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The 13th Symposium on Polar Science/Special session [S] Towards the next six-year Japanese Antarctic Research Project (phase X), Tue. 15 Nov.

Coseismic avalanches and rockfalls, as well as their simultaneous air blast and muddy flow, which were induced by the 2015 Gorkha earthquake in Nepal, destroyed the village of Langtang. In order to reveal volume and structure of the deposit covering the village, as well as sequence of the multiple events, we conducted an intensive in situ observation in October 2015. Multitemporal digital elevation models created from photographs taken by helicopter and unmanned aerial vehicles reveal that the deposit volumes of the primary and succeeding events were 6.81 ± 1.54 × 106 and 0.84 ± 0.92 × 106 m3, respectively. Visual investigations of the deposit and witness statements of villagers suggest that the primary event was an avalanche composed mostly of snow, while the collapsed glacier ice could not be dominant source for the total mass. Succeeding events were multiple rockfalls which may have been triggered by aftershocks. From the initial deposit volume and the area of the upper catchment, we estimate an average snow depth of 1.82 ± 0.46 m in the source area. This is consistent with anomalously large snow depths (1.28–1.52 m) observed at a neighboring glacier (4800–5100 m a.s.l.), which accumulated over the course of four major snowfall events between October 2014 and the earthquake on 25 April 2015. Considering long-term observational data, probability density functions, and elevation gradients of precipitation, we conclude that this anomalous winter snow was an extreme event with a return interval of at least 100 years. The anomalous winter snowfall may have amplified the disastrous effects induced by the 2015 Gorkha earthquake in Nepal.

The Tenth Symposium on Polar Science/Ordinary sessions: [OG] Polar Geosciences, Wed. 4 Dec. / 3F Seminar room, National Institute of Polar Research

Calving glaciers are rapidly retreating in many regions under the influence of ice-water interactions at the glacier front. In contrast to the numerous researches conducted on fjords in front of tidewater glaciers, very few studies have been reported on lakes in which freshwater calving glaciers terminate. To better understand ice-water interactions at the front of freshwater calving glaciers, we measured lakewater temperature, turbidity, and bathymetry near Glaciar Perito Moreno, Upsala, and Viedma, large calving glaciers of the Southern Patagonia Icefield. The thermal structures of these lakes were significantly different from those reported in glacial fjords. There was no indication of upwelling subglacial meltwater; instead, turbid and cold glacial water discharge filled the region near the lake bottom. This was because water density was controlled by suspended sediment concentrations rather than by water temperature. Near-surface wind-driven circulation reaches a depth of similar to 180 m, forming a relatively warm isothermal layer (mean temperature of similar to 5-6 degrees C at Perito Moreno, similar to 3-4 degrees C at Upsala, and similar to 6-7 degrees C at Viedma), which should convey heat energy to the ice-water interface. However, the deeper part of the glacier front is in contact with stratified cold water, implying a limited amount of melting there. In the lake in front of Glaciar Viedma, the region deeper than 120 m was filled entirely with turbid and very cold water at pressure melting temperature. Our results revealed a previously unexplored thermal structure of proglacial lakes in Patagonia, suggesting its importance in the subaqueous melting of freshwater calving glaciers.

A large number of glaciers and ice caps (GICs) are distributed along the Greenland coast, physically separated from the ice sheet. The total area of these GICs accounts for 5% of Greenland’s ice cover. Melt water input from the GICs to the ocean substantially contributed to sea-level rise over the last century. Here, we report surface elevation changes of six ice caps near Qaanaaq (77°28′N, 69°13′W) in northwestern Greenland based on photogrammetric analysis of stereo pair satellite images. We processed the images with a digital map plotting instrument to generate digital elevation models (DEMs) in 2006 and 2010 with a grid resolution of 500 m. Generated DEMs were compared to measure surface elevation changes between 2006 and 2010. Over the study area of the six ice caps, covering 1215 km2, the mean rate of elevation change was −1.1 ± 0.1 m a−1. This rate is significantly greater than that previously reported for the 2003–2008 period (−0.6 ± 0.1 m a−1) for GICs all of northwestern Greenland. This increased mass loss is consistent with the rise in summer temperatures in this region at a rate of 0.12 °C a−1 for the 1997–2013 period.

