What is the impact of the lahars on streams and rivers?
[As Brian mentioned, lahars may choke the streams, but rivers may also direct their flow. At Mt. St. Helen’s, after the outrush of the avalanche and ash cloud, enormous mudflows slid off the mountain down several of the adjacent river valleys. These flows were caused by water from blast-melted glaciers and snow that mixed with the already powdered rock to form pasty, muddy flows. These hot and cold masses of mud swept down the valleys of several rivers, sweeping away buildings, vehicles, trees, and even bridges. Trees amounting to more than four billion board feet of salable lumber were damaged or destroyed by the near-supersonic lateral blast of rock, ash, and hot gases. One of these flows even reached and blocked the shipping channel of the Columbia River, 55 miles downstream. (http://www.cotf.edu/ete/modules/volcanoes/vsituations4.html)] How could we estimate the primary blast area that would result from a Mt. Rainier eruption? [Using the Mt. St. Helen’s eruption as a guide, all tho
