Monument Avalanche
I would assume this avalanche on Mammoth Mountain's Monument ski run was the result of control work and not naturally-triggered, but it is nevertheless impressive to regard.
This image is also a wonderful example of some of the mechanics of avalanches: what you see is the result of wind-effected snow creating a slab (atop a weaker layer) which then fractured right around the 37-38° mark when (I presume) ski patrol bombed it.
The upper crown line, then, is showing you where on the mountain the slope was at or near that angle. Notice that the headwall above, which is steeper, did not break loose. Notice also that when the angle moderates below, the snow similarly did not fracture—though the avalanche, via momentum, of course ran farther below.
— March 2, 2007
Andy Lewicky is the author and creator of SierraDescents