Certain volcanos seem to erupt with no forewarning, but scientists have now seen that it is actually an accumulation of gas over several days that is prompting the eruptions. This finding may change the way scientists observe active and dormant volcanos.

Scientists generally believed that volcanic eruptions were incited by a collection of pressure resulting from the slow buildup of gas-laden magma. This bubbly magma was thought to accumulate over decades or hundreds of years. However, this new study indicates that sudden volcanic eruptions are generated by a rapid accrual of gas-over only a few months or even days. The gas bubbles head to old magmas chambers, according to the study published in Nature Geoscience.

The study authors from the University of Oxford and the University of Durham used Campi Flegrei volcano, located near Naples, Italy, as an example. With the help of the Vesuvius Volcano Observatory in Italy, the scientists were able to come up with an explanation as to why more and more volcanic eruptions are taking place with little warning.

Instead of looking to seismic activity or ground deformation alterations as a sign of an imminent eruption, gas composition at the Earth's surface is a better indicator a coming explosion, according to the study.

"When the magma forms bubble, the composition of gas at the surface should change, potentially providing an early warning sign," lead author Mike Stock, of the Department of Earth Sciences at the University of Oxford, said in an official statement.

Campi Flegrei, which has not erupted since 1538, has shown recent hints of unrest. The scientists studied small crystals of apatite, a mineral that came out during the ancient eruptions of Campi Flegrei. By studying the apatite at different times during the evolution of the volcano's magma, the crystals act as a time capsule of sorts offering the researchers information about when the magma became saturated with gas. To the surprise of the scientists, the magma had minimal gas during the majority of its lifetime and did not begin to bubble until a short time before eruption. This shows that the movement of the ground and earthquakes may point to the arrival of "new batches of magma" under the ground rather than a sign of an impending eruption.

"This has significant implications for the way we monitor active and dormant volcanoes, suggesting that the signals we previously thought indicative of pre-eruptive activity - such as seismic activity or ground deformation - may in fact show the extension of a dormant period between eruptions," Stock explained.

Since the analysis of apatite worked in this instance, the scientists are interested to see if this pattern is common throughout all volcanos.

"This research will also help us refine our ideas of what we want to measure in our volcanoes and how we interpret the long-term monitoring signals traditionally used by observers," Prof. David Pyle, volcanologist and co-author of the study, said.

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