Geological reconstruction of the retreat history of the East Antarctic Ice Sheet (EAIS) since the Last Glacial Maximum (LGM) is essential for understanding the response of the ice sheet to global climatic change and the mechanisms of retreat, including a possible abrupt melting event. Such information is key for constraining climatic and ice-sheet models that are used to predict future Antarctic Ice Sheet AIS melting. However, data required to make a detailed reconstruction of the history of the EAIS involving changes in its thickness and lateral extent since the LGM remain sparse. Here, we present a new detailed ice-sheet history for the southern Soya Coast, Lutzow-Holm Bay, East Antarctica, based on geomorphological observations and surface exposure ages. Our results demonstrate that the ice sheet completely covered the highest peak of Skarvsnes (400 m a.s.l.) prior to ∼9 ka and retreated eastward by at least 10 km during the Early to Mid-Holocene (ca. 9 to 5 ka). The timing of the abrupt ice-sheet thinning and retreat is consistent with the intrusion of modified Circumpolar Deep Water (mCDW) into deep submarine valleys in Lutzow-Holm Bay, as inferred from fossil foraminifera records of marine sediment cores. Thus, we propose that the mechanism of the abrupt thinning and retreat of the EAIS along the southern Soya Coast was marine ice-sheet instability caused by mCDW intrusion into deep submarine valleys. Such abrupt ice-sheet thinning and retreat with similar magnitude and timing have also been reported from Enderby Land, East Antarctica. Our findings suggest that abrupt thinning and retreat as a consequence of marine ice-sheet instability and intrusion of mCDW during the Early to Mid-Holocene may have led to rapid ice-surface lowering of hundreds of meters in East Antarctica.

The Ninth Symposium on Polar Science/Special session: [S] Antarctic ice-ocean interaction ～observation, reconstruction, and modeling～, Tue. 4 Dec. / Entrance Hall (1st floor) at National Institute of Polar Research

On 3 September 1998, a glacial lake outburst flood (GLOF) that originated from Tam Pokhari occurred in the Hinku valley of the eastern Nepal Himalaya. This study analyses the lake's geomorphic and hydrologic conditions prior to the outburst, and evaluates the conditions that could contribute to a future flood through photogrammetric techniques. We processed high-resolution Corona KH-4A (2.7 m) and ALOS PRISM (2.5 m) stereo-images taken before and after the GLOF event, and produced detailed topographic maps (2-m contour interval) and DEMs (5 m × 5 m). We (re-) constructed lake water surfaces before (4410 ± 5 m) and after (4356 ± 5 m) the outburst, and reliably estimated the lake water surface lowering (54 ± 5 m) and the water volume released (19.5 ± 2.2 × 106 m3) from the lake, showing good agreement with the results obtained from ground-based measurements. The most relevant conditions that may have influenced the catastrophic drainage of Tam Pokhari in 1998 include the presence of: (i) a narrow (75 ± 6 m), steep (up to 50°) and high (120 ± 5 m) moraine dam; (ii) high lake level (8 ± 5 m of freeboard) and (iii) a steep overhanging glacier (>40°). The lake outburst substantially altered the immediate area, creating a low and wide (>500 m) outwash plain below the lake, a wide lake outlet channel (~50 m) and a gentle channel slope (~3–5°). Our new data suggest that the likelihood of a future lake outburst is low. Our results demonstrate that the datasets produced by photogrammetric techniques provide an excellent representation of micro-landform features on moraine dams, lake water surfaces and the changes in both over time, thereby allowing highly accurate pre- and post-GLOF (volumetric) change analysis of glacial lakes. Furthermore, it enables precise measurement of several predictive variables of GLOFs that can be useful for identifying potentially dangerous glacial lakes or prioritizing them for detailed field investigations. Copyright © 2015 John Wiley & Sons, Ltd.

To better understand recent rapid recession of marine-terminating glaciers in Greenland, we performed satellite and field observations near the calving front of Bowdoin Glacier, a 3 km wide outlet glacier in northwestern Greenland. Satellite data revealed a clear transition to a rapidly retreating phase in 2008 from a relatively stable glacier condition that lasted for >20 years. Ice radar measurements showed that the glacier front is grounded, but very close to the floating condition. These results, in combination with the results of ocean depth soundings, suggest bed geometry in front of the glacier is the primary control on the rate and pattern of recent rapid retreat. Presumably, glacier thinning due to atmospheric and/or ocean warming triggered the initial retreat. In situ measurements showed complex short-term ice speed variations, which were correlated with air temperature, precipitation and ocean tides. Ice speed quickly responded to temperature rise and a heavy rain event, indicating rapid drainage of surface water to the bed. Semi-diurnal speed peaks coincided with low tides, suggesting the major role of the hydrostatic pressure acting on the calving face in the force balance. These observations demonstrate that the dynamics of Bowdoin Glacier are sensitive to small perturbations occurring near the calving front.

