2008-11-01 猛犸山（在线收听）

Every day people come to soak in Hot Creek, a place to rest, created by geologic unrest. Sudden geyser eruptions, driven by heat from magma below the Earth surface, can change water temperatures so fast that going into the water is not recommended. But here in the eastern Sierra Mountains, few people have their minds on what's beneath their feet. The Town of Mammoth Lakes, California, and the resort known as Mammoth Mountain are major draws for those who love to play outdoors.

Dave Hill is a seismologist with the US Geological Survey. And he will tell you Mammoth Lakes’ shakes. Typically, several earthquakes of Magnitude 2 or less are recorded in the Mammoth Lakes region every day. It's not so much the quakes that concern Dave. It's the volcanic eruption they might foreshadow.

760,000 years ago, a catastrophic volcanic eruption spewed, approximately 600 cubic kilometers of pyroclastics. An underground magma chamber collapsed, forming the crater known as the Long Valley Caldera. A younger line of domes and craters that make up what is called the Inyo-Mono Craters Volcanic Chain, stretches north from Mammoth Mountain at the Caldera southwest rim. Eruptions from this valley of the volcanoes have left behind some geological wonders.

This is a young volcanic area. And some day you can see another eruption.

In May, 1980, one week after the eruption of Mount St. Helens, four strong Magnitude 6 earthquakes rocked the Long Valley Caldera. Yet it took a few years before the general public seemed to realize the volcanic hazard. While earthquakes are common precursors to volcanic eruptions, there were none. But the Long Valley Caldera was identified as resurgent, a growing magma-fed bulge. Scientists are keeping a close eye on the slightest degree of movement.

We are trying to see if and when we measure distance change; if that's associated with volcanic activity.

The resort town not only lives with magma on the move, but puts it to good use. This power plant is run by water, naturally heated from below ground. There are recent signs of geologic disturbances and volcanic activity. In 1990, trees on Mammoth Mountain Volcano began dying. Since then, more than 150 acres of trees have been killed by large amounts of carbon dioxide that is released into the soil by magma, suffocating the tree roots.

No one doubts this volcanic system will erupt again. But seismologist Dave Hill says the persistent unrest from this youthful volcanic system has finally been put in perspective. Today the geology of the Long Valley Caldera is monitored by scientists, respected by residents, and admired and appreciated by everyone. The US GS has established procedures and a response plan to promptly alert the public well in advance of a possible eruption. But the chances of it happening in the coming years are very, very small.