 "Photo:")
Yellowstone's giant volcano is rising and nobody knows why.
The "supervolcano" in Wyoming has risen at three times its average rate since mid-2004 and hasn't stopped yet. For the past three years, the volcano has risen almost three inches every year.
U scientists Robert Smith and Wu-Lung Chang, who study the volcano, are stumped.
"We don't know why it's suddenly started changing," Chang said. "We're still trying to understand everything."
One theory is that the supply of magma 50 miles under the surface is increasing. The hot molten rock lies beneath Yellowstone's caldera, a 40-by-25-mile area which collapsed after one of Yellowstone's eruptions. When the rock under the caldera heats up, it decreases in density and becomes more buoyant, possibly causing the surface to rise.
Yellowstone is one of the few hot spots in North America where hot molten rock rises. When pieces of magma break off and rise higher, the magma chamber below is refilled.
There is no way as of yet to know whether magma is the reason for the rising of the caldera. The boiling water underneath the surface that releases steam could also cause rising surface.
"It's like when you boil a pot of water, and the lid pops off," Chang said.
Old Faithful, a geyser in Yellowstone, is likely to keep erupting regularly, Chang said. The energy source that is causing the surface to rise is likely to keep the geysers and hot springs working. Without the energy source, the hot springs and geysers could die, he said. "There is no evidence of an imminent volcanic eruption or hydrothermal explosion," said Smith, a U professor in geophysics "We think it's just a natural reaction.".
More information is needed to determine whether the volcano could erupt or if Yellowstone's geysers and hot springs could go off more often, Chang said.
Although a volcano isn't likely to erupt, scientists said, that doesn't rule out every natural disaster.
Earthquake activity seems to have decreased since 2004 when the caldera began rising, but past records of earthquake activity usually occurred during periods when the surface level rose.
Yellowstone's caldera has been recorded to have risen and dropped twice since 1923, and there has been an increased amount of earthquake activity around those times. Between 1976-1984, surface level rose 2.2 centimeters per year, and there was a number of earthquakes in 1985 after it began to decrease. The same occurred when the surface rose in the mid-1990s.
Since 2004, Smith has noticed a decrease in earthquake activity to mirror the surface level rise.
"We're certainly looking for seismic activity, but earthquakes are pretty common in the Yellowstone and surrounding area, which counts from St. George up to Wyoming," Smith said. "We're still learning about the process of how Yellowstone works, which is very important to basic science."
Hank Heasler, a geophysicist at Yellowstone National Park, has seen the study and the data and said there is nothing to be concerned about.
"The park isn't concerned about any activity that will likely not occur from this uplift," he said.
l.groves@chronicle.utah.edu
