Figure 191                                                   Figure 192

 Click here for larger NASA image of Figure 191
Click here for larger NASA image of Figure 192
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A low Sun angle, larger scale view (right) of part of the area shown in figure 191. Rima Prinz I (1) graphically displays many of the features considered to be indicative of lunar basaltic lava channels. The rille starts in a crater on the side of the ancient crater Prinz (just off the photograph) and descends about 300 m, becoming narrower and shallower downslope. It is a "two story" channel with a broader older channel and crater inside of which is a younger, more sinuous, channel with its source vent. Samples returned by Apollo 15 from the very similar looking Rima Hadley were from a vesicular (full of holes formed by gas bubbles) flow of layered basalt. The next channel to the west (2) also gets narrower and shallower downslope. It is the best example of distributaries-that is, a branching network of smaller channels at the downstream end of a larger channel.

Krieger (3) is a "Gambart type" crater inferred to be volcanic in origin. Its flat floor, irregular shape, and highly irregular external deposits resemble the crater Gambart south of Copernicus, which was studied in 1967 by Apollo 17 astronaut H. H. Schmitt. The deposits from Krieger lie on the surface of the mare basalts, indicating that the crater is quite young. Its youthfulness is confirmed by the freshness of the crater floor deposits and the characteristic shape of these deposits. A nice example of a sinuous rille, interpreted as a lava channel (4), runs out of the crater onto the mare surface. This lava surface is marked by wrinkle ridges (5)- complex mare ridges, generally asymmetric, with a braided ridge along one edge. These ridges are interpreted to be faults or breaks in the mare lava flows along which a later generation of molten lava has been both intruded, raising the already cooled mare lava flows, and extruded onto the mare surface.

A small (8 km diameter), young impact crater (6) is excavated into the mare material. The continuous ejecta blanket formed by the base surge-turbulently flowing ejecta riding on the surface-is particularly well shown. It forms a typical dune pattern (7); the crest to crest distance (200 m) is an index of the velocity of flow of the base surge. Similar dune lava features have been seen forming around terrestrial experimental craters.   -H.M.

Report Source: NASA SP-362, Page 185, Figure 192

This web page was created by Francis Ridge for The Lunascan Project
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