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Regarding the "Basal Surge" hypothesis, What really did create the Meridiani layered deposits?
Guest_Richard Trigaux_*
post Mar 19 2006, 06:44 PM
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QUOTE (Steve @ Mar 19 2006, 02:19 PM) *
Richard:

Thanks for the nice qualitative description of your model -- surely more detailed than my crude "fire extinguisher." I guess I still see a few questions.

The most crucial, perhaps, involves the thermal energy involved to convert sufficent quantites of water to steam that will produce "rainfall and mudfall of a magnitude unknown on earth" over "half of the planet or more." Since we're probably discussing rare catastrophic phenomena, we can allow for very large numbers, but a rough estimate of the amount of energy involved (and its source) would be helpful.

Almost as important is to estimate the amount of water involved and postulate likely local sources for such large quantities of water.


The energy source is simple: volcanic eruption. On Mars, the overal volcanic energy is much lower than on Earth (perhaps 5% if we assume the same uranium percentage, and no phase transition in the core). But, for whatever reason, the volcanoes are much less numerous (about 16 great volcanoes, against thousand on Earth) and eruptions are much more spaced in time (by periods of tens of millions years). So when an eruption occurs, it is understandable that it is much larger in size and energy, as testify the hugeness of calderas in those volcanoes. This is for the energy source.

And where the water comes from? Understand that before the eruption, this water is mixed with the magma (with lava) a thing which is made possible thanks to the high pressure underground. So it is understandable that when such a mixture arrives in free air, it boils very violently. On Earth, in eruptions of this type, like the Pinatubo, the mixtures boils in the volcano chimney, gets foamy, and with the loss of pressure it cools, and the foam turns to a mixture of steam and dust, which erupts to the surface at supersonic speed through a trumpet-shaped pipe of sometimes hundred of metres in diametre.

And why water would be mixed with lava? On Earth, this happens in subduction zones, when submarine alluvions are dragged inside the crust and mantle. As they are soaked with water, this water acts as a melting agent (the lava-water mixture melts more easily than the surrounding rocks). Being lighter than the surrounding rocks, the mixture rises to the surface into an explosive volcano.

But how water would mix with lava on Mars? Not by subduction (there is none). Two only possible explanations:
-the water is already into the mantle. And it concentrates into magma chambers, as they naturally rise up and maturate.
-the water comes from a huge and deep watertable. (In this case the eruption process is different: it is a phreatomagmatic eruption, where the heat of the lava evaporates vast quantities of water and creates huge explosions). Such watertables seem also involved into huge water surges like in Valles Marineris and around. What drives all this is still largely unknown, some invoke a mixture of water and carbon dioxyd which would boil suddenly and trigger huge floods.
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CosmicRocker
post Mar 20 2006, 06:27 AM
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QUOTE (nprev @ Mar 17 2006, 06:38 PM) *
I have to ask where the blueberries fit into this debate? Concretions would seem to require a substantial period of groundwater saturation, if not actual surface pools, to form...and Meridiani is full of these things, apparently across different geological units based on the observations from Endurance and other exposed vertical sections. To me, this argues for multiple aqueous events rather than one... huh.gif

QUOTE (MichaelT @ Mar 18 2006, 02:50 AM) *
Thanks for the highly interesting overview Bruce! Like nprev I'd also be interested in your opinion on how the hematite spherules fit into the whole story. As far as I remember they required water to be involved in their formation, didn't they? So how could they have formed without it?

Michael

The blueberries are definitely an important part of this debate. From what we know of them, they do nicely fit with theories involving a concretionary origin, but I think some may be suggesting that such spherical objects might also be volcanic lapilli or impact melt spherules. I suppose you might also form them as concretions in a pile of acidic, steam-saturated basal surge deposits.

Regarding the general discussion in here, it's been fascinating reading all of the different hypotheses regarding the Meridiani rocks. I mean, really fascinating. It seems to me that in the absence of many of the key observations that one would need to come to some reasoned conclusions, individual imaginations allow for quite a number of different scenarios. Bruce started this off with a summary of the inital four, and several variations have been added. I think I could add a couple more based on things that are not certain about this period of time in Martian geologic history.

