Canaries were once used in coal mining as an early warning system for toxic gases leaking into the mine. Signs of distress, or worse, a dead bird, would caution the miners that it was time to retreat from the mine.
Last week, a warm airmass brought our first real taste of spring to the Elk Mountains. Nothing out of the ordinary as far as Crested Butte weather goes, but enough that pale white skin made its spring debut on Elk Street before hastily retreating to aloe vera treatments. On Sunday and Monday (March 9 and 10), temperatures rose to just above freezing at 12,000 feet under an intense March sun. Days later, following a few inches of snow and cooler temperatures, we observed the results of some very unnerving deep slab avalanches. Sometime after Monday evening, a huge slab tore off of the south face of Mt. Owen. This appeared to be triggered by a cornice falling onto a shallow part of the slope, but it propagated to parts of the slab that were 12 feet deep.
|Deep slab on Mt. Owen, first spotted 3/12/14|
On Wednesday night, another monster ripped off of a southwest facing ridge near Avery Peak. This one raised the hairs on the back of my neck. Two deep slabs back to back, under relatively mild and stagnant weather. The Avery slide did not appear to be cornice-fall triggered, and has raised a lot of questions and spurred a lot of speculation on the failure mechanics among local and statewide avalanche professionals. Although meltwater on high elevation terrain has been pretty minimal to this point, it seems plausible that a hot spot on the slope, such as a sunbaked rock or simply an oven-like part of the slope, could have channeled heat and meltwater into a shallow part of the snowpack. Once meltwater percolates to a buried weak layer, it can compromise the layer’s strength causing a wide and destructive failure. The timing of these events can be unpredictable. Maybe warming had subtle effects on the slab properties that added up just enough on this slope. We're still not sure.