Abstract
AbstractSpatial evolution of supraglacial debris cover on mountain glaciers is a largely unmonitored and poorly understood phenomenon that directly affects glacier melt. Supraglacial debris cover for 93 glaciers in the Karakoram, northern Pakistan, was mapped from Landsat imagery acquired in 1977, 1998, 2009 and 2014. Surge-type glaciers occupy 41% of the study area and were considered separately. The time series of debris-covered surface area change shows a mean value of zero or near-zero change for both surging and non-surging glaciers. An increase in debris-covered area is often associated with negative regional mass balances. We extend this logic to suggest that the stable regional mass balances in the Karakoram explain the zero or near-zero change in debris-covered area. This coupling of trends combined with our 37 year time series of data suggests the Karakoram anomaly extends further back in time than previously known.
Highlights
Debris-covered portions of a glacier alter surface energy fluxes relative to bare ice and can have a significant impact on total glacier melt (Østrem, 1959; Nakawo and Rana, 1999; Reid and Brock, 2010)
We considered the optimized threshold value found at Virjerab Glacier for Landsat 5 Thematic Mapper (TM) and Landsat 8 Operational Land Imager (OLI) data to produce successful results when applied to the surrounding glaciers, but while the optimized Landsat 2 Multispectral Scanner (MSS) threshold was adequate for Virjerab Glacier, visual examination of the value applied to other glaciers showed many errors
While translated features that are not parallel to the glacier flowline reveal dynamic information, our analysis relies on summed debris-covered area change over a single glacier, eliminating any debris-covered area change from features that are translated without a change in area
Summary
Debris-covered portions of a glacier alter surface energy fluxes relative to bare ice and can have a significant impact on total glacier melt (Østrem, 1959; Nakawo and Rana, 1999; Reid and Brock, 2010). During recent decades, mapping supraglacial debris cover and quantifying its effect on glacier melt has been identified as an important component of monitoring and modeling mass balances of mountain glaciers (e.g. Nakawo and others, 2000; Lejeune and others, 2013; Pellicciotti and others, 2014). Before the effect of debris cover on glacier melt can be included in a distributed glacier melt model, the location of the debris must first be known, and, in order to resolve glacier volume change through time, measured or simulated debris-covered area should evolve with time (Jouvet and others, 2011). Landsat satellites have been acquiring data continuously since 1972 and it is plausible that this duration offers a sufficient timescale to map debris-cover evolution (Stokes and others, 2007), provided a method can produce debris-covered area maps of comparable quality over two or more scenes
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