Three decades of debris-covered area change for 94 glaciers in Northern Pakistan

Abstract:

Debris-covered portions of a glacier alter surface energy fluxes relative to bare ice and can have a significant impact on total ice melt. The net volume and distribution of rock debris on a glacier surface is subject to continuous reworking and volume change from glacier dynamics, mass balance, erosion, englacial transport and debris evacuation at the terminus. While models of melt under debris have been developed and used extensively, very few studies have investigated the temporal evolution of debris cover. We used Landsat imagery to measure supraglacial debris-covered area change for 94 glaciers within the Shimshal and Hispar watersheds in Northern Pakistan over 32 years (1977-2009). Preliminary results show that the change in debris-covered area over the entire region is close to zero for the 32-year period, but analysis at an individual glacier scale shows a wide spectrum of area changes. We propose that these results complement the positive or stable glacier mass balances that have been observed in the Karakoram. Nine of the studied glaciers, comprising 62% of the observed glacierized area, are surge-type and eight surged between 1977 and 2009. Our results suggest that surge behavior can cause more rapid changes in supraglacial debris-covered area relative to non-surge type glaciers. The main motivation for this research is to identify the major factors and spatial and temporal scales that will best facilitate forward modeling of debris cover evolution.