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Volcanoes Guard Ice Age Secrets

<p>Snow-capped volcanoes are tide marks of vanished ice, carrying information about Earth that doesn't exist in any other form. </p>
Image: Lava flows on top of snow at Tolbachik volcano in Russia in April 2013.
Lava flows on top of snow at Tolbachik volcano in Russia in April 2013.Ben Edwards
/ Source: Live Science

Standing eye level with oncoming lava, in a snow pit he is digging at Tolbachik volcano in Russia, Ben Edwards is hoping his world doesn't violently explode in the next few minutes.

Several years of watching lava trundle over ice and snow has taught Edwards, a volcanologist at Dickinson College in Pennsylvania, that he's probably safe — at this spot, the volcano's incandescent rock rarely sparked the kind of blasts typically seen when lava meets water.

Finished with the snow pit, Edwards clambers out and waits for water to start trickling out of the deep walls. "There was no obvious meltwater at Tolbachik, so we think the water drains immediately from the [lava-snow] interface, down under the snow," Edwards said.

Understanding how snow-capped volcanoes generate meltwater will help scientists better predict flooding from so-called glaciovolcanic eruptions, a significant hazard. Among the worst natural disasters are massive floods from icy urban volcanoes such as Washington's Mount Rainer. In Iceland in 1996, a sudden flood called a jökulhlaup destroyed part of the national highway after Grímsvötn volcano melted its overlying glacier.

But for Edwards, working at the extremes of fire and ice means more than predicting future hazards. He is also among a handful of geoscientists pioneering a new way to make sense of past ice ages — with volcanoes that erupted through ancient ice sheets.

"These are volcanoes with unique features that we can use to understand what's happened to Earth's climate over the last 10 to 15 million years," Edwards told Live Science's Our Amazing Planet. [Fire and Ice: Images of Volcano-Ice Encounters]

When fire meets ice

Most of Earth's climate history comes from the ocean floor, from chemical signatures preserved in mud and microscopic sea creatures. Drilling into the seafloor rewards researchers with cores holding millions of years of natural temperature swings. (Even during an ice age, Earth's temperature shifts back and forth a little bit.) But matching these mucky cores to glacial advances and retreats on land is complicated by the glaciers themselves.

Like giant erasers, glaciers scour away much of their record of past movement as they shrink and grow. In North America, only the last few glacial cycles can be found by geologic detectives. And the rubbly piles left behind may be impossible to pin down with an accurate age, which is key to matching glacial history to ocean climate records.

Enter the weird volcanoes called tuyas.

Tuyas are like little pushpins marking where and when ice covered the land. Though each tuya volcano may have erupted thousands of years apart, reconstructing their history is yielding new insight into the advance and retreat of continental ice sheets.

"They act as tide marks of vanished ice, and this information doesn't exist in any other form," said Dave McGarvie, a volcanologist at the Open University in Scotland.

Picture a volcano that looks like a towering bakery cake, with steep sides and a flat top. To those with a trained eye, the bottom layers obviously formed underwater. The rocks are bulbous pillow lavas and exploded lava glass, called hyaloclastite. But the frosting on top is a normal-looking lava flow, like those that cool in air.

In the 1940s, a Canadian geologist first figured out how this strange stack of rocks appeared. The flat-topped volcano, called Tuya Butte, erupted underneath a long-gone ice sheet that once covered much of British Columbia. First, the volcanic heat thawed the ice, producing the bottom layers, called pillow lavas. As the ice thinned and a small meltwater lake formed, the overlying pressure lessened, and the lava had room to explode.

"One bit of basalt can melt about 10 to 14 times its own volume of ice, so you get a lot of water appearing very, very quickly during an eruption," McGarvie said.

The confining ice kept everything piled up into a steep-sided hill. When the volcano was tall enough to burst through the ice sheet, the lava could cool in the air, creating the flat top. (If enough lava pours out, the volcano will build a traditional cone shape on top.)

"Imagine this amazing-looking island sitting in this moat of water surrounded by an ice wall," McGarvie said. "When it all melts away, you're left with a flat-top mountain."

Digging a snow pit near a lava flow at Russia's Tolbachik volcano in April 2013Ben Edwards

Frozen in time

The beauty of tuyas is that their hard rock preserves the height of the ice sheet, even though glaciers may grind away at the volcano. The transition from the waterline to aerial lavas is like the ring left on the inside of a bathtub. And tiny minerals in the lavas provide a precise age. [Image Gallery: Wild Volcanoes]

"Every time a volcano erupts it gives you a photograph of the ice," said John Smellie, a volcanologist at the University of Leicester in the United Kingdom.

In western Canada, where scores of volcanoes erupted in the past millennia, geoscientists are quilting together the past thickness of the North American ice sheet with lava, and linking it to ocean cores. For example, ocean cores are often correlated by changes in oxygen isotopes (atoms with different numbers of neutrons) in ocean sediments. Edwards can now point to a volcano in British Columbia and say the ice on land was at least 300 meters [985 feet] thick during a certain marine isotope stage that corresponds to a cold Earth.

"With these volcanoes we have 2 million years of records," Edwards said. "We have some volcanoes that erupted 10 to 15 times. It's not continuous, but we can start to think about whether the ice was always the same thickness," he said.

"This is important for people doing big-scale climate models, because there's really not much of a check on their models for ice sheets growing and disappearing. These kind of studies provide points that modelers can use, and they darn well better have ice that's a kilometer thick in B.C. volcanoes," Edwards said.

In Iceland, where tuyas are called table mountains, glacier-volcano records can also provide a chronology of the ice sheets immediately south of the Arctic Circle, McGarvie said. More than half of Iceland's glaciers lie nearby or flow directly over volcanoes today.

McGarvie is also scaling volcanoes in Chile to estimate the past thickness of tropical ice and link it to the marine climate record. Part of the Patagonian ice field, the glaciers were once more extensive and scientists think their expansion and contraction provides a sensitive record of past climate change.

— Becky Oskin, Live Science

This is a condensed version of a report from Live Science's Amazing Planet. Read the full report.

Email Becky Oskin or follow her @beckyoskin. Follow @OAPlanet on Twitter, Facebook and Google+.