Articles | Volume 11, issue 1
Brief communication
18 Jan 2017
Brief communication |  | 18 Jan 2017

Brief communication: Thinning of debris-covered and debris-free glaciers in a warming climate

Argha Banerjee

Abstract. Recent geodetic mass-balance measurements reveal similar thinning rates on glaciers with or without debris cover in the Himalaya–Karakoram region. This comes as a surprise as a thick debris cover reduces the surface melting significantly due to its insulating effects. Here we present arguments, supported by results from numerical flowline model simulations of idealised glaciers, that a competition between the changes in the surface mass-balance forcing and that of the emergence/submergence velocities can lead to similar thinning rates on these two types of glaciers. As the climate starts warming, the thinning rate on a debris-covered glacier is initially smaller than that on a similar debris-free glacier. Subsequently, the rate on the debris-covered glacier becomes comparable to and then larger than that on the debris-free one. The time evolution of glacier-averaged thinning rates after an initial warming is strongly controlled by the time variation of the corresponding emergence velocity profile.

Short summary
Measurements of debris-covered and debris-free glaciers in the Himalaya-Karakoram show similar decadal scale thinning, despite a suppression of melt under the debris. Using physical arguments, supported by simulations of 1-D idealised glaciers, we analyse the evolution of thinning rates on both glacier types under a warming climate. The dynamics of the emergence velocity profile control the thinning rate evolution in general and lead to the observed trends in the thinning rate data.