fauna. Although the south-west monsoon would have been weak or absent after Toba, the enhanced north-east monsoon would have brought an adequate supply of precipitation to the region. Archaeological evidence indicates that the upland areas of the Eastern Ghats were occupied from the Lower Paleolithic through to the later Pleistocene periods. Today, these areas are still inhabited by a number of tribal populations. The

107

Srisailam and Mannanur plateaus, both located in the Nallamala Hills, are reported to have offered food security during periods of resource depletion in other regions, being ideal for sustaining small huntergatherer populations (Reddy, 2001). These and similar areas are argued here to have acted as refugia for hominin groups after Toba. In sum, although certain characteristics of hominin technology and behavior did change after Toba, there are also a number of persisting characteristics. There appears to have been relatively more technological stasis than there was technological change. This suggests that the population as a whole only suffered minor disturbance under post-Toba conditions, as a result of localized group extinctions and responsive adaptation of subsistence strategies in order to cope with a remodeled environment. Most notably, hominins reoccupied the Jurreru valley relatively soon after the eruption, implying a nearby persistence through the course of the event, perhaps in areas such as the Erramala or Nallamala Hills. In fact, there were few technological and behavioral changes from immediately post-Toba (w74 ka) until w38 ka. This indicates that technology changed very little throughout MIS 4, further supporting the notion that climate change did not have a significant effect on hominin technology and behavior in this region of India. Fig. 3 summarizes the cultural and demographic changes in the Jurreru valley during the Upper Pleistocene and in relation to Toba. 3.2. The Middle Son valley: evidence and interpretation The first YTT deposits to be discovered in India were found in the Middle Son valley in the early 1980s (Williams and Royce, 1982), where ash has been recorded in at least four areas, extending over w30 km (Basu et al., 1987; Acharyya and Basu, 1993). Five separate studies have geochemically characterized the ash from the Middle Son as YTT (Rose and Chesner, 1987; Acharrya and Basu, 1993; Shane et al., 1995; Westgate et al., 1998; Jones, 2007b). Surveys of the

Fig. 3. A temporal model of hominin demographic processes in India during the course of the Upper Pleistocene, indicating the position of the Toba eruption (black horizontal line). The oxygen isotope temperature curve (left) is derived from the SPECMAP composite chronology for stacked oxygen isotope records from several marine cores (after Martinson et al., 1987; Lowe and Walker, 1997: Fig. 5 p. 32). This illustrates shifts in temperature over the last w250 ka and oxygen isotope stages (MIS) of the late Middle Pleistocene and Upper Pleistocene periods.

108

S.C. Jones / Quaternary International 258 (2012) 100e118

valley, as well as several large excavations, have revealed artifacts ranging in age from the Lower Paleolithic to Neolithic (Sharma and Clark, 1983). YTT and these artifacts are preserved within thick alluvial deposits that accumulated during the Upper (and possibly Middle) Pleistocene and Holocene periods. These alluvial sediments have been assigned to different geological formations; from oldest to youngest, these are the Sihawal, Patpara, Baghor and Khetaunhi formations (Williams and Royce, 1982, 1983). Studies disagree on the stratigraphic position of the ash-fall in this sequence; some argue that the eruption occurred after the aggradation of the Patpara formation and before (Williams and Clarke, 1995; Jones and Pal, 2005, 2009) or during the early stages of Baghor coarse member accumulation (Williams and Royce, 1982; Basu et al., 1987; Acharyya and Basu, 1993), or prior to Patpara formation deposition (Williams et al., 2006). Although excavation and survey have indicated that the Jurreru and Middle Son valleys preserve evidence of both YTT deposits and a rich Paleolithic record that is unparalleled by any other sites in India, there exists a large divide between the two valleys in terms of the quality of the archaeology-ash associations. Where the Jurreru preserves artifacts that are directly associated with YTT deposits in excavated and dated trenches, this kind of evidence is currently unavailable for the Middle Son valley. Investigations in the valley since the 1980s, however, have produced several important collections of lithic artifacts from excavated, surface and within-section contexts. Using the relative chronology proposed in Jones and Pal (2009; Fig. 3), these can be placed in a temporal sequence that traverses the Toba eruption. An analysis of these artifacts documents changes in lithic technology and hominin behavior in the valley during the Upper Pleistocene (Jones, 2007b; Jones and Pal, 2009). Although the analyzed assemblages can be assigned a pre-Toba or post-Toba age, they must be considered to pre- and post-date the eruption in the very broadest sense. This is due to the almost complete absence of chronometric dates directly associated with the assemblages recovered since the 1980s. Thus, while it is currently not possible to correlate any technological changes that occurred in the valley to the Toba event, the large-scale temporal changes in technology and behavior that occurred either side of the w74 ka eruption can be described. Several aspects of lithic technology remained unchanged after the Toba eruption, including flake size, flatness, and marginal angle, in addition to platform shape, retouch intensity, and rates of microlith production. The latter remained rare until the later Pleistocene Baghor 3 assemblage when intentional and systematic microlith production became well-established (Jones and Pal, 2009). Levallois, disc, single platform and multiple platform cores are all found both before and after Toba. In spite of these similarities between pre- and post-Toba technology, far more differences exist that point to the occurrence of significant technological change at some point after the Toba eruption. For example, fine-grained raw materials became used more frequently (e.g. chert rather than quartzite and limestone), new methods of core reduction were employed, and retouch strategies and methods of blank selection changed. In comparison with postToba artifacts, pre-Toba artifacts show a higher frequency of faceting on both cores and flakes, radial patterns of flake removals were more common, cores were rotated more frequently (leaving multiple platforms), and flake platforms were proportionally larger when compared to the rest of the flake. Bifaces and cleavers, including diminutive forms of both, are found only in pre-Toba contexts. Core reduction strategies changed after Toba; cores and flakes show a higher frequency of overhang removal as a means of platform preparation, cores were more intensively flaked around the circumference of the last platform, and both cores and flakes show a higher number of non-feather terminations. In addition, flakes in post-Toba contexts are more elongated, crested blades are recorded for the first time as are bidirectional, microblade, bidirectional blade,

unidirectional blade, and Levallois blade cores. A tendency towards increased blade production may have already been underway shortly before the eruption, as suggested by the small Late Patpara assemblage. Retouch strategies also changed after Toba; pre-Toba retouched flakes show a higher frequency of notching, convex retouch and retouch exclusively on the ventral surface. In contrast, post-Toba flakes reveal backing for the first time and a higher rate of alternating retouch and retouch on the dorsal surface only. Certain practices of blank selection were in place before Toba; more quartzite and particularly chert flakes were preferentially retouched as were the larger flakes. After Toba, there was no selection for specific raw materials, flake sizes or shapes for retouch. Analysis of stratigraphic features, sediments and tephra from two ash-bearing sections in the Middle Son (Ghoghara and Khuteli) reveals the processes by which Toba ash was redeposited throughout the valley. The characteristics of sediments underlying the ash at both localities suggest that the catchment area was hydrologically active and wet prior to the eruption. At Ghoghara section (24
30.120 N; 82
1.050 E), the identification of at least six different phases of ash redeposition, where the ash was derived from multiple source regions, suggests that the ash was mobile on the surrounding landscape for a significant length of time prior to redeposition and burial. Other sedimentary features in post-Toba contexts suggest that a period of substantial aridity occurred after Toba, coincident with MIS 4 and probably also with the stadial in between D-O interstadials 19 and 20 (Jones, 2010). This is supported by findings in Williams et al. (2009) who conducted stable carbon isotopic analyses of soil carbonates from contexts underneath and above the YTT layer at two sites in the Middle Son. Together with palynological data from a marine core in the Bay of Bengal that preserves YTT, they argue that their results show reduced tree cover post-Toba with a prolonged drought for at least a millennium after the eruption (Williams et al., 2009). It is particularly difficult to accurately establish if a volcanic event caused cultural and environmental change, and that any changes were not merely coincidental with it. While there is an archaeological record both dated and in direct association with an ash layer (Grattan and Torrence, 2007b, p. 7) in the Jurreru valley, this is lacking for the Middle Son archaeological record. As a result, propositions about cultural and demographic changes post-Toba in the Middle Son valley will require further testing to determine if the changes that have been observed are as a direct result of the Toba eruption. Nonetheless, this still remains currently the secondbest locality in India for assessing Toba’s hominin and environmental impacts, and a tentative model is proposed that hypothesizes the cultural and demographic shifts in the valley during the period in question (Fig. 3). Before the Toba eruption, hominins in the Middle Son valley were utilizing Middle Paleolithic technologies, mainly consisting of the reduction of multiplatform cores, occasional disc cores and, rarely, Levallois cores. The preferential selection of chert for retouch could suggest that this material was less available in the valley and that groups had to travel further to obtain it, with this relatively valuable material being repeatedly resharpened to extend its uselife. The analyzed pre-Toba Middle Paleolithic assemblages belong to different chronological periods, as dictated by their varied stratigraphic contexts, and a distinction has been made between an “early” and “late” Middle Paleolithic of the Middle Son (Sharma and Clark, 1982; Clark and Williams, 1987). Differences between these industries are plausibly linked to fluctuations in climate and hominin demography, for example, with variation caused by the influence of population migrations into and out of the valley. These technological and hence behavioral changes were probably associated with the marked climatic fluctuations of MIS 5, such as the various sub-stages, stadials and interstadials of this period.

