Volcanoes that explode violently usually have tall cones. This is because the materials they send up into the air fall down around the cone and build it higher.

Exploding volcanoes have magma chambers deep below them that are filled with sticky magma (molten rock). The vent (pipe) of the volcano is usually filled with old lava from the previous eruption, so pressure has to be very high inside the magma chamber before the plug can be dislodged. When this happens, the magma shoots out behind the plug.

When magma reaches the surface as a liquid it is called lava. Because the lava is sticky, it is often blown apart by the gases in the lava and so tiny drops of liquid lava are shot high into the air. They cool and fall as ash.

Most exploding volcanoes form where two parts of the earth's crust are colliding. The edge of the Pacific Ocean is where most exploding volcanoes are found.