Slumps caused by thawing ground on Mars and Earth

The Planetary Geomorphology Working Group of the International Association of Geomorphologists has a rather nice article online comparing the landforms caused by slumping during thawing of the ground with similar features that have been seen on Mars. The article is available here:

http://www.psi.edu/pgwg/images/dec09image.html

On Earth, thaw slumps occur in permafrost areas like Alaska. This is an oblique aerial image of these features, taken from the site above:

The Natural Resources Canada has quite a nice (although I suspect somewhat old) cartoon to illustrate how these landslides work:


Essentially, the thaw of permafrost (ground that is usually frozen) allows the weak materials to fail and flow. This typically exposes a new face of frozen ground that, if the temperatures are high enough again, thaws and flows. Thus, over time, the back scarp of the landslide moves back into the hill - i.e. it retrogresses. This is what one looks like in a vertical view on Google Earth:


The features observed (by satellite obviously) on Mars have much the same morphology as retrogressive thaw slides on Earth:


The arrowed features are interpreted as pingos, which are only found in permafrost areas on Earth. Thus, the arcuate features upslope of the pingos are interpreted as the arcuate backscarp of the landslides. The existence of these features of course implies that at some point the ground thawed and there was liquid water present at some point in the past.

Intriguing long runout landslide in Death Valley

Thanks to reader Gregory T. Farrand who brought my attention to a very intriguing feature located in Death Valley in California. This is a feature that was first identified and mapped as a long runout landslide by Michael W. Hart. Greg and Michael, together with Brian Olson and Phil Shaller, are currently studying this slide, which they are terming the "Eureka Valley Landslide". The source rocks for the landslide are Cambrian marine sediments, mostly dolomite (dolostone). The slide is partially buried by Holocene alluvial fan deposits.

The landslide shows up really well on Google Earth. First, a vertical view with north almost at the top of the image:

Next an oblique view looking eastward:


Michael and Gregory are writing a paper on the slide, which will be very interesting indeed when it comes out. In the meantime, a few observations:

• Identifying this is a great spot. Finding features like this is far from easy;
• In fact, our understanding of landslides in very arid environments is rather poor, so such observations are definitely interesting;
• The slide has appeared to have moved in such a way that it has formed a narrow tongue-like deposit. Such deposits are rare but certainly not unknown. Incidentally, the runout distance across the fan is about 1.7 km by my reckoning, although from the source area it may be twice this;
  
• There is that interesting feature NNW of the toe of the slide deposit. I wonder if this is just a result of the landslide preventing the debris fan channels from actively depositing in this area, perhaps allowing wind erosion, or is it landslide material that has perhaps eroded and then been deposited;
• The type of landslide of which this most reminded me is those seen in imagery from Mars. The image below was collected by the NASA Mars Global Surveyor Mars Orbitor Camera in 2004. The size of the landslide is very similar to that in Death Valley. I guess in some ways the conditions are similar (i.e. very arid), which is interesting in itself.

I hope that Gregory and Michael will let me know when the paper is published - I'll note on the blog when this is the case.

Mars Odyssey image of landslide

Although landslides on other planets have not been a major theme of this blog, there is an interesting area of science that focuses on these intriguing phenomena. Of course a great deal of this research is quite difficult given our poor knowledge of the conditions on and in the slopes when they occur. The availability of increasingly high resolution imagery is however helping in the understanding of these features. There is a hope that we might understand terrestrial landslides better if we can see how slides operate in other environments, although to date I must admit that I am unconvinced that this has really happened.

Yesterday NASA released the image below, which shows an area of Mars with a quite interesting landslide. It was collected by Mars Odyssey THEMIS (acknowledgement to NASA/JPL/Arizona State University):

Fig 1: Mars Odyssey THEMIS (acknowledgement to NASA/JPL/Arizona State University) image showing a landslide on Mars.

At first the landslide might not be obvious, but look closely on the centre right side - it is clear that the slide is a ridge failure with a reasonably long run-out. I have zoomed into the image to show the landslide below (Fig. 2):

Fig 2: Enlargement of Mars Odyssey THEMIS (acknowledgement to NASA/JPL/Arizona State University) image showing a landslide on Mars.

I have processed and annotated the image (Fig. 3) to highlight some key features. I think (though this is unconfirmed) that the landslide is about 2 km wide and 6 km long. Note that the presumably more resistant material that forms the ridge appears to be intact on the landslide body. The landslide has two smaller failures on its flank. Finally, it also appears to have a few small craters on it, which presumably means that it is not too recent (UPDATE: thanks to Dr Mauri McSaveney for pointing out that not too recent in this case probably means 2-3 billion years old).

Fig 3: Annotated enlargement of the Mars Odyssey THEMIS (acknowledgement to NASA/JPL/Arizona State University) image showing a landslide on Mars (Click on the image for a better view in a new window).

Similar landslides do occur on Earth. For example, Fig. 4 shows the Frank landslide, which I have described before. Note that in the Mars case the slipped block has only partially broken up, whilst at Frank it disintegrated completely to form a rapid flow. I am sure that there are better examples from Earth, but I cannot think of them at the moment. Can anyone come up with one?

Fig 4: Natural Resources Canada photograph of the Frank landslide, Turtle Mountain, Alberta, Canada.