S.C. Jones / Quaternary International 258 (2012) 100e118

Assuming that the Late Patpara collection of the “late” Middle Paleolithic has been correctly assigned to a context relatively shortly before Toba (Jones and Pal, 2009), then it appears that notable technological changes had already occurred prior to the eruption, during MIS 5a. Sources of chert were being accessed more frequently, more elongated flakes were being produced and there was an increase in Levallois core reduction. These changes could mark a demographic shift in the populations occupying the valley, or changing use of the valley. Some time after the Toba eruption, there was a notable shift in lithic technology and hominin behavior in the Middle Son. While this technology still falls within the Middle Paleolithic, it can be defined as a later phase of the Middle Paleolithic. Disc, multiplatform and Levallois cores were still being manufactured, as were scrapers. There was also a marked increase in blade production, sometimes using the crested reduction technique, and Levallois blades were produced for the first time. Backed blades are encountered and quartzite was barely used, yet chert was acquired in abundance. All these changes are documented amongst the artifacts found within the Baghor coarse member (Williams and Royce, 1982), the aggradation of which is argued to have resulted in the introduction of supplies of chert cobbles from several kilometers to the west that originated in the eroded Deccan Traps (Clark and Williams, 1987). Several aspects of lithic technology are, therefore, notably different in post-Toba contexts. These signal a stark change in hominin behavior, and, most significantly, a probable change in demography. The nature of the sediments that pre-date Toba appear to support the existence of a relatively wet and humid climate, when a braided river system prevailed (Sharma and Clark, 1982). Following the Toba ash-fall, tephra was initially redeposited by wind into tributary channels, with later phases of redeposition driven by fluvial and aeolian processes. This process may have extended over a number of years, with redeposition events appearing to be higher in energy than those that occurred in the Jurreru valley. This was caused by the existence of a significantly more active fluvial system in the Middle Son prior to the ash-fall as well as a substantially larger catchment area. A change in sedimentology occurred after the eruption, in association with the onset of the last cold stage (MIS 4) and perhaps the stadial in between D-O 19e20, although the resolution of current data prohibits precise dating. The accumulation of the thick reworked loess deposits of the Baghor formation, suggested to have originated from a northerly direction (Williams and Clarke, 1984), is argued to have taken place throughout this period (MIS 4 to MIS 2: w74 ka to w10 ka). While a shift in monsoonal dynamics had a comparatively minor effect on hominins in the Jurreru valley after Toba, it is proposed that this shift had a profound impact on Middle Son paleoenvironments. These changes were amplified after the Toba eruption and throughout MIS 4, with some respite during MIS 3. The start of Baghor coarse member deposition is suggested to mark the return of wetter conditions, corresponding with the onset of MIS 3. Climatic conditions continued to fluctuate during this period, supported by the presence of a wide variety of faunal species in Baghor coarse member deposits (Dassarma and Biswas, 1977; Blumenschine and Chattopadhyaya, 1983; Badam et al., 1989) that favor a broad range of habitats from humid, tropical and forested areas to semi-arid, grassland and steppe environments. Phases of Baghor coarse member deposition are argued to signal the return of relatively normal summer monsoonal conditions, rather than the predominantly strong and dry winter monsoons that are suggested to have prevailed post-Toba and throughout MIS 4. Using this archaeological and paleoenvironmental data, changes in hominin occupation patterns and demography can be hypothesized (Fig. 3). It is unlikely that the Middle Son area acted as a refugium; it appears to have been strongly impacted by a combination of

109

climate change and the ash-fall. The Middle Son is one of several major rivers in north-central India; a network that could have acted as a key dispersal route during periods of the Upper Pleistocene. Riparian routes possess abundant supplies of raw material, water and plant and animal resources, thus providing conditions that encouraged an increase in population size, social contact between groups and populations, hominin dispersals and relatively rapid range expansion. The Toba eruption, its ash-fall, MIS 4 and the associated climatic changes (i.e. increased aridity and decreased temperature) are argued here to have significantly interrupted this system, thus influencing population dynamics. A pronounced demographic shift would not have been out of the question in the Middle Son valley at some point after Toba. This would correspond to the stark shift in lithic technology and probably in hominin behavior. Two scenarios can be proposed, both of which would have resulted in the local extinction of the pre-Toba hominin population. First, as viable habitats shrunk and resources became less available in the years after the eruption, the pre-Toba population inhabiting the valley decreased in size; genetic drift may have followed but ultimately, local population extinction occurred. The region was later reoccupied by a different population with different technologies. Second, the pre-Toba population still underwent these phases of contraction and drift, rendering hominin groups within the population vulnerable to extinction. Due to some form of competitive advantage, caused by greater group size or certain behavioral and technological adaptations, the incoming post-Toba population out-competed the pre-Toba Middle Son population, ultimately resulting in their extinction. On the basis of all current evidence, both scenarios are equally plausible and local population extinction could have occurred shortly after the Toba eruption or at some point during MIS 4. Reoccupation may have taken place by pre-Toba hominin populations that had persisted within India. As post-Toba technologies in the Middle Son valley are dissimilar from those in the Jurreru valley, the populations that reoccupied the Middle Son are argued to have come from a different region. Yet, behavioral adaptation of populations from southern India to environmental contexts in north-central India, which would result in technological change, cannot be ruled out as a possibility. Equally plausible, however, is that reoccupation of the Middle Son took place by hominin populations that originated in areas outside India.

4. Regional-scale impacts of the Toba eruption across the Indian subcontinent 4.1. Regional impacts of paleoclimatic change on Indian environments Although doubts remain as to the severity of Toba’s direct impact on global climate (e.g. Oppenheimer, 2002), the eruption is coincidental with climatic changes (i.e. the stadial between D-O 19 and 20) evident in Greenland ice cores and marine cores from southern Asia. Marine core resolution, however, is not sufficient to either confirm or refute the hypothesized occurrence of a volcanic winter after Toba; a volcanic winter of several years in length would be conflated into climatic changes that occurred over at least centuries. While some marine core evidence from southern Asia does reveal a temperature decline post-Toba, it is not comparable to the high amplitude temperature changes apparent in the Greenland ice-core records. Even if a pronounced temperature decline did not occur in India after the Toba eruption, a far more serious climatic consequence for hominins and their habitats is the aridity that appears to have affected some areas of southern Asia during this period, caused by a shift in monsoonal dynamics. As the stadial in between D-O 19 and 20 appears to have had a relatively sudden

110

S.C. Jones / Quaternary International 258 (2012) 100e118

onset, where cooling may have been accelerated by Toba, a shift in the character of the monsoons could have been similarly sudden. This post-Toba stadial appears to be associated with changes in the relative strengths of the Asian monsoons. The south-west monsoon weakened and the north-east monsoon strengthened, as supported by evidence of an increase in loess deposition in Pakistan and China. Shifts in monsoonal dynamics would have resulted in pronounced changes in vegetation coverage in India, with fluvial input and water supply to a number of areas also diminishing. It is argued here that the effects of these changes varied throughout India, having differing regional impacts on hominin populations. Several broad refugia can be hypothesized, as can the areas that were most affected by these climatic changes. Although high resolution paleoenvironmental data is required from multiple areas in order to test these hypotheses, the following represents a plausible account of the differing regional impacts of post-Toba paleoclimatic change on Indian environments. Areas of Sri Lanka and south-west India (e.g. the Western Ghats) normally receive high levels of rainfall from the south-west monsoon. A notable decline in precipitation in these regions, coupled with a sudden temperature decline if a volcanic winter occurred, may have had a significant impact on the distribution and survival of tropical evergreen forests, and hence on faunal composition. Decreased rainfall to the Western Ghats would have had a far greater impact on regions further to the east that lie in the rain shadow of the Ghats. A decline in the supply of water to rivers that originate in the Western Ghats and flow eastwards across the Deccan would have initiated droughts in the latter, probably rendering large areas of south-central India uninhabitable for hominins. Marine core evidence from both the Bay of Bengal and Arabian Sea suggests that areas of northern India became very arid post-Toba. During MIS 4, grasslands expanded in north-west India, accompanied by an expansion in the Thar Desert. Decreased vegetation coverage, increased aridity, atmospheric volcanic sulphate aerosols, the Toba ash-fall, and global increase in snow and ice cover all contributed to an increase in the albedo effect, exacerbating and enhancing cooling trends. This may have resulted in decreased rainfall in northern, and particularly, north-east India, yet increased rainfall in southern India. Therefore, large areas of northern India, particularly the Indo-Gangetic Plain and Thar Desert, would have been relatively inhospitable post-Toba due to increased aridity and drought. In contrast, eastern and particularly south-eastern areas of India are argued to have acted as refugia to this aridity post-Toba. These areas benefited from greater rainfall resulting from enhanced north-east monsoons. Areas of the modern-day states of Tamil Nadu, Andhra Pradesh, Orissa, as well as Sri Lanka, are proposed to have escaped the droughts that affected other regions of India. In sum, it is argued that prolonged periods of drought occurred post-Toba and during MIS 4 that had a particularly negative impact on areas of northern and western India. 4.2. Regional impacts of the Toba ash-fall on Indian paleoenvironments The w74 ka Toba eruption blanketed most of peninsular India in volcanic ash, of a primary thickness in the order of w5 cm. Primary ash thickness decreased in a westerly direction; discrete layers of YTT are very thin (w0.1 cm) in marine cores from the northern Arabian sea (von Rad et al., 2002; Schulz et al., 2002), whereas those undisturbed and not bioturbated YTT layers in the northern Bay of Bengal are thicker (Ninkovich et al., 1978a, b; Ninkovich, 1979; Gasparotto et al., 2000), with a mean thickness of w5 cm. On average, the thickness of discrete YTT layers in marine cores located to the south of India, until as far south as the Central Indian Ocean Basin (14
S), are slightly thicker (w8 cm) (Ninkovich et al.,