It seems to me that as scientists, we need to focus on the few observations that we have precisely framed in their observed physical context, and then look for the simplest models that would explain them. That's not a simple task, considering the important advancements that have recently been achieved in remote observation technology. I thought I was going to come to a conclusion here, but the more I think about it, I think I'll step back and wait for the major contendors to duke it out in the boxing ring. I still like the water hypothesis, though. wink.gif


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Guest_paulanderson_*
post Mar 20 2006, 07:17 AM
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QUOTE (CosmicRocker @ Mar 19 2006, 10:27 PM) *
The blueberries are definitely an important part of this debate. From what we know of them, they do nicely fit with theories involving a concretionary origin, but I think some may be suggesting that such spherical objects might also be volcanic lapilli or impact melt spherules. I suppose you might also form them as concretions in a pile of acidic, steam-saturated basal surge deposits.

One thing I've read is that the double and triplet berries seen early on (where they are "fused together" as such) are evidence of water origins, since that process requires liquid water, and couldn't happen with airfall deposits, impacts, etc.. Plus the high hematite content, of course. The MER team had ruled out lapilli or other types of spherules, in their opinion after long analysis. Can anyone comment further on this?
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Shaka
post Mar 20 2006, 07:22 AM
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QUOTE (CosmicRocker @ Mar 19 2006, 08:27 PM) *
The blueberries are definitely an important part of this debate. From what we know of them, they do nicely fit with theories involving a concretionary origin, but I think some may be suggesting that such spherical objects might also be volcanic lapilli or impact melt spherules. I suppose you might also form them as concretions in a pile of acidic, steam-saturated basal surge deposits.

Yeah, Tom. Some are saying the BBs ain't legit. I dunno nothin' about no "volcanic lapilli"; I know somethin' about impact microtektites. I know they are beautiful little balls when they first land (usually smaller than a millimeter), but, the more diagenesis acts on them, the worse they look. They start out as glass beads and end up as clay blobs, and they don't grow over time. How you can start with beautiful beads, form rock around each one, and end up with bigger, even more beautiful beads is way over my head. blink.gif Unless, they started in that rock, and grew while the passing liquids continued to feed them.
QUOTE (CosmicRocker @ Mar 19 2006, 08:27 PM) *
I thought I was going to come to a conclusion here, but the more I think about it, I think I'll step back and wait for the major contendors to duke it out in the boxing ring. I still like the water hypothesis, though. wink.gif

You got it on the water front, Man! 'At's gotta be where it's at! We can't take a dive on'is hypothesis, Tom! It coulda been a contenda'! It coulda had class! ph34r.gif

StellaaaAAAAA!!


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Shaka
post Mar 20 2006, 07:56 AM
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QUOTE (paulanderson @ Mar 19 2006, 09:17 PM) *
One thing I've read is that the double and triplet berries seen early on (where they are "fused together" as such) are evidence of water origins, since that process requires liquid water, and couldn't happen with airfall deposits, impacts, etc.. Plus the high hematite content, of course. The MER team had ruled out lapilli or other types of spherules, in their opinion after long analysis. Can anyone comment further on this?

The only thing I know about volcanic airfall deposits is that they are supposed to have as many or more non-spherical products (up to Pele's Hair) as spheres. As to impact microtektites, they can collide while in a molten state to form doublets, but triplets are much more improbable. But, again, other shapes, like dumbbells, teardrops etc, which are produced as the molten droplets spin and separate in the atmosphere, should also be common. I do not recall seeing a dumbbell or teardrop BB in Meridiani. When they have cooled and solidified, microtektites can continue to collide at high speed, causing impact microcraters in their glass surface, again something I have not seen in Meridiani.


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Bill Harris
post Mar 20 2006, 01:27 PM
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Tom, my first thought upon seeing the Blueberries was "lapilli". But knowing their composition and examining their occurance in place the only thing they can be is concretions. To think anything else is quixotic.

