The Rhône Glacier is one of the natural wonders of Switzerland, a massive river of ice that is among the most visited glaciers in the world. It is not only an entrancing tourist destination, but its health is critical to the larger ecosystem—it is the source of the Rhône river, a major waterway, and helps fill Lake Geneva, the largest body of water in Switzerland.

But the Rhône Glacier, like many glaciers around the world, is receding. Accurately measuring how fast that is happening is essential to understanding the glacier’s evolution and forecasting expected changes in the years ahead. Those changes have major implications for tourism as well as energy security, as the glacier’s flow sustains hydroelectric power generation in the region.