Paraglacial landform assemblages in the Hindukush and Karakoram Mountains

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Geomorphology 95 (2008) 27 – 47 www.elsevier.com/locate/geomorph

Paraglacial landform assemblages in the Hindukush and Karakoram Mountains Lasafam Iturrizaga ⁎ Geography/High Mountain Geomorphology, Institute of Geography, University of Göttingen, Germany Received 6 June 2005; received in revised form 13 December 2005; accepted 7 July 2006 Available online 6 May 2007

Abstract The paper focuses on the evolution of debris landforms in subtropical high-mountain areas. The Karakoram and Hindukush Mountains are characterized by their high volume and variety of debris accumulations. The valley flanks are coated by unconsolidated debris slopes up to 1000 m in height. The valley floors are occupied by expansive debris-flow cones and alluvial fans with escarpment heights of over 100 m. The field investigations in over twenty valleys showed that the major part of those landforms is governed by the late and post-glacial glaciation history. A key role in this glacially-controlled landscape system is played by the slope moraines, which cover the valley flanks up to several hundred meters above the valley floor. The secondary debris supply by resedimentation processes of moraine material and glacially-induced rock failures exceed by far the primary debris production due to weathering processes. Landforms which have been formerly classified as “periglacial talus cones” rather can be considered as glacial or glacially-controlled-landforms. The identified paraglacial landforms can serve as useful palaeoclimatic indicators for the ice-age reconstruction. © 2007 Elsevier B.V. All rights reserved. Keywords: Paraglacial processes and landforms; Paraglacial sediment recycling; Deglaciation

1. Introduction In 1992, the author has carried out geomorphological investigations on natural hazards in the Shimshal valley and adjacent valley systems in the northern Karakoram. The study revealed that not the parent rock, but rather moraine material has been mostly the source area for a variety of mass movements such as rock fall and debris flows (Iturrizaga, 1994, 1995, 1996, 1997). A subsequent survey on the evolution of debris accumulations in High Asia was undertaken between 1994 and 1997 in selected valley systems of the Eastern Hindukush, the ⁎ Tel.: +49 551 3912135; fax: +49 551 397614. E-mail address: [email protected]. 0169-555X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2006.07.030

NW-Karakoram, the Nanga Parbat Massif (Pakistan), the Ladakh and Zanskar Ranges, the Nun Kun Massif, the Kumaon and Garhwal Himalayas (Kamet, Trisul and Nanda Devi Massifs, India) and in the central Himalayas with the Kanjiroba, Annapurna, Manaslu and Makalu massifs (Nepal) in order to set up a general typology of debris landforms in high-mountain areas (Iturrizaga, 1999a,b). Using geomorphological standard methods, such as mapping, grain-size analysis and interpretation of sediment outcrops, the field observations proved that the majority of the development of the debris accumulations is linked to the late glacial to post-glacial glacier extent in the Karakoram Mountains. The origin of the investigated debris accumulations is explained by a concept related to the overall glacial-history, based on

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the topographical relationship between individual landforms. New field evidence of the paraglacial landscape assemblage has been collected by the author from the Hindukush and Karakoram in previous years and includes the Shimshal, Hispar, Chogolungma (Basha), Braldu, Indus, Hunza, Chapursan, Hassanabad, Kukuar, Bagrot, Karambar, Yarkhun, Mastuj, Ghizer and Batura valleys from which representative case examples will be presented in this paper (Fig. 1). 2. Research review The interdependence between deglaciation and landscape transformation has been widely recognized in alpine mountain areas. Especially, glacially-induced rock failures have been studied in detail in the European Alps (Heim, 1932; Abele, 1969; Müller, 1999). Less attention has been paid to the modification of valley-side tills. Most studies on moraine-mantled slopes were carried out in glacier forefield environments or relatively close to the recent ice-margins. Ballantyne and Benn (1994, 1996) and Curry and Ballantyne (1999) showed with case studies from Norway the paraglacial landscape modification in recently deglaciated mountain areas. In contrast, in the Karakoram we are dealing with glacially-induced-landforms which are located up to several hundred kilometers downstream of the recent glacier tongues. Moreover a wealth of paraglacial landforms occurs in the lateroglacial environments along the present glacier streams (Iturrizaga, 2003). Li Jijun et al. (1984), Owen and Derbyshire (1989) and Owen (1991, 1994) have already stressed the importance of resedimentation of glacigenic deposits in the Karakoram and identified paraglacial processes as a significant agent in the geomorphological system. Kuhle (1994, 2001) has reconstructed for the dry Karakoram north side and more recently for the Baltoro- and Hispar Muztagh ice thicknesses of up to 2900 m, indicating the high amount of glacial transformation in this mountain region. Owen and Sharma (1999) provide further evidence from paraglacial landscapes from the Garwhal Himalayas. However, talus cones – especially at low altitudes at about 2500 m such as in the Hunza valley (Karakoram) – have been previously considered mainly as periglacial phenomena as result of frost-weathering processes (Wiche, 1960; Brunsden et al., 1984; Goudie et al., 1984; Goudie, 2002). The present study showed that these are mainly glacially-induced-landforms. Recently, Ballantyne (2002a) provided an extensive literature review on “paraglacial geomorphology” as a comprehensive concept in geomorphology. He has modified the original definition of “paraglacial” of