Glaciar Perito Moreno (GPM) and Glaciar Ameghino (GA), Southern Patagonia Icefield, are in contact in the accumulation area, but have shown contrasting frontal variations in the past few decades. To investigate recent changes of the two glaciers and processes controlling the different responses to similar climate conditions, we measured surface elevation change from 2000 to 2008 and terminus positions from 1999 to 2012 using several types of satellite data. GPM shows no significant changes in terminus position and 0.4 ± 0.3 m a–1 thickening over the period, whereas GA retreated 55 ± 2 m a–1 and thinned 2.6 ± 0.3 m a–1. Mass-balance measurements over the period 1999/2000 show that accumulation at GPM was ten times greater than that at GA, but ablation was only three times greater. The mass-balance–altitude profile is similar for the two glaciers; differences in the mass-balance distribution are caused by differences in the accumulation–area ratio (AAR). Our results suggest that the AAR and the calving flux exert strong control on the evolution of glaciers in the region.

To improve the understanding of the mechanism driving recent changes in outlet glaciers in East Antarctica, we measured changes in the terminus position, ice flow velocity and surface elevation of the Langhovde Glacier located on the Sôya Coast. From satellite images from 2000–12 and field measurements taken in 2012 the glacier terminus position and flow velocity showed little change between 2003 and 2007. After this quiescent period, the glacier progressively advanced by 380 m and the flow velocity increased near the calving front by 10 m a-1 from 2007–10. No significant change was observed in surface elevation during the study period. The changes in the terminus position and flow velocity imply a reduction in the calving rate from 93 m a-1 (2003–07) to 16 m a-1 (2007–10). This suggests that calving was inhibited by stable sea ice conditions in the ocean. Theses results indicate that the Langhovde Glacier was in a relatively stable condition during the study period, and its terminus position was controlled by the rate of calving under the influence of sea ice conditions.

The grounding line (GL) of the Antarctic ice sheet forms the boundary between grounded and floating ice along the coast. Near this line, warm oceanic water contacts the ice shelf, producing the ice sheet's highest basal-melt rate. Despite the importance of this region, water properties and circulations near the GL are largely unexplored because in-situ observations are difficult. Here we present direct evidence of warm ocean-water transport to the innermost part of the subshelf cavity (several hundred meters seaward from the GL) of Langhovde Glacier, an outlet glacier in East Antarctica. Our measurements come from boreholes drilled through the glacier's similar to 400-m-thick grounding zone. Beneath the grounding zone, we find a 10-24-m-deep water layer of uniform temperature and salinity (-1.45 degrees C; 34.25 PSU), values that roughly equal those measured in the ocean in front of the glacier. Moreover, living organisms are found in the thin subglacial water layer. These findings indicate active transport of water and nutrients from the adjacent ocean, meaning that the subshelf environment interacts directly and rapidly with the ocean. (C) 2014 The Authors. Published by Elsevier B.V.

流域の土地利用・土地被覆状況が河川水質を通じて沿岸域で進行する磯焼けに与える影響を検討するため、北海道南西部 上ノ国町を流れる天ノ川・石崎川の2河川流域を対象に調査を行った。その結果、人為的な改変の大きな天ノ川流域では、河川溶存成分の濃度が高くなった。しかし、流量の大きい石崎川でより多くの溶存成分が沿岸域に輸送され、これが原因で、石崎川の右岸側で磯焼けの進行が進まないと結論した。, Evaluations of water quality and land use, the mapping of land cover, and investigations into sea desertification were made at two river basins—namely, the Amanogawa and Ishizakigawa watersheds, in southwestern Hokkaido—in order to assess the impacts of land use and land cover changes on river water quality and estuary ecosystems. It was found that heavier land use in the Amanogawa watershed had increased the volumes of soluble components in the river water. However, the total discharge of various soluble components was comparatively larger in the Ishizakigawa watershed, due mainly to its larger water discharge; this has resulted in a relatively lower degree of sea desertification in the estuary area of the Ishizakigawa watershed., 室田武教授古稀記念論文集, Dedicated to Professor Takeshi Murota on his 70th birthday, 第3部物質循環(Part III Material cycles)

