‘Gem’ captures infrasound from Earth’s hazardous environments

Jerry Mock at the summit of Villarrica volcano in November 2025 unloading Gems for deployment to listen to the volcano. Photo by Jeff Johnson

Volcanoes, landslides, snow avalanches, earthquakes, wildfires and other geophysical phenomena produce sounds well below the range of human hearing - otherwise known as infrasound. But just because humans can't hear these sounds doesn't mean they aren't extremely valuable.

For geophysics researchers like Jeffrey Johnson and Jake Anderson, "hearing" the infrasound created by geophysical phenomena could help provide early warnings for communities affected by volcanic hazards.

Historically, infrasound sensing and logging equipment has been expensive - not something you place lightly at the edge of an erupting volcano or within range of a blazing wildfire. Johnson and Anderson discovered this firsthand in 2015, when their team lost instrumentation deployed at the summit of Chile's Villarrica volcano during its eruption of a two-kilometer-high fountain of lava.

"In an instant, our hardware, including seismic and infrasonic sensors and their commercial multichannel data loggers, was entombed beneath falling lava," Johnson said. "This financial loss incentivized our work to develop low-cost loggers that would match the technical specifications and fidelity of commercial systems."

Geoscience researchers Madeline Hunt, Jerry Mock, and Jake Anderson installing infrasound sensors in the Sawtooth Mountains in January 2024, where they listen to avalanches, earthquakes, and fires. Photo by Jeff Johnson

So Johnson and his colleagues at Boise State began developing their own low-cost, in-house manufactured infrasound devices. First, Johnson created the infraBSU infrasound sensor, an inexpensive, low-power sensor that is connected to off-the-shelf seismic-style data loggers for a variety of roles. Anderson advanced it significantly by creating a custom low-power Arduino-based data logger and combining it with the sensor as a small lightweight integrated device.

Although they designed Gem for low cost, the team quickly realized that Gem's main strength was actually its flexibility. Hiking to a remote field sites with 20 Gems in a backpack is no problem because they require so little battery weight.

They are easy to hide in touristy sites, can be flown on drones and high-altitude balloons, and - unconstrained by cable lengths - can be arranged in whatever geometric arrangement is needed.

This enabled new types of data collection and research that would have been risky or impractical with other sensors. The amazing story of the team's Gem sensor can be read in the American Geophysical Union news magazine Eos.

Throughout creation and testing, Gem sensors have been deployed at research sites as far away as the Villarrica volcano and as close as the mountains of Idaho. Each time, these sensors have delivered their weight in research gold: infrasound data from some of the world's most extreme environments.

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