I do not usually cover snow and ice avalanches in my blog, but the recent Keystone Canyon avalanche, and other avalanches on the Richardson Highway in Alaska, requires that I make an exception.\u00a0 The largest of many avalanches occurred on Monday at Keystone Canyon as a consequence of the recent combination of exceptional temperatures and high levels of precipitation through the winter (Jeff Masters has a blog post<\/a> about the meteorology of this event).\u00a0 It appears that there were actually two large avalanches at Keyston Canyon, one natural and one caused by blasting to try to remove the remaining unstable snow.\u00a0 The net effect of this has been to block the Richardson Highway, the only road to the town of Valdez (population 4,000) people.\u00a0 The best view of the avalanche deposit is a video from a helicopter that flew over the site<\/a>:<\/p>\n