There are indeed volcanoes at Mammoth Lakes, and there is a good chance that there will be more to come. The big question is when? Will there be an eruption and growth of a new volcano in the next few years? That is the question that geologists are trying to answer.

Seven hundred thousand (700,000) years ago a volcanic eruption larger than any that has been recorded in history, occurred at Mammoth and formed a twenty mile long crater that we now call Long Valley. This eruption was 600 times larger than the eruption of Mount Saint Helens in 1980; another eruption just as big could happen again. There are two places in the 48 connected states of the United States that are most likely to have a volcanic eruption in the near future, and Mammoth Lakes is one of them (the other is Mount Saint Helens).

Long Valley is no longer a smooth, flat crater depression because other smaller volcanoes have grown on the valley floor. One of them is Mammoth Mountain, where there is a large ski area. Mammoth Mountain is a volcano that began eruption 150,000 years ago and may still be active. The most vocanically active part of the area is between Mono Lake and Mammoth Lakes, just outside the edge of Long Valley.

Four hundred thousand (40,000) years ago the Mono Craters and Inyo Craters began erupting, and they have erupted off and on almost until the present. Over 30 new volcanic vents opened in the last 2000 years, and the last eruption was about 500 to 600 years ago. The most likely volcanic hazard in the area is that there will be another small eruption like the ones that have created the Mono and Inyo Craters. Such an eruption might deposit a layer of ash eight inches thick, 20 miles downwind and two inches thick even as far away as 50 miles. The eruption might last a few weeks or months.

The only volcanic event in the Mammoth Lakes region that has been recorded by eye-witness accounts, is a steam blast that occurred on Mammoth Mountain in 1890. The recent swarm of earthquake activity, however, may be an indication that another eruption like those that produced Inyo and Mono Craters is soon to occur. Such an eruption would be extremely damaging to towns like Mammoth Lakes, Lee Vining, and Bishop. Buildings and streets would be covered with ash, and there is a good chance that many people would be killed.

Another danger has to do with the water supply for Los Angeles. An eruption in the Mammoth Lakes area would contaminate the largest source of water for the city, Crowley reservoir, and make it undrinkable. Then Los Angeles would have to get a lot more water from other places like northern California and the Colorado River. This would be very expensive and potentially damaging to ecosystems.

Well, that is a long answer to your question. I didn't know all of this myself. I found most of this information in a Book called Fire Mountains of the West: The Cascades and Mono Lake Volcanoes, by Stephan L. Harris.

The information about the water supply to Los Angles, I read in a newpaper article (the LA Times, I think, although I couldn't find it again!). Let me know if you have any more questions!

Seven hundred thousand (700,000) years ago there was a HUGE eruption in LONG VALLEY, near Mammoth Lakes. The amount of magma erupted was about 600cubic kilometers !!!...The residual activity that we see today is related to that giant eruption 700,000 years ago.

More recently there were small eruptions near the Chain of Craters road...about 600 years ago..the indians saw these eruptions.

As far as the future, no one can say...it is very likely that there will be eruptions in the future...however, it is virtually impossible to say if they will come within the next year, 10 years, 100 years or even more!!!!

You see, geologic time scales are far longer than human lifetimes...what is needed is to monitor the Mammoth Lakes area for quakes as well as the release of volcanic gases, so that we can make better volcano predictions. Also, the swelling of the ground due to magma movement and /or storage can tell us that something MAY happen...but to predict an actual time is impossible now; we just dont know enough. If you study hard and learn a lot aboout geology maybe someday you can be a geologist who specializes in volcanology and therefore work on a problem like this, as I do.

Basically, no one knows for sure what will happen at Mammoth mountain because it is impossible to make an accurate prediction. Scientists have to make an educated guess based on the data that they have. The problem is that there is not much data to warn when a volcano eruption is coming. (It is similar to the way that a light bulb burns out. After you have been using a light bulb for a long time, you know that the chance that it will burn out becomes greater, but you can't predict just exactly when it will burn out.)

Scientists are worried about Mammoth mountain because the number of earthquakes in the area around the mountain have increased recently. Also, the amount of gases like carbon dioxide in the air near the lakes has increased. This means that the chance for an eruption is greater, but no one can be certain.

The clues that an eruption will occur are very small and not always reliable, but as technology improves, scientists can measure these clues better and make better guesses about volcano eruptions.

Here's a web site I found if you want to learn more:

http://www.frw.ruu.nl/fg/volcanoes.html