If you’re in the vicinity of Mount St. Helens tonight and feel a sudden rumble, don’t panic: It's just scientists detonating parts of the volcano for an ultrasound. Researchers from a conglomerate of universities spent the weekend placing 3,500 seismic sensors and will be setting off 23 planned explosions tonight and tomorrow to study their effects, according to a Rice University press release. “Mount St. Helens and other volcanoes in the Cascade Range threaten urban centers from Vancouver to Portland, and we’d like to better understand their inner workings,” says the lead scientist on the project.
The explosions are to be carried out in garbage dumps, gravel pits, and other already-disturbed areas on the mountain; the sensors will then measure the resulting seismic waves in much the same way that a CAT scan does, a seismologist tells the Columbian. A few final detonations are planned for July 30. And actually, Washington state residents who live in the area probably won’t notice anything amiss: Researchers say the boreholes are so far underground—80 feet deep—and the magnitude of the vibrations will be so weak that they don’t believe anyone will hear or feel a thing. (In Hawaii, the planet's biggest volcano may be waking up.)