when was the last time a volcano erupted in california
Lassen Peak 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 km2), 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.