Mammoth Mountain was formed in a series of eruptions that ended 57,000 years ago. Mammoth mountain still produces hazardous volcanic gases that kill trees.[5]
Geology
Mammoth Mountain is a lava dome complex in Mono County, California. It lies in the southwestern corner of the Long Valley Caldera[6] and consists of about 12 rhyodacite and dacite overlapping domes.[7] These domes formed in a long series of eruptions from 110,000 to 57,000 years ago, building a volcano that reaches 11,059 feet (3,371 m) in elevation.[8] During this time, massive dacite eruptions occurred roughly every 5000 years.[9] The volcano is still active with minor eruptions, the largest of which was a minor phreatic (steam) eruption 700 years ago.[3]
Mammoth is outgassing large amounts of carbon dioxide out of its south flank, near Horseshoe Lake, causing mazuku in that area. [citation needed] The concentration of carbon dioxide in the ground ranges from 20 to 90 percent CO2. [citation needed] Measurements in the 1990s of the total discharge of carbon dioxide gas at the Horseshoe Lake tree-kill area ranged from 50 to 150 short tons (45 to 140 t) per day; this high concentration caused trees to die in six regions that total about 170 acres (0.69 km2) in size (see photo).[15]
The tree-kills originally were attributed to a severe drought that affected California in the late 1980s and early 1990s. Another idea was that the kills were the result of a pathogen or other biological infestation. However, neither idea explained why all trees in the affected areas were killed regardless of age or health. Then, in March 1990, a U.S. Forest Service Ranger became ill with suffocation symptoms after being in a snow-covered cabin near Horseshoe Lake.[16]
Overabundance of carbon dioxide in the soil from a natural underground volcanic source has killed a large area of trees
Measurements around the lake found that restrooms and tents had a greater than 1% CO2 concentration (toxic) and a deadly 25% concentration of CO2 in a small cabin. CO2 concentrations of less than 1% are typical and healthy in most soils; however, soil concentrations of CO2 in the tree-kill areas ranged from 20% to 90%. This overabundance of CO2 was found to be the cause of the tree-kills because tree roots need to absorb O2 directly and the high CO2 level reduced available O2. Researchers also determined that Mammoth releases about 1,300 short tons (1,200 t) of CO2 every day.
As of 2003,
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the concentration of carbon dioxide in soil gas at Mammoth Mountain was being monitored on a continuous, year-round basis at four sites—three at Horseshoe Lake and one near the base of the previous Chair 19 at the ski area.[15]
The most likely [opinion] sources of the CO2 are degassing of intruded magma and gas release from limestone-rich metasedimentary rocks that are heated by magmatic intrusions. [citation needed] The remarkable uniformity in chemical and isotopic composition of the CO2 and accompanying gases at different locations around Mammoth Mountain indicates that there may actually be a large reservoir of gas deep below the mountain from which gas escapes along faults to the surface.[15] Measurements of helium emissions support the theory that the gases emitted in the tree kill area have the same source as those discharged from Mammoth Mountain Fumarole.[12][17]
There is evidence, published in 2007, that the rate of CO2 discharge has been declining,[18] with emissions peaking in 1991.[19]
In April 2006, three members of the Mammoth Mountain Ski Area ski patrol died while on duty when a fumarole caused a snow bridge to collapse under the patrollers.[20] The 2005/2006 winter season delivered significant snow depth of 52 feet (16 m).[21] As the ski patrollers assessed the fumarole for skier safety, the perimeter snow collapsed, dropping the patrollers 21 feet (6.4 m) into the bottom of the fumarole, exposing them to extremely high levels of carbon dioxide.[22] It is unclear if they died as a result of the fall or as a result of the gas.[22]
Climate
Climate data for Mammoth Mountain 37.6279 N, 119.0338 W, Elevation: 10,541 ft (3,213 m) (1991–2020 normals)
Mammoth Mountain is home to the Mammoth Mountain Ski Area, founded by Dave McCoy in 1953. Mammoth is a ski, snowboard, and snowmobile mountain during the winter months. Mammoth is the highest ski resort in California and is notable for the unusually large amount of snowfall it receives compared to other Eastern Sierra peaks—about 400 in (1,000 cm) annually and about 300 out of 365 days of sunshine—due to its location in a low gap in the Sierra crest.[24] The ski area has more than 3,500 acres (1,420 ha) of skiable terrain, with 3,100 ft (940 m) of vertical serviced by 25 lifts.[25] In the summer months the ski gondolas are used by mountain bikers and tourists who wish to get a summit view of Long Valley Caldera directly to the east and Sierra peaks to the west, south and north.[4] To the south of the mountain, there are a number of lakes that serve as tourist attractions in the summer.
^Hildreth, Wes (September 14, 2004). "Volcanological perspectives on Long Valley, Mammoth Mountain, and Mono Craters: several contiguous but discrete systems". Journal of Volcanology and Geothermal Research. 136 (3–4). Elsevier B.V.: 169–198. Bibcode:2004JVGR..136..169H. doi:10.1016/j.jvolgeores.2004.05.019.
^Farrar, C.D.; Bergfeld, D. (December 2007). Magmatic Carbon Dioxide Emissions From Mammoth Mountain, California —- A Decreasing Trend From 1996 to 2007. American Geophysical Union, Fall Meeting 2007. American Geophysical Union. Bibcode:2007AGUFM.V21C0722F.
^"PRISM Climate Group, Oregon State University". PRISM Climate Group, Oregon State University. Retrieved October 8, 2023. To find the table data on the PRISM website, start by clicking Coordinates (under Location); copy Latitude and Longitude figures from top of table; click Zoom to location; click Precipitation, Minimum temp, Mean temp, Maximum temp; click 30-year normals, 1991-2020; click 800m; click Retrieve Time Series button.
Alt, David; Hyndman, Donald (2000). Roadside Geology of Northern and Central California. Missoula, Montana: Mountain Press Publishing Company. ISBN978-0-87842-409-2.
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