Lava Rocks A volcano is a crack in the earth's crust.
Volcanoes start at the edges of huge rocky plates that make up the earth's crust.
When these plates hit each other, one plate pushes down underneath the other plate. At the rocky stuff is pushed down, it melts to form magma. The magma bursts up through the surface and makes the volcano. Lava is magma that comes to the earth's surface. Lava bombs are blobs of rock spat out by the volcano.