1978a, b; Ninkovich, 1979; Pattan and Shane, 1999; Pattan et al., 1999, 2002). This suggests that the thickness of primary air-fall ash over the subcontinent gradually decreased in a northwesterly direction, with more ash being deposited in south-eastern regions of India when compared to north-western areas. This hypothesis depends largely on the accurate measurement of primary ash thickness in the northern Arabian Sea cores. From descriptions of the ash layer (von Rad et al., 2002), reworking of ash into thinner layers in secondary contexts cannot be ruled out. Several factors would have determined the severity of the ashfall’s impacts, including the particle size and chemistry of the distal ash, and eruption duration, where the eruption is estimated to have lasted for approximately two weeks (Ledbetter and Sparks, 1979). In addition, regional geography, the mode of ash deposition, and mode, speed and frequency of redeposition events, should also be taken into account. Variation in these factors would have introduced regional differences in the eruption’s impacts. The mode of YTT deposition over India has yet to be investigated. Areas of high rainfall could have received larger volumes of ash, with rainfall causing the aggregation of ash particles during atmospheric circulation as well as the relatively rapid removal of ash from the atmosphere. This process might explain the varying thicknesses of discrete ash layers in marine cores that are located at similar distances from the Toba caldera. The mode of ash redeposition is closely linked to regional climate and geography. For example, in areas with steep slope gradients, relatively rapid redeposition of ash into lower lying areas or “sinks” would have occurred. Some of the best exposures of YTT are preserved in narrow river valleys bordered by relatively steep hill ranges; however, higher incidences of ash exposures are known in these topographies because they have been revealed via fluvial incision. Areas possessing both high sediment accumulation and low erosion rates are conducive to the relatively rapid burial of ash deposits by overlying material. Both rapid redeposition and burial in areas of high relief would have probably resulted in a correspondingly rapid succession of vegetation, limiting the longevity of habitat disruption. In contrast, ash redeposition and burial would have taken place over a significantly longer period of time in areas of low relief (e.g. plains and plateaus). In these areas, ash remobilization by aeolian processes would have been commonplace, preventing its consolidation. Further, areas with limited or absent water supplies and precipitation would have prevented both the movement and consolidation of ash into sinks, as well as the mixing of ash and sediment, the latter containing the organic material required to promote plant succession. Understanding the mode and speed of ash redeposition and the frequency of redeposition events are crucial factors in determining the impact of the Toba ash-fall on Indian environments. The more rapidly ash was redeposited and buried, the lower the frequency of ash remobilization events and the smaller the impact on vegetation, animals and hominins. The increase in aridity that appears to have followed the Toba eruption in some areas of India further increased the length of ash residence in the environment. Spatial and temporal differences in wind strength could have helped or hindered the speed of ash redeposition. While aeolian processes forced ash into topographic depressions, promoting rapid burial, these processes also resulted in the re-entrainment of ash and its further movement across the landscape, thus contributing to the length and extent of environmental damage. Fine-grained distal Toba ash may have had a greater impact on vegetation when compared to larger particles (Hotes et al., 2004) because fine-grained deposits become more compacted, inhibiting the growth of any underlying plants (Dale et al., 2005a). The grain size of ash also determines its toxicity. In this instance, the proportion of thoracic ash (particulate matter less than 10 mm in diameter,

S.C. Jones / Quaternary International 258 (2012) 100e118

PM10) and respirable ash (PM4: particulate matter less than 4 mm in diameter, entering the alveoli of the lungs) (Baxter et al., 1999; Horwell and Baxter, 2006) in Toba ash is rather low when compared to some other eruptions. For example, w5% of Toba ash is PM4. In comparison, w12% for Mount St Helens (in 1980) and w17% for Vesuvius (AD 79) is PM4, where YTT is most comparable to Soufrière Hills, Monteserrat (1997 eruption) where PM4 ash is w6% (Horwell, 2007). Because of this low reading for YTT respirable ash, it is argued that inhalation of distal Toba ash probably did not present any serious consequences for hominin health. Given the great distance between India and Toba it is unclear to what extent, if at all, water sources were rendered toxic by fluorine, heavy metal leachates and acid rain, as these products have yet to be quantified at Indian sites. In areas of increased rainfall, dilution would have reduced the toxicity of the water. In areas with scarce water sources, or enclosed bodies of water that lacked freshwater input, the toxicity may have been greater. The ash-fall may have had a particular impact on grazing animals, reducing population size in areas worst affected by the ash-fall, such as in some river valleys or on grassland plains. The least impacted areas for animals would have been regions possessing variable relief, vegetation coverage and springs or hill streams. Substantial regional variation in the impacts of the Toba ash-fall on Indian environments is proposed here. Areas of varying topography (e.g. the Western Ghats, the hill ranges of the Eastern Ghats, or the Vindhya, Satpura and Aravalli ranges), coupled with adequate sources of potable water from springs or hill streams, are argued to have acted as refugia (see below). In contrast, arid areas, broad and flat plains (particularly grasslands), and wide river valleys, would have been more susceptible to the detrimental impacts of ash-fall on vegetation, animals and water sources. Such areas included, for example, the Thar Desert, large areas of the Indo-Gangetic plain, and flat areas of the Deccan plateau to the east of the Western Ghats. Frequent episodes of ash re-entrainment and redeposition would have been particularly dominant in some of these areas, possibly lasting for decades. 4.3. The impacts of Toba on hominin demography in India Three broad outcomes can be postulated for hominins in India following the Toba eruption; population continuity (with or without adaptation), population extinction, or the extinction of some populations but survival of others in areas of refugia. A number of processes could have produced these outcomes, such as habitat contraction and fragmentation, intra- and inter-specific competition, genetic drift and founder effects, population (and perhaps species) replacement, or forced population migrations. A key question to ask is: did enough individuals survive in order to reproduce and maintain (or even increase) pre-eruption population size, or did populations pass through a demographic bottleneck caused by a net loss of individuals over subsequent generations? The survival rate following the Toba eruption (either immediately afterwards or during the course of several generations) depends upon the extent to which natural selection resulted in the reproductive success of individuals within populations. A decline in reproductive success would lead to a decrease in population size, possibly resulting in genetic (and cultural) drift. Alternatively, hominins may have developed certain adaptations in response to new post-Toba conditions that could have improved overall fitness and reproductive success. Adaptations can represent short-term acquired or learnt responses or they represent the result of natural selection that has taken place over a number of generations (Foley, 1987, p. 55, ). The survival rate following an adaptive shift depends upon the intensity of selection for those adaptations. If reproductive success does not significantly increase as a result of

111

adaptation, then a group or population is again vulnerable to processes of genetic drift. The response of hominin populations to the Toba eruption and resultant ecological disturbances would have been driven by these microevolutionary processes. High amplitude climatic fluctuations had been occurring throughout the earlier phases of the Upper Pleistocene. Therefore, why is it argued that the cold phase that coincided with Toba had a more substantial impact on hominin populations than any of the preceding climatic fluctuations of the Upper Pleistocene? This raises the issue of human adaptation and adaptability. Surely by w74 ka hominin populations had the capacity to cope with and persist through frequent climatic oscillations and environmental changes. The importance of the w74 ka Toba event, however, is undeniable; this was a unique event in hominin evolution, its sheer magnitude, extensive distal ash-fall and putative volcanic winter would have presented hominins in India with a unique set of conditions. The existence or not of environmental refugia in the Indian subcontinent during this interval is critical when considering the extent of Toba’s impact on hominin populations. Here, several geographic areas are proposed to have acted as potential refugia for post-Toba populations in India (Fig. 4). The location of refugia is based on interpretations of evidence discussed above; in other words, evidence at both the local and regional scales regarding the impacts of both paleoclimate change and responses to the ash-fall. In these refugial areas, hominin populations survived, with only minor adaptations. Most areas designated as refugia are in hill ranges. For example, areas of varying relief extending from the southern tip of India to northern Orissa (including the Eastern Ghats and the area around the Chota Nagpur plateau) are hypothesized to have acted as refugia post-Toba. In addition, refugia could have existed in areas of central and eastern Sri Lanka. Some central areas of India can benefit from stronger north-east monsoons (Korisettar, 2007, p. 82). Small areas of the Nilgiri Hills and other regions of the Western Ghats could have also acted as refugia; however, the extent of aridity brought about by weakened south-west monsoons post-Toba and during MIS 4 may have brought drought to these areas. Small isolated refugia could have existed in the hills of the Vindhyas, Satpuras and Aravallis. Areas without refugia likely included the Thar Desert, Indo-Gangetic Plain and parts of the Deccan plateau; the latter was affected by both ashfall and climate change, and the former two areas were predominantly affected by increased aridity. Therefore, large refugia are hypothesized to have existed in areas of southern and eastern India after Toba. In contrast, hominin habitats in areas of northern and western India were relatively fragmented. A decrease in the size and number of viable habitats could have had several consequences. Hominin groups and certain faunal species could have aggregated in small isolated refugia, resulting in an increase in species and hominin population densities. This would concentrate resources of animals, yet the benefits were probably short-lived; in small territories, intra- and interspecies competition, resource decline, population decline, genetic drift and local extinctions could have occurred. By comparison, hominins occupying larger refugia in southern and eastern India would have been less vulnerable; intra-specific competition may have increased to a certain extent but without a major impact on hominin demography or resulting in genetic drift. Hominins occupying areas outside these refugia at the time of Toba would have been greatly affected by depletions in resource density, with the probability that local extinctions occurred being substantially higher. Group mobility could have decreased in non-refugia, if surrounded by inhospitable areas that prevented range expansion. Conversely, narrow corridors with relatively optimal habitats may have provided passage for hominins, resulting in greater mobility

112

S.C. Jones / Quaternary International 258 (2012) 100e118

Fig. 4. Broad areas of India that are hypothesized to have acted as refugia for hominin populations after the Toba eruption. A distinction is made between predicted areas of major refugia (solid black lines) and relatively minor refugia (dotted black lines). Numbered hill ranges are as follows; (1) Aravalli Range; (2) Malwa Plateau; (3) Vindhya Range; (4) Panna Hills; (5) Kaimur Hills; (6) Satpura Range; (7) Gawilgarh Hills; (8) Mahadeo Hills; (9) Maikala Range; (10) Baghelkhand Plateau; (11) Chota Nagpur Plateau; (12) Rajmahal Hills; (13) Garo and Khasi Hills; (14) Patkai Range; (15) Simlipal Massif; (16) Satmala Hills; (17) Ajanta Range; (18) Balaghat Range; (19) Western Ghats; (20) Eastern Ghats; (21) Nilgiri Hills; (22) Cardamom Hills; (23) Palni Hills. Other relevant locations include, (24) Indus river valley; (25) Thar Desert; (26) Rann of Kachchh; (27) Kachchh Hills; (28) Gangetic plain; (29) Ganges-Brahmaputra delta; (30) Karnataka Plateau; (31) Narmada river; (32) Middle Son valley; (33) Jurreru valley.

