History shows we don’t need an eruption. Mount Rainier has an active hydrothermal system, which acts like an acidic sauna that essentially steams the mountain’s rocky interior into soft, gooey clay. The rock eventually becomes so weak that it can collapse under it own weight. There are also 25 glaciers on the mountain, covering some 36 square miles with an average depth of 100 feet of ice. This ice does its share of damage, freezing and expanding, slowly eroding the volcanic rocks, and dripping melted water into the acidic interior.
Looking at Mount Rainier, you might think there is a large chunk missing from the top. You would be right. Apparently, some 5,600 years ago, the summit collapsed and turned into one of the biggest mudflows in history. This lahar, called the Osceola mudflow, was so big and fluid that it traveled at least 100 miles before stopping in Puget Sound. An ancient forest of vast trees — some ten to fifteen feet wide — covered the valley floors, but did little to slow the powerful flow.
http://www.pbs.org/wnet/savageplanet/01volcano/03/indexmid.html
You’ve restated, quite clearly, all the things my geologist ex-wife told me about Mt. Rainier. I just hope it doesn’t happen soon.
On another note, that California-made Vitamin R is quite tasty !