--Bill


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CosmicRocker
post Mar 20 2006, 04:04 PM
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Don't get me wrong, people. I am not a proponent of a lapilli or impact spherule origin for the berries. I am pretty thoroughly convinced that they are diagenetic concretions. I only noticed that nprev and MichaelT asked about the significance of the blueberries in the context of the basal surge discussion and I was trying to resopond to their question. At the LPSC Grottzinger very effectively countered the other origins with an analysis of the berry distribution. I have been meaning to post more of my notes from that. I'll try to do that this evening.


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dvandorn
post Mar 20 2006, 05:06 PM
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QUOTE (Bob Shaw @ Mar 17 2006, 06:21 PM) *
Bruce:

Sounds like somebody should be trying some Mars analogue minerals experiments - it'd hardly be rocket science!

Nope -- more like rock science...

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-the other Doug


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Guest_BruceMoomaw_*
post Mar 20 2006, 05:58 PM
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There's been at least one LPSC abstract in the last couple of years listing reasons why the Blueberries are concretions rather than lapilli of any sort. Once I can find the damn thing in my records, I'll describe them.
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Guest_AlexBlackwell_*
post Mar 20 2006, 06:13 PM
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QUOTE (BruceMoomaw @ Mar 20 2006, 05:58 PM) *
There's been at least one LPSC abstract in the last couple of years listing reasons why the Blueberries are concretions rather than lapilli of any sort. Once I can find the damn thing in my records, I'll describe them.

LPSC abstracts are certainly good starting points for discussion and it's true that a lot of conference ideas eventually get published. Having said that, however, one should note that LPSC abstracts, even though they are more comprehensive than the typical conference presentation, are, like virtually every other conference abstract, not peer-reviewed. Just because something was presented at LPSC does not confer upon it some magical status. In fact, in my opinion, a lot of junk gets put into LPSC abstracts, and other conferences, too.

I only note this because you seem to rely a great deal on abstracts and very little on publications in peer-reviewed journals.
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SteveM
post Mar 20 2006, 08:45 PM
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QUOTE (Steve @ Mar 19 2006, 08:19 AM) *
Richard:

Thanks for the nice qualitative description of your model -- surely more detailed than my crude "fire extinguisher." I guess I still see a few questions.

The most crucial, perhaps, involves the thermal energy involved to convert sufficent quantites of water to steam ... a rough estimate of the amount of energy involved (and its source) would be helpful.

Almost as important is to estimate the amount of water involved and postulate likely local sources for such large quantities of water.


QUOTE
Thank you Steve for your message. To reply exactly would require a whole study -or nothing. Even specialists would not come with all precise answers. In more I have no time for this. Are you preparing a paper or something? (If so, you may have to quote my name as a contributor!)

Thanks Richard, I'll take on the problem. Rather than give an exact reply to my own question, here's a quick and dirty calculation which confirms that the energy involved is on the order of the largest recorded terrestrial volcanoes.

If we were to cover half the surface of Mars to a depth of 30 cm (yes I know its a foot smile.gif but it's also an amount I found scattered in the meteorological literature for torrential rainstorms on Earth) we would get 2.7x10^13 cubic meters or 2.7x10^16 kg of water.

The volcanologists estimate the magnitude of earthquakes using the formula m = log(Mass)-7, where mass measures the ash deposit (as best I can tell from the limited sources at hand). I only have indirect access to the defining article Pyle, David M. "Mass and Energy Budgets of Explosive Volcanic Eruptions". Geophys Res Lett (1995) 5:563–566 as it is cited in Ben G. Mason, David M. Pyle, and Clive Oppenheimer. "The Size and Frequency of the Largest Explosive Eruptions on Earth". Bull Volcanol (2004) 66:735–748). Incidentally, this scale is defined to be consistent with the more widely known Volcano Explosivity Index, which emphasizes volume rather than mass of deposit.

This formula gives a magnitude for the postulated martian volcano of 9.3, ignoring the contribution due to solids. FWIW, cranking in the heat of fusion and vaporisation it would require 5.6x10^22 Joules to convert that ice to vapor (or if you prefer, it's a 1.3x10^7 megaton explosion).

