There are three kinds of volcanoes shield,composit, and cone. There are two kinds of low silica lava Pahoehoe and Aa, Pahoehoe is the fast moving hot lava and Aa is the slow moving hot lava. Volcanoes are the weak spot in the earth's crust were molten material, or magma, comes to the surface. About 600 volcanoes are on land and many more are below sea level. The ring of fire is a major volcanic belt formed by the many volcanoes that rim the Pacific Ocean. Most volcanoes occur along dividing plate boundaries,such as the Mid-ocean ridge or in subduction zones around the edges of the ocean. There is a volcanic string of which is called the island arc. A hot spot is where magma from deep withen the mant.