AS17-2224 (P)

Figure 95

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Resembling a dome whose top has collapsed, this unusual structure (see large arrow) may be just that. It is located in the southeastern part of Mare Crisium, a large mare-filled circular basin near the Moon's east
limb. The mare ridges shown are part of an extensive ridge system that encircles the floor of the basin. The broad circular depression occupying the center of the dome may be analogous to the calderas that occupy the center of many volcanic edifices on Earth. It may have formed as the pressure exerted on a mass of molten rock being forced upward toward the surface was released, allowing the overlying rocks to settle. A similar appearing but smaller dome with a summit depression occurs on the northwest flank (lower right side as this picture is oriented) of the larger one. Another large circular structure (see small arrow) may have formed in the same manner, but the evidence is less compelling. It can just as easily be interpreted as being the remnant of a lava-flooded impact crater that was later blanketed by the dark material covering much of the area shown here.   -G.W.C.