- Email: [email protected]
Interglacial geomorphic dynamics during the Quaternary: Does glacial erosion dominates interglacial adjustment?
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Abstracts / Quaternary International 279-280 (2012) 121–232
started to disappear from that time onward resulting in the development of pingo remnants – isolated depressions with a diameter of 50 to 300 meters, either with or without a rampart. The presence of these pingo remnants vary in depth between 5 meters in the southern Netherlands to 20 meters in the northern Netherlands, indicating a minimum thickness of permafrost in the order of these values. Melting of the permafrost layer that was several meters thick presumably lasted several hundreds of years. Implications for the disappearance of permafrost during the Lateglacial in the Netherlands are given by the basal organic infilling of pingo remnants, dated to begin between 12,500 and 11,900 14C BP. The fills of the pingo remnants in the Netherlands form a unique record of environmental change since the last deglaciation containing for instance pollen, aeolian sand, chironomids, and tephra. A number of these depressions are filled with calcareous gyttja, implying that hydrostatic pressure and groundwater exfiltration continued after the decay of the ice-body. Others show distinct water level fluctuations and can be used to reconstruct changes in effective precipitation. The fills of clusters of pingo remnants that are situated closely together can be used to estimate local variation within and between basins. GEOMORPHOLOGICAL AND SEDIMENTOLOGICAL ANALYSES OF POSSIBLY HUMAN-INDUCED LATE-HOLOCENE VALLEY FILLS IN THE CENTRAL APENNINES, ITALY Philipp Hoelzmann. Freie Universität Berlin, Germany E-mail address: [email protected]
We report on geoarchaeological, geomorphological and sedimentological investigations on the late-Holocene landscape evolution in several smallscaled catchments in the Sabinian Mountains, Italy. Basic morphometric analyses and automated landscape classifications were generated on the basis of digital elevation models and resulted in catchment-area specific morphometric characteristics such as asymmetric valleys, levelled plains, tectonic structures etc. In several subcatchments of the Turano River (Lazio, Central Apennines) up to 10 m thick alluvial valley fills were sampled continuously with a closed drilling system. Based on 14C dating sediment formation occurred mainly during the last 2000 years. Within this period phases of accumulation (fluvial and alluvial sedimentation) alternated with erosion (fluvial incision of terraces). The trigger-pulses have not been identified so far. Into consideration come:- Tectonic movements: such as time-transgressive tectonic uplift or subsidence and/or event controlled tectonics (e.g. earthquakes). - Climate change: alluvial phases in the Central Apennines correspond to glacier advances of the Grand-Sasso-Massif which correlate with intensified flood events of the Tiber and its delta propagation. Catastrophic flood events were also proven for various Mediterranean rivers between 2100 to 1600 cal a BP. - Human influence: anthropogenic alterations of the landsurface conditions (e.g. land-use, forest clearance) within the catchments may have led to intensified bed-load with sediment accumulation. This line of argument was proven for the northward situated supra-catchment of the Arno river since the Middle Ages. The evaluation of historical sources in combination with further geomorphological, stratigraphical, sedimentological and palynological studies serve as an approach to understand the timing and the involved processes that formed these young sediments. INTERGLACIAL GEOMORPHIC DYNAMICS DURING THE QUATERNARY: DOES GLACIAL EROSION DOMINATES INTERGLACIAL ADJUSTMENT? Thomas Hoffmann. University of Bonn, Germany E-mail address: [email protected]
High mountains are generally sculptured by glacial erosion that resulted in the formation of glacial cirques and U-shaped valleys with strongly oversteepened hillslopes and widespread glacial deposits. The abundance of glacial (erosion and depositional) landforms in high mountains has been attributed to very effective glacial erosion and sediment transfer. Furthermore, it has been argued that geomorphic activity remains increased after the retreat of valley glaciers at the transition between glacial and interglacial periods. Thus, geologists and geomorphologist
generally tend to look at glaciers as geomorphic agents that strongly enhance erosion and sediment fluxes. An important but overlooked aspect of glacial erosion is the affect of glacial erosion on the decoupling of headwater basins from main river systems. Strong glacial erosion results in flat valley bottoms and glacial over-deepenings, with reduced transport capacities of the interglacial rivers draining formerly glaciated headwaters. In this paper, we will present evidences of increased erosion but decreased sediment yields in glacial headwaters, which results from the transition of glacial to peri-/paraglacial process regimes. These evidences are derived from geomorphomteric analysis, numerical sediment flux models and sediment budget approaches of headwater basins with different degree of glacial erosion in the Kananaskis Valley (Canadian Rocky Mountains). Through the comparison of the duration and erosion rates of glacial and interglacial periods during the Quaternary, we will discuss the wider implications of the results with respect to the landform evolution of glaciated mountains during the Quaternary. WHEN WAS THE TAUPO ERUPTION? Alan G. Hogg. Waikato Radiocarbon Dating Laboratory, University, New Zealand E-mail address: [email protected]
