Wrangell Lulled to Sleep by Denali Fault Earthquake?
Mount Wrangell hasn't been itself lately. For the past few years, the volcano had averaged about 10 internal earthquakes per week, but its inner rumblings have died down since the Denali fault earthquake of November 3, 2002.
Geophysical Institute Professor Steve McNutt, of the Alaska Volcano Observatory in Fairbanks, along with graduate student John Sanchez and their colleagues monitor the volcano with four seismometers, two of them anchored near its summit at 14,163 feet. They report that the lack of shaking within the volcano coincides with a decrease at another Alaska volcano, Veniaminof.
"The decrease in activity in Alaska caught our interest because people normally look for an increase in volcanic activity following an earthquake," McNutt said.
While Veniaminof Volcano on the Alaska Peninsula has resumed a somewhat normal rate of shaking, Mount Wrangell, 50 miles east of Copper Center, has remained quiet after the earthquake. Scientists have documented Wrangell's apparent sensitivity to large earthquakes before.
Carl Benson, a professor emeritus at the Geophysical Institute at the University of Alaska Fairbanks, was part of a group of scientists who noticed that the north crater of Mount Wrangell started heating up after the magnitude 9.2 Prince William Sound earthquake in 1964. Their measurements showed that the crater warmed up enough to melt 40 million cubic meters of ice from the crater in the 12 years following the earthquake. The crater also heated up after a 7.5 earthquake struck near Mt. St. Elias in February 1979, and locals recalled seeing the mountain belch more steam and ash after two giant earthquakes rocked Yakutat in September 1899.
The warming of the north crater on Mount Wrangell and increased emissions following earthquakes could both be due to a decrease in internal earthquakes, McNutt said. Large earthquakes near Mount Wrangell might be shaking its plumbing enough to relieve some internal pressure deep within the volcano, where molten rock mixes with water.
"If you increase the number of cracks within the volcano or open old ones, you're not building up the pressure that causes local earthquakes," McNutt said.
If the Denali fault earthquake is helping Wrangell let off some steam, it might have done the opposite for Yellowstone and other Lower 48 volcanic features. Within 17 hours after the main shock of the Denali fault earthquake hit Alaska, more than 200 small earthquakes struck the Yellowstone area.
"Yellowstone just lit up," said Stephan Husen, a postdoctoral fellow at the University of Utah.
Other Lower 48 areas affected by the Denali fault earthquake were Long Valley Caldera, The Geysers, and Coso Hot Springs in California, and Mount Rainer in Washington.
Why did lower 48 volcanoes "light up" while a few Alaska volcanoes nodded off?
"Most of those are sealed systems," McNutt said of the Lower 48 volcanoes. "Those earthquakes were deeper, where aquifers and geothermal systems are confined."
McNutt is now teaming with Benson, a glacier specialist, on a proposal to monitor the north crater on Mount Wrangell. They would like to acquire new aerial photos of the crater to compare the snow within to its former depth, and to further document the strange relationship between a snow-covered volcano and Alaska's giant earthquakes.