Mason, Pyle, and Oppenheimer assign the largest known terrestial volcano, The Fish Canyon Tuff deposit (La Garita Caldera, Colorado, USA; 27.8 million years ago) a magnitude of 9.1 to 9.2 on Pyle's scale.

Despite all the approximations, the Martian volcano needed to produce the postulated flooding is close to the largest terrestrial volcano. Thus from the question of energies alone this model does not seem as totally unreasonable as I had first suspected.

sad.gif Correction: For "magnitude of earthquakes" read "magnitude of eruptions."

This post has been edited by Steve: Mar 20 2006, 10:38 PM
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Guest_BruceMoomaw_*
post Mar 20 2006, 08:46 PM
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Alex: "LPSC abstracts are certainly good starting points for discussion and it's true that a lot of conference ideas eventually get published. Having said that, however, one should note that LPSC abstracts, even though they are more comprehensive than the typical conference presentation, are, like virtually every other conference abstract, not peer-reviewed. Just because something was presented at LPSC does not confer upon it some magical status. In fact, in my opinion, a lot of junk gets put into LPSC abstracts, and other conferences, too.

"I only note this because you seem to rely a great deal on abstracts and very little on publications in peer-reviewed journals."

True, and the reason for that is simply that I can't get to most journal articles via Internet. I have to go running all the way down to the nearest university libraries to see them -- when they finally come in, that is, and when the students haven't made off with them -- and that, in my case, involves drives of about 30 miles (to CSU-Sacramento), or 50 miles (to UC-Davis), not to mention their extortionate parking fees.
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helvick
post Mar 20 2006, 09:16 PM
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QUOTE (Steve @ Mar 20 2006, 08:45 PM) *
This formula gives a magnitude for the postulated martian volcano of 9.3, ignoring the contribution due to solids. FWIW, cranking in the heat of fusion and vaporisation it would require 5.6x10^22 Joules to convert that ice to vapor (or if you prefer, it's a 1.3x10^7 megaton explosion).


Interesting to compare to potential asteroid impacts - A 14.5km diameter porous rock asteroid hitting mars at 45 deg. gives a yield of 1.29x10^7 megatons and the final crater is ~129km diameter.

There are lots of potential candidates for such impacts in mcaplinger's msss page on determining the age of the surface which has a nice map of the distribution of craters of 100km diameter and above.

On average I'd be incliined to think that impacts would be a more likely source for such events although clearly there is plenty of evidence for vulcanism.
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Guest_BruceMoomaw_*
post Mar 20 2006, 11:51 PM
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Big news on this subject, in the form of an E-mail to me last night from Steve Squyres -- who says flatly that not only I, but also McCollom and Hynek, have been totally misinterpreting what the MER team thinks really happened at Meridiani, and that their real views are almost totally identical to my "fourth, simplest" model of how the layers were formed -- namely, that they were formed, on the spot, by exposure of basalt sand or ash to liquid groundwater with a large amount of sulfuric acid mixed in:

"... I would like to correct some points. Our observations at Meridiani reveal nothing about where the original interaction of acidic groundwater with basalt took place. The most likely scenario is probably that it happened right there at Meridiani Planum. Interaction of acid groundwater with basalt will produce both altered siliciclastic materials and -- when the groundwater evaporates -- sulfates rich in the very same cations (mostly magnesium, calcium, and iron) that were removed from the original basalts. This mix of siliciclastics and sulfate salts has then been 'reworked' locally by the wind. 'Reworked' does not mean that materials were carried in from some far-away location. It can simply mean that the wind took material that was already there, blew it around (as sand-sized grains), and piled it up into dunes. And in some locations, where we see the ripples, it was also reworked by small amounts of surface water.

"So, the scenario we have inferred based on our data is much simpler than the one you describe. Acid groundwater interacts with basalt, creating a mix of altered siliciclastics and, when the water evaporates away, sulfate salts. This siliciclastic/sulfate mix gets stirred around, as sand-sized grains, by the wind and occasionally by surface water. While it's certainly possible to invent more complex versions of this story, such complexity is not required by the data.

