REDUCING THE RISK FROM VOLCANO HAZARDS

UNITED STATES GEOLOGICAL SURVEY

S

Invisible CO2 Gas Killing Trees at

Mammoth Mountain, California

ince 1980, scientists

have monitored geoMammoth Mountain is a young volcano on the southwestern rim of Long Valley Caldera, a large volcanic depression in

eastern California. The Long Valley area,

well known for its superb skiing, hiking,

and camping, has been volcanically active

for about 4 million years. The most recent

volcanic eruptions in the region occurred

about 200 years ago, and earthquakes frequently shake the area. Because of this, the

U.S. Geological Survey (USGS) operates

an extensive network of instruments to

monitor the continuing unrest in the Long

Valley area.

Mammoth Mountain, a young volcano in eastern California, rises above the floor of a large volcanic

depression known as Long Valley Caldera. The scenic Long Valley area, popular with skiers, hikers, and

campers, has been volcanically active for about 4 million years. High concentrations of CO2 gas have been

detected in the soil on Mammoth Mountain. This invisible gas, seeping from beneath the volcano, is killing

trees on the sides of the mountain.

Numerous small earthquakes occurred

beneath Mammoth Mountain from May to

November 1989. Data collected from

monitoring instruments during those

months indicated that a small body of

magma (molten rock) was rising through a

fissure beneath the mountain. In the following year, U.S. Forest Service rangers

noticed areas of dead and dying trees on

the mountain. After drought and insect infestations were eliminated as causes, a geologic explanation was suspected. USGS

scientists then made measurements and

discovered that the roots of the trees are

being killed by exceptionally high concentrations of CO2

 gas in the soil. Today areas

of dead and dying trees at Mammoth

Mountain total more than 100 acres. The

town of Mammoth Lakes, just east of this

volcano, has not been affected.

Although leaves of plants produce

oxygen (O2) from CO2 during photosynthesis, their roots need to absorb O2

 directly.

The high CO2 concentrations in the soil on

Mammoth Mountain are killing trees by

denying their roots O2 and by interfering

with nutrient uptake. In the areas of tree

kill, CO2 makes up about 20 to 95% of the

logic unrest in Long Valley

Caldera and at adjacent

Mammoth Mountain, California. After a persistent

swarm of earthquakes beneath Mammoth Mountain

in 1989, earth scientists

discovered that large volumes of carbon dioxide

(CO2) gas were seeping

from beneath this volcano.

This gas is killing trees on

the mountain and also can

be a danger to people. The

USGS continues to study

the CO2 emissions to help

protect the public from this

invisible potential hazard.

 Areas of dead and dying trees at Mammoth

Mountain volcano in eastern California total more

than 100 acres. In 1990, the year after a persistent

swarm of small earthquakes occurred beneath the

volcano, U.S. Forest Service rangers first noticed

areas of tree kill. When U.S. Geological Survey

scientists investigated, they discovered that the roots

of the trees are being killed by high concentrations of

CO2 gas in the soil. The seepage of this CO2 gas

from below Mammoth Mountain and the continued

occurrence of local earthquakes are signs of the

ongoing geologic unrest in the area. The upper part

of the 11,027-ft-high volcano (above 9,500 ft) is

shown in dark green.

203

Horseshoe Lake

Earthquakes magnitude 1.5 and higher (1989–95)

Fault

Locations of tree kill areas as of 1995

EXPLANATION

Mammoth

Mountain

Reds

Lake

1 MILE

Lake

Crowley

Convict Lake

Mammoth

Lakes

Mammoth

Mountain

Inyo

Craters

volcanic

chain

0 5 MILES

395

LONG 

VALLEY 

CALDERA

Hot Creek

Mamm oth Creek

Owens River

INDEX

CALIF

MAP
U.S. DEPARTMENT OF THE INTERIOR • U.S. GEOLOGICAL SURVEY

For more information contact:

Earthquake Information Hotline (415) 329-4085

U.S. Geological Survey, Mail Stop 977

345 Middlefield Road, Menlo Park, CA 94025

http://quake.wr.usgs.gov/VOLCANOES/LongValley/

See also Living With a Restless Caldera—Long

Valley, California (USGS Fact Sheet 108–96).

U.S. Geological Survey Fact Sheet-172-96

1996

gas content of the soil; soil gas normally contains 1% or less CO2

.

