How Volcanoes Are Formed
The Earth and other planets have volcanoes because they are hot inside. Volcanologists think there were volcanoes 3.5 billion years ago. They found volcanic rocks in large areas covered with lave flow in these places and here is how old the are:
Canada 3.5 to 2.8 billion years
Rhodesia 3.4 billion years
South Africa 3.3 billion years
West Australia 3.1 billion years
The early volcanoes were probably very different than the ones we are used to seeing today. They erupted at higher temperatures and the lava traveled farther distances.
Only a few people have seen the start of a volcano. In these cases, the volcano started after many earthquakes took place. The most famous birth of a volcano was the Paricutin in Mexico. A Mexican farmer finished plowing his corn field at 4:30 PM when he noticed a vent open up in his field. He came back at 8:00 AM the next morning and found a young volcano cinder cone 10 meters high. This proves that young volcanoes can form quickly.
Scientist do not fully know how volcanoes are formed, but they have many theories on this topic. Volcanoes are a natural way for the earth to cool off. First, magma, a semi-solid hot rock, is under the surface of the earth. Pieces of rocks break off and go into the magma, making a gas. The gas filled magma rises towards the earths surface from the upper mantle and goes into the magma chamber about two miles from the surface. The magma chamber is like a huge bucket that holds all the hot materials. The hot magma is putting pressure on the earths crust and finally finds a weak spot or crevice. It erupts out of the center vent from the chamber and lava starts to flow out. As the lava and ash cool, it starts to flow out and over the sides of the mountain. After it erupts, a bow-shaped hole is formed at the top of the volcano. Volcanoes form from the repeated eruption of lava flow and/or ash. These eruptions can happen over a few hundred to a few hundred thousand years.
Volcanoes can either grow by intrusion or extrusion. Intrusion is when the magma moves up the volcano and stops. It never erupts so the volcano grows from the inside. An extrusion is when a volcano erupts. It grows by adding layers of lava and ash on the outside of the volcano.
Volcanoes start at three main places: hot spots, divergent margins, and subduction zones. Volcanoes usually form on plate boundaries. Many volcanoes are located in and by the Pacific Ocean. Japan, Hawaii, and Galapagos Islands were all formed from volcanic eruptions.