## granular flow

Two mathematicians' visit to the desert sheds new light on avalanches.

*granular flows*.

**Herbert Huppert**tells us what happens when two fluids of different densities meet, for example when volcanos erupt and hot ash-laden air is poured out into the atmosphere.

**Jim McElwaine**tells Plus how he combines his two loves - mathematics and mountaineering - in avalanche research.