Comments on: Tiny lunar volcanoes

By: PurpleOzone

PurpleOzone — Thu, 15 Dec 2011 01:41:02 +0000

I’m struck by the relative recentness of the small crater on the left side of the large crater. The crater and small boulders around it have sharp walls, while old features have softened edges.
Some decades ago when lunar photos were first available several people did detailed studies to identify the ages of origin of features. Shoemaker is the only name I can remember now.
The boulders are newer than the small crater, or fell back upon it. Note that the right rim shows as many boulders on it as a bad case of acne on a face. Also, it doesn’t look like the boulders are strewn in the typical patterns of ejecta from a crater. As I remember Shoemaker’s diagrams.
Curious.

By: Brad

Brad — Tue, 13 Dec 2011 13:21:56 +0000

I guess I have to buy 3-d glasses now.
Flipping the picture so the illumination comes from the top, that crater seems…too conical, and there are fewer impact craters inside compared to the surrounding plain. My amateur guess is that this is two lava domes along a subsurface magma channel, one of which collapsed to form a pit as the lava tube became depleted. I think I see some linear features in the crater where rocks could have slid or rolled to the bottom before becoming buried.

Definitely cool, whatever caused it.

By: Los Viejos Volcanes de la Luna. | Pablo Della Paolera

Los Viejos Volcanes de la Luna. | Pablo Della Paolera — Tue, 13 Dec 2011 12:45:25 +0000

[...] Tiny lunar volcanoes [...]

By: JB of Brisbane

JB of Brisbane — Tue, 13 Dec 2011 09:08:24 +0000

Once again I am reminded of The Little Prince, and his asteroid with three volcanoes, two active (on which he heated up his breakfast in the morning) and one extinct.

By: DutchMeteor

DutchMeteor — Tue, 13 Dec 2011 06:05:11 +0000

Could it be a low-angle impact crater? Doesn’t really explain the boulders, but might explain why they are scattered mostly on one side only…

By: DLC

DLC — Tue, 13 Dec 2011 01:25:11 +0000

[lunar conspiracy theorist] photoshopped! Fake! it’s mountains in Arizona/Iceland/Movie Studio!
Radiation Belt, gravity electric universe . . . stop me if you’ve heard this before. [/lunar conspiracy theorist]

but, coming back to reality — that’s a cool set of pics.

By: Yuri

Yuri — Mon, 12 Dec 2011 23:51:34 +0000

This maybe a silly question, but couldn’t whatever effect caused boulders to occur on only one side also cause a volcanic dome to build up asymmetrically? e.g. if the dome was built up by ejecta (Xenogeologist question: could lava fly higher in the low g’s and stay hot longer in a vacuum, thus acting more liquid when it landed, allowing dome formation from ejected material rather than ‘flows’?) then asymmetric ejection of lava could cause uneven dome buildup…

It seems to me that observing one feature which is asymmetric, it may be a bad assumption to think that the symmetry of other processes will be maintained. Not saying that it necessarily isn’t an impact crater, just that without understanding why the boulders are only on one side, it might be a bad idea to dismiss the volcanic crater proposition purely on the basis of symmetry, if that’s the only reason the judgement is being made.

By: Randy A.

Randy A. — Mon, 12 Dec 2011 22:18:26 +0000

I’m a plain old Earth geologist, and I have a comment and a question:

First, there are many examples of small volcanoes on Earth where the main vent is not at the peak. However, the explanation is always wind, which piles up pyroclastic material higher on one side of the vent than the other. Wind isn’t a factor on the moon…

My question: the high resolution image seems to show the same boulders inside the crater as outside the crater on the flanks of the volcano. To me, that implies that the crater formed before the boulders formed, or perhaps at the same time. Are there other impact craters with boulders scattered around in a similar fashion? Or perhaps this is a volcanic crater after all, and the boulders are large volcanic bombs? Or perhaps the boulders resulted from an impact into poorly consolidated volcanic material?

Any thoughts Phil (or anybody else)?

By: lunchstealer

lunchstealer — Mon, 12 Dec 2011 21:01:40 +0000

Chris, I’m guessing that it’s not the asymmetry of the crater itself that’s the issue, but the fact that it’s not at the top of the dome. Most (most but maybe not all, I haven’t studied it directly) volcanic craters are pretty much at the top of the volcano, since they’re the source of the volcanic material. Certainly on the big stratovolcanoes the highest point on the mountain is usually along the rim of the vent crater.

That said, for a more lumpy shield-volcano type critter, you might expect to find vent craters on the side without there necessarily being one at the top. And of course, the geochemistry (lunachemistry?) is different enough on the moon that volcanoes may act differently. Apparently hydrates make melts act differently, and the relative dearth of water on the moon means that the minerals are less likely to be hydrate forms.

Any planetary geologists care to weigh in with something more than half-remembered coursework from 20 years ago?

By: chris j.

chris j. — Mon, 12 Dec 2011 20:22:42 +0000

out of curiosity, why does being off-center rule the visible crater out as the volcanic vent? there are plenty of asymmetric craters on earth.

By: Jess Tauber

Jess Tauber — Mon, 12 Dec 2011 19:51:55 +0000

Nah, its just those pesky space antlions again.

By: Chris

Chris — Mon, 12 Dec 2011 19:14:27 +0000

Oh yes! Finally some new astronomy to talk about!