Taupo volcano in northern New Zealand is the world's most frequently active and productive rhyolite volcano. The latest eruption was the extremely powerful Taupo eruption. It involved 5 phases of plinian/ultraplinian and phreatomagmatic fall activity; the climactic 6th phase generated violent emplacement of nonwelded (loose) Taupo ignimbrite from hot pyroclastic density currents moving 200-300 m/s radially away from vent for w80 km. The total bulk volume of eruptives is w105 km3. Taupo deposits provide a widespread marker bed of importance to paleoenvironmental studies because it pre-dates the earliest arrival of humans in NZ in wAD 1280. The Taupo eruption occurred in (austral) late summer-early autumn on the basis of fruit and seeds, and a lack of latewood on the final growth rings on logs, preserved in a buried forest at Pureora. The eruption year has been estimated from a range of evidence including calibration of multiple 14C dates from carbonized wood, leaves or seeds; putative, disputed historical observations of sunsets in Rome and China (wAD 186); an acid peak in Greenland ice-cores (AD 181 2); and wiggle-match dating. We report here a new 14C-wiggle match date for the eruption of AD 232 5 (95%). It was obtained by high-precision dating decadal blocks from a log (bark intact) of celery pine (Phyllocladus trichomanoides) killed by Taupo ignimbrite and preserved at Pureora. The 14C ages were wigglematched against two new calibration curves, one on NZ kauri and the other on Tasmanian huon pine. Both curves generated statistically-identical dates. A previous 14C-wiggle match date for the Taupo eruption of AD 232 15 by Sparks et al. (1995; revised to AD 233 13 in 2008), was fortuitously correct because these authors used Northern Hemisphere calibration curves without correcting for interhemispheric offset (assumed erroneously to be zero years), and because age assays were systematically too young by the same value as the offset (w40 years). ARE THE CHANGES OBSERVED IN THE THERMAL REGIME AND THE CHEMICAL PROPERTIES OF A HIGH ARCTIC LAKE RELATED TO PERMAFROST MELTING IN THE CATCHMENT? Trine M. Holm. University of Innsbruck, Austria E-mail address: [email protected]
High arctic lakes are highly responsive to climate change as they are strongly affected by changes in both the catchment (snow cover duration, permafrost melting), and in lake processes (thermal regimes, limnochemistry). In addition these remote ecosystems are currently altered by anthropogenic impacts, especially long range transport of nitrogen, which functions as nutrient in these systems. In order to study climate and anthropogenic impacts in the High Arctic, we obtained short and long sediment records from Kongressvatn, a lake located in Spitzbergen within a karst system. Limnochemical properties had been measured in the 1960ies and have been monitored since summer 2005. Over the last decades we observed distinct changes in the chemical properties, and the
Abstracts / Quaternary International 279-280 (2012) 121–232
started to disappear from that time onward resulting in the development of pingo remnants – isolated depressions with a diameter of 50 to 300 meters, either with or without a rampart. The presence of these pingo remnants vary in depth between 5 meters in the southern Netherlands to 20 meters in the northern Netherlands, indicating a minimum thickness of permafrost in the order of these values. Melting of the permafrost layer that was several meters thick presumably lasted several hundreds of years. Implications for the disappearance of permafrost during the Lateglacial in the Netherlands are given by the basal organic infilling of pingo remnants, dated to begin between 12,500 and 11,900 14C BP. The fills of the pingo remnants in the Netherlands form a unique record of environmental change since the last deglaciation containing for instance pollen, aeolian sand, chironomids, and tephra. A number of these depressions are filled with calcareous gyttja, implying that hydrostatic pressure and groundwater exfiltration continued after the decay of the ice-body. Others show distinct water level fluctuations and can be used to reconstruct changes in effective precipitation. The fills of clusters of pingo remnants that are situated closely together can be used to estimate local variation within and between basins. GEOMORPHOLOGICAL AND SEDIMENTOLOGICAL ANALYSES OF POSSIBLY HUMAN-INDUCED LATE-HOLOCENE VALLEY FILLS IN THE CENTRAL APENNINES, ITALY Philipp Hoelzmann. Freie Universität Berlin, Germany E-mail address: [email protected]
We report on geoarchaeological, geomorphological and sedimentological investigations on the late-Holocene landscape evolution in several smallscaled catchments in the Sabinian Mountains, Italy. Basic morphometric analyses and automated landscape classifications were generated on the basis of digital elevation models and resulted in catchment-area specific morphometric characteristics such as asymmetric valleys, levelled plains, tectonic structures etc. In several subcatchments of the Turano River (Lazio, Central Apennines) up to 10 m thick alluvial valley fills were sampled continuously with a closed drilling system. Based on 14C dating sediment formation occurred mainly during the last 2000 years. Within this period phases of accumulation (fluvial and alluvial sedimentation) alternated with erosion (fluvial incision of terraces). The trigger-pulses have not been identified so far. Into consideration come:- Tectonic movements: such as time-transgressive tectonic uplift or subsidence and/or event controlled tectonics (e.g. earthquakes). - Climate change: alluvial phases in the Central Apennines correspond to glacier advances of the Grand-Sasso-Massif which