Glacial lakes are potentially dangerous sources of glacial lake outburst floods (GLOFs), and represent a serious natural hazard in Himalayan countries. Despite the development of various indices aimed at determining the outburst probability, an objective evaluation of the thousands of Himalayan glacial lakes has yet to be completed. In this study we propose a single index, based on the depression angle from the lakeshore, which allows the lakes to be assessed using remotely sensed digital elevation models (DEMs). We test our approach on five lakes in Nepal, Bhutan, and Tibet using images taken by the declassified Hexagon KH-9 satellite before these lakes experienced an outburst flood. All five lakes had a steep lakefront area (SLA), on which a depression angle was steeper than our proposed threshold of 10° before the GLOF event, but the SLA was no longer evident after the events. We further calculated the potential flood volume (PFV); i.e., the maximum volume of floodwater that could be released if the lake surface was lowered sufficiently to eradicate the SLA. This approach guarantees repeatability to assess the possibility of GLOF hazards because it requires no particular expertise to carry out, though the PFV does not quantify the GLOF risk. We calculated PFVs for more than 2000 Himalayan glacial lakes using visible band images and DEMs of ASTER data. The PFV distribution follows a power-law function. We found that 794 lakes did not have an SLA, and consequently had a PFV of zero, while we also identified 49 lakes with PFVs of over 10 million m3, which is a comparable volume to that of recorded major GLOFs. This PFV approach allows us to preliminarily identify and prioritize those Himalayan glacial lakes that require further detailed investigation on GLOF hazards and risk.

The Patagonia Icefields are characterized by a large number of outlet glaciers calving into lakes and the ocean. In contrast to the recent intensive research activities on tidewater glaciers in other regions, very few observations have been made on calving glaciers in Patagonia. We analysed satellite images of Glaciar Upsala, the third largest freshwater calving glacier in the Southern Patagonia Icefield, to investigate changes in its front position, ice velocity and surface elevation from 2000 to 2011. Our analyses revealed a clear transition from a relatively stable phase to a rapidly retreating and fast-flowing condition in 2008. The glacier front receded by 2.9 km, and the ice velocity increased by 20–50%, over the 2008–11 period. We also found that the ice surface lowered at a rate of up to 39 m a−1 from 2006 to 2010. This magnitude and the rate of changes in the glacier front position, ice velocity and surface elevation are greater than previously reported for Glaciar Upsala, and comparable to recent observations of large tidewater glaciers in Greenland. Our data illustrate details of a rapidly retreating calving glacier in Patagonia that have been scarcely reported despite their importance to the mass budget of the Patagonia Icefields.

Co-seismic avalanches and rock falls, and their simultaneous air blasts, which were induced by the 2015 Gorkha earthquake in Nepal, destroyed the village of Langtang. In order to reveal volume and structure of the deposit covering the village, and sequence of the multiple events, we conducted an intensive in-situ observation in October 2015. Multi-temporal digital elevation models created from photographs taken by helicopter and unmanned aerial vehicles reveal that the deposit volumes of the primary and succeeding events were 6.81 × 106 m3 and 0.84 × 106 m3, respectively. Visual investigations of the deposit and witness statements of villagers suggest that the primary event was an avalanche composed mostly of snow, while the contribution of collapsed glacier ice could account for a few percent of the total mass. Succeeding events were multiple rock falls which may have been triggered by aftershocks. From the initial deposited volume and the upper catchment area, we estimate an average snow depth of 1.56 m in the source area using density assumptions of snow and ice. This is consistent with anomalously large snow depths (1.28–1.52 m) observed at a neighboring glacier (4800–5100 m a.s.l.), which accumulated over the course of four major snowfall events since October 2014. Considering long-term observational data, probability density functions, and elevation gradients of precipitation, we conclude that this anomalous winter snow was an extreme event with a return interval of at least 100 years, which amplified or even caused the disaster induced by the 2015 Gorkha earthquake in Nepal.

