Dao Vallis: A giant river of ice on Mars
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.
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.
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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.
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
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 ??
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?
These are great, Robert! I really appreciate all the effort you’ve put into all these postings intimately exploring and introducing Mars to us over the years.
While here, I should mention, FYI, that even though the uahirise.org page for this HiRISE pic that you pointed to talks about it being “near Dao Vallis”, still the Planetary Nomenclature Gazetteer map for this region (select MC-29: Eridania) separately names this apparent long tributary of Dao Vallis as “Niger Vallis.” Not sure how long it has borne that name, mind you…
No need to modify the foregoing posting proper, as far as I’m concerned. Which, once again, is great!
Ah! According to the MC-29 regional map, the last nomenclature change shown on it was dated June 1, 2018.