Water on Mars - Page 3

Previous 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 Next
Author Message
Serpens


Posts: xxx

Reply: 41



PostPosted: April 13, 2011 8:07 PM 

I really can’t see anything that is not completely consistent with mass wasting. The ejecta blocks at the rim are fractured and since the material cannot flow through the blocks themselves it seems most reasonable that it would follow the gravitational gradient through the cracks, Ben’s analogy of an hourglass is a good generic explanation of the effect. But the particles are too small to be termed sand and would be pretty smooth, reworked basaltic material. Given that they are absolutely dry there would not seem to be any way that they could ‘clog’ in cracks. (Yes absolutely dry. Mono hydrated magnesium sulphate equals no water whatsoever and at Tyrone we saw the higher hydrated salts lose their moisture in a one way exchange which indicates that the atmosphere is the dominant dessicant). We have seen clear evidence of subsidence in some cracks between blocks on the annulus and at Burnes Cliff we got up close and personal with the effect.
By inspection it was confirmed that (very) small particles are lofted out of Victoria to form the dark streaks and At Victoria and Santa Maria particles from the crater floor have been deposited against the downwind crater walls. . But almost all of the mass wasting material will be the result of Aeolian erosion of the fragile ejecta at the rim. Why do craters erode competitively quickly compared to the plains. No lag deposit on the more vertical surfaces and the ejecta is shocked and more fragile. But the process takes a long time and the mass wasting ‘trickle’ is an almost static creep rather than a slide, although a minor collapse/slide would occur when the accumulation reaches a certain point.

Serpens


Posts: xxx

Reply: 42



PostPosted: April 13, 2011 10:29 PM 

test

Ben


Posts: 2270

Reply: 43



PostPosted: April 14, 2011 12:25 AM 

MPJ; Your image is very interesting and varies from the normal dust covered slopes to one of broken up bedrock.
It looks to me like impact ejecta debris from what may have been a large ice-rock oject.

The vuggy surface holes being left when chunks of ice melted out of the debris pile.

I know this is off the wall but maybe the fluid that seeps out and flows downward is melt from chunks of ice still buried in debris.

I usually start out with some rash idea like this and test it with help from you guys.

Once in a while they survive the scrutiny Shocked

Serpens


Posts: xxx

Reply: 44



PostPosted: April 14, 2011 9:54 AM 

I did comment but the post went to the censorship bin?

hortonheardawho


Posts: 3465

Reply: 45



PostPosted: April 14, 2011 10:53 AM 

Serpens, I freed your comment from the spam bucket. As usual, I have no idea what in the comment triggered the spam filter. Maybe the phrase "Mono hydrated magnesium sulphate" is regarded by the spam filter as "dirty".

In the future if you comment that a comment is being held after the comment is held then I will know to look at the spam and release the comment.

Serpens


Posts: xxx

Reply: 46



PostPosted: April 14, 2011 8:09 PM 

Thank you Hortonheardawho.

Kye Goodwin. My reply 41 above attempts to address your reservations about a purely physical process.

Kye Goodwin


Posts: 1166

Reply: 47



PostPosted: April 16, 2011 2:42 PM 

Serpens, re your 46 and 41, I'm not suggesting anything that isn't physical, but I am suggesting something that isn't dead.

In your 41 it seems that you are suggesting a primarily non-aeolian explanation for Oppy's slope streaks originating from rocky outcrops, so we may have a lot in common already. One problem for a mass-wasting theory is explaining why the mass-wasting takes the form of trickles of uniformly fine material when we would expect multi-sized talus. How could gravity alone accomplish this reduction of rock to fines all in one step? I think you will be going back to an aeolian hypothesis before long because that is the only "mainstream" way to get sorted particles.

Then there is Time to consider. Associated with the trickles of material, where deposits of fines have accumulated, there is much evidence of avalanche-like disturbance on deeply laden slopes:

In the fracture a little lower-left of center there are a few (subtle) signs of avalanche, some looking fairly fresh. One appears to show both a break-away line above and a run-out lobe below. There are dozens of other examples of these in the library. I think that this activity is caused by the same phenomenon as the trickles of material across rock evident in several places along this escarpment at Erebus. This process seems to be very active in the present day, so I'm surprised that you would attribute it to mass-wasting rather than wind. I think that this material would have to be defined as sand, because of the way it appears to move by gravity across rock without being dispersed by wind. To think of this as local material that has not moved across the plains in the wind is roughly where I'm coming from these days, and far from the Mainstream. You write "But almost all of the mass wasting material will be the result of Aeolian erosion of the fragile ejecta at the rim." So it results from aeolian erosion but then stays local? But the conditions that would allow sand-scouring of the rim would be moving a much greater volume of scouring particles than eroded particles. Why wouldn't the much more numerous scouring particles dominate the post-storm deposits?

Kye Goodwin


Posts: 1166

Reply: 48



PostPosted: April 18, 2011 1:52 PM 

Looking again at the image I linked in 47, I think that I've clarified my thinking about the time element in this system. The fractures above and behind the escarpment are brimming full of sand, sand is moving down the escarpment, and sand has accumulated in piles along the base of this half-metre drop but is still moving downward in little avalanche-like disturbances on the surface of the piles. If this is a system that is recharged by aeolian events then one of those events must have just happened and they must happen frequently to create a reasonable chance that we would "catch" the system it in this fully-loaded active state. (Hikers get really nervous when they see that water is still running into the tracks of a bear. The bear must have been there just a moment earlier.) I'm thinking that it might be more reasonable to think of the flow process as something that goes on more or less continuously and that it is linked to the another really surprising observation about Erebus: There seems to have been relatively recent erosion and gravity wasting of the bright rock leaving plenty of angular rubble:

I think that the flow of material is an integral part of the system that is creating the talus, and also quite likely the escarpment itself. This is a simple idea based on what we see, but I can't think of a boring explanation for WHY it should be happening.

