October 25, 2008

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Why Here?

image by Mike Wirths, Baja California, Mexico

Why do domes cluster together so often? I called the area west of Copernicus Domeland because there are so many domes, and Mike's excellent image illustrates another regional concentration of domes. The northeast corner of Mare Tranquillitatis - including the nearby Sinus Amoris - contains dozens of domes from the classic and even lettered ones just south of the Cauchy Rille to small or nearly flat ones almost anywhere you look. Nearly all domes occur in maria, just not every where. Many maria, such as Imbrium, Crisum, Serenitatis, Nectaris and Humorum, have few, but where domes do occur lava thickness is thin. For example, the domes shown here are near the mare edges, and the Domelands examples are on thin lavas that barely cover Imbrium ejecta. Domes are generally low and represent relatively small volumes of lava - most are just a few cubic kilometers according to data from the GLR study, so many early formed domes could be completely buried under thick maria. But this isn't necessarily true for few are seen in basins with only thin ponds of lava (Nectaris and Orientale), so burial is probably not a reason for a lack of domes in various maria. For domes lavas to erupt to the surface there must be conduits or fractures from the magma source region to the surface. Certainly the Cauchy Fault and Rille show that there are significant fractures in this area, but there are few obvious ones in the Domelands. Although our list of domes and understanding of their eruption conditions have increased greatly in recent years, our understanding of why they occur where they do is still fragmentary.

Chuck Wood

Technical Details
October 18, 2008, 6:00-6:30 pm pacific time. 18" Starmaster + 2.5 Televue barlow + Infinity 2-2 camera + R/IR true tech filter. Processed in Registax 4 and PS CS.

Related Links
Rükl plate 36
Geologic Lunar Research Group study of Cauchy domes.

Yesterday's LPOD: Inside Shackleton

Tomorrow's LPOD: Rille Cut


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