New York, Jun 24 (IANS): Seismic quietness occurs immediately before volcanoes erupt and can, thus, be used to forecast an impending eruption for restless volcanoes, say researchers.

The findings showed that the duration of the silence could indicate the level of energy that will be released when eruption occurs.

Further, the longer the quiet phase preceding an explosion, the more energy was released in the ensuing explosion.

"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," said Diana Roman, Volcanologist at Carnegie Institution For Science, a US-based research organisation.

The quiet periods ranged from six minutes before an explosion to over 10 hours (619 minutes) for the largest explosion, said the paper published in the journal Earth and Planetary Science Letters.

The correlation between duration of quiet periods and amount of energy released is tied to the duration of the gas pathways being blocked.

The longer the blockage, the more pressure builds up resulting in more energy released, the researchers said.

"It is the proverbial calm before the storm. We can use these quiet periods to forecast the amount of energy released," Roman added.

For the study, the team monitored a sequence of eruptions at the Telica Volcano in Nicaragua between 2009-2011. Out of the 50 explosions that occurred, 35 had preceding quiet periods lasting 30 minutes or longer.