and range expansion. As a result, group mobility could have increased with hominin groups extending their range in search of resources, facilitating and increasing social contact and sharing between groups (e.g. Gamble, 1999, pp. 11e12). Until now, inclusion of specific hominin taxa in this discussion of Toba and its impacts on hominins in India has been avoided. This is simply because there is no hominin paleontological evidence from India that dates to between >236 ka (Cameron et al., 2004) or 150e250 ka (Kennedy, 2001) and w30 ka, with the latter representing H. sapiens from cave sites in Sri Lanka (Kennedy, 1999, 2001). The oldest fossil evidence is represented by a cranium from the Central Narmada valley, assigned to Homo heidelbergensis by some (Kennedy, 2001; Cameron et al., 2004) or Homo erectus by others (Sonakia and Biswas,1998; Athreya, 2007). The taxonomy of this fossil specimen remains controversial. Any suggestions regarding the species that inhabited India w74 ka remain hypothetical and controversial. Ambrose (2003a, b) assumes that H. sapiens was restricted to Africa and Western Asia at the time of the eruption, whereas others argue that H. sapiens also inhabited India (Petraglia et al., 2007) and Southeast Asia (Oppenheimer, 2003) before w74 ka. It is argued here that populations of H. sapiens could have inhabited India both before and after the Toba eruption, even from as early as MIS 5e. The presence of H. heidelbergensis and even Homo neanderthalensis populations in India during this period cannot be ruled out as a possibility, although the presence of Neanderthals in

South Asia seems unlikely given the biogeography of the species and their adaptations to more northerly latitudes and colder climates. Yet, it is more plausible that the documented exodus of early H. sapiens from Africa to Western Asia, where H. sapiens fossils are dated to w130 to 90 ka (Stringer, 2002; Grün et al., 2005) at sites in Israel, may have also extended as far as India. In this scenario, the presence of two species in India during MIS 5e could be envisaged; early H. sapiens and relict H. heidelbergensis populations (or H. sp. indet., to express greater caution over the taxonomic affiliation of the Narmada cranium). Evidence in support of an early eastwards expansion of H. sapiens out of Africa comes from recent research in the United Arab Emirates. Here, lithic assemblages dating to MIS 5e are argued to be similar to MSA assemblages from East and North-east Africa, the authors suggesting an early dispersal of H. sapiens from East Africa into Arabia at the start of the last Interglacial w125 ka (Armitage et al., 2011). Figs. 5e7 present a series of models which place the Toba eruption within the context of hominin evolution in India during the Upper Pleistocene. The models hypothesize the broad-scale changes in demography that may have occurred in India from MIS 6 to MIS 3. The rationale behind hypothesizing hominin population dynamics over such a long timescale has been outlined at the end of the introduction to this paper. The annotations on the figures describe the hypothesized demographic processes and events that occurred during each oxygen isotope stage. The refugia model of Fig. 4 is used to predict the spatial distribution of different

S.C. Jones / Quaternary International 258 (2012) 100e118

113

Fig. 5. Hypothesized demographic events during MIS 7 and MIS 6.

populations post-Toba. The models incorporate two hominin species over this time period; H. heidelbergensis (or H. sp. indet.) and H. sapiens. Perhaps one of the most controversial aspects of these models is that separate periods of colonization by different H. sapiens populations are hypothesized, both after Toba and also a substantial period of time before.

Genetic studies of extant human populations indicates that all present-day populations within India, as well as other regions outside Africa, are descended from dispersals out of Africa dated to within the time-frame of the Toba eruption; these populations bear the genetic signature of mtDNA haplogroups M and N, daughter clades of the African L3 haplogroup (e.g. Kivisild et al., 2006;

Fig. 6. Hypothesized demographic events during MIS 5.

114

S.C. Jones / Quaternary International 258 (2012) 100e118

Fig. 7. Hypothesized demographic events after the Toba eruption, throughout MIS 4 and during MIS 3.

Metspalu et al., 2006). The vast majority of genetic studies provide coalescence dates to indicate that H. sapiens populations bearing the M and N mtDNA haplogroups dispersed into India after the Toba eruption (e.g. Quintana-Murci et al., 1999; Palanichamy et al., 2004; Macauley et al., 2005; Thangaraj et al., 2005; Chaubey et al., 2006; Kivisild et al., 2006; Metspalu et al., 2006). The model presented here proposes that these incoming populations were not the first H. sapiens in the subcontinent; instead, they encountered indigenous populations of H. sapiens that inhabited India possibly since the early part of the Upper Pleistocene. Archaeological evidence reveals that hominins with Middle Paleolithic technologies certainly occupied India during this period and what needs to be explained is which species created this record, and importantly, if more than one species was responsible. While this model is one of several possible scenarios, it presents a plausible version of Upper Pleistocene demographic events in the subcontinent, informed by genetic, archaeological and paleontological evidence from India and regions beyond. Testing of this hypothesis can only take place when more evidence from India, and in particular hominin fossil evidence, comes to light. 5. Concluding remarks Distinguishing cause from coincidence continues to present a challenge to volcano-impact studies, particularly those dealing with evidence of such antiquity. This is the case with sites dating to the time-frame of the Toba eruption, where error margins of at least a thousand years in association with absolute dates are the norm. Nonetheless, the geological and archaeological deposits of the Jurreru valley provide the best record in India of in-situ archaeology lying in direct association with Toba ash dating closely to both before

and after the eruption. Although comparable ash-archaeology associations in the Middle Son valley have yet to be pin-pointed, there is every reason to anticipate that continued interdisciplinary and collaborative investigations, which have proven so productive, will continue to refine our picture of this promising record. Studies of the Paleolithic period in India that incorporate and synthesize evidence related to archaeology, geology, paleoenvironment and hominin evolutionary theory are still rare. This paper has hopefully demonstrated the benefits that come from such integration and has provided a reasoned interpretation of the impact of the Toba supereruption on hominin evolution, strongly informed by the current extent of empirical evidence. Here, it is argued that Toba had highly varied impacts throughout India on both habitats and hominin populations, with localized population extinctions in certain areas yet population survival and continuity in refugia. This heterogeneity of responses to Toba should not be surprising given the regional diversity that existed across India in terms of starkly contrasting geographies, palaeoclimatic regimes, ecosystems and hominin socio-cultural behaviors. This complex interplay between multiple factors would have rendered some populations more vulnerable than others (Sheets, 2007, p. 85). Explaining and quantifying this variation is critical when assessing the impacts of the Toba eruption on hominin populations and their habitats in India and in regions beyond. Acknowledgments This research was supported by doctoral research studentships from Newnham College and an Allen, Meek and Read scholarship from the University of Cambridge. Additional grants were awarded by the Sir Richard Stapley Educational Trust, The Prehistoric

