Deaths show hazards of life at Mammoth

The deaths of three ski patrol members at Mammoth Mountain in central California on Thursday highlight the many hazards facing people who live, work and play atop one of the nation’s largest active volcanic systems.

Earthquake swarms, toxic gases that are deadly when concentrated, the unlikely event of a cataclysmic eruption – such risks are permanent features of life in the exquisitely scenic area.

Geologists, public safely officials and resort managers do their best to protect residents and visitors from the dangers, but deaths do occasionally occur.

Eight years ago, a healthy 58-year-old man from Torrance, Calif., who was cross-country skiing in the nearby Horseshoe Lake area, was found dead. His death was believed to have resulted from breathing carbon dioxide gas, according to the Mono County coroner. The fumes that emanate from volcanoes include the potentially lethal gases carbon dioxide and hydrogen sulfide, which gives the fumes their characteristic rotten-egg smell. Both are denser than air, so they tend to sink and pool in hollows where volcanic heat has melted the snow.

At the volcanic vent, or fumarole, where Thursday’s accident occurred, the emissions measured there in 2002 were 98 percent carbon dioxide and 0.005 percent hydrogen sulfide, said Dave Hill, a U.S. Geological Survey scientist who is in charge of the observatory in the Long Valley Caldera, the volcanic basin that includes the Mammoth area.

Although we exhale carbon dioxide and take in a small amount (0.03 percent) with each breath of fresh air, carbon dioxide levels of just 10 percent to 20 percent can be lethal. Hydrogen sulfide can be lethal in far lower amounts.

“At high concentrations, CO2 displaces oxygen from your lungs. At 70 or 80 percent, it just takes a couple of breaths,” Hill said. “People can expire very quickly.”

Thursday’s accident was mainly due to abnormally high snow conditions, geologists agreed.

“The vent has been there as long as people have been skiing on the mountain,” Hill said. “They’ve recognized it and tried to keep it fenced off. When snow accumulates gradually, it’s clear there’s a hole there. But when the snow accumulates really fast, you can’t keep track of where it is.”