Why do volcanoes occur in earth?
Techtonic plates move over eachother, and over time they push up to for a mountain or some type of land mass (a possible Volcano). Volcanoes form when magma (molten rock) from within the Earth erupts to the surface. If you have lots of eruptions from the same place, eventually a large volcano will build up. Some volcanoes only erupt once and never again. They tend to be the small ones. Volcanoes are continually being born, so there will be new ones coming along all the time. If you look at a map of volcanoes you will notice that they do not occur all over the Earth, but instead, in rather definite areas. This is because magma does not reach the surface at just any old place.
