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Mount Tehama (also called Brokeoff Volcano or Brokeoff Mountain) is an eroded andesitic stratovolcano in the Cascade Volcanic Arc and the Cascade Range in Northern California. Part of the Lassen volcanic area , its tallest remnant, Brokeoff Mountain, is itself the second highest peak in Lassen Volcanic National Park and connects to the park's ...
Former extent of Mount Tehama (Brokeoff Volcano) The earliest volcanic activity of the Lassen Volcanic Center commenced 825,000 years ago. [2] The Rockland complex formed between 825,000 and 609,000 years ago. It was the source of lava domes and lava flows of dacitic composition.
It is also the southernmost non-extinct volcano of the Cascade Range (specifically, the Shasta Cascade part of the range). The 10,457 ft (3,187 m) tall volcano sits on the north-east flank of the remains of Mount Tehama, a stratovolcano that was a thousand feet (305 m) higher than Lassen and 11 to 15 mi (18 to 24 km) wide at its base. [8]
Local activity began 600,000 years ago with the formation of Brokeoff Volcano (alternatively known as Mount Tehama). [36] Around the same time, about 614,000 years ago, an explosive eruption southwest of Lassen Peak produced 20 cu mi (83 km 3) of pumice and ash, covering the area between the vent and what is now the city of Ventura, California.
As part of Mount Tehama's main vent, Bumpass Hell is the result of fissures that tap the volcanic heat, thought to be a cooling mass of andesite, perhaps three miles (5 km) below the surface. It is named after Kendall Vanhook Bumpass, a cowboy and early settler who worked in the Lassen Peak area in the 1860s. Bumpass discovered the geothermal ...
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The snowcapped peak of Mount Rainier, which towers 4.3 kilometers (2.7 miles) above sea level in Washington state, has not produced a significant volcanic eruption in the past 1,000 years.
An ancient volcano, known as Mount Tehama is believed to have been much larger and taller than Lassen Peak. Its erosion is responsible for the topography of the national forest and the national park: a volcanic rim, with elevations beginning at 6,000 feet (1,800 m) above sea level. A rock mesa in Lassen National Forest, Caribou Wilderness ...