What volcano was most recently active in the continental US?

Answer

I would have to say Mt St. Helens in Washington State. Mount St. Helens erupted on May 18, 1980 killing 57 people and destroying 250 homes, 15 miles of railways, 185 miles of highway and many miles of forest. It uprooted trees like matchsticks and spewed a combination of mud, ash and debris 63,000 feet in the air. Yakima, a city across the Cascade Mountains from Mt. St. Helens was covered with six feet of ash. Drivers of cars had to put nylons over their tailpipes to keep them from clogging. Mt. St. Helens continues to be active today but this was its most spectacular eruption.

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