Volcanoes are most common around the Pacific basin, often referred to as the Pacific Ring of Fire. Of the almost 1,900 volcanoes that are active today, nearly 90 percent of them are located within this ring. Thatís because the Earthís surface is made up of huge slabs called tectonic plates. These plates move because of forces and movements deep within the planet. And the plates associated with this region coincide with some of the youngest mountain ranges on Earth. When these plates move, the shifting rocks allow magma to squeeze up within the cracks the movement created in the Earthís crust. This happens frequently near where continents and oceans meet. As soon as the magma reaches the surface of the Earth, it is referred to as lava from that point on.