Volcanoes

The most awe-inspiring event on Earth is the eruption of a volcano. The crust's weak spot is a volcano where molten material or magma come out. Magma is a molten mixture from rock forming substances. Lava is magma after it reaches a surface.Solid rock is cooled lava. Earth's surface is built up of the lava that is released during a volcanic activity.

On land there are about 600 active volcanoes. There are more that lie beneath the sea. Volcanic belts form along the boundries of Earth's plate. Plate boundries have huge pieces of lithosphere that diverge (pull apart) and/or converge (push together). Some volcanoes form at "hot spots" far from the boundries of the continental or oceanic plates.

Along the mid-ocean ridge is where volcanoes form. Lava pours out of cracks in the ocean floor along the ridge. In only a few places the valocanoes of the mid-ocean ridge rise above the surface of the ocean.

Most volcanoes form around the plate boundries. Slabs of oceanic crust that sinks through a deep ocean trench into the mantle are caused by subductions. When the crust melts it forms magma. Volcanoes are formed from the magma after it has erupted.

Lots of volcanoes occur on islands. The denser plate dives under the other plate forming a deep ocean trench. The lower plate sinks beneath the deep ocean trench. It then begins to melt forming magma. The magma is less dense than surrounding rocks which makes the magma seep upward through cracks in the crust. Soon enough, the magma will break through the ocean floor and create a volcano.

An island arc is a string of resulting volcano. The curve of a deep ocean trench echos from the curve of an island arc. The Aleutians, the Philippines, the Carribean Islands, Indonesia, New Zeland, and Japan are the major island arcs.