[X] My Assistant

[Harkeppler]

Another example of holes and possibly caverns can be seen in MGS photo R0701365

http://www.msss.com/moc_gallery/r03_r09/fu...07/R0701365.gif

There are a lot of sinks along some ridges along the northwest flank of Arsia Mons.

The most prominent feature is given as attachment, but there are several more.

Besides this, in the upper part of the original frame there are some black

streaks at another ridge which may indicate water or ice rich sediments

common to the Arsia Mons terrain.

So it could be said that the area is a collaps region loosing its icy layers and the caves may be sinkholes.

The center of the original image is at 238.11°E and 5.40°S.

Interestingly, dark downward running streaks and gullies are slso found in the higher layers of the Tharsis vulcanos and even across the caldera of Ceraunius Tholus.

Due to the lower pressure at high altitude the streaks should be shorter than those in valleys.

Harkeppler

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[CosmicRocker]

Those are interesting images. I'd like to see a HiRise image of this region. I'm not sure I would describe it as a "complex" cave system, but it did look like a lava tube that has some sinks being buried by sand/dust.

[mchan]

Question from a non-geologist. Why would a lava tube (if that is what it is) follow a ridge?

[djellison]

Maybe the tube makes the ridge, the lava drains from the middle while the outside cools solid making the tube - and then sand etc form over the top of it to make a ridge? Then the ceiling of the tube collapses. Pure guesswork.

Doug

[Harkeppler]

Interestingly, the holes are on the highest level of the landscape at the side of the rigde and there are several bright sediment layers at their walls.

I do not think it is a dune system or a a lava tunnel. It looks more like a collapsed region which has lost ground ice which seems to be presents in all Tharsis Montes. If one browse through the MGS picture collection showing the flanks of these mountains (especially Arsia Mons), there are a lot of ridges showing black streaks and gullies similar to them indicating water or brine flows.

Larges amounts of ice inside the mountains would form a lot of mud in case of eruptions, and I think the aureole around Olympus Mons and that around the Northeast of Arsia Mons are nothing else.

At the Arsia Mons I think that some of the large "lava tunnel" are water drainage and collapse features and not empty lava tubes (they are very large, probably too large to be stable when hollow).

But this is only an idea.

Gullies in the summit caldera (!) of Ceraunius Tholus can be seen here:

http://www.msss.com/moc_gallery/r03_r09/fu...07/R0701361.gif

Gullies at tha flank of Pavonis Mons:

http://www.msss.com/moc_gallery/s05_s10/fu...06/S0601434.gif

Gullies at the flank of Ascraeus Mons:

http://www.msss.com/moc_gallery/s05_s10/fu...07/S0700545.gif

Dark gullies at the Arsia Mons flank were shown in the thread before.

So, water seems to be present an the Tharsis Montes.

Some years ago there was an interesting theory that the Tharsis Planitia was situated billions of years before at the pole due to a slow wandering of the whole planetary crust (one large continent drift) against the core and Olympus Mons and the others penetrated the polar cap.

Harkeppler

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[Gray]

The depressions along the top of the ridge are quite fascinating, and they do look different from the ones on the flanks of Arisia Mons. Has anyone tried to estimate their depth?

[marsbug]

Um.. I hate to be the dense one yet again but am I looking at gullies or dark streaks here? I may just have missed something but I see dark streaks running down the slopes on a lot of these pictures, rather than gullies with heads incised chanels and debris aprons at the bottom. Sorry but could someone clarify this for me or just point out what we're looking at?

[Harkeppler]

To explain the feature:

The dark gullies (indicated yet for clarity) give a hint that water (or brine) is draining from the walls of the ridges at the flanks several Mars vulcanos. This gives the idea, that the lava tunnels in that area may be collapse structures in ice rich regions when volcanic heat melted the ice and produced a lot of mud. Some of the lava tunnels are mud streams or collapsed and drained areas.

So, the Tharsis landscape seems to be water rich and a cave system in water rich sediments is of more biological interest than a dry magmatic one.
The gullies at the Arsia Mons flank are in the ultimate vicinty of the multiple-hole-cave-complex mentioned above.

In other words: If I have to look for life on Mars I would look in these caves at the Arsia Mons flanks.

Harkeppler

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[djellison]

So, the Tharsis landscape seems to be water rich

From a few streaks, you're making an entire region 'water rich'.

That's a leap of faith.

Doug

[CosmicRocker]

... Why would a lava tube (if that is what it is) follow a ridge?

The context image on this page shows what appears to me to be a large, meandering lava channel. I'm not an expert on these things, but it looks like inverted topography. Apparently the material around the channel was softer, so it eroded away leaving the filled channel as a ridge.

Like marsbug, I see lots of dark streaks, but no gullies. Calling for a water explanation seems quite a stretch.

[babakm]

The dark streaks a) start at different levels and b ) leave no long-term flow signatures on the surface. I'm sticking to the dust streak explanation.

[MarsIsImportant]

The very dark and faily short streaks in this image maybe shadows instead of water streaks...just a trick of the light.



I suppose some of the others could be dust streaks of some sort; yet some seem more like water streaks to me. It's hard to be sure.

[Harkeppler]

From a few streaks, you're making an entire region 'water rich'.

That's a leap of faith.

Doug

It may be.

I think it is interesting that at 5.5 km hight these gullies can be seen at the summit of Ceraunius Tholus. I am sure that there must be an ambient temperature and an sufficent pressure to allow the spilling of a fluid. So, I would not wonder that there are no such gullies at higher levels, so at the summits of the Tharsis main vulcanos.

Maybe it is possible to calculate the lenght of such gullies in dependence of the temperature, pressure and inclination of the walls.

Harkeppler

[Harkeppler]

The context image on this page shows what appears to me to be a large, meandering lava channel. I'm not an expert on these things, but it looks like inverted topography. Apparently the material around the channel was softer, so it eroded away leaving the filled channel as a ridge.

Like marsbug, I see lots of dark streaks, but no gullies. Calling for a water explanation seems quite a stretch.

Yes, it looks like a channel. But the holes are at the upper level of the landscape and persisted although the tunnel collapsed and got broader then before. All in all it looks strange.

[mcaplinger]

I think it is interesting that at 5.5 km hight these gullies can be seen at the summit of Ceraunius Tholus.

These are not the features usually called gullies; the conventional view is that they are dry dust avalanches and do not involve a liquid. See, for example, Rob Sullivan's abstract http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1911.pdf