Lassen Peak

Lassen Peak
Lassen Peak volcano
Highest point
Elevation	10,457 ft (3,187 m) NAVD 88[1]
Prominence	5,229 ft (1,594 m)[2]
Listing	US most prominent peaks 113th US most isolated peaks 91st California county high points 13th
Coordinates	40°29′17″N 121°30′18″W / 40.48806°N 121.50500°W / 40.48806; -121.50500[1]
Geography
Lassen Peak Show map of California Lassen Peak Show map of the United States
Location	Shasta County, California, U.S.
Parent range	Cascade Range
Topo map	USGS Lassen Peak
Geology
Rock age	Less than 27,000 years
Mountain type	Lava dome
Volcanic arc	Cascade Volcanic Arc
Last eruption	1914 to 1921
Climbing
Easiest route	Hike

Lassen Peak (/ˈlæsən/ LASS-ən),^[3] commonly referred to as Mount Lassen, is a 10,457 ft (3,187 m) lava dome volcano in Lassen Volcanic National Park in Northern California. Located in the Shasta Cascade region above the northern Sacramento Valley, it is the southernmost active volcano in the Cascade Range of the Western United States, and part of the Cascade Volcanic Arc stretching from southwestern British Columbia to northern California. It supports many flora and fauna among its diverse habitats, which reach high elevations and are subject to frequent snowfall.

Lassen Peak has a volume of 0.6 cu mi (2.5 km³), making it one of the largest lava domes on Earth. The volcano arose from the former northern flank of now-eroded Mount Tehama about 27,000 years ago, from a series of eruptions over the course of a few years. The mountain has been significantly eroded by glaciers over the last 25,000 years, and is now covered in talus deposits.

On May 22, 1915, a powerful explosive eruption at Lassen Peak devastated nearby areas, and spread volcanic ash as far as 280 mi (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 in Washington were the only two volcanoes within 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, to protect the nearby volcanic features, and to keep anyone from settling too close to the mountain. The park, along with the nearby Lassen National Forest and Lassen Peak, have become popular destinations for recreational activities, including climbing, hiking, backpacking, snowshoeing, kayaking, and backcountry skiing. Lassen Peak is dormant, meaning the volcano is merely inactive, and it has a functioning magma chamber under the ground still capable of eruptions. Thus it poses 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 observed with sensors by the California Volcano Observatory.