May 30, 2012

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A Bump in an Ocean

image by Alexander N. Zaitsev, Lipetsk, Russia

The Moon has a number of apparently unique landforms - the Aristarchus Plateau, Schröter's Valley, Descartes Hills, Marius Hills, Reiner Gamma, and Rümker probably top the list. Some of these are simply more spectacular versions of other features; Rümker is and isn't in that category. Rümker is a complex of domes, each of which is similar to other isolated examples. But the pile up of domes, building a kilometer high mass, is unlike any other lunar volcanic feature. Why did this happen? Long ago Jack McCauley of the USGS Astrogeology office pointed out that three unique volcanic features - Rümker, the Aristarchus Plateau complex, and the Marius Hills - occur along a centerline of Oceanus Procellarum. On Earth we would say that such an alignment was controlled by tectonic fracturing. McCauley, who recently died, suggested that the alignment of volcanic mountains in the middle of a broad expanse of lava was reminiscent of terrestrial plate tectonics. There is no evidence that plate tectonics ever occurred on the Moon, but faults within the Oceanus - the mare ridges - would have provided conduits for magma to rise to the surface and erupt. So perhaps a better question is why was the volcanism associated with these three volcanic islands so much more voluminous than at other places? The answer is probably related to their occurrence within the PKT - Procellarum KREEP Terrain - the northwestern quadrant of the nearside that is more highly radioactive than other parts of the Moon. Presumably that extra heat led to the widespread mare volcanism in the area, and perhaps to the increased amount of volcanism at vent areas, transforming what would have been normal volcanic landforms into major volcanic provinces.

Chuck Wood

Technical Details
2012/05/03 Time: 19:11:35 GMT. Telescope SW 305/1500 + Camera Basler asA640-100gm + infrared filter Astrodon >700 nm + barlow 5X; processed with AutoStakkert and Fitswork4.

Related Links
Rükl plate 8

Yesterday's LPOD: Smaller Frac - Again

Tomorrow's LPOD: Silvery Spendor


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