<P> On May 22 , 1915 , a powerful explosive eruption at Lassen Peak devastated nearby areas , and spread volcanic ash as far as 280 miles ( 450 km ) to the east . This explosion was the most powerful in a series of eruptions from 1914 through 1917 . Lassen Peak and Mount St. Helens were the only two volcanoes in the contiguous United States to erupt during the 20th century . Lassen Volcanic National Park , which encompasses an area of 106,372 acres ( 430.47 km ) , was created to preserve the areas affected by the eruption , for future observation and study , and to protect the nearby volcanic features . The park , along with the nearby Lassen National Forest and Lassen Peak itself , represent popular destinations for recreational activities including climbing , hiking , backpacking , snowshoeing , kayaking , and backcountry skiing . Lassen Peak is still considered active , and it continues to pose a threat to the nearby area through lava flows , pyroclastic flows , lahars ( volcanically induced mudslides , landslides , and debris flows ) , ash , avalanches , and floods . To monitor this threat , Lassen Peak and the surrounding vicinity are closely monitored with sensors by the California Volcano Observatory . </P>
<P> On May 22 , 1915 , a powerful explosive eruption at Lassen Peak devastated nearby areas , and spread volcanic ash as far as 280 miles ( 450 km ) to the east . This explosion was the most powerful in a series of eruptions from 1914 through 1917 . Lassen Peak and Mount St. Helens were the only two volcanoes in the contiguous United States to erupt during the 20th century . Lassen Volcanic National Park , which encompasses an area of 106,372 acres ( 430.47 km ) , was created to preserve the areas affected by the eruption , for future observation and study , and to protect the nearby volcanic features . The park , along with the nearby Lassen National Forest and Lassen Peak itself , represent popular destinations for recreational activities including climbing , hiking , backpacking , snowshoeing , kayaking , and backcountry skiing . Lassen Peak is still considered active , and it continues to pose a threat to the nearby area through lava flows , pyroclastic flows , lahars ( volcanically induced mudslides , landslides , and debris flows ) , ash , avalanches , and floods . To monitor this threat , Lassen Peak and the surrounding vicinity are closely monitored with sensors by the California Volcano Observatory . </P>
when was the last time a volcano erupted in california
when was the last time a volcano erupted in california
May 22 , 1915
May 22 , 1915