Petroleum pits

Petroleum Pits

A tar pit, or more accurately known as an asphalt pit or asphalt lake, is a geological occurrence where subterranean bitumen leaks to the surface, creating a large area of natural asphalt. This happens because after the material reaches the surface its lighter components vaporize, leaving only the thick asphalt

Examples of these Tar Pits can be found on many planets (Such as Alvor's Cove )