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Cold-Based Glacier Advance in the Allan Hills, South Victoria Land

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Cold-Based Glacier Advance in the Allan Hills, South Victoria Land UvA-DARE (Digital Academic Repository) A polar paradise: the glaciation of South Victoria Land, Antarctica Lloyd Davies, M.T. Publication date 2004 Link to publication Citation for published version (APA): Lloyd Davies, M. T. (2004). A polar paradise: the glaciation of South Victoria Land, Antarctica. UvA. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:23 Sep 2021 Cold-basedCold-based glacier advance in Antarctica CHAPTERR 5: COLD-BASED GLACIER ADVANCE IN THE ALLAN HILLS,, SOUTH VICTORIA LAND, ANTARCTICA: EVIDENCE ANDD PRESERVATION POTENTIAL1 Abstract t Neww evidence is presented from the Allan Huls, South Victoria Land, Antarctica that confirmss cold-based glaciers are capable of erosion, substrate deformation and deposition.. Four types of erosion, three types of deposition and three scales of glacitectonismm resulting from cold-based glacial advance are described, and a model derivedd from these observations and those of advancing cold-based glaciers elsewhere. Thee model entails: (i) ice block apron overriding and entrainment and (if) ice-bed separationn leading to the formation of a cavity on the down-glacier side of escarpments. Thee model is most effective for a horizontally stratified, lithified sedimentary bedrock substrate.. The preservation potential for cold-based glacial features is high in polar climatess (e.g. Antarctica) but is very low beyond on account of the more rapid weathering inn sub-polar or temperate climates. This explains the perceived absence of cold-based glaciall features in the Pleistocene record of today's temperate regions that most likely experiencedd cold-based glaciation during past glacial maxima. 1.. INTRODUCTION Thee interface between glacier ice and the underlying substrate has attractedd considerable interest over recent years, following general acceptancee that processes operating at the base of glaciers and ice sheets affectt their behaviour (Boulton and Jones, 1979; Engelhardt and Kamb, 1998;; Hooke et al., 1992). However, the vast majority of these studies have focusedd on warm, wet-based ice masses, in particular the 'deformable bed' (e.g.. Hart and Rose, 2001). Very few studies have addressed the behaviour off cold-based glaciers and ice sheets. This is because of the universally held assumptionn that basal sliding, abrasion and bed deformation do not take placee beneath cold-based ice (Boulton, 1972; Hubbard and Sharp, 1989; Holmlundd and Naslund, 1994; Naslund, 1997) and that consequently, '' In review with Quaternary Science Reviews LloydLloyd Dairies, M.T. InstituteInstitute for Biodiversity and Ecosystem Dynamics-Physical Geography, Universiteit van Amsterdam, NieuweNieuwe Achtergracht 166,1018 WVAmsterdam, The Netherlands Atkins,Atkins, CLft AntarcticAntarctic Research Centre and School of Earth Sciences, Victoria University of Wellington, New Zealand vanvan der Meer, Jaap JM. DepartmentDepartment of Geography, Queen Mary, University of London, Mile End Road, London. E14NS, UnitedUnited Kingdom Barrett,Barrett, PJ. AntarcticAntarctic Research Centre and School of Earth Sciences, Victoria University of Wellington, New Zealand Hicock,SJi. Hicock,SJi. DepartmentDepartment of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada 51 1 Chapters Chapters relictt features (and therefore 'older' landscapes) are actually protected beneathh cold ice. (Falconer, 1966; Bergsma et al., 1984; Sugden et al., 1991; Kleman,, 1994; Stroeven and Kleman, 1999; Kleman and Hattestrand, 1999;; Clarhall, 2002; Naslund et al., 2003). Ass Waller (2001) states, "a growing body of field evidence suggests that basall processes may remain active beneath cold-based, ice masses". Such evidencee is cold-based glacier basal sliding at —5°C (Echelmeyer and Zhongxiangg Wang, 1987) and -vfC (Cuffey et al., 1999), as well as entrainmentt (Cuffey et al., 2000) and cold-based glacier ductile and brittle deformationn of entrained debris (Fitzsimons, 1996a; Fitzsimons et al., 1999;; Bennett et al., 2003). Additionally, evidence from Quaternary, glaciall environments (Broster and Claque, 1987) such as ductile deformationn in permafrost of Pleistocene age (Astakhov et al., 1996) have beenn reported. Thee purpose of this chapter is to develop further the model outlined in Atkinss et al., (2002) and provide more comprehensive documentation of cold-basedd features found in central Allan Hills, Antarctica (Fig. lA-C). We alsoo discuss the preservation potential of these features, so as to provide criteriaa for the recognition of cold-based glaciation elsewhere. 