The Earth's largest volcanic eruptions have a lot in common with bubbles rising up in a glass of soda or beer.
New experiments and computer simulations show that gigantic eruptions like those which blasted open the Yellowstone caldera are caused by vast pools of hot magma so buoyant they press incessantly on the rocks above until they break through with incredible eruptive force.
The new research, presented by two teams in two papers in the Jan. 5 issue of Nature Geoscience, suggests the magma's buoyancy triggers these rare super eruptions rather than some local trigger like an earthquake or an injection of more magma into the magma chamber from below.
The supervolcanic trigger appears to be markedly different from how smaller, more frequently erupting volcanoes blow their tops.
Volcanoes like Stromboli and Mount St. Helens have much smaller magma sources and are thought to erupt when, for instance, a quake shakes the magma up like a bottle of soda.
The eruption releases gases that dramatically increase the pressure -- or the shaking causes a large landslide that essentially uncaps the mountain that's holding the magma in, as happened at St. Helens in 1980.
“In general there may be some local triggers (for supervolcanic eruptions), but the magma chamber must be in critical condition,” said Luca Caricchi of the University of Bristol and University of Geneva. It's the buoyancy which makes it critical.