A warming Earth causes the volume of mountain glaciers and their extent to decline globally for decades. At the same time, the cover of many glaciers with debris changes. However, this debris coverage has been rarely recorded so far. A study led by  Dirk Scherler of the German Research Centre for Geosciences GFZ and two colleagues from Switzerland – one of them employed by Google – now shows a possibility to detect the extent of debris on mountain glaciers globally and automatically via satellite monitoring.

Quoting from the GFZ news website: “In their work, the scientists used the cloud computing platform “Google Earth Engine”. This is a web-based development environment and database of satellite imagery from forty years of remote sensing that is freely accessible to researchers. The images for the study in the journal Geophysical Research Letters came from the satellites Landsat-8 and Sentinel-2 and have a spatial resolution of 30 by 30 and 10 by 10 meters respectively per pixel. The scientists compared the images from space with an electronic glacier catalog, the Randolph Glacier Inventory, to determine the debris coverage. For this they have developed an automatic method that makes pixel-by-pixel comparisons across the globe. “Our approach, in principle, allows rapid mapping of changes in debris coverage for any period for which satellite imagery is available,” says Dirk Scherler.”

“According to this, 4.4 percent of the glacier surface in mountains is covered with rubble (the Greenland ice sheet and the Antarctic were not included in the study). The distribution is uneven: Towards the poles, the debris coverage decreases as the landscape here is rather flat. In steep mountain regions, such as the Himalayas, there is more debris on the glaciers. Moreover, the study showed that the coverage ratio is higher for smaller glaciers than for larger ones. With global glaciers shrinking, the percentage of debris coverage is expected to increase, making it more important to monitor debris coverage.”

Here is an overview of the places in the world where surface debris affects the glaciers:

Scherler, D., Wulf, H., Gorelick, N. (2018): Global Assessment of Supraglacial Debris Cover Extents. Geophysical Research Letters, doi: 10.1029 / 2018GL080158.

This data is now provided as an add-on the Randolph Glacier Inventory v6.0 and you can get the dataset from the GFZ. This method and dataset will be pretty useful for including the effects of debris in global glacier models and also for our IACS working group on Debris Covered Glaciers.