Church and Ryder (1972) into “nonglacial earth-surface processes, sediment accumulations, landforms, landsystems and landscapes that are directly conditioned by glaciation and deglaciation”. In this sense, the term “paraglacial” is used for the landforms described in this paper. Previously the author had addressed those landforms as “glacial transitional debris landforms” or “transglacial landforms” (Iturrizaga, 1999b, 2003, 2005), because the term “paraglacial” has been already applied in the German language for sediments deposited along the lateral glacier margins (Klebelsberg, 1950; Eggers, 1961). 3. Physiogeographical and climatic setting The NW-SE trending Karakoram (72°–79°E/35°– 36°N) consists of three parallel mountain chains, the Rakaposhi–Haramosh, the Spantik Sosbun-, Hisparand Batura–Muztagh, and the Ghujerab–Lupghar chains. The highest catchment areas are located in the upper Baltoro Muztagh region with four mountain peaks rising over 8000 m. The hypsographic curve indicates that a major part of the land surface is concentrated between 5000 m–6000 m (Hewitt, 1989). Due to the high relief energies the Karakoram shows one of the highest sediment transfer rates in the world (Palt, 2001). In contrast to the Himalayas, the Karakoram Range is largely divided by longitudinal valleys, some of them are up to 2–3 km wide and offering favourable conditions for debris deposition. The Hunza valley is the only transverse break-through valley in the western Karakoram. The Karakoram Mountains are undergoing active orogenesis with uplift rates of up to 7 mm per year during the last 10 Ma (Zeitler, 1985; Searle and Tirrul, 1991) resulting in large-scale mass movements (Kalvoda, 1992). Glacioisostatic uplift processes following the Last Glacial Maximum deglaciation (LGM) (Kuhle, 1995) might as well play a role in geomorphodynamic processes. The Karakoram Mountains possess the largest concentration of glaciers outside the polar regions and inherit eight glaciers over 50 km in length. Nevertheless, the glacier streams are flanked by an expansive debris landscape in the lateroglacial valleys (Iturrizaga, 2001, 2003). During the Pleistocene, the Hindukush–Karakoram Mountains were extensively glaciated (Drew, 1875; Lydekker, 1881; Oestreich, 1906; Dainelli, 1922; Trinkler, 1930; Visser, 1938; Desio and Orombelli, 1983; Derbyshire et al., 1984; Kuhle, 1988; Haserodt, 1989; Shroder et al., 1989; Kamp, 1999). They have been therefore prone to an intensive landscape transformation after deglaciation.

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Fig. 1. The research areas in the Hindukush–Karakoram Mountains.

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The Karakoram is a winter precipitation area dominated by the westerlies. The amount of precipitation in the valley locations scarcely exceeds 130 mm/y at altitudes between 1500 m to 3000 m and increase exponentially with increasing altitudes (Weiers, 1995). Heavy rain events such as cloudbursts in summer time play an important role in the sediment cascade system (Hewitt, 1993; Iturrizaga, 1996). It has been stated that freeze–thaw cycles occur at changing elevations in the Karakoram at all seasons (Hewitt, 1989), having most impact at elevations between 4000 m and 6000 m especially between May and October. Precipitation levels between 500 mm and 1000 mm and temperatures around freezing supply the necessary moisture and freeze–thaw conditions required for frost action. However, the main distribution area of debris cones and slopes discussed here reaches far below the snow line (Fig. 2). Therefore the necessary water for frostweathering processes is not available in those lowlying valley sections and other factors should be considered for the debris supply as described below. 4. The distribution and genesis of debris accumulations deduced from the glacial-history

occur mainly between 1500 m and 4000 m. At those elevations, the principal sources of debris supply are slope moraines. Many valleys display a conspicuous disproportion between catchment size and the size of the debris accumulations. Huge, fluvially shaped debris accumulations have been deposited at the exits of comparatively small and short valleys. Such accumulations do not derive only from the autochthonous debris produced in the catchment itself. They rather emanate from resedimented morainic material deposited in the tributary valleys. The centre-to-periphery change in regard to debris accumulation types along the valleys is primarily dependent on relief conditions and on the configuration of main and tributary valleys. It is especially noteworthy that the occurrence of slope moraines decreases upstream towards the modern glacier terminus. The glacially-induced debris cones are replaced upvalley by debris cones originating from weathering processes on the parent rock. Hence, starting at the middle section of a valley, a reduced vertical relief amplitude has been transformed by glacial processes towards the mountain interior due to the lesser height of the glacier level in the upper catchment areas. 5. The paraglacial landscape system

Fig. 2 presents a schematic overview of the altitudinal distribution of selected types of debris accumulations in the Karakoram. The paraglacial debris accumulations

The classic categories of debris accumulations – talus cones, alluvial cones, debris-flow cones and related

Fig. 2. Schematic overview on the vertical distribution of selected debris landforms in the Hindukush–Karakoram Mountains.

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Fig. 3. Types of paraglacial landforms.

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Fig. 4. Overview map of the Shimshal valley.

forms – apply only to a limited extent when classifying debris accumulations in the Karakoram. The same is the case for the conventional geomorphological nomencla-

ture of glacial landforms. The seemingly homogeneous, largely conical appearance of the debris accumulations causes them to be attributed overhastily to the

Fig. 5. View from the Chatmerk Pass (4200 m) towards the Pamir Tang valley and the Shimshal Pamir. The valley flanks are coated with thick moraine mantles (⋄) which are incised by the tributary valleys. The debris cones (▵) in the foreground consist of redeposited moraines. They are not periglacial talus cones. Photo: L. Iturrizaga 26. Aug. 1992.

