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Surrogate for the martian surface Vatnajokull: The eruption of a volcano under Europe's largest glacier last year fascinated geologists. Similar glacial flooding may have carved up Mars a billion or so years ago.

VATNAJOKULL GLACIER, ICELAND — VATNAJOKULL GLACIER, Iceland -- Jim Garvin is working frantically in the bucking cockpit of a NASA research plane, preparing for Earth's next mission to Mars.

A planetary scientist from the Goddard Space Flight Center, Garvin is using space technology to survey a landscape scoured by a catastrophic flood, maybe the biggest on Earth in 60 years.

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He and a team of NASA scientists are trying to study the effects of a rare but immensely powerful natural disaster, the eruption of a volcano under a glacier. These explosive mixtures of fire and ice have killed tens of thousands of people in recent decades -- and could one day cause history's most devastating flood.

Garvin is a geologist interested in natural calamities and other forces that can suddenly reshape our planet. But since his college years, his consuming passion has been Mars. As a budding scientist, Garvin once wrote a letter to NASA volunteering to be sent to Mars -- one way, if necessary.

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It's his love of the red planet that first brought him to Iceland, and it's why he keeps returning.

There are sprawling glaciers, steep cliffs, volcanoes and rugged terrain -- all of which make it a pretty good surrogate for the martian surface.

Then last fall, Iceland got even more interesting.

A volcano erupted under the Vatnajokull glacier, a slab of ice about the size of Puerto Rico. Meltwater gushed into a huge lake bed that was capped by about 600 feet of ice. The lake overflowed. Then the meltwater squeezed through fissures and rivers that vein the belly of the ice.

Finally, on Nov. 5, a cubic mile of water exploded from the bottom of the face of the glacier. Thirty-foot waves crashed across the black volcanic sands. Stretches of highway, bridges and blocks of ice the size of small office buildings tumbled across miles of uninhabited landscape and into the North Atlantic.

No one died, and roads are already being repaired.

'Excellent analogy'

But the event fascinated geologists. Garvin thinks similar deluges probably carved up Mars a billion or so years ago. He says that a glacial flood about a thousand times larger than Iceland's excavated a martian valley called Ares Vallis -- the broad, boulder-strewn plain where the Pathfinder spacecraft landed.

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Iceland, Garvin says, "is an excellent analogy on the Earth for landscapes on Mars where we think liquid water ran, at times catastrophically, in a wetter time in the history of Mars."

That's important to anyone interested in extraterrestrial life. If liquid water once flowed on Mars, there's a chance life could have emerged.

Last fall wasn't the first time a melting glacier inundated Iceland; smaller ones occur every few years. Perhaps 60 of the large-scale events have occurred since the Vikings arrived in the ninth century.

But last year marked the first time that humans have been in a position to witness the entire process, from the first earthquakes and slumping of the glacier's surface to the ebbing floodwaters. This outburst gave many scientists their first glimpse of the awesome power of the events, in Icelandic called jokalhlaups. "In Iceland, a lot of the volcanism -- the active flow of the Earth's energy to the surface -- occurs under ice," Garvin says.

And it's important to study subglacial volcanism, he says, because there are a number of other areas of the world where a catastrophic glacial flood could have far more serious consequences.

A tsunami of rock, mud and debris buried Armero, Colombia, in 1985, killing 23,000 people -- a direct result of a volcano erupting and melting its glacial mantle. Resort towns in Chile sit under a restless, ice-capped volcano called Villarrica. In Washington state, if Mount Rainier erupted, melting its glacial cap, flooding would devastate sections of Tacoma, Seattle and their suburbs.

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Garvin points out that the western Antarctic ice sheet is sitting on a range of volcanoes. "Only instead of being under a few hundred yards of ice, in Antarctica it's under a mile of ice," he says.

Those volcanoes could "melt enough of the west Antarctic ice sheet to produce an extraordinarily catastrophic event, releasing hundreds of thousands of times the amount of water that was released here" in Iceland. That would raise sea levels worldwide.

Profile of the surface

Garvin and his team are now busy gauging the strength of Iceland's latest flood, using a device called a laser altimeter.

The instrument was designed to map planets from space. One flew aboard the ill-fated Mars Observer spacecraft, which vanished as it approached its destination in 1993.

Now there's a laser altimeter aboard the Mars Surveyor, due to begin orbiting the planet by mid-September.

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In Iceland, Garvin's team fires beaded streams of green laser light through a series of mirrors and out the belly of the plane. The device bounces the light off the landscape and records its return. By measuring the round-trip time for each pulse, the team creates a profile of a narrow swath of the surface.

By using Global Positioning System satellites, to fly the plane and to determine its exact position second by second, Garvin can make these profiles with astonishing precision -- to within an accuracy of a few inches, as measured against Earth's center.

As the laser silently strafes the flood plain, Garvin ricochets around the cabin of the aircraft. He peers out windows, points excitedly at the volcano's caldera, riffles through maps, and leans over to confer with pilot Virgil Rabine.

Garvin apologizes that the plane can't fly any lower than about 2,000 feet because of 60-knot winds near the surface.

"That could tear the airplane apart," he says, with a hint of a smile. He's wearing a baseball cap ominously embroidered with "Mars Observer."

"Terrain, terrain. Pull up! Pull up!" a computerized voice announces, as the plane closes in on sheer cliffs at the western end of the flood plain. Rabine casually overrides the robotic controls, and the P3 Orion lurches skyward.

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Weeks later, Garvin is back from Iceland. He watches the first pictures from Mars Pathfinder and is "phenomenally excited."

He points to unmistakable signs of catastrophic flooding at the landing site, and he thinks that the rover may already have turned up ancient rocks.

Having stumbled on "stuff of that exotic nature," he says, now "they can actually taste it and figure out what it's like. That could tell us the whole history of how Mars really put itself together."

"Mars really, for a lot of us, is very provocative. It operates in a lot of Earth-like ways, and in a lot of ways we don't understand. It's like having an Earth with no plants and no ocean. So it's like, 'Let's see what happens.' It's a great natural experiment."

Pub Date: 7/17/97


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