Double Ridges on Mahabharat Lekh (Range), Lower Himalaya Zone, South Nepal

Abstract

Double ridges composed of uphill-facing scarp and linear depression are one of the most remarkable topography on high mountain slope. In this paper double ridges are examined on the ridge-top of Mahabharat Lekh (Range) north of Dang Dun (Basin), Lower Himalaya Zone, South Nepal.Low relief surface develops on the ridge around the study site. The lower slope is very steep. The cross section of the ridge shows a dome like skyline because of overburdened mountain top with it's own load. Mahabharat Lekh (Range) is composed of Quartzite, Quartzose sandstone and Phyllite. They had experienced slight metamorphism. Their strikes are parallel to the ridge and the dip angles range between 25°N and 60°N.Uphill-facing scarps 5-15m high and linear depressions develop parallel to the ridge at the altitude of 1, 700-1, 900m a. s. l.. An exposure across the double ridges (G-H cross section) shows that highly fractured zone is formed along the underground extension of the line between the ridge-top and the bottom of the linear depression, and that slickenside is formed on the surface of unfractured bedrock beneath the highly factured zone. The boundary between them is parallel to the bedding plane of the bedrock.Considering from the above mentioned features on the double ridges developing on the main ridge of Mahabharat Lekh (Range), their origins are due to the gravitational slide of the ridge-top and the mountain slope to the north along the bedding plane of the bedrock.