Boulders - Rock On!
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Paul_Johnson
just wanted to expand this area for debate about boulders.
I was wondering if they sit on top of the ice and sink through it, or they poke up through the ice and create a weak point for the gas to escape? I can't believe the rocks are on top-how would they get there? If they are poking through, well, they must have been doing it for many millenia, you would have thought wind erosion would have smoothed them all down?
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Paul_Johnson
No, I'm sticking to the 'Stalagmite Position'......! I reckon they form because of the vent, and the added gradual accretion of CO2 being blown into them at 250mph!
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Kitharode
moderator
in response to Paul Johnson's comment.
" If they are poking through, well, they must have been doing it for many millenia, you would have thought wind erosion would have smoothed them all down?" What convinces you that what we see today is not a collection of ancient, eroded boulders?
Can I take it that the katabatic winds are still part of your working hypothesis? I know there was talk of 'the missing hill', but this problem may simply be a consequence of the scale of the images. If we could zoom out a little, it is not impossible that the neccessary landscape for the winds to occur would come into view. (But we need to know more about atmospheric 'density').
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wassock
moderator
shurely the kabatic wind is a monodirectional wind by definition and thus doesn't apply to the multi directional fans?
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Kitharode
moderator
in response to Paul Johnson's comment.
PS. If the stalagmites accrete CO2 due to wind, can we assume that the accretion takes place on the same side of the structure, ie, the side facing the wind? If so, given long enough timescales would we not expect a more oval structure to build up. Timescales need to be long enough to 'grow' the stalagmites, so maybe long enough to oval-ise the structure. Any temporal observations come to mind?
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Paul_Johnson
I think the missing hill is the South Pole! Cold air (well CO2 anyway) moces down from it at 250mph. Wouldnt it be packed with CO2 ice crystals....which should sandblast anything poking up, just as sand does here on Planet Three....of course, we are talking over millions of years....maybe billions? I thought I read somewhere that there hasnt been a volcano on Mars for 2 billion years-so (guessing now) the surface could only have been afftected by wind erosion......
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Kitharode
moderator
in response to wassock's comment.
Wazzock, that's an excellent observation (if the kabatic exists). So what's that telling us ... seems important somehow.
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Paul_Johnson
The katabatic wind seems very relevant in all this, as does how it interacts with the boulders.
I can imagine it would swirl around and change direction depending on air pressure, time of day (sun affecting it) etc....also through valleys and around hills.
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Kitharode
moderator
I agree that the katabatic wind might well be very important. Any mileage in starting a "Katabatic Winds: Scientist Required" discussion. Might be fruitful. I'm happy to start it, or you can, if it's a goer.
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wassock
moderator
A Katabatic wind doesn't have to blow every where - theres lots of very evenly coloured dark fans which are essentially monodirectional, which seem like good evidence for a long term (covering more than one eruption) wind in more or less the same direction. If it is essentially a one way wind then it either doesn't blow all the time or it doesn't affect the regions with the v fans. If the boulder (or whatever it is) is causing the rupture in the ice by getting warm then it would make sense that we get a fissure which goes all the way round it. Thus we have decompressing gas/particulate passing over its whole surface, evenly, all the way round.
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wassock
moderator
Still need to find a reason why the dust would stick together, would help if we had some idea of what it was made of. And seems to me that lots of dust rubbing up against itself ought to be a recipe for a bit of static to build up.
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Kitharode
moderator
in response to Paul Johnson's comment.
I think you're right about the volcano and how long ago it occured - I read similar. However, over these timescales wind-erosion is obviously a major factor but perhaps also impact craters. There aren't many in the S Polar region, but big 'uns even near the equator might well have 'rippled' an effect on the more southerly regions.
Wassock. You make an interesting point. If the boulders do indeed rupture the ice, then yes, we might well expect a 'wrap-around' emission. (This might be see-able in some images). Also, would the boulder not be subject to a maximum velocity emission. Could this idea be incorporated into the stalagmite theory (oooh, this is interesting). I was thinking that 'stalagmites' might require some sort of 'seed' to get them going. A certain type of rock or boulder might do.
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Kitharode
moderator
in response to Kitharode's comment.
An addition to my previous post....
Boulder ruptures underlying layer. This triggers a high velocity emission, perhaps powerful enough to 'suspend' the boulder until pressure drops and - ta daaaa - the boulder seals the hole. Smaller emissions, perhaps from a 'settling leak' occurs later, after a change of wind direction.
Do we need a katabatic wind anymore?
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Paul_Johnson
An intriguing notion Kitharode, I would love to see that happening!
Probably not needing a katabatic, I see what you are getting at......but how did the rock get up on top of that ice sheet?
wassock - static.?.....interesting......kaboom!!!!...
