Volcanoes are named after Vulcan, the Roman god of fire. The Romans believed he lived under an island called Vulcano in the Mediterranean Sea. This island is a volcano. They thought he was a blacksmith and made weapons for the other gods. When Vulcan made these weapons, the earth would shake and the island would erupt.

The earth is made of four layers. We live on the earth’s crust made of rocks broken into small pieces. The continents, ocean floors, mountains, and valleys of the earth’s surface are in the earth’s crust. Below the crust there are pockets of melted rock. Under the melted rock is the mantle. The mantle is made of solid hot rock with temperatures from 900 to 3,000 degrees Celsius. The outer core is the third layer. It is liquid metal melted from temperatures between 3,000 and 4,000 degrees Celsius. The inner core at the center of the earth is solid metal and the temperature is between 3,000 and 6,500 degrees Celsius.

Many scientists believe that millions of years ago all the earth formed one big continent called Pangaea. They think the hot liquid mantle, called magma, under the earth’s crust bubbles like water boiling on a stove. This process is called convection. The magma tosses and turns and breaks apart the earth’s crust. Scientists have found 12 to 15 large pieces called plates in the earth’s crust. The earth’s crust looks like an eggshell that has been broken by a spoon.

The plates are like floating rafts, moving on layers of soft rocks under them. The huge plates of the earth’s crust move all the time, but do not move more than an inch or so every year. The continents and the ocean floors are on these plates. The earth’s crust is weaker at the edges where two plates meet and this is where most volcanoes are found.

Volcanoes are formed in different ways. The simplest to understand is when the hot magma breaks through a weak spot in the crust. As the magma shoots out of the crust, the cooling magma called lava becomes hard. After a while, this hard lava forms a volcanic mountain. The second way is more complicated. The convection process in the magma causes the earth’s plates to shift and move. The plates collide into each other. Sometimes one plate is pushed down into the mantel below the crust and melts. This melted material with the magma can then create a volcano.

There are also different kinds of volcanoes. The differences are the way they are made, the type of lava and the kid of volcanic material. The most common are the shield, the dome, the cinder cone and the stratovolcano.

Shield volcanoes are the type found in Hawaii. They are in the shape of wide, sloping mounds. The lava from shield volcanoes is liquid and flows from the crater and the sides of the volcano.

The most dangerous volcanoes are the dome volcanoes. The volcano in Lassen Peak, California, is a dome volcano that erupted in 1915. The lava from dome volcanoes is a thick lava that forms cones shaped like steep domes.

The cinder cone volcanoes can be explosive also. Their cones are formed from cinders, which are small, jagged pieces of rock and ash. When a cinder cone volcano erupts, these small cinders are scattered all over. The Paricutin volcano in Mexico is a cinder cone volcano.

Most volcanoes are stratovolcanoes. They are more active than shield volcanoes, but not as explosive as the cinder cone or the dome volcanoes. They are built in layers of lava, cinder and ashes. Mount Fuji in Japan is a stratovolcano.

Volcanoes are different sizes and shapes. Many volcanoes are shaped like cones. Others are long cracks in the earth’s crust. Some are very small and very steep. Volcanoes that are very high mountains usually have been formed by earlier eruptions. When the lava cools, it make the mountain bigger and higher.

Volcanoes are made of three parts. There is a reservoir inside the earth filled with melted rock called magma. At the top of the reservoir is a chimney that the magma climbs through to the top. The cone is a large hole on top of the volcano. The magma and other volcanic material come out of the cone when the volcano erupts.

A crater is formed from the lava and other volcanic material during an eruption. When lava erupts from a volcano, it falls in a circle around the chimney and makes a crater. If you throw sand in a circle around you, you will stand in the middle of a circle built up at the sides. Not all volcanoes have a crater. If the lava is thick, it will fall in strips down the mountainside and not form a crater. A lake will form sometimes from rain and snow in the crater. Crater Lake near Klamath Falls, Oregon, is a lake formed in the crater of a volcano. If the weather gets too cold, the water will freeze into ice. An eruption will melt most of the ice and can cause very serious mudslides.

Sometimes a volcano will die when the magma sinks back into the earth’s mantle. The rock that supports the volcano becomes weak and falls into the volcano. If the center of the volcano sinks, a large crater forms. This is called a caldera. Caldera will fill with rain water and become a lake just like a crater.