Yall locally keep an eye peeled on those steep forested slopes above you when driving. We are over a third above average rainfall since 1 January (30 inches against a 20-inch average), much of the increase in the last couple weeks, with some monster deluges last night. Contrary to the news media, trees do NOT hold that hillside topsoil in place, but behave exactly the opposite for the most typical shallow slide. As tree growth increases, the additional weight eventually reaches the point where the thin layer of soil above the slippery, clay-till hardpan acts as a slip sheet and slides. The Oso slide was a deep slide with other causes, notably a huge pocket of glacially-deposited sand with its toe in the river and its upper edge penetrated by (probably) a fractured hardpan leaking rainfall into the sand pocket.
Posted on: Sat, 29 Mar 2014 19:58:13 +0000