Word: caldera
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Dates: during 2000-2009
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...live along Montana's Yellowstone River are downstream from a simmering caldera, a geologic hot spot that has become especially active recently. Indeed, Yellowstone National Park contains the floor of a gigantic volcanic cauldron, one that rises and sinks with the forces that lie beneath - hence the picturesque geysers and steam holes. But a wave of recent earthquake activity is raising fears that have their origins 642,000 years ago, when a Yellowstone "supervolcano" exploded so violently that it created the caldera itself. Today, such an explosion - 1,000 times more powerful than the explosion of Mount St. Helens...
...activity relaxed in magnitude early this week but then flexed upward again to top 3.0 by early New Year's Eve. "This December 2008 earthquake sequence is the most intense in this area for some years," YVO reported, "and is centered on the east side of the Yellowstone Caldera," the ancient collapsed volcano beneath Yellowstone Lake. The scientists said they cannot immediately "identify any causative fault or other feature without further analysis." (See a gallery of recent volcanic eruptions...
...released last year, the United States Geological Survey (USGS) said possible hazards could include hydrothermal explosions, when steam breaks through the surface and forms a crater. That has happened 26 times in the park's 127 years of record-keeping. The USGS discounted chances for cataclysmic eruption of the caldera, noting that the hot, active magma chamber below Yellowstone has turned into "largely crystallized mush." But the same study also said: "Depending on the nature and magnitude of a particular hazardous event and the particular time and season when it might occur, 70,000 to more than 100,000 persons...
...Yellowstone Caldera - formed by the massive upheaval 642,000 years ago that spread airborne debris all the way to the Gulf of Mexico - is nowhere close to being extinct. Areas of the park's topography inflate like a bellows because of magma infusing into volcanic chambers about 6 miles below the surface. About 1,000 to 2,000 tremors a year (mostly small) have been recorded since 2004, when interpretation of satellite imagery with GPS readings indicated the caldera had been rising as much as 3 in. a year. The past week's number of tremors - about 400 - is considered...
...project was abandoned last March when a new government team took over management of the site. More recently, a Japanese team proposed building a 130-ft.-high (40 m high) dam to contain the mud. Scientists familiar with Lusi have dismissed that idea. Because the ground beneath the caldera is still sinking, a heavy concrete dam would likely rupture...