Friction with the atmosphere has little effect in slowing down a very large, fast-moving meteorite. When it reaches the earth, it strikes with tremendous force and becomes buried beneath the surface. This sudden impact causes great compression, heating, and partial vaporization of the outer part of the meteorite and of the materials in the ground; expansion of the gases thus formed and of steam produced from groundwater causes an explosion that shatters the meteorite and carves out a crater in the ground. Such a crater is the huge Meteor (or Barringer) Crater near Winslow, Ariz. More than 160 impact craters have been identified on earth. The largest known craters believed to have been produced by meteorites have been discovered in Manicouagan, Canada; Vredefort, South Africa, and Chicxulub (off the coast of the Yucatán peninsula), Mexico. The concentration of craters is much greater on the moon and Mars because they lack an atmosphere capable of burning up—or reducing to small meteorites—all but the largest meteors before they reach the surface. The fractured rock of buried impact craters may act as a trap for oil and natural gas rising from deep underground, as is the case with Chicxulub.