Lassen Volcanic Center

The Lassen Volcanic Center consists of the andesitic Brokeoff stratovolcano SW of Lassen Peak, a dacitic lava dome field, 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 is the most recent eruptive activity in the southern Cascade Range. Activity spanning about 825,000 years began with eruptions of the Rockland caldera complex and was followed beginning about 590,000 years ago by construction of Brokeoff.

Beginning about 310,000 years ago activity shifted to the N flank of Brokeoff, where episodic, more silicic eruptions produced the Lassen dome field, a group of 30 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 27,000 years ago. The Chaos Crags dome complex, ~3 km NNW of Lassen Peak, was constructed about 1,100-1,000 years ago.

The Cinder Cone complex 17 km NE of Lassen Peak was erupted in a single episode several hundred years ago and is considered part of the 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.