Scientists monitor potential volcanic eruptions because the ability to predict when volcanoes are about to blow up can save lives and reduce damages to properties.

Forecasting the eruption of dormant volcanoes is easy. Some of the signs that may indicate that a sleeping volcano will explode soon include the outflow of gases, geologic deformation and increased seismic activities.

Monitoring active volcanoes, though, is more difficult because of constant seismic activities and emission of gas and steam. Because of their restlessness, there has been no way of forecasting eruptions of active volcanoes.

A new study, however, has come up with a quantifiable method that can help predict when an active volcano is about to explode and how powerful the explosion will be. Findings of the research suggest that a long period of quiet often precedes an explosive volcanic eruption.

In 2009, researchers started to install a system of instruments around Telica Volcano, one of the most active volcanoes in Nicaragua, to monitor a series of eruptions. By tracking 50 explosions during a broader eruption period, the researchers found that 35 of these explosions were preceded by quiet period. Only two of these 50 explosions occurred without any quiet warning period.

The quiet periods ranged from six minutes to more than 10 hours with the longest period of quiet linked to the largest explosion. The association suggests that longer quiet periods at an active volcano will likely be broken by a powerful eruption.

Based on data from quiet and explosion pairs and the length of quiet period, the researchers were also able to forecast the minimum energy that will be released by impending explosions. This is so because the duration of quiet periods is correlated to the duration that gas pathways are being blocked. The longer the blockage, the more pressure builds up, which results in more energy release.

"Precursory seismic quiescence is interpreted as the result of sealing of shallow gas pathways, leading to pressure accumulation and eventual catastrophic failure of the system, culminating in an explosion," researchers wrote in their study, which was published in Earth and Planetary Science Letters on June 23.

"Longer periods of sealing and pressurization lead to greater energy release in the ensuing explosion."

Study researcher Diana Roman from the Carnegie Institution for Science said that the findings of the study suggest that it is possible to use the quiet period to forecast the amount of energy that a volcano will release. Roman said that using this method of monitoring active volcanoes in realtime can serve as a tool for short-term forecasts of eruptions.

"Similar observations of this phenomenon have been noted anecdotally elsewhere," Roman said. "Our work has now quantified that quiet periods can be used for eruption forecasts and that longer quiet periods at recently active volcanoes could indicate a higher risk of energetic eruptions."

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