Slow-mo avalanches on the rise

Christophe Ancey

Slow-mo avalanches on the rise

Although the word “avalanche” often brings to mind billowing clouds of snow racing downhill to smother skiers and snowmobilers, another type of snow slump is on the rise: a slow-motion slide of thick, wet snow that despite its languid pace can pummel structures with devastating force. (A particularly spectacular example, which demolished a ski lift at Saint-François-Longchamp ski resort in the French Alps in March 2012—image, above—was caught on video.) Scientists understand the conditions that trigger these so-called glide avalanches, but a new analysis of field data stretching back to the 1930s suggests that conditions inside the snow masses—and therefore the forces and stresses that they impose on structures in their paths—have been woefully underestimated in some cases. In one case the researchers analyzed, the forces exerted on a cable-car tower by a glide avalanche at another ski resort near the France–Spain border in 2013—one traveling downhill at a mere 4 meters each day—were at least seven times those the tower was designed to withstand, the team reported online before print in Reviews of Geophysics. The findings could serve as a warning sign that engineers need to design stronger structures, especially as glide avalanches may become more frequent: Warmer winters in the future may cause snowpacks to become, on average, wetter and denser than those seen in winters of recent decades.