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View Full Version : Ice wedges on recent Curiosity picture?



JohnD
2014-May-16, 12:28 PM
Today's APOD is a Curiosity picture of what has been dubbed "Mt.Remarkable", a hummock on the slopes of Mt.Sharpe( Aeolis Mons ):
http://apod.nasa.gov/apod/ap140507.html

Two prominent features are fissures in the rock layer underlying the hummock, that appear to be parallel and to project towards either side of the vehicle. Tey have raised edges. Could this be evidence that now, or in the past there was enough water there for them to have been raised by the same mechanism as the raised edges of ice polygons?
See: http://apod.nasa.gov/apod/ap140507.html

To identify what I mean see my annotated version of the pic:

19532

Trebuchet
2014-May-16, 09:04 PM
That whole hummock looks like some sort of frost heave. Or pingo (http://en.wikipedia.org/wiki/Pingo).

dgavin
2014-May-19, 01:43 PM
Sorry took so long for me to chime in on this one. But I'm going to side with Trebuchet on this one. It looks like an escarpment that was pushed up by permafrost formation, and then shaped by wind erosion and sublimation of the ice.

JohnD
2014-May-24, 03:20 PM
An apology from me for coming back so slowly.

DG, do I understand the terminology correctly? An escarpment is a large cliff or steep slope, so that makes me think you are not looking at what I'm looking at.
I'm referring to two cracks in the rock layer beneath the hummock. They are straight and parallel, and I marked them on the picture I enclosed above.
In that pic, their structure is obscured by the markings and the copied picture isn't great, so they are better seen on the original APOD.
Each crack appears to have a raised edge on either side, with a slightly lower fissure between the edges.

Their appearance made an Asterisk poster describe them as like 'game trails', worn lines with slightly raised edges. I recognise what he menas but we both know thtat's not proper geological terminiology. I'm sure you would have a better idea, but "escarpment"?

John

PS If you can, please contribute first hand, on the Asterisk? http://asterisk.apod.com/viewtopic.php?f=9&t=33369&start=25 J.

Squink
2014-May-24, 04:31 PM
That raised edge does look suspicious. With everything else on mars scoured by wind, you would not expect rocks to pile up round the edges of a crack, you'd expect them to get blown in and fill the crack. Opportunity's photographed plenty of patterened ground that looks like tundra polygons, so ice wedges on a frost heave like object is certainly possible here.

dgavin
2014-May-24, 09:16 PM
Well I was referring to the entire hill and it's layered erosion pattern as an escarpment, bad choice of word.

It's very similar to the layered appearance that you might see on some duel mesa's.

As to the two fissures, what is odd about them, once you account for perspective, is their width never varies like you'd expect from a melt channel or water. However there is a process that's is very similar where heavy rocks are moved by frost and melting frost and form very similar channels to those two. APOD even had a article about these moving rock in death valley: http://apod.nasa.gov/apod/ap020410.html Granted the DV process is rain and slick mud, but melting frost is even slicker, and would also form local areas of surface mud as well.

My best guess here is there is a similar process at work here on this hill. With this hill it's also assisted by gravity. Because this is sandstone and rather soft, and not granite, it looks like there is even a rubble pile left for the rock that formed the right channel. It likely broke up just from going over that small edge of the lower layer. As Squink mentioned there is also faint hints of the tundra like polygons, especially above those channels, that also supports there is some sort of frost based erosion or activity going on here.

dgavin
2014-May-24, 09:44 PM
Oh, just for the record I am not a profession geologist. I'm more of a self taught amateur volcanologist. I tend to look at known processes, and see how they fit something unknown like here. But in this case I think a frost based assisted sandstone rock migration is the best explanation.

JohnD
2014-May-25, 08:59 PM
Thanks, dg! You may not be a pro-geologist, but you give the best impression of one around here!
JOhn