The landslide in the Surma Khola Valley, High Mountain Region of the Central Himalaya in Nepal

The Surma Khola catchment is situated between 2200-3410 m a.s.l. in an unsettled area with a quasi-natural Abies-Rhododendron arboreum - Rhododendron barbatum forest. The High Mountain Region of the Central Nepalese Himalaya is well known for its active geomorphodynamic processes caused by the Himalayan uplift, the steepness of the slopes and the enormous precipitation amounts during the monsoon. In the early hours of the morning of August 10(th) 1990, a landslide triggered by a light earthquake occurred over a width of 35 m on the western ridge of the Surma Khola Valley. For days great amounts of water had infiltrated into the slope from a leaking irrigation channel. Within minutes, 9000 m(3) of material slipped and tumbled, dragging along the rhododendron-fir-forest and buried old slide material from earlier landslides 120 m further down. During the following 3 days, the suspended sediment concentration in the Surma Khola increased from 0.1 gl(-1) measured before to a maximum of 8.1 gl(-1). The calculated sediment transport increased from 66 gs(-1) to approximately 23 kgs(-1). During these 3 days, the specific suspension delivery totalled 4 tha(-1), twice the annual suspended sediment delivery. (C) 2000 Elsevier Science Ltd. All rights reserved.