Check out our page about Mammoth Lakes here!

The above was what forced me to search out more about Long Valley and Mammoth Lakes
back in 1996. But as things quieted down, and my growing interests for volcanoes bloomed
for full, I just forgot all about Long Valley and Mammoth Lakes, till now when suddenly a
lot of people begin visiting my old page about Long Valley again.

So why not look into the matter again, to see what has happened since then?


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. 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.

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.

Areas of dead and dying trees at Mammoth Mountain volcano in eastern California total more than 100 acres.When U.S. Geological Survey scientists investigated, they discovered that the roots of the trees are being killed by excessive concentrations of carbon dioxide gas in the soil. The seepage of this 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 green.

A preliminary estimate of the current rate of CO₂ gas emission at Mammoth Mountain is 1,300 tons per day.
(Recent measurements indicate that the total rate of CO2 gas emission at Mammoth Mountain is close
to 300 tons per day. - USGS 1996?)

CURRENT STATUS: (2001?) Measurements of the total discharge of carbon dioxide (CO2) gas at the Horseshoe Lake tree kill area range from 50-150 tons per day. Variations are primarily caused by changes in barometric pressure. There is no obvious trend of either increasing or decreasing gas flux at this area; we conclude that the total gas flux coming to the surface at Horseshoe Lake has remained at these relatively high levels since 1996. We do not have enough data from any other gas discharge areas around the mountain to draw conclusions about changes over time at those locations. From "Carbon Dioxide and Helium Discharge from Mammoth Mountain" USGS, Long Valley Observatory

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 large-scale 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. 

It is natural to wonder when and where the next volcanic eruption might occur in the Long Valley area. Geologic processes generally proceed at a slow pace, and when viewed on the scale of a human lifetime, volcanic eruptions and destructive earthquakes happen rarely. Nevertheless, the long history of volcanic activity in the Long Valley area indicates that future eruptions will occur.



The pattern of volcanic activity over the past 5,000 years suggests that thenext eruption in the Long Valley area will most likely happen somewhere along the Mono-Inyo volcanic chain. However, the probability of such an eruption occurring in any given year is less than 1%.

As long as increased volcanic unrest (including earthquake swarms, ground deformation, and CO2 gas emissions) continues in the Long Valley area, the chances of an eruption occurring in the near future will remain somewhat increased. However, evidence from large volcanic areas and calderas worldwide shows that unrest, such as the current activity in eastern California, can persist for decades or even centuries without leading to an eruption. Nevertheless, recent eruptions at Rabaul Caldera in Papua New Guinea (1994) and the Izu volcanic complex in Japan (1989) following short periods of unrest emphasize the need to closely monitor restless calderas.


The three Inyo Craters, stretch northward across the floor of Long Valley Caldera.
During the past 1,000 years there have been at least 12 volcanic eruptions along the chain,
including those that formed the Inyo Craters and South Deadman Creek Dome
(seen here just beyond the farthest Crater).

Most likely, the next eruption will be small and similar to previous eruptions along the Mono-Inyo volcanic chain during the past 5,000 years. Such eruptions typically begin with a series of steam-blast explosions as rising molten rock (magma) encounters and vaporizes underground water near the Earth's surface. These blasts can throw large blocks of rock and smaller fragments hundreds of feet into the air, leaving deep, circular pits like the Inyo Craters.(See picture above)

Although the chance of a volcanic eruption in any given year is small, future eruptions will occur in the Long Valley area. Because volcanic unrest can escalate to an eruption in a few weeks or less, USGS scientists are closely monitoring activity in this region.

Above information collected from diffenrent USGS pages.