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above-mentioned three traditional categories of debris accumulations and often leads to a mistaken interpretation of their origin. In principal three kinds of paraglacial debris landscapes are distinguished: the passive residual debris landscape, the active resedimentation landscape and the glacially-induced collapse debris landscape (Fig. 3). A remarkable fact is that almost every valley in the Karakoram Mountains is more or less masked with

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slope moraines, which provide the parent material for paraglacial processes and which are transformed into secondary debris accumulations. In the Himalayas, these slope moraines are less widespread because they have been largely removed due to the high precipitation amounts or unfavourable relief conditions for debris deposition. Moreover, they are often less obvious than in the Karakoram as they are densely covered with forest.

Fig. 6. A: Initial stage of the transformation of slope moraines (↘) into morainic cones (▵) close to Ziarat (2850 m) in the Shimshal valley. The valley flank is covered by slope moraines up to 400 m above the valley floor. Photo: L. Iturrizaga 05. July 2001. B: Morainic debris cones downstream of the Khurdopin glacier in the Shimshal valley (3450 m). The debris emanates from the redeposition of slope moraines (↘), which have been almost removed. Photo: L. Iturrizaga 06. July 2001.

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The Shimshal valley is one of the Karakoram valleys where paraglacial landscape modification is most striking (Figs. 4–6AB). The valley is almost over its entire length coated with morainic cones at altitudes between 2600 m and 4000 m, in particular in the valley section between Dut (2700 m) and Malungutti (2900 m) as well as further upstream between Shimshal (3100 m) and the Yazghil glacier (3150 m). An outstanding feature of some of the paraglacial debris accumulations is the dual debris accumulation structure of a late glacial ground moraine base overlain by debris deposited during post-glacial time. The moraine relicts along the slope bottoms and valley floors are being gradually destroyed by post-glacial slope processes and covered by slope-derived and fluvial debris. Therefore, a lot of debris accumulations possess a morainic core (Fig. 7A), which is hardly recognizable today, but it often represents the major part of the debris accumulation. The unconsolidated morainic cones often show a thinly layered vertical structure which indicates the contribution of nival and fluvial reworking processes

as well as dry mass movements (Figs. 7B, 8AB). The debris surface can be stratified into fine and coarse material (cf. Wasson, 1979) (Fig. 7A). In the lateroglacial environments along the glaciers, morainic cones occur up to an altitude of about 4200 m (Fig. 9ABC). Embedded erratic boulders evidence their glacial origin (Fig. 10). Even at altitudes which are already dominated by the frost-weathering regime, extensive slope-moraines cover the valley flanks and are transformed by post-sedimentary processes, especially in confluence positions such as at the Khurdopin (3450 m), Yukshin Gardan (3400 m) and Yazghil glaciers (3200 m). 5.1. Glacigenic residual sediments: paraglacial formation of debris accumulations by post-sedimentary fluvial erosion The conical residual sediments are erosional remnants of a formerly continuous morainic cover on the valley sides. In some parts the valley flanks are coated

Fig. 7. A: Moraine-cored debris cone (3050 m) at the orographic left side of the Shimshal valley. The in situ-moraine material (⋄) is gradually covered by redeposited slope moraines (↘) and to a lesser extent by primary debris. This shows, that despite intensive weathering processes in this subtropical mountain area the rock disintegration is not that high as the vast amount of debris would initially imply. The vertical height of the cone amounts approx. 300 m. Photo: L. Iturrizaga 20. July 2001. B: Outcrop profile – about 1 m in height – of the middle part of a morainic cone at 2870 m between Dut and Ziarat in the Shimshal valley. The matrix of this slaty debris cones possess a high fine material content due to the redeposition of slope moraines (↙). In dry conditions those debris cones are rather stable. As soon as they get wet they are susceptible to debris flows. The matrix is clearly layered by wet and dry mass movements. Nival and fluvial processes as well as solifluction processes might have played as well a role in regard to the stratification. The overall slope angle is about 33° and reaches almost its critical amount. Photo: L. Iturrizaga 24. July 2001.

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Fig. 8. A: Grain-size distribution of the coarser part of a layered morainic debris cone in the Upper Yarkhun valley (3300 m) with a clear dominance in the coarse sand fraction (52%). B: Grain-size distribution of a morainic debris cone in the Mastuj valley (2245 m). In contrast to periglacial talus cones with a dominance in the coarser grain sizes, the morainic debris cone shows a relative uniform distribution of all grain sizes. The high content in clay (12%) and in silt (45%) emanating from slope moraines is typical for the grain size distribution of dislocated moraine material.

with moraines which are even nowadays hardly dissected (Fig. 5). The residual moraine cones are similar in shape to talus cones and debris-flow cones. The most conspicuous feature of this passive formation of debris accumulations is that the cone tips do not connect with a feeder channel, but they are carved out of in-situ glacigenic material by post-sedimentary fluvial erosion (Fig. 11A). 5.1.1. Residual slope-moraine cones Residual slope-moraine cones are erosional forms of a ground moraine which covers the valley flanks. Their vertical height ranges from some meters up to several hundred meters. The apex of the moraine cones is connected with a mountain spur and not with an active debris supply channel. They resemble a normal talus cone with a consolidated surface. In the Basha valley, downstream of the Chogolungma glacier tongue, resid-

ual moraine cones cover the valley flanks (Fig. 11B). Debris accumulations are often in a transitional stage from residual debris cones towards resedimented morainic debris cones (Fig. 11C). 5.1.2. Residual moraine fans Residual moraine fans are erosion forms of a ground- and slope-moraine cover. An obvious example is given by the moraine fan in Singal (1900 m) in the Gilgit valley, which at first glance resembles a fluvially deposited debris-flow-alluvial cone (Fig. 11A). The fluvial catchment of this debris accumulation scarcely extends above 3000 m. Close observation shows that the bifurcate cone tip does not derive directly from the steep valley directly upstream, but clings concavely to the craggy mountain flank. The paraglacial debris accumulation is the rest of a ground moraine mantle that covered the valley side up to more than 700 m above

