Volcano Type: Stratovolcano
Volcano Status: Historical
Last Known Eruption: 1917
Summit Elevation: 3187 m 10,456 feet
Latitude: 40.492°N 40°29’30″N
Longitude: 121.508°W 121°30’30″W
The Lassen volcanic center consists of the andesitic Brokeoff stratovolcano SW of Lassen Peak, a dacitic lava dome field, and peripheral small andesitic shield volcanoes and large lava flows, primarily on the Central Plateau NE of Lassen Peak. A series of eruptions from Lassen Peak from 1914 to 1917 marks the most recent eruptive activity in the southern Cascade Range. Activity spanning 600,000 years began with construction of Brokeoff stratovolcano. Beginning 400,000 years ago activity shifted to the north flank of Brokeoff, where episodic, more silicic eruptions produced a field of a dozen dacitic lava domes including Bumpass Mountain, Mount Helen, Ski Heil Peak, and Reading Peak. At least 12 eruptive episodes took place during the past 100,000 years, with Lassen Peak being constructed about 28,000 years ago. The Chaos Crags dome complex was constructed about 1100-1000 years ago north of Lassen Peak. The Cinder Cone complex NE of Lassen Peak was erupted in a single episode several hundred years before present and is considered part of the Lassen volcanic center (Clynne et al., 2000). The 1914-1917 eruptions of Lassen Peak began with phreatic eruptions and included emplacement of a small summit lava dome, subplinian explosions, mudflows, and pyroclastic flows.
Lassen Peak
Lassen Peak, rising above Manzanita Lake on the NW, is the focal point of the Lassen volcanic center, a concentration of volcanic features covering much of Lassen National Park. The massive lava dome forming Lassen Peak was constructed about 25,000 years ago and was the site of California’s most recent eruption during 1914-1917. Chaos Crags, a lava dome complex on the north flank, and the aptly named Cinder Cone to the NE, have also erupted within the past 1200 years.
Lassen Peak and Lake Helen
Luis Argüello, a Spanish officer, was the first European to sight the peak, in 1821. He named it San José, which subsequently became St. Joseph and then Mount St. Joseph. It was renamed for Peter Lassen, a Danish-born explorer and homesteader in the region who guided settlers through the surrounding area in the mid-19th century.
Originally posted 2010-08-19 04:23:37.
