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source SPACE.com
by Dave Mosher, stuff writer
17 October 2007
The three Tharsis volcanoes (bottom, right) straddle the region dominated by Olympus Mons (top left). Scientists think the volcanoes may not be extinct, but rather dormant and waiting for a hot plume of magma to travel beneath them. Credit: NASA
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Mars appears to be a calm and desolate planet, but scientists now think something big is brewing beneath its wind-swept surface.
New research on Hawaiian volcanoes, combined with satellite imagery of Mars, suggests that three Martian volcanoes may only be dormant—not extinct. Instead of Mars' crust moving over stationary magma "hot spots," as occurs on Earth, researchers think the plumes travel.
"On Earth, the Hawaiian islands were built from volcanoes that erupted as the Earth's crust slid over a hot spot—a plume of rising magma," said Jacob Bleacher, a planetary scientist at Arizona State University and NASA's Goddard Space Flight Center in Greenbelt, Md. "Our research raises the possibility that the opposite happens on Mars; a plume might move beneath stationary crust."
Bleacher and his colleagues' findings are detailed in a recent issue of the Journal of Geophysical Research, Planets.
Sleeping giants?
Each of the volcanoes, located in the Tharsis region of Mars, is about 186 miles (300 kilometers) across. The largest volcano on Earth, Mauna Loa, is only 60 miles (97 kilometers) across.
Although scientists have never observed a volcanic Mars, recent images from the European Space Agency's Mars Express missions suggest the volcanoes there have been active within the past two million years and might still be. Also, the sparse impact craters near the three Tharsis volcanoes indicate relatively recent eruptions.
Lava flows show that these recent eruptions oozed from large cracks on the volcanoes' sides, occurring in a chain that meandered northeast.
"We thought we could take what we learned about lava flow features on Hawaiian volcanoes and apply it to Martian volcanoes to reveal their history," Bleacher said. But until recently, images of Mars weren't detailed enough to make a good comparison, he noted.
Traveling hot spot
Armed with new images from NASA's Mars Odyssey and Mars Global Surveyor orbiters, as well as the ESA's Mars Express, the team saw that the three volcanoes were similar in formation. However, each had recently erupted in distinct ways that allowed the scientists to determine the ages of the eruptions.
During the volcanic activity, lava oozed from cracks in the volcanoes' sides and formed "lava aprons;" the smoother the apron, scientists determined, the older the eruption.
Lava aprons on the northern-most volcano, Ascraeus Mons, are the youngest, Bleacher said, while the southern-most volcano, Arsia Mons, has the oldest. Like the Hawaiian volcanoes, the findings show that the volcanoes were fed by a common source of magma—but one that was on the move.
There's an alternative explanation for the chain of activity. Scientists postulate that the plume of magma could have spread out once it impacted the crust from below, like smoke hitting a ceiling.
"Our evidence doesn't favor either scenario," Bleacher said, "but one way to explain the trends we see is for a plume to move under the stationary Martian crust." If true, the traveling plume of magma could pass beneath dormant Martian volcanoes and stir them from sleep.
source SPACE.com
HemuZ Space
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