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Fig. 9. A: Panorama view onto the orographic left Khurdopin valley flank seen from 4100 m. The debris cones, located at altitudes between 3600 m and 4100 m, look like accumulation forms produced by frost-weathering. The valley flank has been glaciated during the Last Glacial Maximum and Late Glacial as erratic boulders prove (see Fig. 13). Therefore those debris landforms are rather a result of deglaciation processes. Photo: L. Iturrizaga 10. July 2001. B: View from 3800 m onto the orographic left valley flank of the Yazghil glacier in E-aspect. The valley flank is still extensively masked with moraine material up to about 300 m above the present glacier surface (——), which supplies the debris for the successive cone formation. At the neighbouring Khurdopin glacier the moraines have been already mostly removed. Photo: L. Iturrizaga 19. July 2001.C: View from 2950 m from the left lateral moraine of the Batura glacier towards the orographic right Batura valley flank in N-aspect with a debris cones assemblages of polygenetic origin. During the Last Glacial Maximum and Late Glacial small hanging and cirque glaciers ( ) were located in the upper catchment areas and supplying debris for the formation of the debris cones. Moreover, erratic boulders on the top of the Patundas surface (↘) as well as vast slope moraines at the northern Batura side evidence that the valley flank has been covered by the LGM-Batura glacier. At present snow avalanches, debris flows and rock falls contribute to the formation of those debris cones. In the foreground the debris-covered Batura glacier and to the far right the Batura ice fall is visible. Photo: L. Iturrizaga 28. Sept. 2002.

the valley floor and is dissected by mass movements from the very steep valleys and gullies that are now free of morainic material. This example, too, shows that the debris accumulation is disproportionately large in relation to its small catchment area, suggesting a glacial origin. 5.1.3. Morainic ramparts (terraced slope moraines) Morainic ramparts are also a residuum of a thick cover of slope moraine and bear resemblance to pediments. The morainic ramparts are only little modified by post-sedimentary slope processes, except that they have been terraced at their base by fluvial undercutting processes. Therefore they are true incision forms. The terrace surface is not flat but converges asymptotically towards the valley flank. The most important feature of this form is that in former times the glacier has

lain upon and not beside the morainic base (Kuhle, 2001). Therefore the morainic ramparts have to be distinguished from the earlier ice-marginal sediments (paraglacial terraces, kame terraces). The latter forms are deposited against the former glacier fill of the valley. The Shimshal valley is masked with morainic ramparts up to an altitude of 600 m above the valley bottom. They are now disintegrated into morainic cones by postsedimentary fluvial processes. They are almost undissected, but terraced by the Shimshal river. Valley-downwards of Shujerab (4240 m), the Pamir Tang valley is completely filled with morainic ramparts (Fig. 5). Morainic gussets are situated at corner positions at confluence areas. They consist of ground moraine which is dissected by fluvial processes. These forms resemble lateral moraines of the tributary valleys.

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Fig. 10. At the confluence of the Kit-ke-Jerav (K) and Yishkuk valleys (Y) at altitudes between 3800 m and 4000 m, the slopes are scattered with erratic granite boulders (↙) which originate from a former ice stream which was connected with the Hunza-ice-stream network. The debris slopes coating the valley flanks about 800 m above the valley floor consist of resedimented moraine material (▵). Photo: L. Iturrizaga 31. Aug. 2003.

5.1.4. Kame cones Kame cones are debris cones and alluvial cones, which were deposited against the trunk valley glacier during times of a more expansive glaciation. After deglaciation they resemble fluvial deposits with very high and steep cliff walls produced by fluvial undercutting. However, at the distal base they can contain remnants of lateral moraine material of the former trunk glacier. They are often disintegrated into organ-pipeshaped pillars. The distal cliff walls of the kame cones can reach more than 200 m. 5.2. Resedimentated glacigenic sediments 5.2.1. Morainic debris cones and morainic debris slopes The morainic debris cones and morainic debris slopes represent the most widely distributed paraglacial sediments. Their debris supply area consists of slope moraines (Fig. 6AB). They are mainly aggradated by gravitational mass movements and to a minor degree by fluvial reworking of moraine material. The morainic debris cones show a wide range of grain-size distribution depending on the composition of the moraine material. Some of them possess a high content of fine material (Fig. 12AB). As soon as they are soaked by moisture, they are prone to debris flows. Sometimes morainic cones are built up by a singular collapse event and a semicircular scar is left behind in the source area. Other morainic cones are mainly open-work deposits. Those landforms can be easily mistaken for periglacial talus cones due to their external convergence, especially

