By combining changes in elevation with other data, scientists have developed a method for estimating the thickness of debris covering glaciers on whose water more than 800 million people depend
— The accelerated melting of Himalayan glaciers—vital sources of water for more than 800 million people—is anticipated to cause acute regional water shortages by 2050. How these glaciers will respond to a changing climate depends in part upon the depth of the rock debris that covers up to 18% of their surfaces; a layer of debris less than a few centimeters thick enhances melting, whereas a deeper layer insulates the ice, reducing the amount of melt. Accurately quantifying the thickness of this debris remains a major challenge, however, especially on a glacier-wide scale.
Rounce et al. have developed a new method to remotely determine this metric. Using pairs of satellite-acquired, high-resolution digital elevation models gathered during different time intervals, the team calculated the changes in elevation and surface velocity for Nepal’s Ngozumpa glacier and then combined the results with local meteorological data to estimate surface debris thickness.
The researchers validated the results by comparing them with two sets of previously collected field measurements and found that the debris thickness decreased higher up the glacier. The new method performed well across both stagnant and active portions of the ice. The researchers then applied this technique to two additional glaciers in the Mount Everest region, including Khumbu, whose maximum calculated debris thickness of 1.89 meters is in close agreement with a 1986 estimate of 2 meters that was based upon 50 field measurements.
This study is the first to validate estimates of glacial debris thickness with multiple independent data sets on a basin scale and thus represents an important advance in the field of glaciology. This method, which should be widely applicable, represents a significant improvement in glaciologists’ ability to model the evolution of debris-covered Himalayan glaciers and changes in the availability of the crucial water they provide. (Journal of Geophysical Research: Earth Surface, https://doi.org/10.1029/2017JF004395 , 2018)
by Terri Cook | Eos