Is there a threat that Mount St. Helens will erupt any time soon? When do you consider a volcano dead? How long do you wait before you say that a volcano will not erupt any more?

rocky

Dear S. Sutherland,

Mount St. Helens erupted at least 10 times in the 200 years before the 1980 eruption. It is considered to be the most active volcano in the Cascades. Volcanologists that study Mount St. Helens believe it is likely to erupt again within a few decades or a century at most.

It can be difficult to know when a volcano is dead. Many cinder cones, are monogenetic, erupting only once before the volcano is dead. Stratovolcanoes can erupt many times in only a few centuries, like Llaima in Chile, which has erupted at least 40 times in the last 350 years. Stratovolcanoes can also go many centuries without an eruption, like Newberry volcano in Oregon, which has not erupted in 1,300 years but will probably erupt again. Large volcanic systems, like Yellowstone, can go hundreds of thousands of years between eruptions.

Thanks for your challenging questions.

Steve Mattox, University of North Dakota 

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