At this point, light enters into the permanent darkness of the cave from above, forming a skylight. Lava tube collapse may begin with the buckling of its roof at one location where the roof is thinnest. This isolated pit crater is located in a lava field that is crisscrossed by long, linear troughs.Ī commonly invoked hypothesis to explain these troughs is that they are collapsed lava tubes, essentially tunnels formed by underground rivers of lava. They are deep holes that may lead to underground caves in volcanic terrain. Garden variety craters are excavated by impacts and are characterized by raised rims, sloped walls and surrounded by ejecta blankets, but pit craters are simply sink holes in the ground with near vertical walls and floors that are only visible when the sun is high in the sky. These pit craters are usually appear in the younger Tharsis volcanic region, but this is one of the first seen in the older Elysium volcanic region. In the center is a small, dark pristine-appearing pit approximately 130 meters in diameter, which is clearly visible among the numerous small impact craters that are heavily covered by dust and sediment.
This image was taken of an area on the lower southeastern flank of the volcano Elysium Mons.
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