Posted: Saturday, August 9, 2003 12:00 am
YELLOWSTONE NATIONAL PARK (AP) - Scientists plan to set up a temporary network of seismographs, Global Positioning System receivers and thermometers to monitor increasing hydrothermal activity in the Norris Geyser Basin and gauge the risk of a hydrothermal explosion.
The goal of the Yellowstone Volcano Observatory is to pinpoint underground sources of hydrothermal steam and learn more about how seismic activity affects the basin.
A caldera that last erupted 70,000 years ago is in the center of Yellowstone. Scientists do not expect a volcanic eruption.
However, small hydrothermal explosions occur in the park almost every year. Usually they are not noticed until after the fact.
A hydrothermal explosion occurs when the pressure on hot groundwater is released suddenly. The water comes to a boil and expands, fracturing rocks and throwing them into the air. The resulting craters can be anywhere from a few feet to thousands of feet across.
The GPS equipment being set up can measure very small movements of the earth and the seismic array can measure earthquakes associated with flow of thermal water and those associated with geologic faults.
Seven seismometers that can record a wide range of seismic frequencies will be placed around the basin.
The Norris Back Basin has been closed since July 23 due to the formation of new mud pots, changes in geyser activity and much higher ground temperatures - as hot as 200 degrees in some areas.
Vegetation has been dying due to thermal activity and altered eruption intervals for several geysers. Increased steam discharge has been continuing, according to park officials.
Hydrothermal activity has been increasing each year in the basin, but the increase in recent weeks has been especially rapid.
The Yellowstone Volcano Observatory is a partnership of the U.S. Geological Survey, the University of Utah and the park.
U.S. Geological Survey scientists studying the bottom of Yellowstone Lake, meanwhile, have expressed concern about a 100-foot-high bulge in the bottom of the lake that may have been formed recently.
The scientists speculate the bulge could have been formed by carbon dioxide or steam and that it could explode.