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if the morainic supply material has been already removed along the valley flanks. Sometimes erratic stones are left behind from the glacial deposits in the morainic cones. The valley flanks in the lateroglacial environment of the Batura glacier are extensively coated with moraine material on S-facing slopes whereas the N-facing slopes are dominated by debris cones. Morainic debris cones occur at altitudes between 2900 m and 3300 m at the northern valley side. At the southern side, the entire valley flank between Yunzbin (2785 m) and Kirgas Washk (3300 m) is taken up by debris cones which resemble pure talus cones (Fig. 9C). But the presence of the moraine material in S-aspect implies that also those from the opposite valley flank are from glacial origin. Moreover, erratic boulders are reported from the upper catchment areas at the Patundas surface (4000 m) (Paffen et al., 1956; Schneider, 1959) located at the top of the Patundas surface. Either the valley-side moraine material has been already removed or they are the result of glacial undercutting and debutressing processes. The paraglacial landscape in the Bar valley (Batura-SSide) provides a good case example for recent deglaciation processes and the transformation of relict lateroglacial sediments by a sudden glacier advance. The Kukuar glacier surface is located about 200 m below the recent crest of the lateral moraine. Wide areas of slope moraines have become ice free in historical times and are already strongly gullied. But also older moraines show a skeletal disintegration. However, the Kukuar and Bar glaciers advanced at the beginning of the 20th century several kilometers downstream to the village of Hugue (2500 m) (cf. Schomberg, 1933; Paffen et al., 1956). During this advance the combined glacier tongue has undercut the prehistorical slope moraines and induced a large-scaled formation of morainic cones (Fig. 13). Further on, earth pyramids are very typical erosional forms of glacigenic sediments which are often located in confluence areas. The parent material consists mostly of glaciofluvial ice-marginal sediments. Earth pyramids serve as indicators for a former moraine cover blanketing the valley flanks. At the Hispar glacier, earth pyramids occur up to altitudes of 4200 m, about 300 m above the present glacier surface indicating that the valley flanks have been transformed by glacial processes. Erratic boulders are the last remnants of the former slope-moraine cover (Fig. 10). In the tributary valleys of the upper Chapursan valley erratic granite boulders are located at the valley flanks at 4000 m–4100 m

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at the confluence Kit-ke-Jerav/Yishkuk glacier. In the lower Kit-ke-Jerav valley, a whole lateral moraine is incorporated in a glacially-induced debris slope indicating the high morphodynamics of this landscape. 5.2.2. Morainic debris-flow cones and alluvial cones Sediment cones with diameters of up to 1.5 km and escarpment heights of 100 m are quite common in the Karakoram valleys (Fig. 14AB). The debris material is mainly supplied by the resedimentation of ground and

slope moraines located in the upper catchment areas of the tributary valleys. They often completely seal the tributary valleys. During the glaciation periods the trunk valley glaciers blocked the side valleys and caused expansive “backfilling sediments” along the valley exits. After deglaciation the moraine material has been reworked by fluvial processes. The formation of debris-flow cones by resedimentation of morainic material can be demonstrated by the debris-flow cone of Bandasar (Fig. 4, Fig. 14AB). It is situated at the valley exit of the Zadgurbin valley on

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Fig. 11. A: View from 1935 m towards the orographic left-hand side of the Ghizer valley close to the settlement of Singal. The debris accumulation shown here resembles a fluvially accumulated debris landform, such as a debris-flow cone. Closer examination reveals that the cone apex does not end in the potential supply valley, but peters out in a concave shape along the valley flank (↙). However, the tributary river (↘) laterally dissects the debris accumulation and deposits an alluvial cone (○), which contains resedimented debris from the main debris accumulation. A look at the adjacent valley flanks shows that they are covered with debris material of glacigenic origin (⋄). They are also in the transformation phase between a mantlelike covering and cone-shaped residual debris accumulations. The debris accumulations might be kame formations. However, both the internal structure and the uniform and only slightly dissected moraine deposits indicate a remnant of ground moraine, which is being fluvially reworked in the post-glacial period. This means that fluvial processes erode a cone-shaped debris accumulation out of the moraine material, so that it represents a residual form of a glacial debris accumulation. Photo: L. Iturrizaga 25. Sept. 1995. B: Conical-shaped debris landforms (▵) occur at the right Basha valley flank, downstream of the Chogolungma glacier (2800 m). Those landforms are carved out by post-sedimentary processes (↙↘) into sediment cones which resemble pure talus cones, but they are relicts of a former compact moraine veil. Photo: L. Iturrizaga 13. July 2000. C: The debris accumulation located in the Ghizer valley at 2915 m demonstrates very clearly the transformation of a former closed moraine mantle (⋄) into resedimented debris accumulations (▵) in combination with the supply of pure slope material (↙) from the higher catchment area, which leads to a composite debris accumulation of pure slope debris and glacial debris. Subordinate gullies alongside the main direction of free fall are still filled with moraine material (↘), whereas the main supply channels are already occupied by slope debris. The conical debris accumulation is composed of dark, coarse slope debris and fine, light-coloured moraine material. Owing to the latter, mudflow-like debris flows are able to develop on the cone surface. Photo: L. Iturrizaga 24. Sept. 1995.

the orographic right-hand side of the Shimshal valley at an altitude of 3050 m with a diameter of about 1 km. In the lower part the steep Zadgurbin valley is completely covered by late glacial morainic deposits, providing the source material for large-scale debris flows. The debris-flow cone was presumably formed in a few catastrophic events. Steep tributary-valley gradients combined with sometimes high meltwater rates provide favourable conditions for displacement of the morainic material. The Yarkun and Mastuj valleys are up to 2 km broad and provide favourable conditions for sediment fan deposition over several decakilometers, especially between Mastuj (2280 m) and Brep (2435 m) (Fig. 5). The aggradation of all the sediment cones is influenced by

the redeposition of slope moraines and also underlain by ground moraine. 5.3. Glacially-induced collapse debris accumulations There is a direct link between glacier retreat and the formation of talus accumulations, as almost every historical glacier front vividly demonstrates (Figs. 14A, 15) (cf. Ballantyne, 2002a). Pressure release and loss of support owing to melting ice lead to diverse collapse features on oversteepened valley sides (Augustinus, 1995). As though suddenly released from a mould, parts of the valley sides collapse after deglaciation and leave debris accumulations of catastrophic origin. Many of the valleys are in a transitional phase between a glacially

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Fig. 12. A: Grain-size distribution of a morainic debris cone. B: Grain-size distribution of earth pyramids.