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wassock
moderator
Don't know what the K-wind was for in the first place. A vents juggling boulders probly strectes the credule a bit. The stalagmite theory only (deposition mechanism excepted) needs some thing on the surface beneath the ice thast gets a bit warmer than what's around it. So a vent appears above the feature (a pebble maybe) more often than in the surroundings. If we can arrange deposition then over time the feature will get bigger and will get a vent over it more often. In the early days for a small 'pebble' a vent may only form when the ice is getting thin at the end of the thaw.
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wassock
moderator
in response to Paul Johnson's comment.
The rock doesn't need to be on top of the ice sheet
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Kitharode
moderator
We have two competing theories here. 1) Boulders are boulders. 2) Boulders are not boulders, they are stalagmitic structures (don't know if that's a real word). Can we agree that both theories have the same consequencies, ie, both structures depress the underlying material, which in turn creates venting of material? If yes, the consequencies of both theories are already under heavy discussion so perhaps we should 'take sides' here and set out to prove / disprove what the initial 'seeds' are; boulders or stalagmites. (Baggsy the boulders).
As always, I'm making suggestions not issueing orders 😃
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Wounded_Knee
Crazy boulder theory#1. The K winds that form the tramlines will eventually separate the ridges into boulders, the K wind eddies along the tramlines slowly making boulders to blow down the hill.
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Paul_Johnson
Ok then, I'm pretty sure I'm backing a losing nag but I find the idea that boulders are the catalyst for fan production, well, not quite right.
I imagine there is a weakness in the ice, as gas pressurizes beneath, and the action of venting produces a small deposit, which is then built up by the wind...into a boulder. The wind will eventually erode this away, and just to join another whacky theory....this causes grooves! Bingo!
I wouldn't put serious money on it though, because people who know what they are talking about don't agree with it!
oh well, I must have rocks in my head......!
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Wounded_Knee
Apart from the fans looking different, coundnt they also be formed different?
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Paul_Johnson
WK - yes, of course they could. many fans have extraordinary features.....
http://talk.planetfour.org/#/subjects/APF0000kqa
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Wounded_Knee
in response to Paul Johnson's comment.
http://talk.planetfour.org/#/subjects/APF0000kqa
It reminds me of solar projecting sunspots through binoculars, with a big comet there as well 😉
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Paul_Johnson
....and is that a boulder in the middle....it looks more like a gash in the ice to me.....not very bouldery at all..
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Kitharode
moderator
in response to Wounded Knee's comment.
Crazy #1. I'm intrigued by this. More please. Is the K-wind the katabalic wind? Hope so, cause it's easier to type!
Fill in some gaps - K-wind actually forms the boulders into tramlines? How? No, forget it you've already said it's the eddies. Yes, I can see that. Good thinking.
So, does the K-wind travel across an initial randomly spread boulder field, with undulating 'waves' of air at the wind-surface interface forming the tramlines, or are the boulders 'brought in' and deposited (less likely to me)?
I think you should persue this idea.
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Wounded_Knee
The K wind forms the tramlines, the K wind and eddies/dust etc slower carve the ridges between channels into boulders.
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Wounded_Knee
gotta think timescale like the spiders 10^5+ years
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wassock
moderator
Think we're getting off track here a bit. Think I've seen somewhere someone who ought to know what's going on saying that the tramlines are wind features caused by a reasonably constant prevailing wind - the k word. There are clearly lots of causes of vents, some appear to be centred on bright objects/boulders, the fissure type vents are clearly? coming from straight or curved line features which cannot be coming from an array of boulders; there are fans associated with spiders and fans in seemingly featureless terrains, there are diffuse fans, Fat dark fans, and fans of many colours. So boulders or stalagmites don't need to be competing theories, both, or neither, can be right.
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Wounded_Knee
in response to Paul Johnson's comment.
If you zoom right in using paint it looks like a Klingon Bird of Prey, ship is facing bearing 045 mark 0.
was a response to whats the light area inside http://talk.planetfour.org/#/subjects/APF0000kqa
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Paul_Johnson
Yes it does!
The fan and blotch look like Wilson, the football from Castaway (Tom Hanks).......Wilson!
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Kitharode
moderator
in response to Wounded Knee's comment.
Yes, agree about timescales. Big number involved whatever it is. So, there are linear channels flanked by ridges. The K-wind sandblasts across these ridges and, mega-years later, the ridge is transformed into a line of boulders. Am I right so far?
Does the K wind create both the channels and the ridges, sweeping the channels clean and piling the debris into ridges? Thats a nice idea, at first glance. Or are the channels and ridges formed first and given enough time to 'solidify', so that when the K wind gets there its got something to erode?
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Wounded_Knee
K wind forms the tramlines and over time tramlines erode into boulder fields, as boulders get numerous they create the geyser fields. But these will be one (maybe) of many different forms of geyser events i made up 😃
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wassock
moderator
Ok lets explore this one - most of the terrain with boulders is fairly flat and featureless(ish) with isolated boulders. So how do we get to there from a 'ploughed field' with boulders in nice neat lines?