S.C. Jones / Quaternary International 258 (2012) 100e118

Society, The Society of Antiquaries of London, Newnham College, the Faculty of Archaeology and Anthropology (Anthony Wilkin Fund), and the University of Cambridge (Smuts Memorial Fund, Worts Travelling Scholars Fund). The Jurreru valley data is the product of a team effort, and for their help I would like to thank Michael Petraglia, Ravi Korisettar, Clive Oppenheimer, Chris Clarkson, Peter Ditchfield, Kevin White, Preston Miracle, Dorian Fuller, Bert Roberts, Jean-Luc Schwenninger, Lee Arnold, Kevin Cunningham, Ceri Shipton, Jinu Koshy, Janardhana B., Arawazhi, M. Kasturi Bai, Pragnya Prasanna and numerous villagers from Jwalapuram and Pathapadu. Collection of the Middle Son data would not have been possible without the help of J.N. Pal and M.C. Gupta at the University of Allahabad who facilitated and supported fieldwork in the valley and my analysis of artifacts in the G.R. Sharma Memorial Museum and. I thank David Pyle, Jason Day, Chris Hayward, Chris Rolfe, Steve Boreham, Craig Chesner and John Westgate for assistance regarding tephra and sedimentological analyses. Paul Mellars and Larry Barham are thanked for discussions and Ryan Rabett is thanked for his comments on an earlier draft of this paper. References Acharyya, S.K., Basu, P.K., 1993. Toba ash on the Indian subcontinent and its implications for correlation of Late Pleistocene alluvium. Quaternary Research 40, 10e19. Ambrose, S.H., 1998. Late Pleistocene human populations bottlenecks, volcanic winter, and differentiation of modern humans. Journal of Human Evolution 34, 623e651. Ambrose, S.H., 2003a. Population Bottleneck. In: Robinson, R. (Ed.), Genetics, vol. 3. Macmillan, New York, pp. 167e171. Ambrose, S.H., 2003b. Did the super-eruption of Toba cause a human population bottleneck? Reply to Gathorne-Hardy and Harcourt-Smith. Journal of Human Evolution 45 (3), 231e237. Antos, J.A., Zobel, D.B., 1986. Recovery of forest understories buried by tephra from Mount St. Helens. Plant Ecology 64 (2e3), 103e111. Armitage, S.J., Jasim, S.A., Marks, A.E., Parker, A.G., Usik, V.I., Uerpmann, H.-P., 2011. The southern route “Out of Africa”: evidence for an early expansion of modern humans into Arabia. Science 331, 453e456. Athreya, S., 2007. Was Homo heidelbergensis in South Asia? A test using the Narmada fossil from central India. In: Petraglia, M.D., Allchin, B. (Eds.), The Evolution and History of Human Populations in South Asia. Inter-disciplinary Studies in Archaeology, Biological Anthropology, Linguistics and Genetics. Springer, Dordrecht, pp. 137e170. Badam, G.L., Misra, V.D., Pal, J.N., Pandey, J.N., 1989. A preliminary study of Pleistocene fossils from the Middle Son valley, Madhya Pradesh. Man and Environment 13, 41e47. Baillie, M.G.L., Munro, M.A.R., 1988. Irish tree rings, Santorini and volcanic dust veils. Nature 322, 344e346. Barboni, D., Bonnefille, R., 2001. Precipitation signal in pollen rain from tropical forests, South India. Review of Palaeobotany and Palynology 114, 239e258. Basu, P.K., Biswas, S., Acharyya, S.K., 1987. Late Quaternary ash beds from Son and Narmada basins, Madhya Pradesh. Indian Minerals 41 (2), 66e72. Baxter, P.J., 2005. Human impacts of volcanoes. In: Martí, J., Ernst, G.G.J. (Eds.), Volcanoes and the Environment. Cambridge University Press, Cambridge, pp. 273e303. Baxter, P.J., Bonadonna, C., Dupree, R., Hards, V.L., Kohn, S.C., Murphy, M.D., Nichols, A., Nicholson, R.A., Norton, G., Searl, A., Sparks, R.S.J., Vickers, B.P., 1999. Cristobalite in volcanic ash of the Soufriere Hills volcano, Montserrat, British West Indies. Science 283, 1142e1145. Bekki, S., Pyle, J.A., Zhong, W., Toumi, R., Haigh, J.D., Pyle, D.M., 1996. The role of microphysical and chemical processes in prolonging the climate forcing of the Toba eruption. Geophysical Research Letters 23, 2669e2672. Blong, R.J., 1982. The Time of Darkness. University of Washington Press, Seattle and London. Blumenschine, R.J., Chattopadhyaya, U.C., 1983. A preliminary report on the terminal Pleistocene fauna of the Middle Son valley. In: Sharma, G.R., Clark, J.D. (Eds.), Palaeoenvironments and Prehistory in the Middle Son Valley. Abinash Prakashan, Allahabad, pp. 281e284. Blunier, T., Brook, E., 2001. Timing of millennial-scale climate change in Antarctica and Greenland during the last glacial period. Science 291, 109e112. Boyd, W.E., Lentfer, C.J., Parr, J., 2005. Interactions between human activity, volcani eruptions and vegetation during the Holocene at Garua and Numondo, West New Britain, PNG. Quaternary Research 64, 384e398. Cameron, D., Patnaik, R., Sahni, A., 2004. The phylogenetic significance of the Middle Pleistocene Narmada hominin cranium from central India. International Journal of Osteoarchaeology 14 (6), 419e447. Capron, E., Landais, A., Lemieux-Dudon, B., Schilt, A., Masson-Delmotte, V., Buiron, D., Chappellaz, J., Dahl-Jensen, D., Johnsen, S., Leuenberger, M.,

115

Loulergue, L., Oerter, H., 2010. Synchronising EDML and NorthGRIP ice cores using d18O of atmospheric oxygen (d18Oatm) and CH4 measurements over MIS5 (80e123 kyr). Quaternary Science Reviews 29, 222e234. Chamyal, L.S., Maurya, D.M., Raj, R., 2003. Fluvial systems of the drylands of western India: a synthesis of Late Quaternary environmental and tectonic changes. Quaternary International 104, 69e86. Charman, D., West, S., Kelly, A., Grattan, J., 1995. Environmental change and tephra deposition: the Strath of Kildonan, Northern Scotland. Journal of Archaeological Science 22, 799e809. Chaubey, G., Metspalu, M., Kivisild, T., Villems, R., 2006. Peopling of South Asia: investigating the caste-tribe continuum in India. BioEssays 29, 91e100. Chesner, C.A., Rose, W.I., 1991. Stratigraphy of the Toba Tuffs and the evolution of the Toba Caldera complex, Sumatra, Indonesia. Bulletin of Volcanology 53, 343e356. Clark, J.D., Williams, M.A.J., 1987. Paleoenvironments and prehistory in North Central India: a preliminary report. In: Jacobsen, J. (Ed.), Studies in the Archaeology of India and Pakistan. Aris and Phillips Ltd, Warminster, pp. 19e41. Colin, C., Kissel, C., Blamart, D., Turpin, L., 1998. Magnetic properties of sediments in the Bay of Bengal and the Andaman Sea: impact of rapid North Atlantic Ocean climatic events on the strength of the Indian monsoon. Earth and Planetary Science Letters 160, 623e635. Cronin, S.J., Hedley, M.J., Neall, V.E., Smith, R.G., 1998. Agronomic impact of tephra fallout from the 1995 and 1996 Ruapehu volcano eruptions, New Zealand. Environmental Geology 34 (1), 21e30. Cronin, S.J., Manoharan, V., Hedley, M.J., Loganathan, P., 2000. Flouride: a review of its fate, bioavailability, and risks of fluorosis in grazed-pasture systems in New Zealand. New Zealand Journal of Agricultural Research 43, 295e321. Cruz, F.W., Burns, S.J., Karmann, I., Sharp, W.D., Vuille, M., Cardoso, A.O., Ferrari, J.A., Silva Dias, P.L., Viana, O., 2005. Insolation-driven changes in atmospheric circulation over the past 116,000 years in subtropical Brazil. Nature 434, 63e66. Dale, V.H., Crisafulli, C.M., Swanson, F.J., 2005b. 25 years of ecological change at Mount St. Helens. Science 308, 961e962. Dale, V.H., Delgado-Acevedo, J., MacMahon, J., 2005a. Effects of modern volcanic eruptions on vegetation. In: Martí, J., Ernst, G.G.J. (Eds.), Volcanoes and the Environment. Cambridge University Press, Cambridge, pp. 227e249. Dansgaard, W., Johnsen, S.J., Clausen, H.B., Dahl-Jensen, D., Gundestrup, N.S., Hammer, C.U., Hvidberg, C.S., Steffensen, J.P., Sveinbjörnsdóttir, A.E., Jouzel, J., Bond, G., 1993. Evidence for general instability of past climate from a 250-kyr ice-core record. Nature 364, 218e220. Dassarma, D.C., Biswas, S.,1977. Newly discovered late Quaternary vertebrates from the terraced alluvial fills of the Son valley. Indian Journal of Earth Sciences 4 (2), 122e136. del Moral, R., Grishin, S.Y., 1999. Volcanic disturbances and ecosystem recovery. In: Walker, L.R. (Ed.), Ecosystems of Disturbed Ground. Elsevier, Amsterdam, pp. 137e160. Dennell, R.W., Rendell, H.M., Halim, M., Moth, E., 1992. A 45-000-year-old open-air Paleolithic site at Riwat, northern Pakistan. Journal of Field Archaeology 19 (1), 17e33. Eastwood, W.J., Tibby, J., Roberts, N., Birks, H.J.B., Lamb, H.F., 2002. The environmental impact of the Minoan eruption of Santorini (Thera): statistical analysis of palaeoecological data from Gölhisar, southwest Turkey. The Holocene 12 (4), 431e444. Edwards, J.S., 2005. Animals and volcanoes: survival and revival. In: Martí, J., Ernst, G.G.J. (Eds.), Volcanoes and the Environment. Cambridge University Press, Cambridge, pp. 250e272. Flückiger, J., Blunier, T., Stauffer, B., Chappellaz, J., Spahni, R., Kawamura, K., Schwander, J., Stocker, T.F., Dahl-Jensen, D., 2004. N2O and CH4 variations during the last glacial epoch: insight into global processes. Global Biogeochemical Processes 18, 1e14. Foley, R., 1987. Another Unique Species: Patterns in Human Evolutionary Ecology. Longman Group UK Limited, Harlow. Gagneux, P., Wills, C., Gerloff, U., Tautz, D., Morin, P.A., Boesch, C., Fruth, B., Hohmann, G., Ryder, O.A., Woodruff, D.S., 1999. Mitochondrial sequences show diverse evolutionary histories of African hominoids. Proceedings of the National Academy of Sciences 96, 5077e5082. Gamble, C., 1999. The Palaeolithic Societies of Europe. Cambridge University Press, Cambridge. Gasparotto, G., Spadafora, E., Summa, V., Tateo, F., 2000. Contribution of grain size and compositional data from the Bengal Fan sediment to the understanding of Toba volcanic event. Marine Geology 162, 561e572. Gathorne-Hardy, F., Harcourt-Smith, W., 2003. The super-eruption of Toba, did it cause a human bottleneck? Journal of Human Evolution 45 (3), 227e230. Goldberg, T.L., Ruvolo, M., 1997. The geographic apportionment of mitochondrial genetic diversity in East African chimpanzees, Pan troglodytes schweinfurthii. Molecular Biology and Evolution 14, 976e984. Grattan, J., 2006. Aspects of Armageddon: an exploration of the role of volcanic eruptions in human history and civilization. Quaternary International 151, 10e18. Grattan, J., Michnowicz, S., Rabartin, R., 2007. The long shadow: understanding the influence of the Laki fissure eruption on human mortality in Europe. In: Grattan, J., Torrence, R. (Eds.), Living under the Shadow: The Cultural Impacts of Volcanic Eruptions. Left Coast Press, Inc., Walnut Creek, CA, pp. 153e174. Grattan, J., Torrence, R., 2007a. Living under the Shadow: The Cultural Impacts of Volcanic Eruptions. Left Coast Press, Inc., Walnut Creek, CA. Grattan, J., Torrence, R., 2007b. Beyond gloom and doom: the long-term consequences of volcanic disasters. In: Grattan, J., Torrence, R. (Eds.), Living under the

