Correlation

Researchers link earthquakes to volcanic eruptions
The Associated Press, October 28, 1998

Historical records appear to confirm what many researchers have always suspected - large earthquakes can trigger eruptions in nearby volcanoes. A study of records dating to the 1500s found a statistical link between the two, Alan T. Linde and I. Selwyn Sacks of the Carnegie Institution in Washington reported in Thursday's issue of the journal Nature.

While the exact mechanism is not known, an earthquake may cause bubbles to rise from the bottom of reservoirs of molten rock known as magma chambers, increasing the pressure that leads to an eruption, Linde said. "Seismic waves from earthquakes have the potential to increase the pressure in magma chambers even at large distances from large earthquakes," the researchers said. "For a volcano already close to the critical pressure state, this could result in a premature eruption." While earthquakes alone cannot be used to predict eruptions, close monitoring of active volcanoes may be able to determine which volcanoes could be set off by a quake, Linde said. Linde said he and Sacks reviewed 204 so-called great earthquakes, or those with magnitudes of more than 8, and found eight quakes appear to have triggered eruptions, some triggering more than one.

The researchers also compared earthquakes with magnitudes between 7.0 and 7.9 and found a total of nine eruptions in the two days following such earthquakes. Eruptions were only considered if they occurred within 465 miles of great earthquakes and 125 miles from the 7.0-to-7.9 quakes. By comparison, in the 1,000 days before and after all of the quakes studied, there were no more than four eruptions on days other than the days of the quakes. "They show that a volcanic eruption is about eight times as likely on a day of a big earthquake as compared to any other day, within 500 miles or so," said Bill Menke, a Columbia University professor who studies volcanoes. "Earthquakes are kind of the straw that broke the camel's back."

Menke said Linde's work provides a statistical basis for what many had already suspected and also supports one theory on the causes of eruptions. "This work gives more credence to one of the theories that says pressure is slowing building up in the volcano and when it reaches some critical pressure, something breaks," he said. David Hill, a volcano expert with the U.S. Geological Survey in Menlo Park, Calif., said: "I think their paper really provided strong circumstantial evidence that there are relationships like this, but we really have a long way to go to understand this."