Introduction Intensive surface lowering in the ablation area of Debris-covered glaciers (D-type glaciers) debuttresses bedrock slopes and lateral moraines adjacent to the glaciers, and causes landslides, slope failures and their related phenomena. These deformations at inner slopes of lateral moraines or bedrock slopes adjacent to glaciers are important to understand glacial dynamics. This study presents the features of landslides, slope failures and their related phenomena in the Sagarmatha (Everest) region, Khumbu Himal, by field survey and geomorphological mapping, to know the aerial extent and the timing of the landslides.
Methods1. Field survey Field observations were carried out around the Khumbu, Nuptse, Chhukung, and Imja Glaciers in the Sagarmatha (Everest) region between October 9 and November 2, 2004. Among these glaciers, the Khumbu Glacier was chosen for an extensive survey, which includes:
・Mapping of landslides and related phenomena used handy GPS (GARMIN etrex).
・Measurement of landslides area in lateral moraine used GPS (Trimble GPS Pathfinder Pro-XR) and clinometer.
2. Geomorphological mapping A Geomorphological map of the study area was constructed using:
・Topographic map (1:50000; contour interval 40m ; compiled by Survey Department of His Majesty’s Government of Nepal in 1996)
・CORONA satellite photographs (taken in Mar. 1968 and Nov. 1964)
・ASTER satellite images (taken in Nov. 2004)
・Aerial photographs (taken in 1992 )
・Oblique photographs (taken in 1995 by Shuji Iwata)
Results1. Features of landslides, slope failures and their related phenomena Landslides, slope failures and their related phenomena on and around the ablation area of the Khumbu Glacier can be classified into 4 types. (1) Landslides with single or multiple sliding blocks on the inner slopes of lateral moraines. (2) Slope failures on the inner slopes of lateral moraines consisted of steep concave slopes with parabolic profiles and depositional slopes below. (3) Parallel gullies and simple talus slopes on the inner slopes of lateral moraines. (4) Landslide on the bedrock slopes.
The type (1) and (2) are mainly distributed on the south-east facing slopes. Tension cracks or ridge-top depression suggesting the possibility of future landslides are also well developed on south-east facing slopes (Fig. 3). The type (3) is mainly distributed on north-west facing slopes. The type (4) is distributed on the spurs adjacent to the Khumbu Glacier.
In the whole area of the Sagarmatha (Everest) region, the distribution of the type (1) and (2) are dominant in the east, south-east and south facing slopes.
2. Recent landform changes The type (1) and (2) occurred between 1964 and 2004. Both types are observed only on the sunny side of the east, south-east, south and south-west facing slopes.
The type (2) (occurred between 1964 and 2004) is located in two locations; one is in the ablation area of Khumbu Glacier, where the most intensive surface lowering has occurred (Iwata et al. , 2000), and the other is the ablation area of Imja Glacier, where the supraglacial lake has expanded gradually from 1960s.
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