U.S. Volcano Experts Stage Drills in Mammoth Lakes Area

A team of eight U.S. Geological Survey volcano experts has completed a weeklong training exercise at Mammoth Lakes to check on emergency procedures in case of a volcanic eruption in the vicinity. But the team leader said the exercise did not mean the scientists expect an eruption soon.

“It was an exercise to test our response should something happen,” said David Hill of the Geological Survey’s regional headquarters in Menlo Park, Calif. “We wanted to be sure we would be able to operate locally, to test our personal computers and our monitoring technology.”

Seismicity, often a precursor of volcanic activity, rose slightly last year, he said, but this year has declined. Still, he said, ground deformation in Mammoth in recent years has been 10 times that noted on California’s most prominent fault, the San Andreas, so Mammoth is a natural place to watch.

The Geological Survey has closely monitored the Mammoth area since 1980, when a cluster of four magnitude 6 earthquakes sparked fears of volcanic activity in an area where it had occurred as recently as 500 years ago. Mammoth Mountain is a volcano, and the adjacent Long Valley Caldera was the site 700,000 years ago of one of the most powerful eruptions.

Hill said total surface uplift just east of Mammoth Lakes, where studies have indicated an eventual eruption would be most likely, has been about two feet since 1980. But even greater uplifts have occurred elsewhere in the world, such as near Naples, Italy, over the same period, with no eruption, he noted.

“We’re seeing slow changes in subterranean pressure in the Mammoth area which could go on for decades as far as we know without anything happening,” he said. “This bears watching, and we are watching, but there is no cause for alarm at this point.”