Mammoth Mountain is a lava dome complex partially located within the town of

Mammoth Lakes, California Mammoth Lakes is a town in Mono County, California, and is the county's only incorporated community. It is located immediately to the east of Mammoth Mountain, at an elevation of . As of the 2020 United States Census, the population was 7,191, r ...

, in the

Inyo National Forest Inyo National Forest is a United States National Forest covering parts of the eastern Sierra Nevada of California and the White Mountains of California and Nevada. The forest hosts several superlatives, including Mount Whitney, the highest po ...

of Madera and Mono Counties. It is home to a large

ski area A ski area is the terrain and supporting infrastructure where skiing and other snow sports take place. Such sports include alpine and cross-country skiing, snow boarding, tubing, sledding, etc. Ski areas may stand alone or be part of a ski resort. ...

primarily on the Mono County side. Mammoth Mountain was formed in a series of eruptions that ended 57,000 years ago. Mammoth still produces hazardous volcanic gases that kill trees and caused ski patroller fatalities in 2006.

Geology

Mammoth Mountain is a lava dome complex in

Mono County, California Mono County ( ) is a county located in the east central portion of the U.S. state of California. As of the 2020 census, the population was 13,195, making it the fourth-least populous county in California. The county seat is Bridgeport. The coun ...

. It lies in the southwestern corner of the

Long Valley Caldera Long Valley Caldera is a depression in eastern California that is adjacent to Mammoth Mountain. The valley is one of the Earth's largest calderas, measuring about long (east-west), wide (north-south), and up to deep. Long Valley was formed ...

and consists of about 12

rhyodacite Rhyodacite is a volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of those plutonic rocks that are intermediate in composition between monzogranite and granodiorite. Rhyodacites form from rapid ...

and

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...

overlapping domes. These domes formed in a long series of eruptions from 110,000 to 57,000 years ago, building a

volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

that reaches in elevation. During this time, massive

eruptions occurred roughly every 5000 years. The volcano is still active with minor eruptions, the largest of which was a minor

phreatic ''Phreatic'' is a term used in hydrology to refer to aquifers, in speleology to refer to cave passages, and in volcanology to refer to a type of volcanic eruption. Hydrology The term phreatic (the word originates from the Greek , meaning "well" ...

(steam) eruption 700 years ago. Mammoth Mountain also lies on the south end of the Mono-Inyo chain of

volcanic crater A volcanic crater is an approximately circular depression in the ground caused by Volcano, volcanic activity. It is typically a bowl-shaped feature containing one or more vents. During Types of volcanic eruptions, volcanic eruptions, molten magm ...

s. The magma source for Mammoth Mountain is distinct from those of both the

and the Inyo Craters. Mammoth Mountain is composed primarily of

and

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...

, part of which has been altered by

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

activity from

fumarole A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcani ...

s (steam vents).

Volcanic gas discharge

Mammoth is

outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which ...

large amounts of

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

out of its south flank, near Horseshoe Lake, causing

mazuku In geology, a mazuku ( Swahili for "evil wind") is a pocket of carbon dioxide-rich air that can be lethal to any human or animal life inside. Mazuku are created when carbon dioxide accumulates in pockets low to the ground. CO2 is denser than air, w ...

in that area. The concentration of carbon dioxide in the ground ranges from 20 to 90 percent . Measurements of the total discharge of carbon dioxide gas at the Horseshoe Lake tree-kill area range from per day. This high concentration causes trees to die in six regions that total about in size (see photo). 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 In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

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. Measurements around the lake found that restrooms and

tent A tent () is a shelter consisting of sheets of fabric or other material draped over, attached to a frame of poles or a supporting rope. While smaller tents may be free-standing or attached to the ground, large tents are usually anchored using gu ...

s had a greater than 1% concentration (toxic) and a deadly 25% concentration of in a small cabin. concentrations of less than 1% are typical and healthy in most

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former te ...

s; however, soil concentrations of in the tree-kill areas ranged from 20% to 90%. This overabundance of was found to be the cause of the tree-kills because tree roots need to absorb O₂ directly and the high level reduced available O₂. Researchers also determined that Mammoth releases about of every day. As of 2003, the concentration of carbon dioxide in

soil gas Soil gases (soil atmosphere) are the gases found in the air space between soil components. The spaces between the solid soil particles, if they do not contain water, are filled with air. The primary soil gases are nitrogen, carbon dioxide and oxygen ...

at Mammoth Mountain is being monitored on a continuous, year-round basis at four sites—three at Horseshoe Lake and one near the base of Chair 19 at the ski area. The most likely sources of the are degassing of intruded

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

and gas release from

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

-rich

metasedimentary In geology, metasedimentary rock is a type of metamorphic rock. Such a rock was first formed through the deposition and solidification of sediment Sediment is a naturally occurring material that is broken down by processes of weathering and e ...

rocks that are heated by magmatic

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s. The remarkable uniformity in chemical and isotopic composition of the 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. 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. There is evidence that the rate of discharge has been declining, with emissions peaking in 1991.

Ski patrol fatalities incident

In April 2006, three members of the Mammoth Mountain Ski Area ski patrol died while on duty. All three died from suffocation by

when they fell into a

on the slopes of the mountain. The 2005/2006 winter season delivered significant snow depth of . As the ski patrollers assessed the fumarole for skier safety, the perimeter snow collapsed dropping the one patroller into the bottom of the fumarole where the levels are life-threatening within minutes. A second patroller dropped into the fumarole in an effort to rescue the first and then the third patroller followed into rescue where all succumbed fatally to the toxic gas. Ultimately, a team of responders had to enter the fumarole with gas masks to retrieve the bodies.

Recreational use

Mammoth Mountain is home to the

Mammoth Mountain Ski Area Mammoth Mountain Ski Area is a large ski resort in the western United States, located in eastern California along the east side of the Sierra Nevada mountain range in the Inyo National Forest. Mammoth has more than of ski-able terrain, service ...

, founded by

Dave McCoy David McCoy (August 24, 1915 – February 8, 2020) was an American skier and businessman who founded the Mammoth Mountain Ski Area in 1942. Early life McCoy was born in El Segundo, California, in August 1915. He spent the first six years of his l ...

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" (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. In the summer months the ski

gondola The gondola (, ; vec, góndoła ) is a traditional, flat-bottomed Venetian rowing boat, well suited to the conditions of the Venetian lagoon. It is typically propelled by a gondolier, who uses a rowing oar, which is not fastened to the hull, ...

s are used by mountain bikers and tourists who wish to get a summit view of

directly to the east and Sierra peaks to the west, south and north. To the south of the mountain, there are a number of lakes that serve as tourist attractions in the summer.

References

;Further reading *

External links

Mammoth Mountain Ski Area trail map

USGS Volcano Hazards Program, Long Valley Observatory

QTVR of tree kill area

Mammoth Earthquake 1980 May 25 16:33, 16:49, 19:44 UTC Magnitude 6.2, 5.9, 5.9
{{Authority control Inyo National Forest Pleistocene lava domes Mountains of Madera County, California Mountains of Mono County, California Mountains of the Sierra Nevada (United States) Volcanoes of Madera County, California Volcanoes of Mono County, California Mountains of Northern California Volcanism of California Volcanoes of California Holocene lava domes