AS16-4656(P)
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                                                          Figure 211                                           Figure 216

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Click here for larger NASA image of Figure 216
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This oblique view of part of the flat floor of the ancient crater Alphonsus shows faults that break the floor along straight line fractures. Spaced at irregular intervals along some of the rilles are dark halo craters that have broad low rims. The first detailed pictures of these craters were taken by Ranger 9 in 1964 (Click on Section 44 below to see these images). This photograph confirms the detail in the Ranger picture and confirms the hypothesis that the dark halo craters are volcanic in origin. Their constructional rims indicate that they cannot have formed by collapse of material running back into the fault zone. The smooth rim deposits indicate that fine grained material was ejected uniformly from the volcanic vent. These deposits differ markedly from the ejecta patterns around bright, young impact craters.   -H.M.
 
 

Report Source: NASA SP-362, Page 206, Figure 216

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