The novel research sheds light on the fact that the solidified magma residing four-five kilometers beneath surface of dormant volcanoes can become active in few months. Despite the magma lying beneath some of the world's most dangerous volcanoes remains in cool and solid form in 99% of time, the eruption leads flow of hot molten lava.

Scientists have been perplexed for past many years after noticing the volcanoes that are actually dormant, but become active very quickly. Kari Cooper of the University of California, Davis, analyzed isolated crystals from the solidified lava at Oregon's Mount Hood that lasted to about 220 years ago.

Kari and Adam Kent, of Oregon State University in Corvallis, used radioactive decay of uranium in the crystals and found that the crystals in the magma chamber are at least 21,000 years old. They also found increased levels of strontium in the crystals, which is quite strange as the melting point of igneous rock is about 750ºC. It is the temperature at which the strontium gets diffused and mobilized through crystals within a few thousand years.

They believe that volcanoes with high amount of liquid at about 750ºC have higher chances of eruption. Volcano eruption takes place on mixing of hot magma from deep inside the volcano with the cooler magma present on top of the volcano.

"This process of 'defrosting' a magma body could happen before we get any other evidence that an eruption is imminent", said Adam.

They cited that an eruption of Mount Pinatubo in the Philippines in 1991 was the second largest eruption from a land-based volcano of the 20th century.