If this is an entirely aeolian-driven system, why here? We haven't seen any active dunes or ripples at Meridiani. If this material moves down slopes by gravity and also supposedly saltates in the wind why don't we see it forming active dunes or ripples?

Barsoomer


Posts: 344

Reply: 49



PostPosted: April 18, 2011 10:08 PM 

[link]

"Evidence for mechanical and chemical alteration of iron-nickel meteorites on Mars: Process insights for Meridiani Planum"

J. W. Ashley et al.

The paper is behind a paywall, but the abstract makes these points:

"Among our specific findings is evidence supporting (1) at least one possible episode of aqueous acidic exposure for Block Island; (2) ripple migration over portions of the meteorites; (3) a minimum of two separate episodes of wind abrasion; alternating with (4) at least one episode of coating-forming chemical alteration, most likely at subzero temperatures."

Serpens


Posts: xxx

Reply: 50



PostPosted: April 19, 2011 5:51 AM 

Barsoomer. The actual paper holds no surprises. Impact into a wet, acidic environment. Exposed by erosion and then a pretty static environment for a few billion years.

Barsoomer


Posts: 344

Reply: 51



PostPosted: April 19, 2011 11:11 AM 

The actual paper says the meteorites fell after the sulfate bedrock was already in place, during the Hesperian or Amazonian eras. So there seems to be evidence for an episode of aqueous acidic exposure after that.

mann


Posts: 161

Reply: 52



PostPosted: April 19, 2011 2:18 PM 

Every night, it rains down ice.
Ice fog forms every night, then falls from the sky.

Sometimes it could be very acidic, sometimes very (clean and pure) i read somewhere that water, if very pure, takes a temp far below 32 degrees to freeze. So depending on whats in the martian sky at the time of the fog formation, could cause a great deal of different types of ice fall.

In the morning as this ice heats up, some subliminates, and some gets sucked into the soils, rocks.
I think this might explain, lots of what we see in the images.

serpens


Posts: xxx

Reply: 53



PostPosted: April 19, 2011 5:41 PM 

Barsoomer.there was acidic groundwater for a long period after the beds formed. And there is clear evidence of variations in the groundwater table. Exhumation would have occurred after the table dried down and the inflationary cycle started.

Barsoomer


Posts: 344

Reply: 54



PostPosted: April 19, 2011 8:02 PM 

The paper presents evidence that the external dimensions of the meteorites are little altered from when they landed. (The internal cavity does not alter the exterior dimensions.)

It argues that if the meteorites had landed in a wet acidic environment, they would have eroded away completely or at least have been drastically reduced in size.

Granted the water table could have risen momentarily at some time after that.

If the meteorites landed on dry rock, there would seem to be no need for exhumation?

Serpens


Posts: xxx

Reply: 55



PostPosted: April 19, 2011 8:31 PM 

Oh for inflationary read deflationary.

Serpens


Posts: xxx

Reply: 56



PostPosted: April 22, 2011 12:15 AM 

Hi Barsoomer. Sorry I overlooked your response. If the meteorites landed on dry evaporates they would have buried and excavated craters. There is no sign of craters so the surface has deflated considerably and they must by definition have been exhumed. The Widmanstätten structures can be acid etching or aeolian sand blasting in an older, more energetic environment. But the shape and the angular and the shape and structures of the cavities indicates a differential chemical erosive process, not mechanical weathering so immersion in a water table, or with surface water seems almost certain. Lack of rust makes the atmospheric moisture idea a bit tenuous and certainly that is not occurring now.

mann


Posts: 161

Reply: 57



PostPosted: April 22, 2011 2:18 PM 

Hematite, is rust. The darker blue greys we see in bands, under the edges of rocks, on rocks, coming from the sides of craters, all this , is Martian rust.
And a sign of interaction with moisture, Martian style. Smile

Serpens


Posts: xxx

Reply: 58



PostPosted: April 23, 2011 2:25 AM 

Hi Mann. Well atmospheric moisture interaction could create a hematite coating on iron lthough this would be expected to be red hematite, not grey. But the preponderance of kieserite is a clear indication that no liquid water is available to the surface today and I don't think that there was any indication of coatings on the meteorites was there?

Barsoomer


Posts: 344

Reply: 59



PostPosted: April 23, 2011 3:28 AM 

(4) at least one episode of coating-forming chemical alteration, most likely at subzero temperatures.

Serpens


Posts: xxx

Reply: 60



PostPosted: April 23, 2011 10:36 PM 

Hi Barsoomer. The precursor of this paper was originally floated as a poster session at the 2010 LPSC. http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2208.pdf
Something to note is that given the dimensions and weight of Block Island for example, under current martian conditions it would have formed a transient crater around 11 metres diameter. Less with a denser atmosphere but still plenty of energy to bury the projectile.

Previous 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 Next


Join the conversation:















Very Happy Smile Sad Surprised
Shocked Confused Cool Laughing
Mad Razz Embarassed Crying or Very Sad
Evil or Very Mad Twisted Evil Rolling Eyes Wink
Powered by MTSmileys