Tiny lunar volcanoes

By Phil Plait | December 12, 2011 11:19 am

The Moon is packed with all sorts of interesting features that only come to light — literally, in some cases — when very high-resolution imaging is done. For example, the lunar far side has a bunch of small volcanoes, some only a few hundred meters across, like this one:

[Click to enlunenate.]

The image is about 500 meters across, so this is a hill you could climb pretty easily, even though the low Sun angle implies the slope is greater than 13° (remember, the Moon has 1/6th the Earth’s gravity so that would be a pretty easy hike). Those boulders on the top are weird; they only appear to be on one side, and there doesn’t seem to be anything in that direction that would be a source of them. There are none on the plains around it, or at the bottom of a nearby crater, either. The source must be the volcano itself, I’d wager. Note the crater at the top of the mound, too – you might think that’s the volcanic vent, but in fact it’s not centered on the dome, indicating it’s a coincidental impact crater.

Because the Sun is coming from the side, some people might have a hard time seeing this as a dome. It’s a well-known illusion I’ve pointed out on this blog many times, but maybe this red/green 3D anaglyph by Nathanial Burton-Bradford will set you straight:

That one’s really cool; the opposite relief of the crater and volcano makes this one really fun to look at.

The Moon’s ancient volcanism is a pretty ripe field for study, since not a whole lot is known about it (gamma-ray mapping of this area shows it’s rich in the radioactive element thorium, for example — how about that?). I wonder if 3D images like the one above would help scientists understand this better?

Image credit: NASA/GSFC/Arizona State University

Related posts:

Ash hole on the Moon
A lunar illusion you’ll flip over
Raising an impact in Africa
Terra spots an impact on, um, Terra

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (12)

Links to this Post

  1. Los Viejos Volcanes de la Luna. | Pablo Della Paolera | December 13, 2011
  1. Chris

    Oh yes! Finally some new astronomy to talk about!

  2. Jess Tauber

    Nah, its just those pesky space antlions again.

  3. chris j.

    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.

  4. lunchstealer

    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?

  5. Randy A.

    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)?

  6. Yuri

    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.

  7. DLC

    [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.

  8. DutchMeteor

    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…

  9. JB of Brisbane

    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.

  10. Brad

    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.

  11. PurpleOzone

    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.


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