Katsuhiko Asahi

Temporal Changes in Elevation of the Debris-Covered Ablation Area of Khumbu Glacier in the Nepal Himalaya since 1978

Abstract We evaluated elevation changes at four sites on debris-covered ablation area of Khumbu Glacier, Nepal Himalaya, since 1978. In 2004, we carried out a ground survey by differential GPS in the upper- and lowermost areas of the ablation area. The amount of surface lowering was calculated by comparing digital elevation models (DEMs) with 30-m grid size, as generated from survey data corrected in 1978, 1995, and in the present study. Because we could not access the middle parts of the debris-covered area due to surface roughness, for this area we used an ASTER-DEM calibrated by the ground survey data. The amount of surface lowering during the period 1978–2004 was insignificant near the terminus. A remarkable acceleration of surface lowering was found in the middle part of the debris-covered ablation area, where the glacier surface is highly undulating. In the uppermost area, surface lowering has continued at a steady rate. Surface flow speeds have decreased since 1956, revealing that the recent decrease in ice flux from the upper accumulation area would have accelerated the rate of surface lowering of the debris-covered area of Khumbu Glacier during the period 1995–2004.

Timings and causes of glacial advances across the PEP-II transect (East-Asia to Antarctica) during the last glaciation cycle

A comparison of glacial advances through the last glacial cycle between Northern and Southern Hemispheres in the PEP 2 transect (East Asia and Australasia) revealed (1) a relatively good synchrony of glacial advances during the LGM across the whole transect except Antarctica, (2) a rough synchrony in glacial advances in the Karakorums, Himalayas, Japan, and New Zealand during Marine Isotope Stages (MIS) 3 and 4, although the age control is still poor, and (1) a greater glacial extent in MIS 3 and 4 than in MIS 2. The LGM advances are driven by Northern Hemisphere temperature forcing, but the MIS 3 and/or MIS 4 advances appear to be dominantly controlled by the effects of moisture availability or lack of thereof. In mainland Australia and Antarctica glaciers advanced only in the most humid phases. In Himalaya and Karakorum, where the moisture is supplied both by a Summer monsoon and the westerlies, timings of glacier advance coincide with both Summer monsoon enhancement and westerly intensification. In Japan the glacier extent is controlled by monsoon changes, sea-surface temperatures (SSTs) in the Japan Sea (moisture source) and by zonal shifts in westerly circulation. In New Zealand, either insolalion changes or changes in the intensity of westerly circulation are invoked, Lis the main track of the westerlies did not change greatly during glacial times