'Magma P.I.' unearths clues to how crust was sculpted

Dec 03, 2007

About a decade ago, Johns Hopkins University geologist Bruce Marsh challenged the century-old concept that the Earth’s outer layer formed when crystal-free molten rock called magma oozed to the surface from giant subterranean chambers hidden beneath volcanoes.

Marsh’s theory – that the deep-seated plumbing underneath volcanoes is actually made up of an extensive system of smaller sheet-like chambers vertically interconnected with each other and transporting a crystal-laden “magmatic mush” to the surface – has become far more widely accepted. This sort of system, known as a “magmatic mush column,” is thought to exist beneath all of the world’s major volcanic centers.

Now, Marsh – using the windswept McMurdo Dry Valleys of Antarctica as his “walk in” laboratory -- posits that these channels did more than simply transport or supply magma and crystals to form the Earth’s surface: As the magma pushed up through the earth, the pressure fractured the crust in such a way that it provided a sort of “template,” guiding later erosion in sculpting a series of valleys and mountain ranges there.

Marsh described his latest findings to fellow scientists at a recent meeting of the American Geological Society.

“As the magma made its way to the surface, the pressure broke the crust up into pieces," Marsh says. "That fracturing reflected a pattern of stress in the same way that a windshield put under pressure will eventually fracture and the pattern of the broken glass would reflect where the stress was originally applied.

“Magma then seeped in," he says, "and ‘welded’ the fractures, sealing them temporarily until erosion – in the form of snow, rain, ice and wind – went to work on these weaknesses, carving out valleys, mountains and other landforms that we see there today and marking where the solidified magma originally was.”

Marsh said that, in Antarctica, both of these functions date back at least 180 million years to the time when the continents split apart. He points out that this observation brings together the usually disparate study of deep-seated magmatic processes and land-surface evolution.

“It’s one of those situations where, usually, never the twain shall meet, but they do in this case,” the earth scientist said. “Having recognized evidence in this critical process in the McMurdo Dry Valleys is important because it may allow us to recognize it in other areas where the geologic record is scantier and less complete.”

The Dry Valleys makes an ideal place to study these systems because it was eroded into its present form millions of years ago and has, unlike the rest of Earth’s surface, undergone very little subsequent erosion. His colleagues George Denton of the University of Maine and David Marchant of Boston University call this region “a relic landscape,” because it is the only known place on Earth that looks almost exactly as it did millions of years ago.

“The delicacy of the landscape in the Dry Valleys has preserved for us an unusually rich collection of geologic evidence of the processes that formed this terrain,” Marsh said.

For more than a quarter of a century, Marsh -- who could be thought of by fans of 1980s detective television shows as sort of a "Magma P.I." -- has been working to understand the deep underground systems that bring magma to the Earth’s surface. In 1993, he found the Dry Valleys, a walk-in “museum” that he calls “the one place on earth where the plumbing system is exposed in this way."

"You can stand on shelves of solidified lava that were deposited by magmatic activity 180 million years ago,” he said. “It’s awe inspiring.”

Source: Johns Hopkins University

Explore further: New, tighter timeline confirms ancient volcanism aligned with dinosaurs' extinction

add to favorites email to friend print save as pdf

Related Stories

Fogo volcano on Sentinel's radar

Dec 03, 2014

Radar images from the Sentinel-1A satellite are helping to monitor ground movements of the recently erupted Fogo volcano.

And now, the volcano forecast

Oct 22, 2014

Scientists are using volcanic gases to understand how volcanoes work, and as the basis of a hazard-warning forecast system.

Mysterious Midcontinent Rift is a geological hybrid

Oct 16, 2014

An international team of geologists has a new explanation for how the Midwest's biggest geological feature—an ancient and giant 2,000-mile-long underground crack that starts in Lake Superior and runs south ...

Mantle plumes crack continents

Sep 04, 2014

Using a simulation with an unprecedentedly high resolution, Earth scientists from University of Paris VI and ETH Zurich have shown that magma columns in the Earth's interior can cause continental breakup—but ...

55-year old dark side of the Moon mystery solved

Jun 09, 2014

(Phys.org) —The Man in the Moon appeared when meteoroids struck the Earth-facing side of the moon creating large flat seas of basalt that we see as dark areas called maria. But no "face" exists on farside ...

Recommended for you

Improving forecasts for rain-on-snow flooding

7 hours ago

Many of the worst West Coast winter floods pack a double punch. Heavy rains and melting snow wash down the mountains together to breach riverbanks, wash out roads and flood buildings.

The Greenland Ice Sheet: Now in HD

7 hours ago

The Greenland Ice Sheet is ready for its close-up. The highest-resolution satellite images ever taken of that region are making their debut. And while each individual pixel represents only one moment in time, ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.