Takanobu Sawagaki

Rapid retreat, acceleration and thinning of Glaciar Upsala, Southern Patagonia Icefield, initiated in 2008

Abstract 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.

Late Quaternary glaciations in Japan

A general introduction to the Quaternary glaciations in the Japanese high mountains is presented. Particular attention is paid to the two most significantly-glaciated mountain ranges, and recent knowledge of the glacial history in the Japanese Alps and Hidaka Mountains is presented. Six glacial advances are recognised in the Japanese Alps that occurred during the penultimate glacial cycle, the Last Glaciation, and the Holocene. In the high Japanese mountains, the maximum advance during the Last Glaciation is commonly recognised during Marine Isotope Stage (MIS) 4 with subsequent advances occurring just before 24 ka BP, 18–20 ka PB, 11–10 ka BP and in the early Holocene. In the Hidaka Mountains, recent tephrochronological investigations have revealed the age and extent of the maximum glacier advance during MIS 5a, MIS 3, MIS 2 and MIS 6. Mountain glaciers in Japan were less extensive during the Last Glacial Maximum. This is out of phase with the continental ice sheets in the northern hemisphere.

Contrasting glacier variations of Glaciar Perito Moreno and Glaciar Ameghino, Southern Patagonia Icefield

Abstract 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.

Assessment of glacial lake development and prospects of outburst susceptibility: Chamlang South Glacier, eastern Nepal Himalaya

Chamlang South Tsho has been identified as one of the six high-priority glacial lakes in terms of glacial lake outburst flood (GLOF) danger in Nepal Himalaya, despite the fact that no detailed investigations of the lake had been hitherto undertaken. We conducted detailed mapping of the lake and its surroundings along with field surveys in October 2009 to determine the developmental history of Chamlang South Tsho and to assess its potential for GLOF. The lake expanded rapidly between 1964 (0.04 km2) and 2000 (0.86 km2) and has been stable ever since. Future lake expansion is improbable as its sides are confined by relatively stable landforms. The lake is 87-m deep with a water volume of approximately 34.9–35.6 × 106 m3. Hanging glaciers on the steep surrounding mountain slopes and prominent seepage water in the terminal moraine dam could be potential triggers for a future outburst flood. Additionally, the debris-covered dead-ice dam, which is higher than the lake water level, is narrow and low; therefore, it could be overtopped easily by surge waves. Furthermore, the pronounced difference in elevation between the lake and the base of the terminal moraine dam makes the lake susceptible for a large flood.

Thermal structure of proglacial lakes in Patagonia

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 ~180 m, forming a relatively warm isothermal layer (mean temperature of ~5–6°C at Perito Moreno, ~3–4°C at Upsala, and ~6–7°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.

Recent variations in the terminus position, ice velocity and surface elevation of Langhovde Glacier, East Antarctica

Abstract 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.

Influence of Debris Cover on Ogive-like Surface Morphology of Bilchenok Glacier in Kamchatka

ABSTRACT 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 sloping ice. We estimate the effect of the debris thickness on the ice surface profile using a simple model and this model successfully predicts that high ice relief can be caused by different ablation rates in the debris cover thickness.

Evidence of past migration of the ice divide between the Shirase and Sôya drainage basins derived from chemical characteristics of the marginal ice in the Sôya drainage basin, East Antarctica

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 d 18 O values and ion concentrations of the Skallen, Skarvsnes and Hamna terminal ice sections, located along the estuary line in the Soya 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 Soya 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 Soya 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 Soya drainage basin during the glacial period. The ice in the Soya drainage basin then flowed to the marginal part of the sheet after the ice divide had assumed its present position.

Chapter 72 - Late Quaternary Glaciations in Japan

The Taiwanese high mountain range is not glaciated at present, and the modern theoretical equilibrium line altitude (ELA) was calculated at about 3950 ± 100 m. Large erosional glacial landforms are evidence for a high glacier surface elevation in the central parts of the mountain massifs at the maximum stage of the last glacial cycle, but corresponding glacial terminal deposits are still sparsely known and age control is weak. Luminescence dating from Hsueh Shan suggests the widest glacier extent during MIS 4 with an ELA depression of > 1000 m. Surface exposure and luminescence ages of glacial deposits in Nanhuta Shan above 3100 m a.s.l. indicate a subsequent late glacial to early Holocene glacier advance with an ELA depression of 510–610 m.

Geomorphological Examination on the Fortified Camps (Ezo-Jinya) in Hokkaido of the Nineteenth Century

I.はじめに 江戸時代後半,箱館奉行による蝦夷地の直接統治と 東北諸藩(弘前・盛岡・仙台・会津・秋田・鶴岡)お よび松前藩による蝦夷地沿岸部の防備という蝦夷地政 策にもとづいて,幕府の箱館奉行所の亀田土塁,東北 諸藩による陣屋・囲郭が沿岸各地に建設された。それ らの奉行所・陣屋・囲郭の建設計画図や各藩の警備担 当地の沿岸図など多種多様な絵地図が作成,筆写され 現存する。これらの絵地図からは,陣屋の立地・選定 にあたって影響を与えたに違いない地形,気候・気象 環境など自然地理的側面ついて分析をおこなうことは 不可能と言ってよい。しかし,ほとんど未開拓の蝦夷 地において,東北諸藩が陣屋設営に当たって陣屋とそ の周辺の自然環境,とくに地形条件に配慮したか否か, さらにどのように対処したかに関する自然地理学的な 検討・視点があってしかるべきであろう。 このような観点からの検討を可能にする唯一の史料 が,盛岡藩の『松前持場見分帳』である。『松前持場 見分帳』は,盛岡藩が幕府の命令に従って藩士を派遣 し,函館周辺と東蝦夷地の持場(現在の渡島半島太平 洋沿岸から室蘭,白老近傍に至る沿岸)について現地 踏査(見分)をおこない,その結果を幕府(函館奉行 所)に提出したものである。ここでは,陣屋とその周 辺の地形的条件について,1衛星画像などから作成し た 3D地形表現を基礎資料として列挙・提示し,2盛 岡藩士による『松前持場見分帳』の記載に依拠しつつ, 3D地形画像を用いて解釈・検討する。 陣屋とその周辺の地形について,現在の地形学的知 見や解釈を記述することは困難ではない。しかし,単 なる地形環境の記述では,陣屋の立地に関する論点は 明確にはならず,意義に欠けると言わざるを得ない。 『松前持場見分帳』のような史料は,当該陣屋以外の 蝦夷地陣については存在しない。したがって,『松前 持場見分帳』の記載を参考にしながら,他の資料(地 形図や衛星画像およびそれらの 3D表現)を比較・検 討の基礎とすれば,全ての蝦夷地陣屋の自然地理的な 立地条件についての洞察が多少とも可能になると考え られる。以下,この報告において掲載する地形の 3D 画像の意義は,この点をおいて他にない。 検討対象とする陣屋は,砂原,長万部,室蘭および 白老 に限る。函館周辺の陣屋については,3D地形 表現の例を示し,地形に関するコメントを付すに止め る。これは『松前持場見分帳』では,函館周辺につい ての見分記載に多くが充てられているが,それらは主 として警衛上の見解であって,陣屋の地形的立地条件 に関わる記述は少ないためである。