Pit Crater Chains
Pit craters are common near volcanoes in the Tharsis and Elysium system of volcanoes. Pit craters form when a void is produced by a cracking of the surface caused by stretching. Also, lava may drain out of an underground chamber, thus leaving an empty space. When material slides into a void, a pit crater or a pit crater chain forms. Pit craters do not have rims or ejecta around them, like impact craters do. On Mars, individual pit craters can join to form chains or even to form troughs that are sometimes scalloped. Pit craters are not common on Earth. Sinkholes, where the ground falls into a hole (sometimes in the middle of a town) resemble pit craters on Mars. However, on the Earth these holes are caused by limestone being dissolved thereby causing a void. The image below of Arsia Chasmata contains a pit crater chain.
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Arsia Chasmata, as seen by HiRISE. A pit crater chain is visible in the lower right.
Read more about this topic: Phoenicis Lacus Quadrangle
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