oversteepened- and hence unstable-trough valley and the more stable fluvial, V-shaped valley. Collapse debris accumulations can be caused by a singular catastrophic event owing to pressure release after deglaciation. But a lot of glacially-induced collapse debris accumulations are gradually built up (cf. Luckman and Fiske, 1997). In respect of their appearance they are not distinguishable from true talus cones, except for the morphology of their supply area. The periglacial talus cones are mostly connected with a funnel-shaped catchment area, whereas the glaciallyinduced talus cones show an undercutting line in the solid rock, which was produced by the former trunk glacier. They often occur in cirques or in glacier forefield areas. The upper scree limit indicates the height of the prehistoric glacier level. The Momhil valley (3400 m–3600 m) shows large glacially-induced debris accumulations. The forefield of

the Momhil glacier is fringed by gradually formed collapse debris accumulations at the left valley flank (2900 m). It is important to note that recent mass movements do not create the now dominant slope forms but primarily destroy an older form, namely the glacial relief dating from the Last Glacial Maximum to late glacial time. Therefore it is also not possible to deduce the age of debris accumulations from their size and thickness, or from sedimentation rates, because extreme events build up a large proportion of the debris accumulations in only a few hours, days or months, alternating with lengthy phases of non-activity or gradual debris accumulation. In this regard the studies of Hewitt (1998, 1999, 2001) on landslides in the Karakoram are noteworthy. He shows that classical end-moraine positions, such as in the near of Skardu, are not ice-margins but

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Fig. 13. View from Toltar (4000 m) at the confluence of the Baltar valley (B) and the Kukuar valley (K) into the recently deglaciated Bar valley. Dead ice-complexes (←) witness the recent glacier advance of the combined Kukuar–Baltar glacier into the Bar valley down to the settlement Hugue (2500 m) (↙) in the mid of the 20th century. The recent glacier advance has undercut the older slope moraines (——) and led to the formation of morainic cones (▵). In the foreground, the slope moraines are disintegrated into earth pyramids (⋄). Photo: L. Iturrizaga 25. Aug. 2000.

catastrophic landslides. However, these landslides can be considered as glacigenically induced phenomena, so that they are in turn very young post-glacial debris accumulations (Iturrizaga, 1999a,b). 6. The recent debris production rate: primary and secondary debris supply Particularly at elevations between 2500 m and 3500 m, the decisive factor for debris supply is not the bedrock but the type and distribution of the moraine lining of the valley flanks. The current rate of debris production is too low to account for the huge volumes of debris presently blanketing the valleys. High rates of morphodynamic activity in the mountain relief primarily contribute to the remobilization of ancient unconsolidated glacial fill. The outcrop profiles of many debris cones show that the proportion of resedimented and residual glacial debris is several times greater than the production of new debris. Furthermore, a lot of debris cones show a dual structure with ground moraine at the base and fluvial sediments deposited on top. In the long term, the present high redeposition rate of highlevel morainic deposits means that the erosional regime in these mountains is gradually shifting back towards primary debris processes. A quantitative approach to paraglacial processes in general and the exhaustion of sediment supply areas based on field investigations in

glacier forefields of Norwegian glaciers has been carried out by Ballantyne (2002b). The bareness of the debris accumulations in dry highmountain regions suggests enormous recent activity. Compared with other high-mountain regions, this area of debris accumulation is indeed very active. However the absence of vegetation is primarily due to lack of water and not to extreme activity. The fact that the debris surfaces are not stabilized is often due to fluvial undercutting of the talus slope base and not to recent active debris delivery from the catchment. At the present time catastrophic formation of debris accumulation is plainly visible in the Karakoram Mountains (Hewitt, 1993; Fort and Peulvast, 1995). One single event, triggered by rainstorms, sudden meltwater flow or, more rarely, by an earthquake, can bring a debris accumulation close to its maximum extent. Various subsequent debris supply processes have little morphologic impact on the debris accumulation in the whole. A “mega-event” is unlikely to recur at the same locality because the previous event has already removed the easily transportable unconsolidated material in the catchment area. Significant rainstorms, especially local cloudbursts during the summer months are one of the most important factors in the geomorphological processes governing debris production and transport in the Karakoram. The landscape is dominated by expansive debris accumulations generated by these catastrophic

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Fig. 14. A: The fluvially shaped sediment cones, which reach at their cliff edges heights of up to 100 m are in their formation highly influenced by glacial processes. The photograph taken from 3050 m from the Shimshal gravel floor to the orographic right-hand valley flank shows the Bandasar sediment cone. The sediment cone is mainly composed of dislocated glacigenic sediments which are deposited in the tributary valley (see next photo). In the Late Glacial period, probably also during Neoglacial times, the initial sediment cone was deposited against the former trunk valley glacier. The central incision of the cone took place after deglaciation when the base-level of erosion was lower. Morainic cones (▵), which are nourished by slope moraines (↙), are deposited on the mudflow-alluvial cone. The remains of an end moraine (⇩) have also been incorporated in this sediment cone. Nowadays, the glacially-induced cliff walls, which are 60–80 m high, are cut back by gravity processes and fluvial undercutting, as attested by the series of talus heaps (↗). A young secondary cone (○) spreads over the Shimshal gravel floor. The valley flanks are glacially polished and collapse at the convex parts of the trough valley shoulder. Photo: L. Iturrizaga 14. Aug. 1992. B: View from 3780 m downstream into the S-facing Zadgurbin valley, which is being extended by headward erosion into the Ghujerab mountains. Ground moraine (⋄) coats the narrow V-shaped valley, transforming it into a ravine-shaped valley. Talus cones are deposited on top of the moraines. The cliff walls of the moraines (↘) are dissected into the shape of organ-pipes. These glacial sediment relicts provide the source material for debris flows forming the Bandasar sediment cone shown in the previous photograph and which is located at the light-grey gravel floor (○) of the Shimshal valley. The Shimshal valley is lined by glacial-induced debris slopes (▵). Photo: L. Iturrizaga 25. Aug. 1992.