This study used Corona KH-4A and Advanced Land Observing Satellite (ALOS) PRISM images to generate digital terrain models (DTMs) of the distal part of Imja Glacier, where a few supraglacial ponds (similar to 0.07 km(2)) expanded into the large Imja Glacier Lake (Imja Tsho, similar to 0.91 km(2)) between 1964 and 2006. DTMs and subsequently derived topographical maps with contour intervals of 1 m were created from the high-resolution images (Corona in 1964 and ALOS in 2006) in the Leica Photogrammetric Suite (LPS) platform. The DTMs and topographic maps provided excellent representation of the elevation and micro-topography of the glacier surface, such as its supra-glacial ponds/lake, surface depressions, and moraine ridges, with an error of about +/- 4 m (maximum). The DTMs produced from the Corona and ALOS PRISM images are suitable for use in studies of the surface change of glaciers. The topographical maps produced from the Corona data (1964) showed that part of the dead ice in the down-glacier area was even higher than the top of the lateral moraine ridges, while the glacier surface in the up-glacier area was noticeably lower than the moraine crests. This suggests more extensive melting of glacier ice in the up-glacier area before 1964. The average lowering of the glacier surface from 1964 to 2006 was 16.9 m for the dead-ice area west of the lake and 47.4 m for the glacier surface east of the lake; between 1964 and 2002, the lake surface lowered by 82.3 m. These figures represent average lowering rates of 0.4, 1.1, and 2.2 m/year for the respective areas.

Ice originating near the inland ice divide of the ice sheet can reappear as marginal ice at the surface near the ice terminal in the ablation area. We have analyzed δ18O values and ion concentrations of the Skallen, Skarvsnes and Hamna terminal ice sections, located along the estuary line in the Sôya drainage basin, East Antarctica. The data suggest that the upper part of the Skallen terminal ice section could have originated from inland precipitation on the Shirase drainage basin during marine isotope stage (MIS) 5e, while the upper part of Skarvsnes and Hamna terminal ice sections could have originated from inland precipitation on the Sôya drainage basin. We calculate past elevation maps for the Antarctic ice sheet using the three-dimensional model, SICOPOLIS. This model suggests that the upstream portion of the Sôya drainage basin during the glacial period (MIS 2, 3 or 4) was located to the northeast of its present location. A flow history is proposed wherein ice from the inland Shirase drainage area flowed over the present ice-divide line from the Shirase to the Sôya drainage basin during the glacial period. The ice in the Sôya drainage basin then flowed to the marginal part of the sheet after the ice divide had assumed its present position.

A circular hole was discovered on the downstream side of a glacier dam in the Yatude Valley, Langhovde, East Antarctica, during the 2005–2006 austral summer. The opening of this hole is the first opportunity enabling us to observe the interior of the dam. The opening led to a large cave in the dam, raising the possibility of meltwater drainage through the dam. The Yatude Valley is an approximately U-shaped fluvial valley. The valley floor has been incised to form a box-shaped inner valley that contains fluvial terraces and large boulders upon the valley floor. The origin of these features can be explained by a large amount of running water; however, we consider it unlikely that a regular current has flowed through this site for a long period. Instead, it is more likely that large quantities of lake water have been periodically discharged due to collapse of the glacier dam or spilling out through a tunnel channel within the cave. The discovered hole and the ice cave are key features in understanding the historical development of the Yatude Valley in relation to the melting history of the Antarctic ice sheet.

北海道東部，知床半島のほぼ中央に位置する羅臼火山は，過去約2,200年間のうち3時期にマグマ噴火したことが知られており，それぞれ降下テフラ（Ra-1 : 500～700 cal BP, Ra-2 : ca. 1,400 cal BP, Ra-3 : ca. 2,200 cal BP）および火砕流を噴出した．これら羅臼起源のテフラは，いずれも斜方輝石および単斜輝石を含むなど鏡下での特徴が類似するが，脱水ガラス屈折率は異なり，識別が可能である．羅臼火山の南西約4.5kmに位置する天頂山火山から約1,900年前に噴出した天頂山aテフラ（Ten-a）は，多量の石質岩片のほか，フレーク状火山ガラス，斜長石，斜方輝石などの本質物質を含む．その火山活動はマグマ水蒸気噴火だったと推定される．Ten-aの噴出量は約0.02km3である．羅臼岳の南～南南西方向約5km付近，標高500～750mの地域には，羅臼湖など多数の沼沢地や湿原が点在する．複数の湿原での掘削調査の結果，駒ヶ岳c1テフラ（AD1856），樽前aテフラ（AD1739），駒ヶ岳c2テフラ（AD1694），Ra-1，摩周bテフラ（774～976 cal BP），Ten-a, 一の沼火山灰の存在と層序が明らかになった．そのほか，知床半島の南部には，摩周起源の摩周lテフラ（ca. 13,000 cal BP）が分布する．

