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Infrasound refers to acoustic waves with frequencies below the threshold of human hearing (typically below 20 Hz). Volcanic explosions, degassing bursts, and other energetic surface processes generate infrasound signals that can travel long distances through the atmosphere. Because these waves propagate through the air rather than the ground, infrasound provides a complementary perspective to seismic monitoring—detecting activity at or above the surface that seismometers may not clearly resolve.
Infrasound is particularly valuable at remote volcanoes where visual confirmation of explosions is often impossible due to cloud cover, darkness, or distance.

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How it works

Infrasound sensors measure small pressure fluctuations in the atmosphere. An array of multiple sensors spaced apart can be used to determine the direction and speed of incoming acoustic waves, helping distinguish volcanic signals from wind noise or other sources.

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AVERT deployments

Within AVERT, infrasound arrays complement seismic, gas, and imaging data to improve eruption detection and characterization.
  • Cleveland: A 5-instrument infrasound array at the pre-existing CLCO site on Chuginadak Island, along with a single infrasound sensor at CLES, were already in place before the AVERT project began. These instruments detect the frequent explosive activity characteristic of Cleveland.
  • Poas: New infrasound arrays were installed at VPCR (on the crater rim) and VPEM (south of the crater) during the 2024 and 2025 field workshops, adding acoustic detection capability for the phreatomagmatic explosions and degassing events at the crater lake.