loose material.

A newly formed pit crater has steep, overhanging sides and is shaped inside like an inverted cone, growing wider closer to the bottom. Over time, the overhangs fall into the pit, and the crater fills with talus from the collapsing sides and roof. A middle-aged pit crater is cylindrical, but its rim will continue to collapse, resulting in the crater expanding outward until it resembles a funnel or drain--narrower at the bottom than the top.

While pit craters and calderas form through

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