Thursday, November 03, 2005
Yellowstone is due to erupt soon
It started in southeastern Oregon and has produced a series of explosive caldera type eruptions that leave large bowl-like craters instead of building mountains.
University of Utah geologists Barbara Nash and Michael Perkins have identified at least 142 such eruptions in a nearly straight line from southeastern Oregon to Yellowstone National Park, forming the broad lava plain of the Eastern Snake River Plain.
A caldera is a bowl-shaped volcanic depression a mile or more in diameter. The most widely known caldera may be Oregon's Crater Lake in the Cascade Mountains.
The hotspot now sits under Yellowstone where it has produced some of the largest volcanic eruptions known, and a caldera 45 miles long and 30 miles across -- and it's bound to blow again.
The big question is when.
"I'm not holding my breath," Nash said in a telephone interview.
When it does blow, it will give plenty of warning in the form of increased seismic activity and small eruptions.
"It's not going to catch anybody by surprise," she said.
The largest volcanic eruption in "recent" times happened in April 1815 when Mount Tambora on the island of Sumbawa, Indonesia, blew up. The eruption lasted several days and took off the top 4,000 feet of the 13,000 foot volcano.
The eruption left a caldera four miles across. A cloud of ash rose 28 miles into the stratosphere and spread around the world. The following year was known as the year without a summer. The total ash from the eruption would equal about 36 cubic miles of rock. By comparison the Mount St. Helens eruption in 1980 produced about one-quarter cubic mile of rock in the form of ash.
The first of three Yellowstone eruptions spewed out about 600 cubic miles of ash and spread it from southern California to Iowa. The Huckleberry Ridge caldera erupted about 2.1 million years ago in western Yellowstone and eastern Idaho. The second eruption was about 1.3 million years ago. The Lava Creek eruption, the third and smallest, happened about 650,000 years ago.
Ash from Yellowstone's Huckleberry Ridge and Lava Creek, however, covered much of the western United States, from California to Iowa. Deposits 2 to 3 feet thick from two of these eruptions can be found in drill cores in the Great Basin.
The effects are difficult to predict, but judging from past events, another eruption would leave a foot or two of ash on Utah County, Nash said. It would be very dark here possibly for days or weeks, depending on wind patterns.
The ash would smother plants and make breathing difficult. It would interfere with mechanical things, cars and jetliners. And if it rained, the ash would become very heavy, enough to collapse roofs.
An eruption would be subcontinental in scale, affecting large sections of the country with serious ecological effects. It would almost certainly lower temperatures around the world.