Author Topic: JFincannon's Collapsed Voids  (Read 23403 times)

jules

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Re: JFincannon's Collapsed Voids
« Reply #15 on: February 22, 2011, 09:18:43 pm »
There are some amazing images here. Any one would make a great Image of the Week.  Just need a bit more science discussion and we've cracked it! Nice work JF.

JFincannon

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Re: JFincannon's Collapsed Voids
« Reply #16 on: February 22, 2011, 10:03:09 pm »
Just now, I was looking at "Lunar Outgassing, Transient Phenomena & the Return to the Moon II: Predictions and Tests for Outgassing/Regolith Interactions" which shows in figure 1 a nice depiction of what would happen for a possible gas explosion.

JFincannon

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Re: JFincannon's Collapsed Voids
« Reply #17 on: February 23, 2011, 03:28:06 pm »
From that reference.........
"Fig. 1.— A sketch of our 1D spherically-symmetric model explosion. Frame 1: venting gas
builds up at the interface between the megaregolith and the low-diffusivity regolith. It builds
until its pressure is sufficient to lift the overlying cone of regolith to the surface. Frame
2: we assume that this regolith/gas mixture now translates into a hemispherical volume
on the surface. This volume is uniform in gas density, but it is populated with concentric,
hemispherical shells of regolith particles (represented as points 45 degrees up the side of each
arc), each feeling a pressure from the expanding gas. As the cloud expands, the equations
of motion are numerically integrated for each shell in the cloud according to its mass and
regolith particle size composition. Frame 3: the cloud expands until it reaches a point
where it is no longer optically thick as viewed from above, but the dust still entrained in
the cloud continues to expand and a thinner component (τ = 0.1) remains somewhat visible
from above. Figure 2 shows the detailed evolution of these clouds. Regolith that has fallen
out of the gas cloud begins to pile up on the ground around the crater. Frame 4: all of the
gas has escaped and all entrained regolith is deposited on the ground around the crater in a
manner shown in Figure 4."

IreneAnt

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Re: JFincannon's Collapsed Voids
« Reply #18 on: February 26, 2011, 01:59:46 am »
Wow, that is quite some work JFincannon!

I have some more ideas....

Today's LROC Image of the Day shows that you *can* get voids in an impact melt, if the cooling melt drains away leaving behind just a solidified chill crust. In this example, a small melt pond on the floor of Giordano Bruno crater drained away, causing the entire top to collapse, resulting in a spectacular jagged terrain (see my post on this elsewhere). So, it is possible that this may occur in other places, too. Now, Copernicus crater is about 4 times the size of Giordano Bruno and has much more melt, so here you wouldn't get a small melt pond draining, but possibly parts of a large melt sheet draining? I don't know if this is possible, but it's an intriguing idea.

The reference you quote above is very interesting. I'm not sure if it applies in this situation. First, you don't have a regolith/megaregolith boundary, you have a very thin regolith over an impact melt sheet over the highland basement (not sure if you would call that megaregolith at this point?). So, I'm not sure where the gases would come from in this case.  Secondly, the paper predicts features about 15 meters in diameter, while these ones are over 100 meters. Maybe the melt sheet affects the depth at which the gases collect, making that deeper, which results in a bigger cone? I have no idea. But very interesting to think about...

In any case, I agree that the round features you found are not craters. They are bigger and fresher than most of the craters in this area, but have no ejecta and seem to have a more spherical rather than conic morphology.   

Truly interesting features. Thank you for finding these JFincannon!

jules

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Re: JFincannon's Collapsed Voids
« Reply #19 on: February 26, 2011, 09:10:16 pm »
Thanks for the insight Irene.

JFincannon

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Re: JFincannon's Collapsed Voids
« Reply #20 on: February 28, 2011, 03:30:50 pm »
Thanks for the analysis.  It is always interesting to see the synchronicities of life with the LROC pictures being published about this topic area.

I agree that the pressurized gas idea was somewhat inapplicable.  Also, I would expect more rocks fired around the site from the explosion, which is not evident.  On the other hand, explosive shattering of the ceiling into dust which spreads outwards to the remainder of the Copernicus crater might explain the lack of more ceiling boulders.  Looking at the examples I have presented so far I see a considerable amount of dust/particulants in them but not as many rocks as one would expect if the entire ceiling/roof collapsed.  Assuming that the ceiling just did not fire outwards into space nor shattered into dust (or both), the implication is that either (1) dust had accumulated on the dome prior to the collapse (indeed may have triggered it by the weight) and it eventually collapsed partially filling the sink hole like structure OR (2) the dust accumulated afterwords.  Since the dust does not cover some boulders in the pit, I have trouble believing it is due to accumulation after the collapse although they might have fallen after the collapse due to erosion. 

