Lamb and colleagues determined that the spring that now runs through]] Box Canyon isn't powerful enough to have eroded such a steep headwall or move lots of sediment and giant boulders.
They also found unexpected evidence of "plunge pools" that appear to have been the site of ancient waterfalls.
So they concluded that Box Canyon—long considered a textbook case of gradual erosion—was instead scoured by a massive flood or series of floods about 45,000 years ago.
Keith Harrison, a senior research scientist at the Southwest Research Institute in Boulder, Colorado, was not involved in the research.
He said the new analysis "makes a strong case for flooding, and in future studies of Martian valley networks their hypothesis must be taken into account."
But while the authors found that the Box Canyon spring isn't strong enough to erode the headwall and carry boulders away, Harrison cautioned, groundwater on Mars might be.
"The large flood channels on Mars are, in fact, thought to have derived their water from vigorous groundwater seepage at large areas of broken and jumbled rock called chaotic terrain," he said.
"It's not clear exactly how far one can go with a planet-to-planet comparison."
Entombed Fossils on Mars?
Meanwhile, NASA's Spirit rover has sent back data showing nearly pure silica deposits in a region of the red planet called Columbia Hills.
The deposits were formed when acidic hydrothermal fluids came into contact with Martian volcanic rock, researchers say.
"The most important implication of this discovery is that we now believe Mars once sustained surface hydrothermal systems," said Jack Farmer, a study co-author from Arizona State University in Tempe.
Farmer believes the silica deposits may indicate places where fossils could be entombed.
"Hot-spring deposits are among the best places on Earth to explore for a fossil record of an ancient biosphere, a strategy that is also an important facet of the current exploration plan for Mars," he said.
(Related: "Mars Lander Team Prepares for 'Seven Minutes of Terror'" [May 13, 2008].)
Bringing it Home
Ralph Milliken, a planetary geologist at NASA's Jet Propulsion Lab in California, was not involved with either of the new studies.
He said he is anxious to see people explore Mars with future rovers—or in person.
Today's tools are isolating "sweet spots" for future exploration programs, he added, "and silica deposits such as [those described in the Science study] are currently on that list."
As for Lamb, the lead author of the Idaho canyon paper, he said his next research will focus on our own planet.
"We try to understand how Earth is changing, particularly with climate change," he said.
"Where are rivers going to go, how are they going to carve rock, how are they going to move material? To me, that's more fundamental than the Mars water question."
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