Sensing the Sounds from Earth’s Hazardous Environments – Image for illustrative purposes only (Image credits: Unsplash)
Researchers once watched expensive equipment vanish under a lava fountain at Chile’s Villarrica volcano. That single loss in 2015 prompted a shift toward cheap, replaceable instruments that could be placed directly in harm’s way. The result is a family of compact sensors now recording low-frequency sound waves from volcanoes, earthquakes, and wildfires across multiple continents. These devices capture signals that travel long distances with little loss, offering new windows into processes that remain difficult to observe up close.
Why Infrasound Matters for Hazards
Violent events such as landslides, eruptions, and avalanches generate sound below the range of human hearing. These waves, known as infrasound, carry more energy than audible sound and propagate for hundreds of kilometers with minimal weakening. Scientists have long recognized their value for remote monitoring, yet commercial recording systems remained too costly and bulky for dense networks. The 2015 Villarrica incident crystallized the problem: a single eruption destroyed seismic and infrasound gear worth tens of thousands of dollars, including multichannel data loggers that could not be sacrificed again.
That experience drove development of an open-source alternative built around the Arduino platform. The resulting Gem logger matches the performance of professional units while costing far less and weighing roughly the same as a paperback book. Its high dynamic range and built-in GPS timing allow precise synchronization across dozens of units, turning what had been isolated stations into flexible arrays.
Early Field Tests Prove the Concept
In January 2020 a small team carried 32 Gem units up Villarrica’s glaciated slopes. Sixteen sensors ringed the crater rim while another sixteen lined an eight-kilometer transect down the northern flank. Over two weeks the array mapped how sound diffracts around crater walls and weakens with distance, revealing atmospheric effects that can silence signals entirely in certain zones. The same compact design later allowed one researcher on skis to place 22 units near Stanley, Idaho, within four hours after a magnitude-6.5 earthquake struck in March 2020.
That Idaho array recorded hundreds of local aftershocks as well as infrasound from a distant Nevada quake 700 kilometers away. It also picked up thunder from more than 900 kilometers and waterfall noise from 195 kilometers. Processing data from the full set of sensors detected weaker arrivals that vanished when the same recordings were analyzed in smaller three-sensor groups, demonstrating the clear advantage of large numbers of instruments.
Placing Instruments Where Others Cannot Go
The low replacement cost and small size have encouraged deployments that would once have been considered reckless. At Villarrica a Gem was suspended 100 meters above the lava lake on a cable to capture sound from directly overhead. At Guatemala’s Fuego volcano, drones delivered two units to the crater rim; one survived retrieval while the second was lost to wind and later explosions. Similar units have now monitored snow avalanches, river discharge, and even stratospheric acoustics from solar balloons.
Wildfire monitoring represents the newest frontier. In October 2023, 76 sensors were installed ahead of a prescribed burn in Idaho. The following year a rapid response team placed dozens more around Oregon’s Emigrant fire, which ultimately burned 33,000 acres. No instruments were lost, and early analysis shows the array tracked fire advance through continuous infrasound even when smoke or darkness blocked visual observations. Preliminary results indicate the approach could complement aircraft and satellite data by providing an uninterrupted acoustic record of combustion sources hidden from optical sensors.
Next Steps and Remaining Questions
The original Gem has evolved into the Aspen logger, which records four channels at twice the sample rate and accepts simultaneous seismic and infrasound inputs. This combined capability supports emerging work in environmental seismology, where ground motion and air pressure are measured together at the same location. Researchers continue to test whether large, low-cost networks can map fire fronts in real time or improve forecasts at open-vent volcanoes.
Key uncertainties remain. How well do atmospheric conditions mask signals in different terrains? Can the same arrays distinguish overlapping sources during complex events? And will operational agencies adopt the technology for routine hazard response? The answers will determine whether these disposable sensors move from research tools to standard components of early-warning systems.
More details on the open-source designs are available at the Boise State infrasound project site. The work shows that placing many inexpensive ears in dangerous places can reveal processes once considered too risky or too remote to measure directly.