'Superplumes' lift continents on Earth, Tharsis on Mars?
UNIVERSITY OF ARIZONA NEWS RELEASE
Posted: November 11, 2001
A budding theory to describe Earth processes could help solve some martian mysteries as well, believes Victor Baker, Regents' Professor and head of the hydrology and water resources department at the University of Arizona, and a group of his colleagues.
During the annual meeting of the Geological Society of America this week, Baker and Shigenori Maruyama of the Tokyo Institute of Technology are introducing the idea that Maruyama's "superplume" concept of magma dynamics applies to a huge upland area on Mars known as Tharsis.
"The concept of a superplume is a relatively new idea. It's part of current avant-garde thinking of how the Earth works on the long term," said Baker, who has spent several months this year with Maruyama hammering out an interpretation applicable to Mars. Others who have contributed to the superplume hypothesis are UA planetary geologist James Dohm, UA hydrology researcher Justin Ferris and Robert C. Anderson of the Jet Propulsion Laboratory in Pasadena, California.
Maruyama envisions a half-billion-year cycle of superplume activity that first draws continents together and then splits them apart. He fits the concept into the fully accepted theory of plate tectonics, which explains how the thicker, lighter continental plates float on underlying magma and bump into each other and heavier oceanic plates; clashes between plates feed volcanoes (by recycling solid crust back into the liquid magma), cause earthquakes and create mountains.
Baker drew on the earthy concept of a pot of soup on the stove to help explain how a superplume works. In a really thick soup -- a stew rather than a broth, say -- a relatively solid mass might heat up on the bottom until it suddenly broke away and traveled to the top of the mixture in one massive chunk. This would be comparable to the superplume method of transferring heat via magma from a planet's hot inner core toward a surface land mass.
By this line of thinking, which Maruyama describes in a 1994 Journal of the Geological Society of Japan paper, the ongoing collision of Indian with Southeast Asia is not only creating the Himalayan Mountains, it is the future site of a supercontinent. (Don't worry, this would be some 250 million years down the road.) Also, he hypothesizes that an underlying superplume of magma is lifting the continent of Africa. For one thing, the continent is being ripped apart at the African Rift. Also, Africa has the highest average elevation of all seven continents despite a conspicuous lack of tall mountains.
Like Africa, Tharsis bulges out relative to its surroundings, Baker noted. Also, Tharsis shows evidence of a long history of tectonic activity, with faults, rifts, valleys, igneous plateaus and other spectacular features that are similar to the expression of Earth's suspected superplumes, Dohm said.
"There are volcanoes that would sit on top of the state of Arizona and stand 17 miles high. The canyon system would stretch from New York to Los Angeles, really dwarfing the Grand Canyon," Dohm said. "This is the major heat engine of Mars. And it's probably over 3 billion years old."
Tharsis also contains apparent channel beds hundreds of times the size of the Mississippi River. Baker believes they are the remnants of floods, from episodic outbursts on a planet that is cold and dry "99 percent" of the time.
"Why has Mars been able to burp up heat throughout its history? We have the Tharsis superplume, which continues to operate for the rest of Mars history," he suggested. "A whole lot of things that are inexplicable by other theories can be explained by this one."
For instance, the superplume cycle might operate in bursts of volcanic activity on Tharsis that cause a short-term heating of the planet's surface -- along with a melting of glaciers and an ejection of groundwater. Volcanoes spew out carbon dioxide, a greenhouse gas that would warm the planet, and more would bubble out as long-buried water contacted the atmosphere.
Baker has long been convinced that the surface features on Mars that look like one-time riverbeds indeed were created by flowing water. He followed up a 1991 Nature paper on the proposed martian water cycle with a more detailed paper published in Nature this summer (Aug. 15 and July 12, respectively). The latter contained some persuasive high-resolution photographs from a recent mission, some of which will be on display on the third floor of the UA Space Sciences building for about another month.
Despite his enthusiasm about the superplume hypothesis, Baker cautions that it is still being developed. The exposure at the GSA meeting represents the first public appearance of this concept that he hopes will one day develop into a full-fledged theory.
But the real test will come when information starts flowing from the Odyssey mission, which went into orbit around Mars on Oct. 23. Its mission is to determine the composition of the martian surface. Results should start circulating through the scientific community in late January, Baker hopes.
"We're talking about something that's not ready for prime time," Baker said of the superplume hypothesis. "It has an element that a lot of important science has, and that is a lot of people will probably disagree with it. But nature is the one with the answers, not the scientists. So this idea will stand or fall by how it relates to nature."