116

S.C. Jones / Quaternary International 258 (2012) 100e118

Shadow: The Cultural Impacts of Volcanic Eruptions. Left Coast Press, Inc., Walnut Creek, CA, pp. 1e18. Grün, R., Stringer, C., McDermott, F., Nathan, R., Porat, N., Robertson, S., Taylor, L., Mortimer, G., Eggins, S., McCulloch, M., 2005. U-series and ESR analyses of bones and teeth relating to the human burials from Skhul. Journal of Human Evolution 49, 316e334. Gupta, A., Thapliyal, P.K., Pal, P.K., Joshi, P.C., 2005. Impact of deforestation on Indian monsoon e a GCM sensitivity study. The Journal of Indian Geophysical Union 9 (2), 97e104. Hall, V.A., 2003. Assessing the impact of Icelandic volcanism on vegetation systems in the north of Ireland in the fifth and sixth millennia BC. The Holocene 13 (1), 131e138. Halpern, C.B., Frenzen, P.M., Means, J.E., Franklin, J.F., 1990. Plant succession in areas of scorched and blown-down forest after the 1980 eruption of Mount St. Helens, Washington. Journal of Vegetation Science 1 (2), 181e194. Hansell, A., 2003. Respiratory effects of volcanic emissions. Occupational and Environmental Medicine 60, 529e530. Hardardóttir, J., Geirsdóttir, A., Thórdarson, T., 2001. Tephra layers in a sediment core from Lake Hestvatn, southern Iceland: implications for evaluating sedimentation processes and environmental impacts on a lacustrine system caused by tephra fall deposits in the surrounding watershed. In: White, J.D.L., Riggs, N.R. (Eds.), Volcaniclastic Sedimentation in Lacustrine Settings. Blackwell Science, U.K, pp. 225e246. Harpending, H.C., Sherry, S.T., Rogers, A.R., Stoneking, M., 1993. The genetic structure of ancient human populations. Current Anthropology 34 (4), 483e496. Haslam, M., Clarkson, C., Petraglia, M., Korisettar, R., Janardhana, B., Boivin, N., Ditchfield, P., Jones, S., Mackay, A., 2010b. Indian lithic technology prior to the 74,000 bp Toba super-eruption: searching for an early modern human signature. In: Boyle, K.V., Gamble, C., Bar-Yosef, O. (Eds.), The Upper Palaeolithic Revolution in Global Perspective: Papers in Honour of Sir Paul Mellars. McDonald Institute for Archaeological Research, Cambridge, pp. 73e84. Haslam, M., Clarkson, C., Petraglia, M., Korisettar, R., Jones, S., Shipton, C., Ditchfield, P., Ambrose, S.H., 2010a. The 74 ka Toba super-eruption and southern Indian hominins: archaeology, lithic technology and environments at Jwalapuram Locality 3. Journal of Archaeological Science 37, 3370e3384. Haslam, M., Petraglia, M., 2010. Comment on “Environmental impact of the 73 ka Toba super-eruption in South Asia” by M.A.J. Williams, S.H. Ambrose, S. van der Kaars, C. Ruehlemann, U. Chattopadhyaya, J. Pal and P.R. Chauhan. Palaeogeography, Palaeoclimatology, Palaeoecology 296, 199e203. Horwell, C.J., 2007. Grain-size analysis of volcanic ash for the rapid assessment of respiratory health hazard. Journal of Environmental Monitoring 9, 1107e1115. Horwell, C.J., Baxter, P.J., 2006. The respiratory health hazards of volcanic ash: a review for volcanic risk mitigation. Bulletin of Volcanology 69, 1e24. Hotes, S., Poschlod, P., Takahashi, H., Grootjans, A.P., Adema, E., 2004. Effects of tephra deposition on mire vegetation: a field experiment in Hokkaido, Japan. Journal of Ecology 92, 624e634. Huang, C.-Y., Wang, C.-C., Zhao, M., 1999. High-resolution carbonate stratigraphy of IMAGES core MD972151 from South China Sea. Terrestrial Atmospheric and Oceanic Sciences 10 (1), 225e238. Huang, C.-Y., Zhao, M., Wang, C.-C., Wei, G., 2001. Cooling of the South China Sea by the Toba eruption and correlation with other climate proxies w71,000 years ago. Geophysical Research Letters 28 (20), 3915e3918. Inbar, M., Ostera, H.A., Parica, C.A., Remesal, M.B., Salani, F.M., 1995. Environmental assessment of 1991 Hudson volcano eruption ashfall effects on southern Patagonia region, Argentina. Environmental Geology 25, 119e125. Jago, L.C.F., Boyd, W.E., 2005. How a wet tropical rainforest copes with repeated volcanic destruction. Quaternary Research 64, 399e406. Jain, M., Tandon, S.K., 2003. Fluvial response to Late Quaternary climate changes, western India. Quaternary Science Reviews 22, 2223e2235. Jones, M.T., Sparks, R.S.J., Valdes, P.J., 2007. The climatic impact of supervolcanic ash blankets. Climate Dynamics 29, 553e564. Jones, S.C., 2007a. The Toba supervolcanic eruption: tephra-fall deposits in India and palaeoanthropological implications. In: Petraglia, M.D., Allchin, B. (Eds.), The Evolution and History of Human Populations in South Asia. Springer/ Kluwer Academic Publishers, New York, pp. 173e200. Jones, S.C., 2007b. A human catastrophe? The impact of the w74,000 year-old supervolcanic eruption of Toba on hominin populations in India. Unpublished PhD dissertation. Department of Biological Anthropology, University of Cambridge, Cambridge. Jones, S.C., 2010. Palaeoenvironmental response to the w74 ka Toba ash-fall in the Jurreru and Middle Son valleys in southern and north-central India. Quaternary Research 73, 336e350. Jones, S.C., Pal, J.N., 2005. The Middle Son valley and the Toba supervolcanic eruption of 74 kyr BP: youngest Toba tuff deposits and Palaeolithic associations. Journal of Interdisciplinary Studies in History and Archaeology 2 (1), 47e62. Jones, S.C., Pal, J.N., 2009. The Palaeolithic of the Middle Son valley, north-central India: changes in hominin lithic technology and behaviour during the Upper Pleistocene. Journal of Anthropological Archaeology 28, 323e341. Jouzel, J., Stiévenard, M., Johnsen, S.J., Landais, A., Masson-Delmotte, V., Sveinbjornsdottir, A., Vimeux, F., von Grafenstein, U., White, J.W.C., 2007. The GRIP deuterium-excess record. Quaternary Science Reviews 26, 1e17. Juyal, N., Chamyal, L.S., Bhandari, S., Maurya, D.M., Singhvi, A.K., 2004. Environmental changes during Late Pleistocene in the Orsang river basin, western India. Journal Geological Society of India 64, 471e479.

Kataoka, K.S., Manville, V., Nakajo, T., Urabe, A., 2009. Impacts of explosive volcanism on distal alluvial sedimentation: examples from the Pliocene-Holocene volcaniclastic successions of Japan. Sedimentary Geology 220, 306e317. Kennedy, K.A.R., 1999. Paleoanthropology of south Asia. Evolutionary Anthropology 8 (5), 165e185. Kennedy, K.A.R., 2001. Middle and late Pleistocene hominids of South Asia. In: Tobias, P.V., Raath, M.A., Moggi-Cecchi, J., Doyle, G.A. (Eds.), Humanity from African Naissance to Coming Millennia e Colloquia in Human Biology and Palaeoanthropology. Florence University Press, Florence, pp. 167e174. Kivisild, T., Shen, P., Wall, D.P., Do, B., Sung, R., Davis, K., Passarino, G., Underhill, P.A., Scharfe, C., Torroni, A., Scozzari, R., Modiano, D., Coppa, A., de Knijff, P., Feldman, M., Cavalli-Sforza, L.L., Oefner, P.J., 2006. The role of selection in the evolution of human mitochondrial genomes. Genetics 172, 373e387. Korisettar, R., 2007. Toward developing a basin model for Paleolithic settlement of the Indian subcontinent: geodynamics, monsoon dynamics, habitat diversity and dispersal routes. In: Petraglia, M.D., B. Allchin (Eds.), The Evolution and History of Human Populations in South Asia. Inter-disciplinary Studies in Archaeology, Biological Anthropology, Linguistics and Genetics. Springer, Dordrecht, pp. 69e98. Kudrass, H.R., Hofmann, A., Doose, H., Emeis, K., Erlenkeuser, H., 2001. Modulation and amplification of climatic changes in the Northern Hemisphere by the Indian summer monsoon during the past 80 k.y. Geology 29 (1), 63e66. Lahr, M.M., Foley, R., 1998. Towards a theory of modern human origins: geography, demography, and diversity in recent human evolution. Yearbook of Physical Anthropology 41, 137e176. Landais, A., Dreyfus, G., Capron, E., Masson-Delmotte, V., Sanchez-Goñi, M.F., Desprat, S., Hoffman, G., Jouzel, J., Leuenberger, M., Johnsen, S., 2010. What drives the millennial and orbital variation of d18Oatm? Quaternary Science Reviews 29, 235e246. Ledbetter, M., Sparks, R.S.J., 1979. The duration of large-magnitude silicic eruptions deduced from graded bedding in deep-sea tephra layers. Geology 7, 240e244. Lee, M.-Y., Wei, K.-Y., Chen, Y.-G., 1999. High resolution oxygen isotope stratigraphy for the last 150,000 years in the southern south China Sea: core MD972151. Terrestrial Atmospheric and Oceanic Sciences 10 (1), 239e254. Leuschner, D.C., Sirocko, F., 2000. The low-latitude monsoon climate during Dansgaard-Oeschger cycles and Heinrich Events. Quaternary Science Reviews 19, 243e254. Louys, J., 2007. Limited effect of the Quaternary’s largest super-eruption (Toba) on land mammals from Southeast Asia. Quaternary Science Reviews 26, 3108e3117. Lowe, J.J., Walker, M.J.C., 1997. Reconstructing Quaternary Environments. Longman, Harlow. Macaulay, V., Hill, C., Achilli, A., Rengo, C., Clarke, D., Meehan, W., Blackburn, J., Semino, O., Scozzari, R., Cruciani, F., Taha, A., Shaari, N.K., Raja, J.M., Ismail, P., Zainuddin, Z., Goodwin, W., Bulbeck, D., Bandelt, H.-J., Oppenheimer, S., Torroni, A., Richards, M., 2005. Single, rapid coastal settlement of Asia revealed by analysis of complete mitochondrial genomes. Science 308 (5724), 1034e1036. Mack, R.N., 1981. Initial effects of ashfall from Mount St Helens on vegetation in Eastern Washington and adjacent Idaho. Science 213, 537e539. Manville, V., Segschneider, B., Newton, E., White, J.D.L., Houghton, B.F., Wilson, C.J.N., 2009. Environmental impact of the 1.8 ka Taupo eruption, New Zealand: landscape responses to a large-scale explosive rhyolite eruption. Sedimentary Geology 220, 318e336. Martin, R.S., Watt, S.F.L., Pyle, D.M., Mather, T.A., Matthews, N.E., Geord, R.B., Day, J.A., Fairhead, T., Witt, M.L.I., Quayle, B.M., 2009. Environmental effects of ashfall in Argentina from the 2008 Chaitén volcanic eruption. Journal of Volcanology and Geothermal Research 184, 462e472. Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore, T.C., Shackleton, N.J., 1987. Age dating and the orbital theory of the ice ages: development of a high resolution 0e300,000 year chronostratigraphy. Quaternary Research 27, 1e29. McCoy, F., Heiken, G., 2000. Volcanic Hazards and Disasters in Human Antiquity. Geological Society of America, Boulder. McGuire, W.J., Griffiths, D.R., Hancock, P.L., Stewart, I.S., 2000. The Archaeology of Geological Catastrophes. Special Publication 171. The Geological Society, London. Mellars, P., 2006a. Why did modern human populations disperse from Africa ca. 60,000 years ago? A new model. Proceedings of the National Academy of Science 103 (25), 9381e9386. Mellars, P., 2006b. Going East: new genetic and archaeological perspectives on the modern human colonization of Eurasia. Science 313, 796e800. Metspalu, E., Kivisild, T., Bandelt, H.-J., Richards, M., Villems, R., 2006. The pioneer settlement of modern humans in Asia. In: Bandelt, H.-J., Macaulay, V., Richards, M. (Eds.), Human Mitochondrial DNA and the Evolution of Homo Sapiens, vol. 18. Springer-Verlag, Berlin Heidelberg, pp. 181e199. Newhall, C.G., Punongbayan, R.S., 1996. Fire and Mud. University of Washington Press, Seattle. Ninkovich, D., 1979. Distribution, age and chemical composition of tephra layers in deep-sea sediments off western Indonesia. Journal of Volcanology and Geothermal Research 5, 67e86. Ninkovich, D., Shackleton, N.J., Abdel-Monem, A.A., Obradovich, J.D., Izett, G., 1978a. K-Ar age of the late Pleistocene eruption of Toba, north Sumatra. Nature 276, 574e577. Ninkovich, D., Sparks, R.S.J., Ledbetter, M.T., 1978b. The exceptional magnitude and intensity of the Toba eruption, Sumatra: an example of the use of deep-sea tephra layers as a geological tool. Bulletin Volcanologique 41, 286e298.

