March 4, 2010

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The Most Magnificent Flow On the Moon

left image (south to right) from Lunar Orbiter V-103 and right (south up) from JAXA/Kaguya Image Gallery

Note: Wednesday at the Lunar & Planetary Science Conference some magnificent LRO images of impact melt flows on crater rims were shown. I repeat this July 12, 2008 LPOD to remind myself that a few wonderful melt flow images have been available since the 60s. But nothing is as spectacular and as informative as the new images!

The best defined flow on the Moon is made of highland impact melt rather than basaltic lava. The August 13, 2007 LPOD that described this flow - and my earlier mis-interpretation of it as a lava flow - included a piece of the image seen on the left. That view shows a channel that conveyed lava from the rim crest down into the low spot of an earlier crater. The new Kaguya image (right) seen more obliquely and with higher illumination permits a more complete interpretation. The Kaguya view immediately explains one aspect of the distribution of impact melt. The Wiener F crater sits on the rim of a pre-existing slightly larger crater, causing F's northern rim (foreground) to be lower than the southern one. A massive mound of material at the bottom of the southern rim resulted from a huge landslide, creating the steep slope of that rim. The giant slump sloshed impact melt that was on the crater floor up over the opposite lower rim. Some of the southern wall debris created mounds and hills on F's floor. This sequence demonstrates that the impact melt covered F's floor before the wall collapses occurred, but they happened soon enough after the crater formed so that the melt was still liquid. Most of the details of the crater floor is in shadow on the Orbiter image, making it look like the flow started on the rim and hence possibly erupted from a rim fracture. The Kaguya image tells the rest of the story.

Chuck Wood

Related Links
Clementine Atlas plate 31
Note - the Aug 13, 2007 LPOD has a different caption than this one and provides some prehistory.

Yesterday's LPOD: Uncovering Lava Flows

Tomorrow's LPOD: Bringing the Moon Indoors


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