On 3 November 2002, a magnitude 7.9 earthquake rocked the Denali fault in Alaska. Unexpectedly, the huge inland quake set off a tempest 3100 kilometers away, in Yellowstone National Park in Wyoming, where geysers began gushing, setting off a swarm of mini tremblors of their own. Researchers think the unsettled behavior at Yellowstone after the Denali quake offers clear evidence that fluids underground trigger some earthquakes.
Geysers are hot springs heated by magma deep below the surface of Earth. Each geyser has a reservoir of water below ground. When the pressure builds or the temperature tips past the boiling point, a hot cloud of steam rushes upwards and erupts out of the geyser's mouth. Many geysers, like the aptly named Old Faithful, go off at regular intervals.
But after the Denali quake, the geysers at Yellowstone were anything but regular. A volunteer observer who had been sitting near Old Faithful reported that all the geysers around him suddenly burst into boil, spewing superheated steam. “He had time to take a couple pictures, grab his equipment, and run,” says Bob Smith, a seismologist at the University of Utah in Salt Lake City. For the next several weeks, the geysers behaved erratically, spouting much more frequently than usual. A swarm of small earthquakes accompanied the erratic behavior during the first 24 hours. In the June issue of Geology, Smith and colleagues argue that the two phenomena--the erratic geysers and the mini quakes--are related. When the surface waves from the Denali earthquake hit Yellowstone, they shook up the geysers' water supply. Like gas escaping from a shaken bottle of Coke, steam started to fizz out of solution and increased the pressure in the reservoirs, which in turn stressed the ground and led to the swarm of tiny quakes.
“This is great,” says Sharon Kedar, a geophysicist at the Jet Propulsion Laboratory in Pasadena, California. “They make a reasonably strong case that the swarm of earthquakes didn't happen at random, that it was linked to the geysers and the Denali quake.” Kedar hopes that geysers like those in Yellowstone can be used as natural laboratories to study the role of underground fluids in triggering earthquakes.