One of the most explosive volcanoes in U.S. history began its eruption with a trickle, not a blast. Mount St. Helens' gas-laden magma oozed into the cone before the mountain finally erupted in 1980.

Klyuchevskoy volcano in Russia erupted shortly after a powerful 8.8 magnitude earthquake in the same region. When you purchase through links on our site, we may earn an affiliate commission. Here’s ...