Mount Tehama
| Brokeoff Volcano | |
|---|---|
 Broken northeast face of Brokeoff Volcano. | |
| Highest point | |
| Elevation | 9,239 ft (2,816 m) NAVD 88[1] |
| Prominence | 915 ft (279 m)[1] |
| Listing | California county high points 17th |
| Coordinates | 40°26′44″N 121°33′34″W / 40.44556°N 121.55944°W[2] |
| Geography | |
| Location | Shasta / Tehama counties, California, U.S. |
| Parent range | Cascade Range |
| Topo map | USGS Lassen Peak |
| Geology | |
| Mountain type | Eroded stratovolcano |
| Volcanic arc | Cascade Volcanic Arc |
| Climbing | |
| Easiest route | Hike |
Mount Tehama (also called Brokeoff Volcano or Brokeoff Mountain) is an eroded
Brokeoff Volcano was active from 590,000 to 387,000 years ago, during which period it erupted numerous flows with compositions ranging from basaltic andesite to dacite. At its peak, Brokeoff Volcano reached an estimated height of 3,350 metres (10,990 ft) and had a basal circumference of approximately 12 kilometres (7.5 mi). At approximately 313,000 years ago volcanism began shifting to the northeast of Brokeoff Volcano, with volcanism currently focused around the modern Lassen Peak. Following the end of volcanism at Brokeoff Volcano, cooling magma beneath the surface continued to drive hot, highly reactive hydrothermal fluids circulating near the central vent of the volcano. These hydrothermal fluids chemically weathered the volcanic rocks near the central vent, making them particularly susceptible to physical erosion. Glaciers and streams were able to rapidly erode the hydrothermally altered rocks near the central vent, creating the deep Mill Canyon and exposing deep into the core of the ancient volcano.
Many of the lava flows along the flanks of Brokeoff Volcano were not as extensively chemically weathered, resulting in the flanks of much of the volcano being preserved. Remnants of the flanks of Brokeoff Volcano include Brokeoff Mountain, Mount Conard, Pilot Pinnacle, Mount Diller, and Diamond Peak.
History
The area near Lassen Peak became a haven for new settlers throughout the 1800s.
Geography and geology
The state of California is located on the
Brokeoff Volcano represents the Pleistocene component of the Lassen volcanic complex, an area of active volcanism for more than three million years. It formed during a period of eruptive activity approximately 600,000 years ago on a series of
Soon after the formation of Brokeoff, other, smaller volcanoes began to form.
Brokeoff's remains are exposed to the southwest
After volcanism at Brokeoff ended, magmatism became more silicic and began migrating toward Lassen Peak's northern flank. The last 400,000 years have seen at least three known flows, parts of which are still on Raker Peak and Mount Conard. A subsequent explosive eruption ejected 12 cu mi (50 km3) of material and created a large crater, which was soon covered by lava. Twelve lava domes were built throughout the area and the next period of eruptive activity began. Spanning 50,000 years it ejected 3.5 cu mi (15 km3) to 6 cu mi (25 km3) of material and was followed by a third period. At least twelve periods of activity have taken place since Brokeoff formed, consisting of activity including pyroclastic flows, pasty lavas, and additional lava domes.[6] Among the vents built by this activity is Lassen Peak.[9]
Flora and fauna
Near the trailhead at lower elevations,
Recreation
Hiking is especially popular on the mountain during summer. The mountain trail lasts between four and six hours, spans 7.4 mi (12 km), and offers "exceptional" views of Mount Diller, Lassen Peak, Chaos Crags, and Mount Conard.[3]
Due to the characteristically intermittent eruptions of active volcanoes such as Lassen Peak, there is some threat from the volcanoes of the LVNP. Dacitic explosive eruptions have taken place within the last 50,000 years at Lassen Peak, Chaos Crags, and Sunflower Flat, and effusive eruptions of basalt have occurred at Tumble Buttes, Hat Mountain, and Prospect Peak. Pyroclastic flows and lahars could easily occur near glaciated areas and in river valleys like Hat Creek Valley.[8] In addition to the volcanic hazards that could possibly occur, one volcano did erupt in the 20th century in LVNP: (Lassen Peak). Lassen's eruptions (1914–21, though most activity occurred between 1914 and 1917) were very small compared to the 1980 eruption of Mount St. Helens.
See also
Notes
- ^ a b "Brokeoff Mountain, California". Peakbagger.com. Retrieved 2010-02-03.
- ^ "Brokeoff Mountain". Geographic Names Information System. United States Geological Survey, United States Department of the Interior. Retrieved 2010-02-03.
- ^ a b c Heid, p. 227.
- ^ a b c Harris, Tuttle, and Tuttle, p. 542.
- ^ Sinnotte, Barbara.
- ^ a b c d Lopes and Lopes, p. 113.
- ^ a b Harris, Tuttle, and Tuttle, p. 549.
- ^ a b Diggles, Michael (May 24, 2005). "Volcano Hazards of the Lassen Volcanic National Park Area, California". United States Geological Survey. Archived from the original on November 2, 2009. Retrieved May 15, 2010.
- ^ Lopes and Lopes, p. 114.
- ^ Lopes and Lopes, p. 119.
References
- Clynne, Mike; Muffler, Patrick (2010). Geologic Map of Lassen Volcanic National Park and Vicinity, California. Reston, Virginia: United States Geological Survey.
- Harris, Ann G.; Tuttle, Esther; Tuttle, Sherwood D. (2004). Geology of National Parks (6th ed.). Dubuque, Iowa: Kendall/Hunt Pub. Co. ISBN 978-0-7872-9970-5.
- Harris, Stephen L. (2005). Fire Mountains of the West: The Cascade and Mono Lake Volcanoes (3rd ed.). ISBN 0-87842-511-X.
- Heid, Matt (2008). 101 Hikes in Northern California: Exploring Mountains, Valley, and Seashore. Wilderness Press. ISBN 978-0-89997-474-3.
- Lopes, Rosaly M. C.; Lopes, Rosaly (2005). The Volcano Adventure Guide. Cambridge University Press. ISBN 978-0-521-55453-4.
- Sinnotte, Barbara (1996). California: A Guide to the State & National. Hunter Publishing, Inc. ISBN 9781556507335.
- Wood, Charles A.; Jürgen Kienle, eds. (1990). Volcanoes of North America. ISBN 0-521-43811-X.
External links