Bilchenok Glacier is a surging glacier in the Kamchatka Peninsula, Russia, which most recently surged in 1982 and is currently in its quiescent phase. Field research in 1998 revealed an ogive-like repeated pattern of transverse ridges and intervening gently sloping ice at the surface of the ablation area of this glacier. It was also observed that most of the glacial surface was covered by volcanic rocks and ash, and the debris thickness on the ridges was more than 1 m, whereas the gently sloping ice was covered by thin debris. We posit that the pattern of the debris thickness is caused by the unique conditions of Bilchenok Glacier, namely, the restricted position of its debris supply at the foot of the rock walls beside the icefall and its surging behavior. The distance between the ridges might indicate the total horizontal displacement attributable to surges. The dependence of the ablation rate on the debris thickness can result in a highly undulating ice surface between the ridge and the gently...

日高山脈北部のエサオマントッタベツ川において,最終氷期後期の氷河最拡大を示すターミナルモレーン付近の支沢の堆積物中に,木材遺体が埋没しているのを発見した.埋木片は,マツ属単維管束亜属の1種(Pinus subgen. Haploxylon sp.)であると同定され,14C年代測定の結果,12.3cal kaが得られた.この年代は,晩氷期の一時的な寒冷期(新ドリアス期)に相当し,北海道の平野部においてグイマツとハイマツが高率に出現する剣淵亜氷期に相当する.埋木片を採取した堆積物は,氷河底ティルの可能性が考えられるダイアミクトンを覆って押出し状に堆積しており,斜面崩壊堆積物に取り込まれながら,採取地点まで流下したものであると考えられる.本資料の樹種同定結果と年代値は,晩氷期～後氷期の温暖化傾向にある時期の一時的な寒冷期における山地植生や山地斜面の発達史を考える上で,有用な資料となることが期待される.

近年,あいついで惑星探査機が火星に到達し,地表面の詳細な数値標高データが得られたことから,地形の解析は飛躍的に進展した.火星表面の環境は,寒冷・乾燥を主な特徴とする「極地砂漠」であると言われ,地球上のアナロジーとして南極大陸のドライバレー地域に見られる地形が用いられている.また,これまで,火星表面の広範囲に水流の侵食を受けたと考えられる地形が認識されてきたことに加えて,寒冷環境の水に関わる地形として氷河や永久凍土に起因すると考えられる地形も多く確認されており,その詳細な形態も明らかにされつつある.しかし,水が流れた地形と氷が流れた地形に決定的な違いはあるのか,といった両者の判別に関する問題は,地球上の地形についても未解決の部分が多く,火星の地形の解釈に適用する際には注意を要する.雪氷の流れによって形成される,岩石氷河や岩屑被覆氷河などの地形の解釈についても,地球上の研究例を火星の地形に単純に当てはめるには問題がある.

The Bilchenok Glacier in the central part of the Kamchatka Peninsula is located on the Ushkovsky Volcano (3900 m a.s.1.) and is regarded as a surging glacier. A tephrochronological study reveals Holocene fluctuations of the Bilchenok Glacier. Field survey and satellite and aerial photo interpretation indicate that five groups (moraines a to e) of moraines are present around the Bilchenok Glacier. Stratigraphic relationships among glacial deposits and marker tephras define the age of each moraine. Three glacial advances during the Neoglacial period are estimated to have occurred at 8 ka BP, 3 ka BP, and 1 ka BP. The glacier possibly expanded at 2 ka BP. No glacial landforms in the Little Ice Age were identified. Glacier expansion during the Little Ice Age was, therefore, on a smaller scale than that of glacial surges in the 1960s, and the other Holocene advances.

This paper describes one geometrical method of simulating the spatial distribution of snow cover. Geographical Information Systems (GIS) and precise Digital Elevation Model (DEM) were used in the s...

