Volcanoes: Mount St. Helens
In this section you will learn about the structure of the Earth and how volcanoes are formed, more specifically looking at Mount St Helens a volcano in Washington State.
Use the following link to a video showing the 1980 eruption at Mount St. Helens
The structure of the Earth
It may seem like the Earth is made up of one big solid rock, but it's really made up of a number of parts. Some of them constantly moving!
You can think of the Earth as being made up of a number of layers, sort of like an onion. These layers get more and more dense the closer to the center of the earth you get. See the picture below to see the four main layers of the earth: the crust, mantle, outer core, and inner core.
The Earth's crust isn't one solid layer. It is broken up into huge areas called tectonic plates that float on top if the mantle.
Most volcanic eruptions are caused by tectonic plates moving towards each other, which usually produces violent eruptions. Other volcanoes, such as Mauna Loa in Hawaii are caused by hot spots in the Earth’s crust. These do not erupt violently and lava usually flows slowly out of them.
Watch the two videos below for more information on tectonic plates and the formation of a volcano.