My main question now is whether the collapsed voids are due to domes that collapsed such as the attached image (such that we can have a telltale indicator of a potential void) or are they collapsed from the flat surface level. 



JFincannon

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Re: JFincannon's Collapsed Voids
« Reply #21 on: February 28, 2011, 03:35:52 pm »
I created a map of the "caves"/"holes" and "collapsed voids"/"sink holes" I found. 

I need to also generate an identifier relating the images posted to the item number.

jules

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Re: JFincannon's Collapsed Voids
« Reply #22 on: February 28, 2011, 03:56:23 pm »
Good work JF - very useful.

JFincannon

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Re: JFincannon's Collapsed Voids
« Reply #23 on: March 01, 2011, 05:28:08 pm »
For the previous images already posted, these correspond to the map codes.

H1: M135324446LC_pyr_crop5.jpg

C1: M119985215LC_pyr_clip1.jpg
C1: M107006443LC_pyr_clip1.jpg
C1: M104648293RC_pyr_clipb.jpg
C1: M102293451LC_pyr_clip1.jpg
C2: M111728277RC_pyr_clip5.jpg
C2: M124701702RC_pyr_clip1.jpg
C3: M122346704RC_pyr_clip6.jpg
C4: M104648293LC_pyr_clipb.jpg
C5: M104648293RC_pyr_clipa.jpg
C5: M102293451LC_pyr_clip2.jpg
C5: M102293451LC_pyrdome_red.jpg

By the way, does anyone have a good answer why the LRO images are either oriented correctly, oriented such that I must rotate them 180 degrees to get them right, oriented such that I must either flip them vertically or horizontally to get them right.  The first two are due to the spacecraft passing over the site in either direction.  But why the flips?

JFincannon

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Re: JFincannon's Collapsed Voids
« Reply #24 on: March 01, 2011, 08:39:46 pm »
Potential Cave (Map code H5): This one seems associated with a tube or crack.

M109365462L, 3906 pixels from the left, 10265 pixels from the top


jules

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Re: JFincannon's Collapsed Voids
« Reply #25 on: March 01, 2011, 11:23:49 pm »
As far as I know the LRO orientation is right. Some Moon Zoo images are flipped so that illumination always comes from the left.

JFincannon

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Re: JFincannon's Collapsed Voids
« Reply #26 on: March 02, 2011, 03:00:54 pm »
I don't know if this is the the right place to discuss this but....

I am referring to images downloaded from the ASU LRO website.

M111728277LC_pyr.tif (and others) needs to be flipped about the image vertical axis to get the image to overlay with a large correctly oriented Moon image.

M122346704RC_pyr.tif (and others) needs to be flipped about the image horizontal axis to get the image to overlay with a large correctly oriented Moon image.

Depending on whether the spacecraft is heading from the North or South affects whether you must rotate the image 180 degrees to get it to align with a large Moon image, but I can understand this.  They are defining the upper edge of the image the same in both cases (the upper part of the camera lens), so UP for one would seem like DOWN, but really the image orientation is consistent in the physical real world. 

If you look at the corner latitudes and longitudes in the LRO image data files, the above rotations or flips I describe above make sense to get them correctly oriented. It would be nice if they could explain why flips are needed though because it doesn't seem physically possible for the camera to take a flipped image, although it might be possible to process it in a flipped manner.

JFincannon

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Re: JFincannon's Collapsed Voids
« Reply #27 on: March 02, 2011, 03:11:37 pm »
Potential Cave (Map Code H4): This one seems associated with a tube or crack.

M124708491LC_pyrcaveH4b.jpg
M124708491L, 4930 pixels from the left, 38232 pixels from the top

M124701702LC_pyrcaveH4b.jpg
M124701702L, 2314 pixels from the left, 38415 pixels from the top

M109365462RC_pyrcaveH4_h4b.jpg
M109365462R, 4396 pixels from the left, 3714 pixels from the top

JFincannon

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Re: JFincannon's Collapsed Voids
« Reply #28 on: March 02, 2011, 03:14:11 pm »
Potential Cave (Map Code H3): Need more images to check.

M119978417LC_pyr_caveh3b.jpg
M119978417L, 4229 pixels from the left, 50170 pixels from the top

M109358669LC_pyr_caveh3b.jpg
M109358669L, 2388 pixels from the left, 47629 pixels from the top

JFincannon

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Re: JFincannon's Collapsed Voids
« Reply #29 on: March 02, 2011, 03:16:07 pm »
Potential Cave (Map Code H2): Need images with different Sun azimuth.

M137672132LC_pyr_caveh2b
M137672132L, 2563 pixels from the left, 13915 pixels from the top

M122339925RC_pyr_caveh2b
M122339925R, 287 pixels from the left, 18586 pixels from the top