S.C. Jones / Quaternary International 258 (2012) 100e118 Oppenheimer, C., 2002. Limited global change due to the largest known Quaternary eruption, Toba 74 kyr BP? Quaternary Science Reviews 21, 1593e1609. Oppenheimer, S., 2003. Out of Eden. The Peopling of the World. Constable, London. Oppenheimer, S., 2009. The great arc of dispersal of modern humans: africa to Australia. Quaternary International 202, 2e13. Palanichamy, M.G., Sun, C., Agrawal, S., Bandelt, H.-J., Kong, Q.-P., Khan, F., Wang, C.-Y., Chaudhuri, T.K., Palla, V., Zhang, Y.-P., 2004. Phylogeny of Mitochondrial DNA macrohaplogroup N in India, based on complete sequencing: implications for the peopling of South Asia. American Journal of Human Genetics 75, 966e978. Pandarinath, K., Prasad, S., Gupta, S.K., 1999. A 75 ka record of palaeoclimatic changes inferred from crystallinity of illite from Nal Sarovar, western India. Journal Geological Society of India 54, 515e522. Pattan, J.N., Pearce, N.J.G., Banakar, V.K., Parthiban, G., 2002. Origin of ash in the Central Indian Ocean Basin and its implication for the volume estimate of the 74,000 year BP Youngest Toba eruption. Current Science 83 (7), 889e893. Pattan, J.N., Shane, P., 1999. Excess aluminum in deep sea sediments of the Central Indian Basin. Marine Geology 161 (2), 247e255. Pattan, J.N., Shane, P., Banakar, V.K., 1999. New occurrence of youngest Toba tuff in abyssal sediments of the central Indian basin. Marine Geology 155, 243e248. Petraglia, M., Haslam, M., Fuller, D., Boivin, N., Clarkson, C., 2010. Out of Africa: new hypotheses and evidence for the dispersal of Homo sapiens along the Indian Ocean rim. Annals of Human Biology 37, 288e311. Petraglia, M., Korisettar, R., Bai, M.K., Boivin, N., Janardhana, B., Clarkson, C., Cunningham, K., Ditchfield, P., Fuller, D., Hampson, J., Haslam, M., Jones, S., Koshy, J., Miracle, P., Oppenheimer, C., Roberts, R., White, K., 2009. Human occupation, adaptation and behavioral change in the Pleistocene and Holocene of south India: recent investigations in the Kurnool district, Andhra Pradesh. Eurasian Prehistory 6 (1e2), 119e166. Petraglia, M., Korisettar, R., Boivin, N., Clarkson, C., Ditchfield, P., Jones, S., Koshy, J., Lahr, M.M., Oppenheimer, C., Pyle, D., Roberts, R., Schwenninger, J.-L., Arnold, L., White, K., 2007. Middle Paleolithic assemblages from the Indian subcontinent before and after the Toba super-eruption. Science 317 (5834), 114e116. Potts, R., 1998. Environmental hypotheses of hominin evolution. Yearbook of Physical Anthropology 41, 93e136. Prabhu, C.N., Shankar, R., Anupama, K., Taieb, M., Bonnefille, R., Vidal, L., Prasad, S., 2004. A 200-ka pollen and oxygen-isotopic record from two sediment cores from the eastern Arabian Sea. Palaeogeography, Palaeoclimatology, Palaeoecology 214, 309e321. Quintana-Murci, L., Semino, O., Bandelt, H.-J., Passarino, G., McElreavey, K., Santachiara-Benerecetti, A.S., 1999. Genetic evidence of an early exit of Homo sapiens sapiens from Africa through eastern Africa. Nature Genetics 23, 437e441. Rajagopalan, G., Sukumar, R., Ramesh, R., Pant, R.K., Rajagopalan, G., 1997. Late Quaternary vegetational and climatic changes from tropical peats in southern India e an extended record up to 40,000 years BP. Current Science 73 (1), 60e63. Rampino, M.R., Ambrose, S.H., 2000. Volcanic winter in the Garden of Eden: the Toba supereruption and the late Pleistocene human population crash. Special Paper, 345. In: McCoy, F.W., Heiken, G. (Eds.), Volcanic Hazards and Disasters in Human Antiquity. Geological Society of America, Boulder, Colorado, pp. 71e82. Rampino, M.R., Self, S., 1992. Volcanic winter and accelerated glaciation following the Toba super-eruption. Nature 359, 50e52. Rampino, M.R., Self, S., 1993a. Climate-volcanism feedback and the Toba eruption of w74,000 years ago. Quaternary Research 40, 269e280. Rampino, M.R., Self, S., 1993b. Bottleneck in human evolution and the Toba eruption. Science 262 (5142), 1955. Rao, V., Rao, C.V.N.K., 1992. Palaeontological studies of the cave fauna of Kurnool district, Andhra Pradesh. Records of the Geological Survey of India 135 (5), 240e241. Reddy, K.T., 2001. Archaeology of the Eastern Ghats: an ecological overview. Man and Environment 26 (2), 1e16. Rees, J.D., 1979. Effects of the eruption of Parícutin volcano on landforms, vegetation, and human occupancy. In: Sheets, P., Grayson, D.K. (Eds.), Volcanic Activity and Human Ecology. Academic Press, New York, pp. 249e292. Riedel, J.L., Pringle, P.T., Schuster, R.L., 2001. Deposition of Mount Mazama tephra in a landslide-dammed lake on the upper Skagit River, Washington, USA. In: White, J.D.L., Riggs, N.R. (Eds.), Volcaniclastic Sedimentation in Lacustrine Settings. Blackwell Science, U.K, pp. 285e298. Robock, A., Ammann, C.M., Oman, L., Sindell, D., Levis, S., Stenchikov, G., 2009. Did the Toba volcanic eruption of w74 ka B.P. produce widespread glaciation? Journal of Geophysical Research 114, D10107. Rogers, A.R., Jorde, L.B., 1995. Genetic evidence on modern human origins. Human Biology 67 (1), 1e36. Rose, W.I., Chesner, C.A., 1987. Dispersal of ash in the great Toba eruption, 75 ka. Geology 15, 913e917. Rose, W.I., Riley, C.M., Darteville, S., 2003. Size and shapes of 10-Ma distal fall pyroclasts in the Ogallala Group, Nebraska. Journal of Geology 111, 115e124. Schulz, H., Emeis, K.-C., Erlenkeuser, H., von Rad, U., Rolf, C., 2002. The Toba volcanic event and Interstadial/Stadial climates at the marine isotopic stage 5 to 4 transition in the northern Indian Ocean. Quaternary Research 57, 22e31. Schulz, H., von Rad, U., Erlenkeuser, H., 1998. Correlation between Arabian Sea and Greenland climate oscillations of the past 110,000 years. Nature 393, 54e57. Shane, P., Westgate, J., Williams, M., Korisettar, R., 1995. New geochemical evidence for the youngest Toba tuff in India. Quaternary Research 44, 200e204.

