Back At Larry's Lookout Options

[Phil Stooke]

Regarding that weird little slope failure thingy on the south side of Larry's lookout/Watchtower: During the Viking 1 mission there were two events like that, not seen as clearly, but in hindsight very similar indeed to this. Both of them happened during the mission so there were before and after shots. Both on similar steep drift slopes and the best seen one clearly showing a slipped surface layer like this. I don't have my stuff with me as I write this, but it would be easy to track down, it was widely reported.

Phil

[lyford]

Tonight at her talk at JPL (of which I only caught the tail end on NASA TV...curse you inaccurate satellite listings!), Joy Crisp mentioned the slip feature and seemed to imply that the team thinks that ratting earlier caused the disturbance. She even used the word "Duh!" to describe the reaction after they first noticed it.

[CosmicRocker]

Yeah. I missed her lecture, too. Had to work late. It will be repeated on Friday, but it is not clear whether that will be broadcasted or webcasted again.

The sediment in this location is piled up quite steeply and is probablly very close to, if not greater than the expected angle of repose, which is about 35 degrees for normal sediments on earth. I'm not certain if that angle would be different on Mars, but this slope is clearly very steep. http://quest.arc.nasa.gov/mars/ask/soil/Di...Mars_soils_.txt
If it is an over-steepened slope, somewhat stabilized by weak cementation of the grains by precipitated salts or a slight amount of moisture, the slump was probably just waiting to happen.

We may have simply been lucky to have noticed it. But, as Edward has pointed out, we really haven't seen anything that looks like old slumps/slides. As simple as it is, this really is an interesting feature.

The fact that it is visible in images taken quite a few sols ago from a distance makes it difficult to imagine it could have been caused by Sprit's activity/ratting. (Tman spotted it as far back as the sol 438 navcams.) I can imagine it could have been caused by a gust of wind, a loud sound, or a slight seismic vibration.

On Sol 489 a series of pancams were taken of this area. Here is a portion of it that shows the upper part of the slope failure.

Attached thumbnail(s)

 

[jvandriel]

A panoramic view of the top of Larry's Lookout through the eye of the Pancam and L7 filter of Spirit.
Photo's taken on Sol 488.

jvandriel

Attached thumbnail(s)

 

[john_s]

The fact that it is visible in images taken quite a few sols ago from a distance makes it difficult to imagine it could have been caused by Sprit's activity/ratting.  (Tman spotted it as far back as the sol 438 navcams.)  I can imagine it could have been caused by a gust of wind, a loud sound, or a slight seismic vibration.

As I suggested earlier, the slump could have been caused by the ratting on the other side of Larry's Lookout, which was done on sol 416, before there were any images of this slope.

[Phil Stooke]

I don't really think the RAT caused the slump feature. The ratting is a fairly gentle process (and was it only brushing anyway?... can't recall now, but they are limiting the RAT use as it wears out) - and it was quite a distance away from this spot, not right on top of it. And the Viking examples which I mentioned above suggest to me that it's not really so unusual. (see page 38, "The Martian Landscape" , NASA SP-425, for the first and best-seen Viking example).

Phil

[JES]

....On Sol 489 a series of pancams were taken of this area.  Here is a portion of it that shows the upper part of the slope failure.

Can anyone comment on how the surface materials in these drifts are bonded into plates?

[CosmicRocker]

Well, this new hazcam shot really turns my "slump was probably just waiting to happen" hypothesis upside down. If the dust on that slope was so sensitive to vibrations, I suspect Spirit wouldn't have gotten this close without disturbing it further.

http://qt.exploratorium.edu/mars/spirit/fo...EEP1214L0M1.JPG

[mhoward]

Some color (sorry, I don't have time to stitch them together):

[john_s]

I don't really think the RAT caused the slump feature.  The ratting is a fairly gentle process (and was it only brushing anyway?... can't recall now, but they are limiting the RAT use as it wears out) - and it was quite a distance away from this spot, not right on top of it.  And the Viking examples which I mentioned above suggest to me that it's not really so unusual.  (see page 38, "The Martian Landscape" , NASA SP-425, for the first and best-seen Viking example).

Phil

I admit it seems unlikely that ratting the other side of the outcrop would cause this slump (they did grind, not just brush, on Larry's Lookout -see Sol 419 Hazcam image). And I remember the Viking 1 slumps, at least one of which was far enough from the lander that the lander can't reasonably have caused it. I'm just struck by how this looks *so* fresh, and how I can't recall seeing any examples of more degraded slumps previously. It is striking that Spirit's wheels digging into the slope have not precipitated further slumping, though maybe the slope is more susceptible to failure by a push from behind than by digging from below.

[Nix]

Here's a pancam mosaic of four of the images posted by Mhoward. I'm waiting for the other frames with missing data to update, hopefully.
Very intriguing this feature.
Cheers
Nico
awalkonmars new Spirit sol 489

[Bill Harris]

Well, this new hazcam shot really turns my "slump was probably just waiting to happen" hypothesis upside down.  If the dust on that slope was so sensitive to vibrations, I suspect Spirit wouldn't have gotten this close without disturbing it further.

http://qt.exploratorium.edu/mars/spirit/fo...EEP1214L0M1.JPG

The Crusty unit does appear to be thicker and more coherent than the adjacent areas. After detailed MI, she should give this unit a poke and see what it does. It is clearly aeolian, and my guess is that it contains a hygroscopic salt that is cemented with the humour of atmosphaeric moysture...

--Bill

[Bob Shaw]

I agree regarding the slumped material. The platy layers look like a caliche style of cemented deposit, and perhaps the hygroscopic salt hypothesis is the right one. This sort of deposit has been seen right back to Viking 1, though the salt-rich soil is a new bit of the jigsaw!

[Jeff7]

I agree regarding the slumped material. The platy layers look like a caliche style of cemented deposit, and perhaps the hygroscopic salt hypothesis is the right one.  This sort of deposit has been seen right back to Viking 1, though the salt-rich soil is a new bit of the jigsaw!

Well, given that they've gotten right up close to the slump, I imagine that a little brushing with the RAT might be in order. That should be more than adequate to have a look at all the layers, as well as maybe trigger additional landslides.

[Tman]

How about season, alternatively sun dont reached this slope over wintertime?! And now in the actual season the slope get warmness and this has activated "anything" or caused layers in the sandy soil at least?!