What Causes Volcanoes?
Volcanoes form when pressures within the earth force melted rock and gases upward through cracks in the surface. The earth’s crust is made up of huge plates that slowly shift about on the hot, liquid rock in the earth’s interior.
As the plates move about, they grind and bump together. The friction as one plate grinds along the edge of another causes heat. (Most earthquakes occur at these places, too.)
Heat builds up beneath the surface until liquid rock and gases expand and force their way out through cracks. The hot materials form mountains we call volcanoes.
Inside the earth’s core there is a red-hot liquid rock, called magma. When the magma bursts out of the earth, it is called lava. The type of magma in the earth can create different volcanoes.
If the magma is quite thin, the gas can escape easily and there will not be an explosion. The magma just comes out of the mountain and flows down the sides, like Volcanoes in Hawaii and Mount Etna.
But, if the magma is thick and sticky, the gas cannot escape, so it builds up and up until it explodes. This can cause landslides and sends out huge clouds of burning rock and gas, which devastate everything around them, like the famous eruptions at Mount St Helens and Montserrat.
Volcanic eruptions are spectacular sights … chunks of hot rock, red-hot ash and cinders shoot out and huge fiery clouds rise over the mountain. Most volcanic materials erupt through the central vent.
However, some magma may break through the main conduit wall and branch out into smaller channels and escape through vents formed in the sides of the volcano.
Some eruptions occur on volcanic islands. Such islands are the tops of volcanic mountains that have been built up from the ocean floor by repeated eruptions.