Question: Before 1980, when was the most recent eruption of Mount St. Helens?
Answer: 123 years
There was a 123 year dormant interval between the end of the Goat Rocks eruptive phase (1800-1857) and the most recent eruption (1980). The Goat Rocks phase included lava flows, dome growth, mud flows and tephra fall. The last time there was a lateral blast was during the Sugar Bowl eruptive phase (1,080-1,060 AD).