When CO2 from soil leaves the ground,

it normally mixes with the air and dissipates

rapidly. CO2 is heavier than air, however, and

it can collect at high concentrations in the

lower parts of depressions and enclosures,

posing a potential danger to people. Breathing air with more than 30% CO2

 can very

quickly cause unconsciousness and death.

Therefore, poorly ventilated areas above and

below ground can be dangerous in areas of

CO2 seepage. Where thick snowpacks accumulate in winter, the CO2

 can be trapped

within and beneath the snow. Dangerous levels of CO2

 have been measured in pits dug in

the snowpack in tree-kill areas on Mammoth

Mountain, and snow-cave camping in such

areas is not advised.

Geologists have detected CO2 emissions, like those at Mammoth Mountain, on

the flanks of other volcanoes, including

Kilauea in Hawaii and Mount Etna in Sicily.

COOPERATING ORGANIZATIONS

Mammoth Mountain Ski Area

Town of Mammoth Lakes

U.S. Department of Agriculture, U.S. Forest Service

Michael L. Sorey, Christopher D. Farrar,

William C. Evans, David P. Hill, Roy A. Bailey,

James W. Hendley II, and Peter H. Stauffer

Graphic design by

Susan Mayfield and Sara Boore

CO2 gas seeping from the

ground at Mammoth

Mountain likely was derived

from magma (molten rock)

beneath the volcano. In

1989, rising magma may

have opened cracks,

allowing large amounts of

trapped CO2 gas to leak

upward along faults. High

concentrations of CO2 in soil

can kill the roots of trees.

CO2 gas is heavier than air,

and when it leaks from the

soil it can collect in

snowbanks, depressions,

and poorly ventilated

enclosures, such as cabins

and tents, posing a potential

danger to people.

Measuring the rate of such gas emissions on

the flanks of volcanoes or within calderas is

difficult and labor intensive. Readings must

be made at many locations using small gascollection instruments placed on the soil.

A preliminary estimate of the current

rate of CO2 gas emission at Mammoth Mountain is 1,600 tons per day. Similar rates of

CO2

 emission have been measured from the

craters of Mt. St. Helens (Washington) and

Kilauea (Hawaii) volcanoes during periods

of low-level eruptive activity. Past eruptions

at Mammoth Mountain, such as the phreatic

(steam-blast) eruptions that occurred about

600 years ago on the volcano’s north flank,

may have been accompanied by CO2 emissions. Scientists think that the current episode of high CO2

 emission is the first largescale release of the gas on the mountain for

at least 250 years, because the oldest trees in

the active tree-kill areas are about that age.

The characteristics of CO2

 and other

gases seeping from Mammoth Mountain indicate that they were originally derived from

magma. Large amounts of these gases probably were trapped beneath the volcano until

1989. In that year the magma rising through

a fault may have opened cracks, allowing the

gases to leak upward. Although infrequent

small earthquakes continue to occur below

the mountain, there is no evidence of current

magma movement.

Earthquakes and CO2 seepage beneath

Mammoth Mountain are only two signs of

volcanic unrest in the Long Valley area. Mammoth Mountain is the southernmost volcano

in the Mono-Inyo Craters volcanic chain, and

over the past 4,000 years, small eruptions

have occurred somewhere along this chain

every few hundred years.

Scientists with the USGS Volcano Hazards Program are closely monitoring CO2

emissions and other geologic hazards at

Mammoth Mountain. Their continued studies in the Long Valley area of eastern California and in other volcanic regions of the

United States, including Hawaii, the Pacific

Northwest, Wyoming, and Alaska, are helping to protect the citizens of our Nation from

geologic hazards.

In 1989–90, trees in this area on

the south side of Mammoth

Mountain volcano began dying

from high concentrations of CO2

gas in the soil. Although leaves of

plants produce oxygen (O2) from

CO2 during photosynthesis, their

roots need to absorb O2 directly.

High CO2 concentrations in the soil

kill plants by denying their roots O2

and by interfering with nutrient

uptake. In the areas of tree kill at

Mammoth Mountain, CO2 makes

up about 20 to 95% of the gas

content of the soil. Inset shows

U.S. Geological Survey scientists

taking samples of soil gas in this

tree kill area.

Snowbank

Depression

Dying

trees

Basement

Fault

Mammoth Mountain

Fault

Trapping layer

of rock

Trapped

CO2 gas

Magma

CO2 GAS

Above ground

Below ground