For the first time, researchers have identified a quantifiable method for anticipating the eruption of an active volcano. New data suggests a period of quiet almost always precedes an explosive eruption.

A number of signs can tip scientists off to the impending eruption of a dormant volcano. An increase in seismic activity, the outflow of gases and geologic deformation are all warning signals.

But for scientists monitoring active volcanoes, recognizing changes amidst the constant seismic background noise and volcanic emissions is much more difficult.

In 2009, a team of researchers from the Carnegie Institute for Science, Penn State, Oxford University, the University of Iceland and the Nicaraguan Institute of Earth Sciences began installing a system of instruments to better monitor the fluctuations of Nicaragua's Telica Volcano. The cone-shaped stratovolcano erupted in 2011, and researchers were uniquely prepared to decipher the warning signs in the lead up to the eruption.

Their analysis revealed a lack of deep seismicity or deformation in the lead up to the initial explosion. The researchers also identified subtle anomalies in sulfur dioxide gas emissions. Their findings showed that the eruption was not inspired by fresh magma, but by a buildup of pressure following a sealed vent.

The eruption was not actually a single explosion, but a series of small to medium ash explosions lasting more than a month. Of the 50 explosions, 35 were preceded by 30 or more minutes of quiet. Thirteen more were preceded by 5-minute quiet periods. Only two were without warning silence.

"It is the proverbial calm before the storm," Diana Roman, a volcanologist at the Carnegie Institute for Science, said in a news release. "The icing on the cake is that we could also use these quiet periods to forecast the amount of energy released."

Roman and her research partners were able to identify a correlation between the length of the quiet period and the size of the subsequent explosion -- the longer and deeper the silence, the greater the gaseous buildup, the more powerful the eruption.

"Similar observations of this phenomenon have been noted anecdotally elsewhere," Roman added. "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."

The new findings were published online this week in the journal Earth and Planetary Science Letters.