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Dao Vallis: A giant river of ice on Mars

The glacier in Dao Vallis
Click for full image.

Cool image time! The photo to the right, rotated, cropped, and reduced to post here, was taken on December 26, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO). It shows an apparent glacial flow in a canyon heading downhill to the southwest, with evidence of a gully on its western wall whose collapse apparently squeezed into that glacial flow, pushing it to the east.

What makes this particular image interesting is not its uniqueness but just the opposite. Almost every high resolution picture along the length of this 750 mile long canyon, dubbed Dao Vallis, shows the same thing, an ice-filled ravine with that ice flowing like a river downhill.

The overview map below provides some spectacular context.

Overview map

The red rectangle marks the location of this photo. To get a real sense of how much like a river of ice Dao Vallis is, go to the archive of MRO’s high resolution camera and zoom into Dao Vallis. Select the arrow from the icons at the top and then click on any red box along the canyon. Every single image shows similar features, a glacial flow filling the canyon from wall to wall and flowing downhill to the west.

Dao Vallis flows from latitude 30 degrees to 40 degrees south, feeding into Hellas Basin, what I call the basement of Mars. This places it directly inside the southern mid-latitude band where scientists have found numerous features resembling glaciers. Their research has also found a large concentration of such features on the eastern border of Hellas, making this region similar to the northern area I call glacier country along the chaos terrain regions dubbed Deuteronilus, Protonilus, and Nilosyrtis.

Dao Vallis however provides something more. Unlike those chaotic regions in the north, which have many glacial features but no distinct and long channels resembling rivers, this valley provides solid evidence that many of the meandering canyons of Mars that resemble river channels to our Earthbound eyes might instead be channels carved by ice.

In fact, that is what Dao Vallis is. Though there is evidence that the initial formation of this canyon was related to volcanic activity at its source, the Dao Vallis we see today was shaped neither by a river of lava nor a river of water. Instead, what we see is a river of ice, its channel incised over eons by the slow downward flow of glacier that presently fills it.

There are no glaciers as long as this on Earth, and thus Dao Vallis offers us a look at a geological process that while superficially resembling glaciers on Earth, is still significantly alien. And though alien to us it might actually be common on Mars, and a fundamental component of its geological history.

Conscious Choice cover

Now available in hardback and paperback as well as ebook!


From the press release: In this ground-breaking new history of early America, historian Robert Zimmerman not only exposes the lie behind The New York Times 1619 Project that falsely claims slavery is central to the history of the United States, he also provides profound lessons about the nature of human societies, lessons important for Americans today as well as for all future settlers on Mars and elsewhere in space.

Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space, is a riveting page-turning story that documents how slavery slowly became pervasive in the southern British colonies of North America, colonies founded by a people and culture that not only did not allow slavery but in every way were hostile to the practice.  
Conscious Choice does more however. In telling the tragic history of the Virginia colony and the rise of slavery there, Zimmerman lays out the proper path for creating healthy societies in places like the Moon and Mars.


“Zimmerman’s ground-breaking history provides every future generation the basic framework for establishing new societies on other worlds. We would be wise to heed what he says.” —Robert Zubrin, founder of founder of the Mars Society.


All editions are available at Amazon, Barnes & Noble, and all book vendors, with the ebook priced at $5.99 before discount. All editions can also be purchased direct from the ebook publisher, ebookit, in which case you don't support the big tech companies and the author gets a bigger cut much sooner.


Autographed printed copies are also available at discount directly from me (hardback $24.95; paperback $14.95; Shipping cost for either: $5.00). Just email me at zimmerman @ nasw dot org.


  • Phill O

    If the canyon was carved out by the glacier, I would expect there to be a large debris pile at the terminus. This is assuming that the glacier is water ice as on earth.

    If the canyon was carved by water, the end of the canyon would fan out more. The look of the canyon sure resembles terrestrial counterparts.

  • Rob in Solana Beach

    Quite striking
    Upper end of the canyon seems to have a lot of
    what I think is ‘head wall’
    An area where the erosion is carrying away the base of strata
    with a harder or more resistant cap.

    In New Mexico this is often hard spreadout lava or other volcanics
    over softer sandstone or tuffa.
    I presume that is what we are seeing here.

    Mechanically is this Martian flowing ice similar to our glaciers ??
    How similar ??

  • Phill O: This glacier is almost certainly water ice.

    And there might not be a moraine at the end because the water ice could be sublimating slowly along the length of the glacier so that it simply fades out

  • Phill O

    The material carved out had to go somewhere. I am assuming the base material is not ice but rock of some sort.

    Introductory chemistry deals with mass balance in equations. The principle can be applied to many different studies. Ever consider where the corals get the Ca and CO3. If the Carbonate came from CO2 in the atmosphere, where did the Ca ion come from and where is the counter ion for it?

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