correlate with intensified flood events of the Tiber and its delta propagation. Catastrophic flood events were also proven for various Mediterranean rivers between 2100 to 1600 cal a BP. - Human influence: anthropogenic alterations of the landsurface conditions (e.g. land-use, forest clearance) within the catchments may have led to intensified bed-load with sediment accumulation. This line of argument was proven for the northward situated supra-catchment of the Arno river since the Middle Ages. The evaluation of historical sources in combination with further geomorphological, stratigraphical, sedimentological and palynological studies serve as an approach to understand the timing and the involved processes that formed these young sediments. INTERGLACIAL GEOMORPHIC DYNAMICS DURING THE QUATERNARY: DOES GLACIAL EROSION DOMINATES INTERGLACIAL ADJUSTMENT? Thomas Hoffmann. University of Bonn, Germany E-mail address: [email protected]
High mountains are generally sculptured by glacial erosion that resulted in the formation of glacial cirques and U-shaped valleys with strongly oversteepened hillslopes and widespread glacial deposits. The abundance of glacial (erosion and depositional) landforms in high mountains has been attributed to very effective glacial erosion and sediment transfer. Furthermore, it has been argued that geomorphic activity remains increased after the retreat of valley glaciers at the transition between glacial and interglacial periods. Thus, geologists and geomorphologist
generally tend to look at glaciers as geomorphic agents that strongly enhance erosion and sediment fluxes. An important but overlooked aspect of glacial erosion is the affect of glacial erosion on the decoupling of headwater basins from main river systems. Strong glacial erosion results in flat valley bottoms and glacial over-deepenings, with reduced transport capacities of the interglacial rivers draining formerly glaciated headwaters. In this paper, we will present evidences of increased erosion but decreased sediment yields in glacial headwaters, which results from the transition of glacial to peri-/paraglacial process regimes. These evidences are derived from geomorphomteric analysis, numerical sediment flux models and sediment budget approaches of headwater basins with different degree of glacial erosion in the Kananaskis Valley (Canadian Rocky Mountains). Through the comparison of the duration and erosion rates of glacial and interglacial periods during the Quaternary, we will discuss the wider implications of the results with respect to the landform evolution of glaciated mountains during the Quaternary. WHEN WAS THE TAUPO ERUPTION? Alan G. Hogg. Waikato Radiocarbon Dating Laboratory, University, New Zealand E-mail address: [email protected]
Taupo volcano in northern New Zealand is the world's most frequently active and productive rhyolite volcano. The latest eruption was the extremely powerful Taupo eruption. It involved 5 phases of plinian/ultraplinian and phreatomagmatic fall activity; the climactic 6th phase generated violent emplacement of nonwelded (loose) Taupo ignimbrite from hot pyroclastic density currents moving 200-300 m/s radially away from vent for w80 km. The total bulk volume of eruptives is w105 km3. Taupo deposits provide a widespread marker bed of importance to paleoenvironmental studies because it pre-dates the earliest arrival of humans in NZ in wAD 1280. The Taupo eruption occurred in (austral) late summer-early autumn on the basis of fruit and seeds, and a lack of latewood on the final growth rings on logs, preserved in a buried forest at Pureora. The eruption year has been estimated from a range of evidence including calibration of multiple 14C dates from carbonized wood, leaves or seeds; putative, disputed historical observations of sunsets in Rome and China (wAD 186); an acid peak in Greenland ice-cores (AD 181 2); and wiggle-match dating. We report here a new 14C-wiggle match date for the eruption of AD 232 5 (95%). It was obtained by high-precision dating decadal blocks from a log (bark intact) of celery pine (Phyllocladus trichomanoides) killed by Taupo ignimbrite and preserved at Pureora. The 14C ages were wigglematched against two new calibration curves, one on NZ kauri and the other on Tasmanian huon pine. Both curves generated statistically-identical dates. A previous 14C-wiggle match date for the Taupo eruption of AD 232 15 by Sparks et al. (1995; revised to AD 233 13 in 2008), was fortuitously correct because these authors used Northern Hemisphere calibration curves without correcting for interhemispheric offset (assumed erroneously to be zero years), and because age assays were systematically too young by the same value as the offset (w40 years). ARE THE CHANGES OBSERVED IN THE THERMAL REGIME AND THE CHEMICAL PROPERTIES OF A HIGH ARCTIC LAKE RELATED TO PERMAFROST MELTING IN THE CATCHMENT? Trine M. Holm. University of Innsbruck, Austria E-mail address: [email protected]
High arctic lakes are highly responsive to climate change as they are strongly affected by changes in both the catchment (snow cover duration, permafrost melting), and in lake processes (thermal regimes, limnochemistry). In addition these remote ecosystems are currently altered by anthropogenic impacts, especially long range transport of nitrogen, which functions as nutrient in these systems. In order to study climate and anthropogenic impacts in the High Arctic, we obtained short and long sediment records from Kongressvatn, a lake located in Spitzbergen within a karst system. Limnochemical properties had been measured in the 1960ies and have been monitored since summer 2005. Over the last decades we observed distinct changes in the chemical properties, and the