Or it may remain below the surface. Kinds of volcanic materials Three basic kinds of materials may erupt from a volcano. The material that erupts depends chiefly on how sticky or fluid a volcano's magma is. Lava is the name for magma that has escaped onto the earth's surface. Highly fluid lava flows rapidly down a volcano's slopes.
Sticky lava flows more slowly.
As the lava cools, it hardens into many different formations. Pahoehoe and aa cover large areas of Hawaii, where the terms originated. The stickiest lava forms flows of boulders and rubble called block flows. It may also form mounds of lava called domes. Other lava formations include spatter cones and lava tubes.