Drone surveys reveal why steep alpine channels erode so fast during debris flows

A brown mass—a mixture of water, boulders and fine matter—plows through the landscape.

The mountains wash more than a thousand lorryloads of material into the valley on a fairly regular basis, causing damage in excess of CHF 100 million per year in Switzerland alone.

A better understanding of this natural hazard requires data from the debris flow channels, of which there is very little because of the complex surveying process. ...