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Did Water or Lava Carve the Outflow Channels on Mars? Last investigations results

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posted on Apr, 1 2012 @ 04:13 AM
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There has been a lot of controversy on this question lately.

Few years ago, it was widely accepted in the scientific community that only water could have been the cause of the large outflow channels on Mars.
One of the lines of support for the idea that water once flowed on Mars comes from images that reveal details resembling the erosion of soil by water: terracing of channel walls, formation of small islands in a channel, hanging channels that dead-end and braided channels that branch off and then reconnect to the main branch...


Details from the Ascraeus channel (red), meandering across the surface of Mars. The insets in the black boxes show close-ups of some of the structures that lava can form: (left) branched channels, (middle) a snaking channel and (right) rootless vents; the rootless vents are also marked by yellow spots on the main image. Credit: Jacob Bleacher

"These are thought to be clear evidence of fluvial [water-based] erosion on Mars," says NASA scientist Jacob Bleacher. Lava is generally not thought to be able to create such finely crafted features. Instead, "the common image is of the big, open channels in Hawaii," he explains.

However, last year, Texas Tech University professor David Leverington says that an examination of high-resolution photographs and mineralogical data shows that the largest 'ancient riverbeds' on Mars most likely were created not by water, but by massive, fast-moving, low-viscosity lava flows:




"Many scientists realize there are issues with aqueous interpretations of these channels," he says.

"They recognize that if these systems formed by giant subsurface flows of water, there would need to have been extraordinarily high ground permeability, up to a million or more times greater than what we’d expect for the crust of the Earth, just to allow sufficient amounts of water to make it to the outflow locations and erupt to the surface."

While water exists on the planet, most of it appears to be trapped at the poles and at higher latitudes in the form of ice. And, according to Leverington, it's unlikely that there's enough water elsewhere on the planet to have created the channels.

The Martian outflow channels superficially resemble channels on Earth formed by floods from giant glacial lakes. However, unlike Earth’s water-formed channels, the large Martian canyons don't feature obvious river deposits and don’t terminate in delta-like, sediment-laden mouths. Instead, they fade into vast plains composed of volcanic basalt.

"We see abundant evidence for past eruptions of lava at the heads of these large systems, for flows along these systems and for extraordinarily large volumes of lava at the mouths of these systems," he says.

"These characteristics are very similar to what we see at volcanic channels on the moon and on Venus. There’s really no known process for the rapid eruption of large amounts of water from aquifers to form channels that are thousands of miles long. We do have evidence of this happening through past volcanic processes on the moon and Venus."



Outflow channel in the Tharsis region on Mars. Credit: NASA/JPL/University of Arizona

Leverington's work was confirmed by Bleacher studies and close examinations of fluid lava features on Earth:


To find out what kinds of features lava can produce, Bleacher, along with W. Brent Garry and Jim Zimbelman at the Smithsonian Institution in Washington, examined the 51-kilometer (~32 mile) lava flow from the 1859 eruption of Mauna Loa on the Big Island of Hawaii. Their main focus was an island nearly a kilometer long in the middle of the channel; Bleacher says this is much larger than islands typically identified within lava flows. To survey the island, the team used differential GPS, which provides location information to within about 3 to 5 centimeters (1.1 to 1.9 inches), rather than the roughly 3 to 5 meters (9.8 to 16.4 feet) that a car's GPS can offer.

"We found terraced walls on the insides of these channels, channels that go out and just disappear, channels that cut back into the main one, and vertical walls 9 meters (~29 feet) high," Bleacher says. "So, right here, in something that we know was formed only by flowing lava, we found most of the features that were considered to be diagnostic of water-carved channels on Mars."

The new results make "a strong case that fluid lava can produce channels that look very much like water-generated features," says Zimbelman. "So, we should not jump to a water-related conclusion when we see such channels on other planets, particularly in volcanic terrain such as that around the Tharsis Montes volcanoes."



Part of Athabasca Valles, draped in lava. Credit: NASA/JPL/University of Arizona

Now, the interesting thing is that some HiRISE camera (on the Mars Reconnaissance Orbiter) results offer a compromise between these two apparently opposite theories: the channels were originally carved by huge water flows on ancient Mars and later were partially filled in by lava.

