VOLCANOES

Volcanoes are holes or vents in the Earth s crust, created when molten hot magma under the crust of the Earth is forced upward to the surface. Magma collects in a chamber beneath the crust, pressure builds up and forces it up through cracks or fissure and a conduit to the surface is created. Hot gases try to escape but are trapped in the magma. The surface of the Earth begins to bulge until the pressure can no longer be contained. Gases and fragments are released in a violent explosion called a volcanic eruption.

A volcano can erupt many times in its lifetime. The material released over many eruptions gradually builds up a cone shaped mountain. In the center of the mountain is a vent called the central vent, there can be smaller side vents that come off of the central vent. In many volcanoes there is a bowl shaped crater at the top of the central vent. Under the volcano there is a large magma chamber where the magma is. The explosive power of a volcano depends on how much gas is trapped in the magma. When there is a lot of gas trapped in the magma the eruptions are more explosive, and when there is less gas the eruptions are less explosive. Magma oozes out of the volcano in the form of lava. The lava expelled from an erupting volcano settles on the sides of the volcanic mountain and cools forming a hard crust of brand spankin new earth. Depending on how much lava and tephra build up different types of volcanoes can be formed.

There are three major types of volcanoes, cinder cone volcanoes, composite volcanoes, and shield volcanoes. Cinder cone volcanoes are small volcanic mountains made up exclusively of fragmented lava that erupts explosively and is made up of cinders. Cinder cones usually have a short life, that is why they are quite small. The second major type of volcano, the composite volcano, in contrast to the cinder cone can grow much larger. One famous example of a composite volcano is Mt. Fuji in Japan. The third type of volcano is the shield volcano. Shield volcanoes are gently sloping mound shaped volcanoes formed by weak eruptions with liquid lava that spreads out around the crater.

Volcanoes are constantly changing the face of Earth. Even though they are sometimes deadly, volcanoes are an important part of the Earth s geology and they help humans to better understand the internal processes that shape our planet.