"PS: I should also mention that there is compelling evidence for subsequent influxes of groundwater after these materials were put in place, changing the chemistry and texture of the rocks deep in the section, and creating the blueberries. But that all happened after the original emplacement of the rock."

If so, this completely demolishes McCollom and Hynek's main argument -- that the MER team's view chemically requires a very lucky, pure-chance mixture of just the right amount of sulfate salts from elsewhere with on-the-spot phyllosilicate sand to precisely simulate what would have resulted from just mixing on-the-spot basalt with sulfuric acid. And when that argument is removed, it pretty much blows the bejeezus out of both McC. and H.'s volcanic basal-surge theory, and Burt and Knauth's impact basal-surge theory. The only other real arguments they have are:

(1) That (to quote Zolotov) there wasn't any adequately large source of such acid-saturated surface water on Mars. But, as I said earlier, Zolotov never even considers Benton Clark's view that large amounts of sulfuric acid were formed on the surface of Mars by its unique atmospheric processes -- far more than could ever have been spat onto its surface from underground by its volcanoes. And so the problem of an inadequate supply of sulfuric acid solution actually seems to strike much harder at the two basal-surge theories than it does at the MER team's theory.

(2) Quoting Knauth and Burt (abstract #1869): "The identification of the well rounded primary grains 0.1 to 1.0 mm is problematical. Sulfates have perfect cleavage and should be more angular if truly detrital. The 'grains' more strongly resemble diagenetic growths or wind-abraded efflorescences. [Also, a] process that would uniformly mix basaltic grains <100 microns into sulfate grains is difficult to envision. Even if the basalt mud were a component of the grains, density differences make it unlikely that its distribution would be so completely uniform in far-migrating wind ripples. In any case, acid waters would completely alter such tiny basalt particles into clay minerals."

But the MER team itself says (abstract #1655) that those rounded primary grains are rounded precisely because the original, coarser basalt sand or ash was first exposed to large amounts of acidic groundwater, and THEN dried out and blown around locally by winds, which both ground up the sulfate crystals into powder and rounded the little phyllosilicate dreg particles left behind by the acid -- and that this mix was later exposed to liquid water (not necessarily acidic) again, which redissolved the powdered sulfates and fused them into a solid matrix as well as creating the Blueberries: "Observed compositions require either that basaltic sands were altered in place by abundant and pervasive acidic groundwater or that alteration occurred primarily in the source region, followed by the formation, transport and deposition of sulfate-rich sand grains, with subsequent diagenetic redistribution of the most highly labile mineralogical components. The roundness of observed grains and, especially, the locally complete obliteration of grains during diagenesis strongly favors models in which alteration precedes sand generation and transport." The mixture MER-B now sees at Meridiani, contrary to Burt and Knauth, IS a mixture of sulfates with particles of "clay minerals", not with particles of "basalt mud".

Hokay. So -- now that my misunderstanding of what the MER team is actually saying is cleared up -- it looks to me as though they have very definitely got the better side in this fight. It's the two basal-surge theories that require relatively unlikely conincidences to work -- namely, how either type of basal surge could have gotten hold of enough sulfuric acid to chemically modify the original Martian surface rocks so thoroughly. Since I just love sprinking snuff on my hair and then sticking my head into a lion's mouth, I'll contact Hynek (and probably Burt or Knauth) directly on this to see what their replies are.
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Guest_AlexBlackwell_*
post Mar 21 2006, 12:18 AM
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QUOTE (BruceMoomaw @ Mar 20 2006, 11:51 PM) *
Big news on this subject, in the form of an E-mail to me last night from Steve Squyres -- who says flatly that not only I, but also McCollom and Hynek, have been totally misinterpreting what the MER team thinks really happened at Meridiani, and that their real views are almost totally identical to my "fourth, simplest" model of how the layers were formed...

In other words, you've covered yourself by picking every plausible model; therefore, you can claim that you were, ultimately, correct? I like that stock broker-like approach ("The market may go up, or down, or stay the same"). biggrin.gif
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