Scientists solve mystery of supervolcano eruptions
Giants accumulate magma until pressure build-up causes explosion
Geologists have reported fresh insights into supervolcanoes, the brooding, enigmatic giants of the earth's crust whose eruptions are as catastrophic as they are rare.
The buoyancy of molten rock, or magma, is the key explanation as to why these monsters blow their stack, according to the report on Sunday in the journal Nature Geoscience.
Supervolcanoes include Yellowstone, in the US state of Wyoming, which spewed out more than 1,000 cubic kilometres of ash and rock when it last erupted about 600,000 years ago.
Events of this kind can chill the planet's surface by up to 10 degrees Celsius for a decade or more because the ash, carried into the stratosphere, reflects sunlight, according to a 2005 study.
By comparison, the biggest volcanic eruption of the last quarter-century was that of the Philippine volcano Pinatubo in 1991, which discharged a relatively puny 10 cubic kilometres.
Seeking to understand why volcanoes can be so different, a team from Switzerland, France and Britain built a computer model of volcanic activity, basing the age of eruptions on a telltale mineral, zircon, found in volcanic rocks.
Separately, a team from the Swiss Federal Institute of Technology in Zurich (ETH) used a hi-tech X-ray facility to study the density of molten rock below supervolcanoes.