Mt. St. Helens and the Cascade Volcanic Arc: Iceland in America
Mt. St. Helens erupted 30 years ago. With an Icelandic volcano causing global problems today, the Mt. St. Helens anniversary is a reminder of volcanic activity in America's Lower 48 states.
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Mt. Hood is only one of the Cascades’ several iconic stratovolcanoes – symmetrical cones that tower above the landscape and dominate the horizons of the American Northwest.Skip to next paragraph
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The big one: Mt. Rainier
Most prominent among them is Washington State’s Mt. Rainier, the hunched shoulder of snow and rock 54 miles southeast of Seattle. It is a potential Mt. Rainier eruption that poses the greatest threat to the Northwest, say scientists.
Atop the 14,411-foot peak lie 26 major glaciers, making it the most glaciated peak in the Lower 48 states. That is significant because the greatest threat posed by volcanoes in the Cascades is not so much the eruption itself, but the slurry of ice and rock that it sends hurtling down its mountainside. These lahars are the consistency of wet concrete, scalding hot, and on the steep slopes of Mt. Rainier, could travel at highway speeds.
Indeed, Mt. Rainier provides the perfect runway for these massive mudslides. From base to summit-top crater, Mt. Rainier is taller than the K2, the second-highest mountain in the world, which gets a huge upward boost from the Himalayan plateau.
In one Mt. Rainier eruption more then 5,000 years ago, these flows traveled with such speed and force that they ran into Puget Sound, reshaping the geography of the bay.
Another California stratovolcano, Mt. Shasta, apparently erupted last in 1786 – an event reputedly seen by the French explorer Jean-François de Galaup La Pérouse from his ship in the Pacific, though some historians doubt this account.
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