Mount Rainier in Washington State is an active volcano that hasn't erupted in hundreds of years, although volcanic activity has been detected occasionally. Its listed as the third most dangerous volcano in the US, after Kīlauea in Hawaii and Mount St. Helens. Mount Rainier is dangerous because there are highly populated communities nearby: Tacoma, South Seattle, and many various smaller towns. But scientists aren't as concerned with pyroclastic flow or lava or ash as they are with flooding. Flooding from a volcano isn't just water, though.
Mount Rainier is very tall (14,411 feet) and is covered with snow and glaciers. In the event of an eruption, lava and hot gasses would melt that ice quickly, causing a flood called a lahar. The water may be hot or cold, and would be filled with mud, rocks, lava, and debris. The amount of water tumbling down from Mount Rainier would be massive and unstoppable. Communities built in valleys and along rivers would be affected faster than they could evacuate. Around Mount Rainier, that's hundreds of thousands of people. In the Nisqually River Valley, a lahar could wreck the Alder Dam, causing further sudden flooding in a wider area. Read about the potential for a lahar disaster at Mount Rainier at CNN. -via Real Clear Science
(Image credit: Mount Rainier National Park)
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