Monogenetic Volcanoes Lead Violent Lives
October 3, 2012

Study Sheds Light On Violent Lives Of Monogenetic Volcanoes

Lee Rannals for — Your Universe Online

A new study is shedding light on the violent lives of monogenetic volcanoes, which erupt when magma and water meet.

These volcanoes erupt beneath the surface of the Earth just once before dying, although some eruptions can last for years.

Greg A. Valentine, PhD, a University at Buffalo geology professor, said not much is known about maar-diatremes volcanoes.

"The hazards that are associated with these volcanoes tend to be localized, but they're still significant," Valentine said in a statement. "These volcanoes can send ash deposits into populated areas. They could easily produce the same effects that the one in Iceland did when it disrupted air travel, so what we're trying to do is understand the way they behave."

Scientists had previously believed that maar-diatreme eruptions consisted of a series of explosions underground, which took place as magma reacted violently without water.

As each explosion takes place, the subterranean water table would fall, driving the next explosion even deeper.

Valentine and volcanologist James D.L. White of New Zealand's University of Otago propose maar-diatreme eruptions consist not of ever-deepening explosions, but of explosions occurring simultaneously over a range of depths.

With the scientists' new model, deep explosions break up buried rock thousands of feet below ground and push it upward. Shallow explosions eject some of this debris from the volcano's depths, but expel far larger quantities of shallow rock.

Their model fits with recent field studies that have found large deposits of shallow rock ringing maar-diatreme volcanoes, with only small amounts of deeper rock found. Two sites Valentine examined at the San Francisco Peaks Volcanic Field in Arizona were found to be this way.

The scientists' description of the eruptive process corresponds with White's investigation into the "plumbing" of maar-diatreme volcanoes, which are the conduits that carry magma toward the surface.

These conduits become visible over time as a landscape erodes away, showing evidence of explosions, including zones of broken-up rock at a range of depths.

Valentine said under the old model, ever-deepening explosions should cause shallow rocks to be ejected from the mouth of the volcano first, followed by deposits of deeper and deeper rock fragments. However, this doesn't coincide with what scientists are finding when they analyze geological clues at the volcanic sites.

The old model does not account for the fact that even when scientists find deep rock fragments, these bits of rock are mixed with mostly shallow fragments.

The new model uses the strengths of the old model, but accounts for new data.  The results allow geologists to have a better bias for estimating the hazards associated with maar-diatreme volcanoes, according to Valentine.