Burns cliff

This is a fascinating area and it's a shame Oppy is having to turn around and make a backtrack exit. I'd like to see more here but they're erring on the side of caution.

I have no idea what is happening in the area fo thisnew image. I hope we got a close look at that gray material!

To the heatshield and then Victoria...

--Bill

Hi horton

Awesome images! If there was an ion for applause I would use it

At this stage my provisional interepretation is that these gullies are not the result of water. A water carved gully would have a little fan of sediment at the foot. There is also an absence of any of the channel features within the gully you might expect to see. You can see these features in any gully in any roadside roadside embankment.

As for gullies or gully-like forms eroded by wind, these can be found at all scales. For example, many ventifacts consist of grooves eroded into solid rock at a scale of 1-10 cm across See [link] , especially figures 20 and 21.

At a larger scale, hollows between dunes can form parallel to wind direction. See http://www.fao.org/documents/show_cdr.asp?url_file=/docrep/T1765E/t1765e0c.htm

A passing reference to wind grooves and gullies in the dust bowl [link]

Features of this scale (~10 m) on Mars are described at http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1643.pdf

At a larger scale wind grooves can be 10-100's of m across, for example these in a satellite image from Chile http://www.geo.cornell.edu/geology/eos/atmos2/puripicar-ign.gif

Similar sale Martian yardangs can be seen at [link]

I suspect that these "gullies" at Endurance are enlargements on underlying joints that formed as a result of the crater forming process.

Cheers

Jon

I really think they should try to get as close as possible to the unconformity. Perhaps they could inch forward and carefully test the surface as they go. The nearby surface appears to be the stone mosaic that Oppy has had no trouble on so far. If the traction starts to become treacherous, then back out. I think the strata contact is of great importance, and they may not be able to find another exposure like it again. Victoria probably won't be any easier.

Arguably evidence does show that some quantity of water dried up at the bottom of Endurance and left behind a salty crust. The mechanism for water moving through Endurance is likely seepage, in and out of the side-walls, not a flow into the crater. The softness of the rock examined suggests high permeability. If seepage into the crater occurred, water may have trickled down a few cm then infiltrated back into the wall (and may reappear at the crater bottom along some flow path). If, as suspected, salts were left behind at the bottom of Endurance, I’m betting water got there by way of seepage from the soft wall rock, which gets around the necessity of flow structures. This could have occurred under a blanket of snow/frost, obviously which is long gone.

Hi ArizonaSt

Some sort of moisture moevment I think is neccessary to form the surface crusts. However whether this is due to seepage from below or the sides or simply through moisture absorbed from the atmosphere remains to be seen. We know that the atmosphere is near saturation, and that fogs and perhaps frosts are likely. In the atacama desert for example there are very nice surface crusts that form simply from aborption from the atmosphere. The top 10 cm - 1 m of the anhydrite duricrust gets converted to gypsum as a result. This hypothesis is consitent with the physical conditions at the site and the geomorphology.

None of this requires flow of water from saturated ground, which is what a seep is. The ground is never saturated as the moisture is never more than a thin, localised film.

Cheers

Jon

There is good evidence that liquid water flowed on the surface at Meridiani for short distances, the flow was likely a briny slush at the margins of the flat rocks under the cover of frost/ice. Some small spots of soil were wetted enough to compact and collapse to form depressions.

That flow occurred is clear. How? Likely a heavy frost was melted to liquid – at first on top of the larger flat south facing rocks. This liquid collected around the foot of the rocks likely under a cover of ice that remained there at the rocks edge and covering the surrounding ground. Somehow enough collected to flow a short distance before the ice covering the ground was removed. The flow collected and then overtopped small depressions covering “berries” and other hematite lag with a mud.

Inside Endurance crater there is evidence that water also flowed a short distance. The mechanism that produced the liquid is the same – sun warmed rocks – but inside the crater conditions differs on the north facing, south facing, steep, gentle, and flat surface areas. More or less frost would collect in different areas, areas receive differing angles of solar radiation, wind differences as well as small scale atmosphere temperature differences all provide micro climates that produce varying amounts of melt from warmed rocks. On the steep north west facing Burns cliff area some liquid was likely generated on the exposed rock and somehow a small amount “flowed” down a short distance likely under the cover of frost/ice.

Jon, thanks for mentioning the analogy to the Atacama pedogenic salts, very possible.

There is likley liquid water on the in Endurance, too many "flow" features have been seen that can't be discounted.

I recall that the water is near the triple point at the temperature/pressure conditoions on Mars, and the addition of sulfate salts can depree the freezing point, so flowable water is not unlikely.