Alfred McEwen Principal Investigator of the HiRISE camera, explain that the sequence of events provides a better explanation on how outflow channels could have been created:


Large outflow channels can be 10 km or more in width and may be hundreds of kilometers long. From orbital images, they appear to be huge, dry river beds, carved by very large volumes of running water.

While these features are too large to have been caused by flooding from rainfall, other explanations have been offered. One model involves large amounts of water frozen as permafrost in the soil and when a major source of local heating occurred, such as volcanic activity, there was melting and catastrophic flooding.

However, other explanations don’t involve water at all, but suggest flowing lava created these channels.



Walla Walla Vallis (A) Context image. (B) View of Walla Walla Vallis source area and passage through Wallula Crater. (C) A sketch of the river valley is shown offset to the right as a visual cue. The outflow channel emerges from a pit chain south of Wallula Crater; flow entered Wallula Crater, and eroded a channel to the north–northwest. Walla Walla Vallis, which appears to intersect Allegheny Vallis, likely pre-dated it, although concurrent flows are plausible. [Image credit A & C: THEMIS Daytime IR Valles Marineris Mosaic; B: THEMIS V10176001 (Christensen et al.).] (D) MOLA topography crossing pit chain, Wallula Crater, and Allegheny Vallis.


edit on 1-4-2012 by elevenaugust because: (no reason given)

edit on 1-4-2012 by elevenaugust because: (no reason given)




posted on Apr, 1 2012 @ 04:22 AM
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McEwen ,speaking at the 2012 Lunar and Planetary Science Conference last week, talked about Leverington hypothesis exposed above and said that he made some valid points, arguing for a form of Occam’s Razor. But he have been searching extensively with HiRISE and finding things that satisfy Leverington’s challenges:


McEwen said the abundant evidence of water carving the channels is too hard to dismiss. Several examples of outflow channels show deposits from water-based flooding that lava flow can’t explain; additionally, there is ample evidence of bedrock erosion by water on Mars.

McEwen also said crater dating areas of several outflow channels show that the channels themselves are older than the lava flow.



The Kasei Valles, a circum-Chryse outflow channel, which flowed into the Chryse Planitia. Credit: NASA/Texas Tech


“In the Athabasca Valles channels, MRO data showed that lava completely filled the channels and even overflow in places,” he said. “The lava can actually make channels look young.”

Uzboi Valles offers the best counterexample to Leverington’s hypothesis, McEwen said. “No lava fills in this highlands channel, and the channel preserves local layered alluvial deposits and shorelines. So that means we cannot explain all outflows channels from lava erosion.”

McEwen and his team suggest that large floods may have occurred in the Hesperian to early Amazonian, ending about 1 to 1.5 billion years ago, carving the channels. Then, later came the lava flows that formed Mars’ broad plains and sand dunes that we now see – which also filled in some of the outflow channels.



Athabasca Valles is entirely draped by a thin layer of lava. This requires that a fissure eruption fed a large volume of lava through the channels in geologically recent times. Most of the scene is covered by dust, but a few areas appear blue (in exaggerated color) where rocks and sand are exposed


But McEwen said the debate about these channels is good science. “Did water create these channels? That is a good question,” he said. “We shouldn’t just assume the answer is yes. But we propose water must have carved at least some of the channels, and that water outflow is the main mechanism. If you disagree with anything I’ve said, go to the HiRISE website’s “HiWish” page to suggest areas for further imaging of these features. I’ve been disappointed how few members of the science community have used this tool,” he said.


SOURCES:
2012 Lunar and Planetary Science Conference
TG Daily: Martian channels 'caused by lava, not water'
Universe Today: Did Water or Lava Carve the Outflow Channels on Mars?
NASA Elizabeth Zubritsky' paper: Lava likely made river-like channel on Mars
Science direct: High outflowchannels on Mars indicate Hesperian recharge at low latitudes and the presence of Canyon Lakes
Daily Cosmic News: Mars Channels may be Caused by Lava
NASA: Video Exploration of Details in Athabasca Valles on Mars



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