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?

volcano in Nicaragua

Volcanoes dominate the landscape in parts of Central America.

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.

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.


Volcanoes form at the edges of tectonic plates.

volcano in Nicaragua

Steam or lava escapes through vents that extend deep within the volcano.

books by Nancy Sathre-Vogel

About Nancy Sathre-Vogel

After 21 years as a classroom teacher, Nancy Sathre-Vogel finally woke up and realized that life was too short to spend it all with other people's kids. She and her husband quit their jobs and, together with their twin sons, climbed aboard bicycles to see the world. They enjoyed four years cycling as a family - three of them riding from Alaska to Argentina and one exploring the USA and Mexico. Now they are back in Idaho, putting down roots, enjoying life at home, and living a different type of adventure. It's a fairly sure bet that you'll find her either writing on her computer or creating fantastical pieces with the beads she's collected all over the world.

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2 Responses to How Do Volcanoes Form?

  1. Robert Kamau November 20, 2013 at 2:43 am #

    Thanks for a great lesson on volcanoes and lava. How you get your kids to cycle around the americas still beats me. They must be supper charged boys you have there.

    • Nancy Sathre-Vogel November 20, 2013 at 7:48 pm #

      @Robert Kamau, HA! Nope – they are pretty average boys. They just made the decision they were going to do it. Kids don’t second guess themselves like adults do.

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