One puzzler for me is the fine "grey" material in the joints on Burns Cliff. This material seems to be very flat and very smooth in the fractures. Make that "very,very" smooth. My problem is that these fractures are on the face of the cliff, at, what,30-40 degrees and this material could have not settled that smoothly. And there is the (apparent) "painted-on" appearance of the material. I hope (wish?) that we have closer views of that.
I recall seeing, when Oppy was almost stuck near Wopmay, tread marks in a material that impressed me as looking a bit shiny, like a plastic clay. I'll need to go look again, I'm thinking they were front hazcam images.

--Bill

Can't risk a last post or two before going!

There are many problems with sayings that the dark material (probably fine sand-sized haematite) is water laid. There is no sign of water erosion (small sinuous sub channels within the larger gullies, for example) or water deposition (small fans on sediment, levee banks). The gullies don't form a larger intergrated drainage net. There is no obvious source for water either, it can't be runoff, and there are no obvious discharge points.

Some of the haematite sand is smooth, some is rippled. Given the slope close on 30 degrees) smooth to rippled surfaces are consistent with aeolian deposition.

Cheers

Jon

PS, those Oppy hazcam images from post 128:

1F152163428EFF37ELP1214L0M1.JPG

1F152161628EFF37DXP1220L0M1.JPG

Oppy, sol 270, with "clayey" soil

--Bill

Bill/Jon, I tend to agree with the plasic clay analogy, the material appears to have some cohesiveness to it. Perhaps decomposed hematite. Flow features? yes, short duration though, discharge (seepage) and quick infiltration would explain the features we see. Small quantity of flow, not enough for development of drainage net or fan. Perhaps melting ice on face of cliff was source of water???

If the atmosphere is near saturation, then it's for short periods only. The atmospheric pressure and temperature are extremely variable.

I find it intriguing that the evidence of seepage or water of some description is found in the lower parts of the crater. There is very little encrustation further up. Does that imply seepage in the recent past (the ground salt/ice mixture being at a greater depth), or could this be due to some sort of localised atmospheric effect within the crater itself?

More Muddy Flows:

Hey Horton, would you be able to come up with a colour stereo pair for the photo MicroKid posted in reply 102? They're pancam images taken on Sol 114.

Thanks,
Aldo.

L4..L7/R1 of reply 102 area:

Only R1 available for right image.

No "window adjustment" on the 3D -- it would cut off some of the interesting stuff in the lower left corner.

( BTW, the CDs are in the hands of the Posties now.)

Forgot to mention color by horticolor.

(R,G,B)=(L4,0.79(L5),0.84(L6))

I seriously wanted to change the L6 factor, but that's what the numbers said, so I went with it.

( But remember, elephants are color blind.)

John, in re 129 you say:

"There is no sign of water erosion (small sinuous sub channels within the larger gullies, for example) or water deposition (small fans on sediment, levee banks). The gullies don't form a larger intergrated drainage net. There is no obvious source for water either, it can't be runoff, and there are no obvious discharge points."

I think you are drawing too close an analogy from earth. The water erosion features you sugest, channels, gullies, fans, and levee banks, are indicative of much large scale flow, presumably from rainfall. It takes tens of gallons of flow or more to form these features. What we are sugesting is flow on a much smaller scale than that, and the source is frost. We are talking about amounts of water similar to spilling a coffee cup or water bottle. The features you mention would not be formed by such small flow. On earth, even in the driest environments, what little flow you get is generally from rainfall percipitation, and even if you get only a few tenths of an inch, you can get accumulations of more than a hundred gallons per acre, which quickly pools and then drains and creates typical water features we see even in the driest of environments, with the exeception of extremes like atacama.

What we actually do see are very, very small scale events, with small scale features. I propose that what we are seeing in Horton's and MicroKid's posts 133 and 135 in fact are very small scale levee banks, on a mm scale, from only very small flow.

Also, you say there is no obvious source of the water, but what has been sugested is frost, which is an obvious source, or maybe groundwater, which admitadly there is no evidence for, except for the features we are seeing. We know there are clouds, we know there is atmospheric moisture, to spite the fact that the atmosphere is very very thin, so we should not be surprised to see frost. The fact that we haven't seen frost yet is a bit of a mystery, I would expect to see a little bit, not as much as we saw from viking, but there all indications sugest we should see some small frost accumulation.

There's another neat feature in these images that I hadn't noticed before. Looke at the edge of the pavers. They look all chewed up. That's not the kind of weathering that I would expect to be the result of wind abrasion. It looks more like a corrosion process. Perhaps we're seeing the micro effects of freeze thaw, or could this be the result of some chemical rather than physical weathering process?

How long ago. months, years,??

2x3 R1 vertical panorama of cliff:

Warning:3.9 MB link:

I sat on this, waiting for some other filters to make a color pan -- but none have been forthcoming.

I posted a 90% quality JPG of this panorama simply because the 7.1 MB PNG file is simply too big: too big for you, too big for me.

I am having more and more problems with my web server now that I am posting mostly PNG files.

I think I will have to step back to JPGs for now.

I did a companion L7 image -- but it too is too big.

Too big.