The surface of the moon is very mountainous and is classified into Maria and Craters. The craters are not volcanic but were formed by the impact of massive objects, such as asteroids from outer space, on the surface of the Moon. Craters cover around 70% of the surface of the near side of the Moon, and 97.5% of the far side.
Maria ("mare" in the singular), the "seas", are the dark areas on the surface of the Moon and are actually solidified lava flows formed after the formation of the lunar crust.