How does a Volcano Form?

In February, 1943, in the middle of a cornfield in Mexico, people saw a rare and amazing thing taking place. A volcano was being born! In three months it had formed a cone about 300 meters high. Two towns were destroyed and a wide area damaged by the falling ash and cinders.

What makes a volcano from? The temperature under the surface of the earth becomes higher and higher the deeper you go down. At a depth of about 20 miles, it is hot enough to melt most rocks. When rock melt, expands and needs more space.

In certain areas of the world, mountains are ranges, and a reservoir of melted rock (called "magma") may from under them. This material rises along crack formed by the uplift. When the pressure in the reservoir is greater than the roof of rock it, it bursts forth as a volcano.


In eruption hot gaseous liquid, or solid material is blown out. The material piles up around the opening, and a cone-shaped mound is formed. The "crater" is the depression at the top of the cone where the opening reaches the surface. The cone is the result of a volcano.

The material coming out of a volcano is mainly gaseous, but large quantities of "lava" and solid particles that look like cinders and ash are also thrown out. Actually lava is magma that has been thrown up by the volcano. When the magma comes near the surface, the temperature and the press drop, and a physical and chemical change take place that change the magma to lava.

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