Avalanches are powerful forces of nature, but they're also the result of millions of tiny snowflakes bonded — or not bonded — together just so. Looking at avalanches falling down mountains can only tell you so much. At Montana State University's "subzero lab", scientists are studying how avalanches happen by recreating them flake by flake.
The subzero lab is a mountainside in miniature, where temperature and sunlight are all under the control of scientists. "We can recreate a specific day over and over again," says snow mechanics engineer David Walters in the short documentary Avalanche Engineers. Nautilus recently interviewed Walters about the documentary and his work in the subzero lab.
Avalanches form when a slab of snow sits over a weak layer. And what causes these weak layers? Cold, sunny days. Snow is a good insulator, and it can trap the sun's heat an inch or so below the surface. As the snow underneath warms and then evaporates, water vapour rises up to the surface, where it immediately freezes upon contact with the cold air. This creates sharp grains of ice that don't bond together well, hence the weak layer. That weak layer can then be buried under dense snow that forms a slab on top. A slight disturbance can make that whole slab suddenly fall away. Avalanche.
Ice grains growing on the surface of the snow on a cold, sunny day simulated in the lab.
Walters can recreate all these conditions in the subzero lab. CT scanners reveal the microscopic structure of snow. Cameras capture ice grains growing on the snow surface, and how the particles move in the moment a weak layer fails. By understanding the many small forces that build up to an avalanche, scientists can better predict when an avalanche may actually happen. [Nautilus, Avalanche Engineers]
All images screenshots from Abby Kent's Avalanche Engineers