Quiescence: Not Just for Popsicles Any More; A Nicaraguan Volcano Goes Quiet Just Before Eruption

      Volcano semiotics indicating when a volcano is going to erupt include seismographs that display an increase in small tremors which might indicate that magma beneath the mountain is moving, a release of volcanic gases like sulfur dioxide and carbon dioxide, and changes in the physical shape of the volcano such as depressions or growths.

      While these clues tell researchers that the forces that fuel eruptions are moving, they don’t necessarily provide a timeline for when the eruptions will occur.

      By looking at the rate at which earthquakes happen in Nicaragua’s Telica Volcano, a team of scientists studying the volcano have discovered a new method of forecasting volcanic explosions. Their study, published this month in Earth and Planetary Science Letters, describes a period of seismic quiescence, or quiet time, that occurs immediately before an individual explosion.

      Volcanic eruptions are generally made up of many different explosions which can span hours, days, or even months. Depending on how much pressure has been building within the volcano, these individual explosions can range from small bursts of steam to giant, gaseous plumes of ash and smoke. Many smaller eruptions, those on the lower end of the Volcanic Explosivity Index (VEI), occur with little consequence to the people living in the region, while the larger explosions can have devastating effects on nearby communities.

      “We first realized the potential impact of our finding as the 2011 eruption of Telica was in progress and we started to understand that there was a pattern of precursory seismic quiescence prior to each explosion”, says Dr. Diana Roman, one of the study’s co-authors. “We were very excited about the forecasting potential of the quiescence at that time, but we had to do quite a lot more work after the eruption was over to understand the phenomenon and its relationship to the volcano's activity.” [One of the only other time I see the word quiescent is on "quiescently frozen popsicles."]

      Of the 50 explosions studied during Telica’s 2011 eruption, 48 of them were preceded by some sort of seismic silence.

      In addition, there appeared to be a correlation between the length of the quiet time and how catastrophic each explosion was. In short—the longer the quiet time, the more volatile each explosion was. Why does this happen?

     The team discovered that the pathways along which the volcanic gases escape become sealed, which builds pressure. The longer these gases spend trapped beneath the surface, the larger and more catastrophic the ensuing eruption is. The researchers suspect that newly formed minerals might block pathways inside the volcano, or possibly the pathways simply collapse, impeding avenues of escape for volcanic gases.

      Although each eruption is different, and so is each volcano, the implications of a study like this could be far-reaching.

      “I think there is great potential for our findings to be used in a real-time monitoring context,” Dr. Roman says, “the quiescence signal is relatively easy to detect as it requires only one seismometer rather than a large network of seismometers, meaning it can be implemented more cheaply.”

The closer scientists get to predicting volcanic eruptions, the more easily people can learn to live along the flanks of volcanoes such as Telica.

      

Quiescently unfrozen in the Rocky Mountains,
Steph