Exponentially decreasing erosion rates protect the high-elevation crests of the Himalaya

摘要

Glacierised mountains erode rapidly due to efficient glacial erosion around the long-term equilibrium line altitude (ELA), as well as by intense frost-cracking action. This 'glacial buzzsaw' is hypothesised to limit mountain heights globally to within about 1.5 km of the local ELA. However, we show that the high Himalaya contrasts this picture with a precipitous decline in the erosion rate at its high-elevation crests. We obtain headwall-erosion rates at eight Himalayan debris-covered glaciers from estimates of the corresponding supraglacial debris flux. The data reveal large variation of erosion rates in the range of 0.04-1.0 mm/yr. We establish that this variability is controlled by an exponential decrease in erosion rate with decreasing mean annual temperature of the headwall due to a decline in frost-cracking intensity at low temperatures. The implied order of magnitude decline of erosion rate at the high altitude of the Himalaya, apart from the pattern and magnitude of uplift, may be crucial for generating relief, and for protecting the spectacularly high crests from the action of 'glacial buzzsaw'. (C) 2018 Elsevier B.V. All rights reserved.