Volcanoes Get Quiet Before They Erupt, Here's Why

Seismologists have long been working on the challenge of figuring out how to predict when a volcanic eruption is going to happen. In the case of dormant volcanoes, signs of a possible eruption often come in the forms of increased geological activity, disruption of the surrounding terrain, and gas venting out of the ground. With more lively volcanoes, however, constant seismic activity and gas emission can obscure indicators of an increasing risk of eruption. Recently, seismologists monitoring a Nicaraguan volcano have come up with an alternate means of prediction-looking out for a sudden period of quiet.

This promising new finding comes from Carnegie volcanologist Diana Roman, part of a team that includes scientists from Penn State, Oxford University, the University of Iceland, and the Nicaraguan Institute of Earth Sciences. The group monitored the Telica Volcano in Nicaragua as it went through a sequence of eruptions in 2011. The researchers had begun their work on the site in 2009, and by 2011 they had managed to set up an extensive network of monitoring instruments within 4 kilometers of the volcano's summit.

In 2011, the Telica Volcano experienced a month-long run of ash explosions. In the lead-up to the eruption, the scientists noted a lack of significant seismic activity or ground deformation. Dr Roman offered an explanation: the vents through which gas is released got sealed off so that the gas could not escape, resulting in tremendous pressure that brought about the eruption.

The team recorded 50 explosions, and in only two cases out of fifty did an explosion occur without a prior period of volcanic quiet. At all other times, a quiet period of at least five minutes was found to precede an explosion. "It is the proverbial calm before the storm," said Dr. Roman in the Carnegie press announcement.