Earthquakes that occur at volcanoes are usually small and numerous. In fact, most of the earthquakes at Axial were too small to be detected by seismometers on land. Instead, scientists use hydrophones (underwater microphones) to detect submarine earthquakes.

The hydrophones listen for the faint rumbling sounds that the earthquakes emit into the ocean. Several hydrophones have previously been positioned at Axial Volcano and we have been able to get the data they recorded during the earthquake swarm.