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wassock
moderator
And the fans which are clearly associated with 'boulders' tend to have multidirectional fans and thus are not in a region with the constant wind direction needed for the wind blown grooves
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Kitharode
moderator
in response to wassock's comment.
Not too sure about the 'flatlands isolated boulders' sentance, but leaving that aside, your 'ploughed field' question is a good 'un.
"..for the wind-blown grooves" - on the assumption that the grooves are blown by wind.
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Kitharode
moderator
Back to 'Boulders' then: First, going back to my 'hovering boulders on high--velocity vents' idea. I'm not suggesting that the boulder would 'fly' like a skydiver on an indoor wind-jet (or whatever they call them) although I do like the analogy. No, they wouldn't fly, but could they be 'marginally suspended' such that the pressurised material could escape from around and beneath the boulder (the pressure lifts/supports the boulder) until the pressure drops and the boulder returns to rest. The vent is sealed, the pressure can build again.
It's a possible mechanism for a stop-start effect which is implied in the twin fans discussions. Before dismissing the idea completely I'd like to know more about the size/mass of these boulders, and the 'power' of the vent jets. Mars' gravity is just 38% that of Earth, so a 'massive' boulder might not be so tough if it meets up with an angry 'power jet'.
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Kitharode
moderator
Still very much on 'Boulders', but first an apology. I was chastised earlier (and rightly so) for refering to the boulder/stalagmite theories as competitors. You're right, they are much more alternative than competitive. (In my defense, I thought we were in one area with one set of boulders). Anyway, I stand corrected.
Here then is another alternative 'theory of boulders'. This idea does require, I think, a certain type of landscape/terrain, so I'm restricting this idea to those terrains which display this type of phenomena (in the images). Here's an example:
http://www.planetfour.org/subjects/standard/50e73c565e2ed212400008a0.jpg where, if the light is coming in from bottom right, we see the top left corner is lower (and smoother) than the bottom right corner (more ripply) with an assortment of 'boulders' at the interface.
Although it's impossible to tell (we can't zoom out), if I had to make a prediction about the surrounding terrain then I'd say that the lower ground in the above image was a circular(ish) structure, quite possibly with a spider at the bottom. Like this:
http://www.planetfour.org/subjects/standard/50e73cff5e2ed211dc000d27.jpg
There are many images showing this sort of situation. So here's the 'theory'. On the assumption that the land in these hollows is depressed (rather than surrounding land being raised) it is during the process of 'depression' (and I've no idea what that is) that the surrounding 'ripples' are smoothed out at the high/low interface, and it is the highest points on the ripples that survive by breaking off at the tip leaving us with isolated boulders.
One last image 'cause it's relevant - and I like it. The ripply bit runs between two smoother areas and we have boulders at the interface: http://www.planetfour.org/subjects/standard/50e73d155e2ed21240000fe8.jpg
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pocketmoon
So theory is boulder in some way promote jets and thus fans. The scenario is boulder sitting on the surface, which is under up to 1m of co2 ice. During spring sunlight warms the surface (the ice is very transparent ) thus causing sublimation of co2 which under great pressure thread it's way under the ice until it find a weak spot and erupts upwards? With a boulder at in the ice I would expect the sunward side to warm and create a channel for the co2 to erupt through
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Kitharode
moderator
That sums it all up very nicely pocketmoon.
"So theory is..." Yes its still theoretical so there are still questions to be answered (and raised probably). It's all those tricky little questions that this, and various other excellent discussions, are trying to answer (in true citizen-scientist style) that make this sort of project so intrigueing and exciting to me. Lots of info is now being 'leaked' by the science team, all of it adding a little more clarity to our current "clear as mud" situation. But many 'discoveries' have been made and there's real science kicking around.
I'm sure that some of the guys will start to assemble some "ok, here's what we know so far..." threads (I hope so) and maybe a more 'filled-in' theory (clearer picture) can be developed, along with a clear list of questions still left unanswered in that area. It seems to me that the 'process of venting' theory is generally accepted pretty much as you described above (and why not). So does it begin with boulders? Seems a simple enough question.......
There's so much going on, on Mars, for a project like this we need to confine ourselves to one area. There's so much going on there (boulders, vents, ice, chemistry, etc) that we confine ourselves further - I'm currently into 'linear and curved' venting, boundaries and interfaces, and spider classification (and boulders, but less so 'cause others have got it under control).
My investigations are very different, but in many ways very much related. Taking Mars to pieces and putting it back together is awesome, but sometimes my head hurts something awful 😃
Do you have a personal 'take' on boulders? Noticed any facts about them that might be useful here?
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Wounded_Knee
in response to Kitharode's comment.
Just seen this post, I have seen oval looking boulders, i will post links here in future, On a side note i was looking at a contour map of Mars an I think the main area of this study is about 1 to 2km lower than the surrounding terrrain.
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