Late Quaternary glacial fluctuations in the Esaoman-Tottabetsu Valley, inthe northern Hidaka Range, central Hokkaido were reconstructed based on stratigraphy of glacial landforms and sediments. By mean of tephrochronology, the two previously known stadials of the Last Glacial Stage, the Poroshiri and Tottabetsu Stadials, were reassessed. Shikotsu 1 tephra overlain by the terminal moraine of the Poroshiri Stadial at the river bed of 850m a. s. l. indicates that the glacier reached its maximum at around 40ka (Oxygen Isotopic Stage 3: OIS-3). This advance should have been initiated in the preceding cold period of 01S-4. Kuttara 6 tephra (86 ka) in the proglacial outwash deposits indicates that a glacier fluctuated in the vicinity of the cirque bottom even in the relatively warm period of the early Last Glacial Stage (01S-5b). Contrary to this stadial, the glacial and proglacial deposits including Eniwa a tephra (18 ka) show that the glacial advance during the Tottabetsu Stadial (LGM) in this region was restricted within the cirque bottom. The penultimate glaciation, named the Esaoman Glaciation in this study, was suggested by the discontinuously traceable remnant bed topography along the river basin. These features recommend that the glacial advance of this stage reached at 750m a. s. l., lower than during the Last Glacial Stage.

Pleistocene tephras are significant to examine the late Quaternary glaciation in the Hidaka Range, Hokkaido, Japan. Six marker tephras are found in the glacial deposits around Mt. Tottabetsu and Mt. Esaoman-Tottabetsu. On the basis of their mineral compositions and the refractive indices of volcanic glass and orthopyroxene, these tephras are correlated with such tephras in the Tokachi Plain as Toya, Kuttara-6 (Kt-6), Rakko-3 (RP3), Kuttara-3 (Kt-3), Shikotsu-1 (Spfa-1), and Eniwa-a (En-a). Identification of these tephras makes it possible to discuss the precise chronology of glaciation of the Last Glacial stage and the occurrence of larger glaciation during the penultimate glacial stage in the Hidaka Range. Maximum expansion of valley glacier occurred around 40-42ka represented by Spfa-1. En-a indicating approximately the Last Glacial Maximum is found in the glaciofluvial deposits at many localities. Kt-6 identified in the glaciofiuvial deposits implies that the glaciation had already occurred during Oxigen Isotops Stage 5b.Nozuka pumice (NzP, in this paper) is newly identified in the Tokachi Plain; it is probably a widespread marker tephra indicating the early time of Oxygen Isotope Stage 6.

The formation of the glacial erosional bedforms at the Soya Coast of Lützow-Holm Bay, East Antarctica is discussed. The streamlined bedforms in the studied area are classified into crescentic transverse ridges and tadpole rocks, and these bedforms are accompanied by small erosional marks (s-forms) which suport the interpretation of subglacial meltwater erosion. Some tadpole rocks are superimposed on a large roche moutonnée, and these two kinds of landform are interpreted to have different modes of formation. Observations and interpretations of these bedforms are used to reconstruct the historical development of the glacial erosional bedforms, and to draw attention to the significance and implications of subglacial meltwater erosion on the marginal area of the Antarctic Ice Sheet in the past. An initial episode of glacial plucking and abrasion produced roches moutonnées and basic large-scale landforms. Subglacial meltwater flowing peiodically into the Lützow-Holm Bay sculptured s-forms and streamlined bedforms in bedrock over much of the area. During this period, except for water-flowing phases, ice again came in contact with the bedrock to form striations superimposed on the s-forms and the hillocks.

Two characteristic landforms, landslide blocks and drainage channels, were investigated in Adventdalen, central Spitsbergen. The landslides in the middle reaches of Adventdalen comprise large-scale bedrock slumps which form a hummocky surface on the south slope of Arctowskifjellet. The fourteen recognized landslide blocks are divided into upper and lower sections, according to altitude. The drainage channels consist of tributary rivers to Adventelva which flow in two distinct directions, either parallel with or oblique to the direction of the main river. Glacial deposits were found to cover the ridges between these tributary channels. The upper and lower landslide divisions may indicate former positions of the ice surface, and the channels appear to have originated during the existence of lateral moraine ridges with high ice content. These geomorphological findings have allowed reconstruction of former ice marginal positions, and they strongly suggest the existence of stagnant ice or minor re-advance phases during the course of deglaciation in Adventdalen.