117

Sharma, G.R., Clark, J.D., 1982. Palaeo-environments and prehistory in the Middle Son valley, northern Madhya Pradesh. Man and Environment 6, 56e62. Sharma, G.R., Clark, J.D., 1983. Palaeoenvironments and Prehistory in the Middle Son Valley. Abinash Prakashan, Allahabad. Sheets, P., 1980. Archeological Studies of Disaster: Their Range and Value. Working Paper 38. Hazards Center: Institute of Behavioral Science, University of Colorado, Boulder. Sheets, P., 2007. People and volcanoes in the Zapotitan valley, El Salvador. In: Grattan, J., Torrence, R. (Eds.), Living under the Shadow: Cultural Impacts of Volcanic Eruptions. Left Coast Press, Ltd., Walnut Creek, CA, pp. 67e89. Sheets, P., Grayson, D.K., 1979. Volcanic Activity and Human Ecology. Academic Press, New York. Singh, I.B., Sharma, S., Sharma, M., Srivastava, P., Rajagopalan, G., 1999. Evidence of human occupation and humid climate of 30 ka in the alluvium of southern Ganga Plain. Current Science 76 (7), 1022e1026. Sonakia, A., Biswas, S., 1998. Antiquity of the Narmada Homo erectus, the early man of India. Current Science 75 (4), 391e392. Song, S.-R., Chen, C.-H., Lee, M.-Y., Yang, T.F., Iizuka, Y., Wei, K.-Y., 2000. Newly discovered eastern dispersal of the youngest Toba Tuff. Marine Geology 167, 303e312. Spate, O.H.K., Learmonth, A.T.A., 1967. India and Pakistan: A General and Regional Geography. Methuen, London. Srivastava, P., Singh, I.B., Sharma, M., Singhvi, A.K., 2003. Luminescence chronometry and late Quaternary geomorphic history of the Ganga plain, India. Palaeogeography, Palaeoclimatology, Palaeoecology 197, 15e41. Stone, A.C., Griffiths, R.C., Zegura, S.L., Hammer, M.F., 2002. High levels of Y-chromosome nucleotide diversity in the genus Pan. Proceedings of the National Academy of Science 99 (1), 43e48. Stringer, C., 2002. Modern human origins: progress and prospects. Philosophical Transactions of the Royal Society of London. Series B 357, 563e579. Telford, R.J., Barker, P., Metcalfe, S., Newton, A., 2004. Lacustrine responses to tephra deposition: examples from Mexico. Quaternary Science Reviews 23 (23e24), 2337e2353. Tewari, R., Pant, P.C., Singh, I.B., Sharma, S., Sharma, M., Srivastava, P., Singhvi, A.K., Mishra, P.K., Tobschall, H.J., 2002. Middle Palaeolithic human activity and palaeoclimate at Kalpi in Yamuna valley, Ganga plain. Man and Environment 27, 1e13. Thangaraj, K., Chaubey, G., Kivisild, T., Reddy, A.G., Singh, V.K., Rasalkar, A.A., Singh, L., 2005. Reconstructing the Origin of Andaman Islanders. Science 308 (5724), 996. Thorarinsson, S., 1979. On the damage caused by volcanic eruptions with special reference to tephra and gases. In: Sheets, P., Grayson, D.K. (Eds.), Volcanic Activity and Human Ecology. Academic Press, New York, pp. 125e159. Timmreck, C., Graf, H.-F., Lorenz, S.J., Niemeier, U., Zanchettin, D., Matei, D., Jungclaus, J.H., Crowley, T.J., 2010. Aerosol size confines climate response to volcanic super-eruptions. Geophysical Research Letters 37, L24705. Torrence, R., 2002. What makes a disaster? A long-term view of volcanic eruptions and human responses in Papua New Guinea. In: Torrence, R., Grattan, J. (Eds.), Natural Disasters and Cultural Change. Routledge, London and New York, pp. 292e312. Torrence, R., Grattan, J., 2002a. Natural Disasters and Cultural Change. Routledge, London and New York. Torrence, R., Grattan, J., 2002b. The archaeology of disasters: past and future trends. In: Torrence, R., Grattan, J. (Eds.), Natural Disasters and Cultural Change. Routledge, London and New York, pp. 1e18. Torrence, R., Pavlides, C., Jackson, P., Webb, J., 2000. Volcanic disasters and cultural discontinuities in Holocene time, in West New Britain, Papua New Guinea. In: McGuire, W.J., Griffiths, R.C., Hancock, P.L., Stewart, I.S. (Eds.), The Archaeology of Geological Catastrophes. Geological Society, London, pp. 225e244. van Campo, E., Duplessy, J.C., Rossignol-Strick, M., 1982. Climatic conditions deduced from a 150-kyr oxygen isotope-pollen record from the Arabian Sea. Nature 296, 56e59. von Rad, U., Burgath, K.-P., Pervaz, M., Schulz, H., 2002. Discovery of the Toba ash (c. 70 ka) in a high-resolution core recovering millennial monsoonal variability off Pakistan. In: Clift, P.D., Kroon, D., Gaedicke, C., Craig, J. (Eds.), The Tectonic and Climatic Evolution of the Arabian Sea Region. The Geological Society, London, pp. 445e461. Voorhies, M., 1992. Ashfall: Life and Death at a Nebraska Waterhole Ten Million Years Ago. University of Nebraska State Museum. Museum Notes Number 81. Voorhies, M., Thomasson, J.R., 1979. Fossil grass anthoecia within Miocene rhinoceros skeletons: diet in an extinct species. Science 206 (4416), 331e333. Webster, P.J., 1987. The elementary monsoon. In: Fein, J.S., Stephens, P.L. (Eds.), Monsoons. John Wiley and Sons, New York, pp. 3e32. Westgate, J.A., P.A.R., S., Pearce, N.J.G., Perkins, W.T., Korisettar, R., Chesner, C.A., Williams, M.A.J., Acharyya, S.K., 1998. All Toba tephra occurrences across Peninsular India belong to the 75,000 yr B.P. eruption. Quaternary Research 50, 107e112. Williams, M., Ambrose, S.H., van der Kaars, S., Ruehlemann, C., Chattopadhyaya, U.C., Pal, J.N., Chauhan, P., 2009. Environmental impact of the 73 ka Toba super-eruption in south Asia. Palaeogeography, Palaeoclimatology, Palaeoecology 284, 295e314. Williams, M.A.J., Ambrose, S.H., van der Kaars, S., Ruehlemann, C., Chattopadhyaya, U.C., Pal, J.N., Chauhan, P., 2010. Reply to the comment on ’Environmental impact of the 73 ka Toba super-eruption in South Asia’ by M. A. J. Williams, S. H. Ambrose, S. van der Kaars, C. Ruehlemann, U. Chattopadhyaya, J. Pal, P. R. Chauhan. Palaeogeography, Palaeoclimatology, Palaeoecology 296 (1e2), 204e211.

118

S.C. Jones / Quaternary International 258 (2012) 100e118

Williams, M.A.J., Clarke, M.F., 1984. Late Quaternary environments in north-central India. Nature 308, 633e635. Williams, M.A.J., Clarke, M.F., 1995. Quaternary geology and prehistoric environments in the Son and Belan valleys, north central India. In: Wadia, S., Korisettar, R., Kale, V.S. (Eds.), Quaternary Environments and Geoarchaeology of India. Geological Society of India, Bangalore, pp. 282e308. Williams, M.A.J., Pal, J.N., Jaiswal, M., Singhvi, A.K., 2006. River response to Quaternary climatic fluctuations: evidence from the Son and Belan valleys, north-central India. Quaternary Science Reviews 25, 2619e2631. Williams, M.A.J., Royce, K., 1982. Quaternary geology of the Middle Son valley, North Central India: implications for prehistoric archaeology. Palaeogeography, Palaeoclimatology, Palaeoecology 38, 139e162. Williams, M.A.J., Royce, K., 1983. Alluvial history of the Middle Son Valley, North Central India. In: Sharma, G.R., Clark, J.D. (Eds.), Palaeoenvironments and Prehistory in the Middle Son Valley. Abinash Prakashan, Allahabad, pp. 9e22. Wilmhurst, J.M., McGlone, M.S., 1996. Forest disturbance in the central North Island, New Zealand, following the 1850 BP Taupo eruption. The Holocene 6, 399e411.

Wilson, T.M., Cole, J.W., Stewart, C., Cronin, S.J., Johnston, D.M., 2011. Ash storms: impacts of wind-remobilised volcanic ash on rural communities and agriculture following the 1991 Hudson eruption, southern Patagonia, Chile. Bulletin of Volcanology 73, 223e239. Witham, C.S., Oppenheimer, C., Horwell, C.J., 2005. Volcanic ash-leachates: a review and recommendations for sampling methods. Journal of Volcanology and Geothermal Research 141, 299e326. Yadav, R.R., 1992. Dendroindications of recent volcanic eruptions in Kamchatka, Russia. Quaternary Research 28, 260e264. Zielinski, G.A., Mayewski, P.A., Meeker, L.D., Whitlow, S., Twickler, M., 1996a. A 110,000-year record of explosive volcanism from the GISP2 (Greenland) ice core. Quaternary Research 45, 109e118. Zielinski, G.A., Mayewski, P.A., Meeker, L.D., Whitlow, S., Twickler, M., Taylor, K., 1996b. Potential atmospheric impact of the Toba mega-eruption w71,000 years ago. Geophysical Research Letters 23, 837e840. Zobel, D.B., Antos, J.A., 1997. A decade of recovery of understory vegetation buried by volcanic tephra from Mount St. Helens. Ecological Monographs 67 (3), 317e344.