New Concept Proposes that ‘Superplumes’ Lift Continents on Earth and Tharsis on Mars
By Melanie Lenart
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.”
Contact Information
Victor R. Baker
520-621-7875
baker@hwr.arizona.edu
James M. Dohm
520-626-8454
jmd@hwr.arizona.edu
