Feb 23,2007 00:00
A study being published this week suggests that gas and vapor movement to the top of the magma body may have caused fairly rapid increases in pressure and could have been the triggering mechanism that caused Mount St. Helens to erupt in both 1980 and 2004.
Researchers used analysis of the trace element lithium to reach these conclusions, finding that crystals in the erupting lava were highly enriched with lithium in the first few weeks after each eruption, but then levels dropped back to a normal range. This suggests, they said, that lithium diffused into rising bubbles and added to a gas-rich pocket that formed just in the months preceding the eruption.
The study was just published in Geology, a professional journal, by scientists from
“An explosive volcano may be a little like a shaken-up pop bottle,” said Adam Kent, an OSU assistant professor of geosciences. “This research suggests that gases move to the top of magma chambers under volcanoes, where they can help break through the overlying crust and cause an eruption. This is leading us to a better understanding of how volcanoes behave and what the potential triggers are.”
In September of 2004,
The newest findings were made possible by some “helicopter dredging” done by the U.S. Geological Survey, scooping up material coming out after the 2004 eruption. A laser technique called “inductively coupled plasma mass spectrometry” allowed scientists to determine element concentrations at parts per million, and the one thing that stood out was the high level of lithium immediately following the first eruption.
“We still don’t know exactly what causes a volcano to erupt, especially when they have been quiet for a long time,”
“What this study indicates is that in the months prior to an eruption, there was in fact a rapid increase in vapor pressure in the magma stored under the volcano,” he said. “The lithium, which is soluble as a vapor and very mobile, rose rapidly along with other gases just prior to the eruption.”
As a technique for future use,
Other collaborators on the study included Michael C. Rowe from OSU, and researchers from the
The study was funded by the National Science Foundation.