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Fig. 15. Glacially-induced debris cones in the Braldu valley downstream of the Baltoro glacier tongue at 3450 m. The bedrock has been partly undercut by the glacier (——), but also processes of unloading after deglaciation (↘) might have played a role in the formation in those debris cones. Photo: L. Iturrizaga 21. Aug. 1997.

rainstorm events. Deviations from annual mean precipitation values at the level of extreme events can be decisive factors in debris accumulation. Furthermore, the

reworking of moraines takes place by nival- and glacially-induced meltwater discharges, in particular between July and September.

Fig. 16. Determining the minimum extent of glaciation by means of paraglacial landforms.

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7. Discussion Generally, frost-weathering processes are considered as the principal form of mechanical rock disintegration in high-mountain areas, especially in the altitude zone of the recent snow line. Therefore talus cones and talus slopes have been mainly classified as key forms of the periglacial landscape environment. The work of Högbom (1914) highlights frost-weathering processes as an important geomorphological agent. In the light of the history of science, it might have widely influenced the geomorphologic research approaches in cold environments and led to an overestimation of frost-action on the parent rock. Detailed studies have been provided on the genesis of talus cones and slopes from the European Alps (Höllermann, 1964; Vorndran, 1969; Stäblein, 1977) and the Scandinavian mountain ranges (Rapp, 1960). However, already in the mid 20th century, several studies had shown that the maximum of freeze–thaw cycles does not correlate with the distribution of talus cones in the Alps (Lauscher, 1947; Hader, 1955; Hastenrath, 1960). Moreover, the rate of frost-weathering turned out to be much too low to account for the formation of talus cones in various high-mountain regions of the world (Rapp, 1960; Luckman and Fiske, 1995, 1997; Sass, 1998). Case studies from the Canadian Rocky Mountains (Johnson, 1984) and Spitsbergen (André, 1985; Mercier, 2002) suggest that paraglacial processes seem to have played a more important role in their formation. New investigations on weathering processes in coldarid regions in the Antarctic cast doubt as well on the frost-weathering paradigm (André, 2003). Hall (1999) considers “thermal stress” to be a major form of weathering in areas of water shortage. Water is also the limiting factor for frost-weathering in the lower altitudes of the Hindukush–Karakoram. Whalley (1984) and Whalley et al. (1984) stressed the importance of chemical and insolation weathering for rock disintegration in the Karakoram Mountains. The present study argues that a major part of the debris accumulations emanates from a glacial origin. In almost no other mountain range is moraine material deposited so widespread on the valley flanks nor is it so well preserved as it is in the Hindukush–Karakoram. The moraine material was originally deposited in the lateral subglacial environment of the glacier. It terms of its topographical location it is located in the transition zone of the ground moraine to the lateral moraine, termed as slope moraine (Iturrizaga, 2001). Therefore the paraglacial landscape assemblage seems to be very different than in mountain areas with comparatively

sediment-starved systems, such as the Sierra Nevada, the Alps or Norway. But in those mountain regions we find similar glacially-induced debris landforms to those discussed here. In the Karakoram the glacigenic sediment source areas are far from exhausted and the paraglacial transformation is still very active. In other mountain areas, such as the Alps or parts of the Himalayas or Andes, the paraglacial cycle seems to be almost terminated. For the Peruvian Andes, Miller et al. (1993) argue on the basis of soil studies and radiocarbon dating for a long-term stability of the landscape after deglaciation, since 8 ka. The Quaternary glaciation of the Himalaya–Karakoram Mountains had already been investigated by the end of the 19th century and evidence was found that the glaciers ended at altitudes below about 2000 m (Pascoe, 1975). Dainelli (1922) proposed a four-fold glaciation and has launched since then a controversial debate about the position of the lowest ice-margin in the Indus valley and Punjab Basin. It is still disputed how far the glacial sediments at the key locality of Sassin–Shatial (900 m) in the Indus valley had been deposited by a main Indus glacier or by tributary glaciers (Desio and Orombelli, 1983; Shroder et al., 1989; Kuhle, 2001; Hormann, 2002). Also the extent of glaciation of the middle and lower Hunza valley (2300 m–1300 m) as well as the middle Indus valley between Skardu (2300 m) and Bunji (1300 m) is not unequivocal. An ice-stream network for the Hunza–Karakoram has been proposed by Derbyshire et al. (1984) showing that the Hunza valley had been glaciated during the Last Glacial Maximum. Kuhle (2001) reconstructed an ice-stream network of about 125 000 km2 during for the Last Glacial Maximum with the Indus glacier reaching down to Sassin. On the whole, the reconstruction of the glacial indicators has been focussed mainly on erratic boulders, striations, end moraines and glacial terraces. It seems to be useful to supplement the classical catalogue with further indicators, in which the paraglacial landscape presented in this paper play a pivotal role (Fig. 16). The upper limit of paraglacial debris cones can be used as a minimum height of the former ice thickness. 8. Summary The extent of glaciation during the Last Glacial Maximum and the Late Glacial, with its glacial valley shaping and legacy of glacial sediments, may be considered as the most important supraregional geoparameter in the distribution of debris accumulation in the Karakoram Mountains. It is the primary control of the distribution of post-glacial debris accumulations. The

