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Museums worldwide may need to change the explanations on their volcanoes models if a new study stands the test of time. One of the most commonly taught ideas in volcanology, that eruptions spring from large chambers of molten magma deep underground, has been challenged. Instead, the authors of a new study claim, volcanoes contain “mush reservoirs” where magma mixes with crystals, like the blend of ice and liquid in a slurpee.
By their nature, volcanoes aren't easy to study, and the closer they get to erupting, the harder testing theories becomes. The vast quantities of magma eruptions spew into the air must come from somewhere, and geologists proposed large chambers filled with magma that replenish between explosions. The fact that we have never seen the process in action didn't seem a problem when there was no other obvious explanation.
More recently, however, an alternative model has been proposed, where magma starts in small pockets between crystals deep between the volcanoes. Although evidence has emerged to support the idea, it has faced opposition, primarily because it couldn't explain how the magma that actually reaches the volcano proper is so liquid, with only small concentrations of crystals. By providing an answer to that question Professors Matthew Jackson of Imperial College, London and Stephen Sparks of the University of Bristol have given the mush reservoir model a whole new credibility.
“Molten rock forms within largely crystalline hot rocks, spending most of its time in little pores within the rock rather than in large magma chambers,” Sparks said in a statement. “However, the rock melt is slowly squeezed out to form pools of melt, which can then erupt or form ephemeral magma chambers.” Unlike water, whose liquid form is more dense than its solid, magma is more buoyant than the solid crystals, and percolates upward, bringing small quantities of older crystals with it.
A description of the process has been published in Nature where a typical example is given of basalt rising from a depth of 18 kilometers (11 miles) beneath the Earth's surface. As time goes on the magma separates based on chemical composition, eventually leaving a layer that is more than 70 percent melted on top of a predominantly solid base.
Attempts to study the contents of volcanic chambers have missed this, the paper proposes, because the largely liquid layer on top is too thin or ephemeral.
“We now need to look again at how and why eruptions occur from mush reservoirs,” Jackson said. The authors hope the work will lead to improved eruption warnings, potentially saving many lives. They also think it may help explain the metal ore deposits ancient volcanoes have left behind.
