Geophysicists will set off 23 explosive charges Tuesday night around Mount St. Helens as part of a study of the magma pipeline far below the volcano.
About 75 scientists, including some based in Clark County, are setting up the project this weekend as part of a four-year study Imaging Magma Under St. Helens.
The 23 charges will be set off in boreholes, about 80 feet deep, drilled in a pattern around Mount St. Helens. Most of the charges — from 1,000 to 2,000 pounds each — will be detonated late Tuesday evening when other activity is at a minimum.
Seismic waves generated by the explosions will be monitored by 3,500 seismological sensors in the region.
Vancouver-based seismologist Seth Moran likened the process to a CAT scan.
In a medical center, “you take energy and put it through some body part, see what the energy looks like on the other side,” said Moran, who works for the U.S. Geological Survey’s Cascades Volcano Observatory in Vancouver.
In the geological technique, which was developed for the oil industry, “you put energy into the earth and see what comes back,” he said.
It’s called an active-seismic experiment because the scientists aren’t waiting for a natural tremor.
Scientists get data from earthquakes, but “an earthquake translates into a fuzzy image,” Moran said. With active seismic testing, “you know exactly what you put into the earth and where it happened.”
Rice University’s Alan Levander, the lead scientist for the IMUSH experiment, said people who live in the area probably won’t notice the detonations. Local residents won’t be able to hear the blasts because of the depth of the boreholes.
And the blasts are unlikely to rattle any dishes: They’ll be the equivalent of magnitude 2 earthquakes, which typically can’t be felt, Levander said in a news release.
If any quaking is felt, it will be “no more than low-level seismic activity that occurs in the area on a weekly basis,” Levander said.
Volunteers will gather all the active sensors — and the data they’ve collected — within a couple of days of the explosions.
After reconfiguring the sensor network, a few more charges will be detonated on the night of July 30.
Peter Frenzen, who worked on getting permits issued for the experiment, said the borehole locations — called shot points — are places where the landscape has already been marred.
They include gravel pits, rock quarries and garbage dumps, said Frenzen, a scientist with the Mount St. Helens Volcanic Monument.
About four weeks ago, researchers worked on another aspect of the project when they set up 70 passive monitoring stations around the peak. Those instruments, which will be in place for two years, are more sophisticated than the ones being used for the explosive experiment, which are about the size of water bottles.