2.. THE ALLAN HILLS Thee Allan Hills (76°43' S, 159°40* E) are a low lying nunatak located high inn the Transantarctic Mountains (TAMS) of South Victoria Land (1600- 21000 metres above sea level or masl; Fig. lA-C). The annual ablation rate forr ice in the Allan Hills is 4-5 cms5*"1 and much of the surrounding ice is stagnantt (Annexstad and Schultz, 1982). Mean annual air temperature (MAAT)) of the region is -30°C (Robin, 1983). Thee centre of the nunatak is occupied by the Manhaul Bay Glacier (informall name), which is approximately 6km long and 200m thick, with basall temperatures of ~-24°C (Atkins et al., 2002), and which flows into thee centre of the Allan Hills from the north. Currently, the Manhaul Bay Glacierr is retreating by sublimation (Atkins et al., 2002) and exposed areas off its snout are bubble rich and fractured (Fig. 2; Lloyd Davies and van der Meer,, 2001) suggesting former glacier advance by ice block apron 52 2 Cold-basedCold-based glacier advance in Antarctica Fig.. l The Allan Hills. A.. Location of the Allan Hills, within South Victoria Land, Antarctica. B.. The shape of the Allan Hills, showing the respective positions of Mount Watters (highestt point in the Allan Hills, 2123 masl), the Manhaul Bay and Odell Glaciers ass well as contemporary ice flow direction (black arrowheads). C.. View of Allan Hills from the south-east. Ice from the South Polar Plateau (left) is heree deflected north before flowing east toward the Ross Sea (right).. Thick arrows indicatee contemporary ice flow direction for the Manhaul Bay and Odell Glaciers. overridingg (Shaw, 1977a). Bordering the eastern Allan Hills is the Odell Glacier,, which flows fromsouth-wes t to north-east, between the Allan and Coombss Hills. It is about 20km long and also estimated at around 200m thick,, from which we conclude that it too is cold-based. Thee geology of the Allan Hills largely comprises sub-horizontal Permian andd Triassic sandstones, carbonaceous siltstones and coal measures of the Beaconn Supergroup. These are intruded by sills and thin dykes of Jurassic Ferrarr Dolerite (Ballance and Watters, 1971), as well as bodies of a co-eval Mawsonn Formation, a volcanic explosion breccia, in the west and southern partss of the nunatak. Central Allan Hills also includes several thin (>iom thick)) patches of Sirius Group tillite totalling around 2km2 in area (Atkins andd Barrett, 2001; Holme, 2001). These deposits record extensive wet- 53 3 Chapters Chapters Fig.. 2 Basal ice at the snout of the Manhaul Bay Glacier (see also Fig. 3 for photograph location).. Note the fractures, large bubble size and their density. Lens cap (circled inn white) for scale. basedd glaciation at least 2 million years ago, based on cosmogenic dating off boulder surfaces in the Sirius (Tschudi, 2000), but more likely at least 155 million years ago, based on the studies of landscape evolution of the Dry Valleyss regionn (Summerfield et al., 1999). Strike and dip measurements of glacitectonisedd bedrock (thick arrows in Fig. 3) demonstrate that flow directionss of the older glacial event which deposited the Sirius tillite were quitee different from the flow directions of the Manhaul Bay and Odell Glacierss today. Thee shape of the Allan Hills and details of many recent glacial features are shownn in a geomorphological map (Fig. 3) based on spot observations fromm four field seasons (1997-2001). They were described and photographedd in the field, the locations being recorded by GPS or compass triangulation.. Aerial photographs and a Topcon© stereoscope were also usedd to confirm sight lines to certain features such as isolated boulders or boulderr trains. The dominating feature is the stepped relief decreasing in elevationn towards the lobes of the Manhaul Bay and Odell Glaciers. Other significantt features include Trudge Valley in central eastern Allan Hills, whichh is over lkm long and nearly lkm wide, its eastern end terminating at thee Odell Glacier. Minor but locally significant features are two dolerite dykes,, one aligned north-west to south-east across central Allan Hills, and thee other, north-south (Fig. 3). Two canyons, containing 'dry' fluvial channels,, mark the ends of Trudge Valley on the south side (Lloyd Davies andd van der Meer, 2002). Parallel crested ridges of possible aeolian origin coverr large areas of floors and sides of valleys within Allan Hills and are foundd in clusters oriented east-west. They range from a few metres long andd centimetres high, to over 200 metres long and nearly 4 metres in height. 54 4 II ï II i I ii $ SS I 'S II f ill» » ii I 11 1 i !! t II * } I 11 11 ** 1 11 i II s || l I | ii S II I 55 1 J 22 E <DD ** c '-CC » ™™ — I .
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