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Lassen Peak

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Lassen Peak

Lassen Peak (also known as Mount Lassen) is the southernmost active volcano in the Cascade Range. It is part of the Cascade Volcanic Arc which is an arc that stretches from northern California to southwestern British Columbia. Located in the Shasta Cascade region of Northern California, Lassen rises 2,000 feet (610 m) above the surrounding terrain and has a volume of half a cubic mile, making it one of the largest lava domes on Earth. It was created on the destroyed northeastern flank of now gone Mount Tehama, a stratovolcano that was at least 1,000 feet (300 m) higher than Lassen.

Lassen Peak has the distinction of being the only volcano in the Cascades other than Mount St. Helens to erupt during the 20th century. On May 22, 1915, an explosive eruption at Lassen Peak devastated nearby areas and rained volcanic ash as far away as 200 miles (320 km) to the east. This explosion was the most powerful in a 1914–17 series of eruptions that were the last to occur in the Cascades before the 1980 eruption of Mount St. Helens in Washington. Lassen Volcanic National Park was created in Shasta County, California to preserve the devastated area and nearby volcanic geothermal features.

Unlike most lava domes, Lassen is topped by craters. In fact, a series of these craters exist around Lassen's summit, although two are now covered by solidified lava and sulfur deposits. Lassen is the largest of a group of more than 30 volcanic domes that have erupted over the past 300,000 years in the Lassen Volcanic Center.

Climate

Lassen has the highest known snowfall amounts for California. With an average annual snowfall of 660 inches (16.8 m), and some years receiving over 1,000 inches (25.4 m) of snow at its base of 8,250 feet (2,515 m) at Lake Helen. Mount Lassen gets more precipitation (rain, hail, melted snow) than anywhere in the Cascades south of the Three Sisters volcanoes. This heavy snowfall allows Lassen to retain 14 permanent patches of snow despite Lassen's modest elevation. Lightning has been known to frequently strike the summit of the volcano during summer thunderstorms.

Geology

Further information: ] and ]
Vulcan's Eye on Lassen Peak from Lake Helen

Lassen is the southernmost in the chain of 18 large volcanic peaks that run from southwestern British Columbia to northern California. The peaks formed in the past 35 million years as the Juan De Fuca plate and the tiny Gorda plate to its south have been pulled under the overriding North American plate. As the oceanic crust in the Juan de Fuca plate melts under the pressure, it creates pools of lava that drive up the Cascade Range and power periodic eruptions.

Northeast side of Lassen Peak, showing the area devastated by mudflows and a lateral blast in 1915.

Roughly 27,000 years ago, Lassen started to form as a mound-shaped dacite lava dome pushed its way through Tehama's destroyed north-eastern flank. As the lava dome pushed grow it shattered overlaying rock, which formed a blanket of angular talus around the emerging steep-sided volcano. It probably looked much like the nearby 1,100-year-old Chaos Crags. Lassen reached its present height in a relatively short time, probably in as little as a few years.

From 25,000 to 18,000 years ago, during the last glacial period of the current ice age, Lassen’s shape was significantly altered by glacial erosion. For example, the bowl-shaped depression on the volcano’s northeastern flank, called a cirque, was eroded by a glacier that extended out 7 miles (11 km) from the dome.

Lassen's most recent eruptive period started in 1914 and lasted for seven years (see below). The most powerful of these eruptions was a 1915 episode that sent ash and steam in a 6-mile (10 km) tall mushroom cloud, making it the largest recent eruption in the contiguous United States until the 1980 eruption of Mount St. Helens. The region remains geologically active, with mud pots, active fumaroles, and boiling water features, several of which are getting hotter. The area around Mount Lassen and nearby Mount Shasta are considered the most likely volcanoes in the Cascade Range to shift to active eruptions.

Human history

Before the arrival of white settlers, the areas surrounding Lassen Peak, especially in the east and south, were the traditional home of the northeastern Maidu.

Lassen Peak was named in honor of Danish blacksmith Peter Lassen, who guided immigrants past the peak to Sacramento Valley in the 1830s. Lassen's trail, however, never found general long-term use because it was considered unsafe. It was replaced by the Nobles Emigrant Trail, named after William Nobles, which linked the Applegate Trail in Nevada to northern Sacramento Valley.

In 1864 Helen Tanner Brodt became the first woman to reach the summit of Lassen Peak. A tarn on Lassen was named Lake Helen in her honor.

Starting in 1914 and ending in 1921 Lassen came alive with a series of phreatic eruptions (steam explosions), dacite lava flows, and lahars (volcanic mud flows). There were 200 to 400 volcanic eruptions during this period of activity. First-hand accounts of the time record at least one fatality, in 1915.

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See also

References

Notes
  1. ^ "Lassen". NGS Data Sheet. National Geodetic Survey, National Oceanic and Atmospheric Administration, United States Department of Commerce. Retrieved 2008-12-20.
  2. "Lassen Peak, California". Peakbagger.com. Retrieved 2008-12-11.
  3. "America's 57 - The Ultras". Peaklist.org. Retrieved 2008-09-28.
  4. "Lassen Peak". Geographic Names Information System. United States Geological Survey, United States Department of the Interior. Retrieved 2008-12-11.
  5. ^ "Eruptions of Lassen Peak, California, 1914 to 1917". U.S. Geological Survey. Retrieved 2008-12-30.
  6. "Cascade Snowfall and Snowdepth". Skiing the Cascade Volcanoes. Retrieved 2008-12-19.
  7. "Glaciers of California". Glaciers of the American West. Portland State University. Retrieved 2008-12-20.
  8. EO Newsroom
  9. "Women Artists of Mount Shasta: 1860s-1930s". The Significance of Mount Shasta as a Visual Resource. College of the Siskiyous. Retrieved 2008-12-20.
Major works
  • Geology of National Parks: Fifth Edition, Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7
  • EO Newsroom (NASA), New Images of Lassen Volcanic National Park (adapted public domain text; Retrieved 18 September 2006)
  • Eruptions of Lassen Peak, California, 1914 to 1917, U.S. Geological Survey Fact Sheet 173-98 (adapted public domain text; Retrieved 18 September 2006)

External links

Cascade Volcanoes
British Columbia Mount Rainier
Washington
Oregon
California
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