Highway To Hell: Some Volcano Eruptions Fueled By Fast-Rising Magma

 @rpalmerscience on July 31 2013 2:46 PM

Scientists have reexamined the 1963 eruption of Costa Rica’s Irazu volcano and found something surprising and a bit unsettling: Some eruptions may happen in a much shorter time span than previously thought.

The rise of magma from the Earth's mantle toward the surface is ordinarily thought to take thousands of years. But evidence is accumulating that some volcanoes can recharge their magma supply in a manner of months, suggesting they can blow their tops relatively quickly. In a paper appearing in the journal Nature on Wednesday, a pair of researchers from Columbia University’s Lamont-Doherty Earth Observatory describes the short fuse of the 10,000-foot-tall, 200-square mile-wide Costa Rican volcano Irazu.

Irazu erupted for two years starting in 1963, claiming at least 20 lives and destroying hundreds of homes. A closer look at the ashes from that eruption led the Columbia researchers to believe that the volcano’s magma traveled directly up from the upper mantle instead of lingering in a mixing chamber located miles beneath the volcano. The researchers nicknamed this direct line to the fiery mantle the “highway from hell.”

“There’s definitely already evidence for fast-rising magmas in smaller volcanoes, but our new observation was that even ‘full-grown’ large volcanoes can also operate very fast,” lead author Philipp Ruprecht said in a phone interview.

Ruprecht and co-author Terry Plank discovered this fast rise of deep magma by looking at crystals of the mineral olivine taken from the ashes of the Irazu eruption in the 1960s. As magma rises from the mantle, crystals of olivine -- a mixture of magnesium, silicon, and oxygen -- start to form. Olivine also has an affinity for the element nickel, which is abundant in the Earth’s mantle. Normally, as the magma was mixed over a very long time, nickel would be distributed more or less evenly among the olivine crystals. But when Ruprecht and Plank looked at the olivine from the Irazu ashes, they found strange spikes of nickel. Those spikes suggest the magma from Irazu was incredibly fresh; the nickel did not have enough time to spread out evenly among the olivine crystals.

By their calculations, the magma underneath Irazu surged up 22 miles through the Earth in just around two months.

There’s still a lot of mysteries remaining, such as which volcanoes are more likely to have fast-rising magmas or what conditions can create a “highway from hell.” Ruprecht says scientists don’t know for sure just yet, but he has a hunch that gases like carbon dioxide may play a role in helping the super-dense magma rise so quickly from the mantle.

Whether or not this discovery can translate into better volcano eruption forecasts isn’t quite clear. Volcanoes are much more heavily monitored today than they were in the 1960s. But current detection methods are more focused closer to the surface, so we might not be able to translate the detection of sudden deep magma rises into a reliable forecasting system.

Still, “the study provides one more piece of evidence that it's possible to get magma from the mantle to the surface in very short order,” John Pallister, the head of the U.S. Geological Survey’s Volcano Disaster Assistance Program in Vancouver, Wash., said in a statement. "It tells us there's a potentially shorter time span we need to worry about."

SOURCE:  Ruprecht et al. “Feeding andesitic eruptions with a high-speed connection from the mantle.” Nature 500, 68-72, 1 August 2013.

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