How Do Volcanoes Form?

Volcanoes dominate the landscape in Nicaragua and Costa Rica – big, massive volcanoes rising up out of nowhere. Occasionally, steam or glowing red lava seeps out of tops. How do volcanoes form, anyway?

Most volcanoes are formed by the movement of tectonic plates on the surface of the earth. These plates are basically huge pieces of rock that ‘float’ on the mantle (a layer of the earth that is sort-of liquid rock). The tectonic plates are in constant motion, albeit very slow motion. They sometimes move toward each other, other times they’ll move apart, and still other times one will sink while the other rises above it.

Volcanoes dominate the landscape in parts of Central America.


When a tectonic plate sinks, it sinks down into the mantle and becomes very hot. So hot, in fact, that the rock melts. This molten rock will gradually make its way up to the surface of the earth through a series of cracks. When it reaches the surface of the earth, we refer to it as lava. As layer upon layer of lava builds up, a volcano is formed.

There are many factors that determine what kind of lava flow will occur and what type of volcano it will be. The amount of gas trapped in the lava, the kinds of minerals making up the lava, and how much pressure can be trapped in the area all affect the eruption and formation of the volcano. You can read about the types of lava and lava flows.

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Steam or lava escapes through.


Volcanoes form at the edges of tectonic plates.



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