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late glacial moraine relicts that are preserved in all valleys and that mask the valley interior by up to several hundred meters above the valley floor, were and are transformed by slope processes in many different ways during post-glacial time, thus producing a wealth of composite debris accumulations presented in this paper. The debris landscape in the Karakoram valley shows that geomorphological forms, which were originally interpreted as “periglacial talus cones” possess a glacigenic origin. Therefore the term “talus cone” is actually not only appropriate for “periglacial talus cones”, it also incorporates “glacigenic” and “glacially-inducedlandforms”. The same applies to alluvial fans and debris-flow cones, which were formerly classified as purely fluvial landform elements. As demonstrated above these landforms are composed of a considerable part of in situ moraine material. The paraglacial landforms are not linked to the climatic-controlled altitudinal zonation, rather they can be classified as azonal phenomenons in the geomorphological landscape assemblage. In order to comprehend the genesis and age of the debris accumulations, it is always necessary to consider the position-specific topographical relationship of the debris accumulation to the corresponding stages of glaciation. The majority of debris accumulations are diverse composite forms. In the final analysis it is the dominant geomorphological processes that govern the type of debris accumulation. This means that it is of great importance to take into account the evolutional element, expressed in the form of a genetic series of debris accumulations. In particular, the transition from an “oversteepened ice-age debris accumulation landscape” to a post-glacial “adjustment debris accumulation landscape” results in polygenetic debris accumulation forms. The widespread distribution of debris cones and debris slopes ranging over a vertical distance of up to 4000 m and more already implies that they represent non-climatically-controlled geomorphological features. Rather, they are the sedimentary legacy of the glaciation of the Karakoram. Most of the debris accumulations are due to the resedimentation of slope moraines. At many locations they are already widely removed so that the original supply area is not visible any more. Only small, conical-shaped morainic remnants on either side of the cone apex below of protecting rock spurs may provide an indication of the parent material. Acknowledgements Thanks are due to the Deutsche Forschungsgemeinschaft (DFG) and the Deutsche Akademische

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Austauschdienst (DAAD), who partly financed the fieldwork in the Karakoram Mountains. Björn Weber, scientific student assistant, carried out the grain-size analysis. I am deeply indebted to the mountain guides Shambi Khan (Shimshal), Ejaz Ali Khan (Passu), Asif Ali (Khyber), Assad Karim (Shimshal), Ajub Khan (Ghulmit) as well as especially to Farhad Karim, Ganj Ali Shah, Gurban Ullah Baig and Mohammad Gurban (all from Shimshal) as well to Alif Mohamad (Chapursan/Ghulmit), who assisted me during the fieldwork. Last but not least I would like to thank the reviewers Jean-Pierre Peulvast and Denis Mercier (both Université de Paris-Sorbonne) for their constructive suggestions on the final draft of this paper. References Abele, G., 1969. Vom Eis geformte Bergsturzlandschaften. Zur Frage der glazialen Umgestaltung der Bergstürze von Sierre, Flims, Ems und vom Fernpaß. Zeitschrift für Geomorphologie. Supplementband 8, 119–147. André, M.-F., 1985. Lichénométrie et vitesses d'évolution des versants arctiques pendant l'Holocène (région de la Baie du Roi, Spitsberg, 79°N). Revue de Géomorphologie Dynamique 34, 49–72. André, M.-F., 2003. Do periglacial areas evolve under periglacial conditions? Geomorphology 52, 149–164. Augustinus, P.C., 1995. Glacial valley cross-profile development: the influence of in situ rock stress and rock mass strength, with examples from Southern Alps, New Zealand. Geomorphology 11, 87–97. Ballantyne, C.K., 2002a. Paraglacial geomorphology. Quaternary Science Reviews 21, 1935–2017. Ballantyne, C.K., 2002b. A general model of paraglacial landscape response. The Holocene 12, 371–376. Ballantyne, C.K., Benn, D.I., 1994. Paraglacial slope adjustment and resedimentation following glacier retreat, Fabergstolsdalen, Norway. Arctic and Alpine Research 25, 255–269. Ballantyne, C.K., Benn, D.I., 1996. Paraglacial Slope Adjustment during Recent Deglaciation and Its Implications for Slope Evolution in Formerly Glaciated Environments. In: Anderson, M.G., Brooks, S.M. (Eds.), Advances in Hillslope Processes, vol. 2. Wiley, Chichester, pp. 1173–1195. Brunsden, D., Jones, D.K.C., Goudie, A.S., 1984. Particle Size Distribution on the Debris Slopes of the Hunza Valley. In: Miller, K.J. (Ed.), The International Karakoram Project, vol. 2. Cambridge University Press, Cambridge, pp. 536–580. Church, M., Ryder, J.M., 1972. Paraglacial sedimentation, a consideration of fluvial processes conditioned by glaciation. Geological Society of America Bulletin 83, 3059–3072. Curry, A., Ballantyne, C.K., 1999. Paraglacial modification of hillslope glacigenic drift. Geografiska Annaler 81A, 409–419. Dainelli, G., 1922. Relazione Scientifiche della Spedizone italiana de Filippi, nell'Himalaia, Caracorum e turchestan Cinese (1913–14) serei II. Resultati Geologici e Geografici, vol. 3. Bologna. Derbyshire, E., Li Jijun, Perrott, F.A., Xu Suying, Waters, R.S., 1984. Quaternary Glacial History of the Hunza Valley, Karakoram Mountains, Pakistan. In: Miller, K.J. (Ed.), The International Karakoram Project, vol. 2. Cambridge University Press, Cambridge, pp. 456–495.

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