Horseshoe Lake Trees - FAQ
Many people think the dead trees at Horseshoe Lake are
the result of a fire, bark beetles, or a disease. None
of these are the cause. Carbon dioxide gas venting up
through the soil is the cause. Measurements of gas in
the soils in the tree kill areas indicate high levels
of carbon dioxide gas. The normal level of carbon dioxide
in the atmosphere is .03% and the level in the soil
within the tree kill areas can be as high as 60%-80%.
Plants use carbon dioxide in the photosynthesis process
in their leaves or needles and have adapted to the .03%
level in the atmosphere. The high levels of carbon dioxide
in the soil actually interfere with the roots' ability
to absorb nutrients.
What is the Source of the Carbon Dioxide?
There may be a link between elevated levels of carbon
dioxide and seismic activity that occurred at Mammoth
Mountain during the fall of 1989. Carbon dioxide, a
naturally occurring gas in magma, appears to be making
its way to the surface, possibly from an intrusion of
magma at great depths. There is no seismic data to support
the theory that this venting of gas indicates increasing
chances of an eruption. Researchers believe that there
would be more seismic activity in the vicinity of Mammoth
Mountain if an eruption were imminent.
How Long has this Been Occurring?
The first indication of carbon dioxide venting to the
surface was in March of 1990 when a Forest Service employee,
on ski patrol, sought refuge from a heavy snowstorm
inside a snow survey cabin near Horseshoe Lake. After
entering the cabin he experienced symptoms of rapid
pulse and breathing, followed by headaches and dizziness.
The following summer, two other Forest Service employees
reported similar symptoms when entering utility vaults
in the Horseshoe area. During the remainder of 1990,
some trees appeared to be dying and a larger area of
tree death was observed in 1991. By 1992 the area of
tree death had reached a size of 15 acres. In 1994 the
area had expanded to 28 acres. As of 1995, the area
had expanded again by 2-3 acres.
Is There Any Threat to our Health from the Carbon
Carbon-dioxide is heavier than air and tends to collect
in low and enclosed spaces. All of the reports of breathing
difficulty have occurred in poorly ventilated spaces
not open to the public. The U.S. Geological Survey and
the Forest Service have been collecting air samples
in the area in both tents and restrooms and have found
the levels of carbon dioxide to be well within public
health standards. There are plans to intensify the monitoring
of the gas. Since carbon dioxide gas dilutes quite quickly
once it enters the soil, persons spending time in the
open air at Horseshoe Lake should experience normal
levels of carbon dioxide.
Why Were Some of the Trees Cut Down?
Trees with potential of striking a campsite, picnic
site, car, or restroom are considered hazard trees and
must be felled. Hazard trees include only 7-9 acres
of the total 30 acres of dead trees. There are no plans
at present to cut down anything but hazard trees.
How is the Wood Being Used?
The wood has been sold to a commercial firewood company
in Mammoth Lakes. Most of the permanent residents in
town depend on firewood for heat during the area's long
For more information, see US
Geological Survey information about monitoring carbon
dioxide gas at Mammoth Mountain.