There are hundreds of active volcanoes all over the world and no two are alike. They differ in size, eruption frequency and intensity and even magma composition. Although the differences are numerous, geologists are able to group volcanoes into broad categories that enforce similarities. One of these broad categories is the principal types of volcanoes, which is based primarily on the geomorphology of a volcano.
The Principal Types of Volcanoes
There are four main groups of volcano type that geologists use to describe the size and shape of a volcano. They are:
- Cinder cones
- Composite volcanoes
- Shield volcanoes
- Lava domes
Cinder Cones
Cinder cones are considered the simplest type of volcano and most often erupt with non-explosive to mild-explosive intensity. Cinder cones, also known as tephra cones and scoria cones, are named for how they are formed – with a relatively gentle shower of magmatic material out of a vent. This magmatic material cools quickly to form small pieces of tephra, such as pumice and scoria, that build up the slopes of the volcano in the shape of a cone. Cinder cones usually do not rise higher than 1,000 feet above their surroundings and their slopes are between 30 and 45 degrees from the ground. A popular cinder cone located in the United States is Sunset Crater Volcano National Monument in Arizona, home to about 600 more cinder cones.
Composite Volcanoes
Composite volcanoes, also known as stratovolcanoes, are the result explosive volcanic eruptions, usually of silica rich magma such as andesite. Composite volcanoes can also have different eruptive styles – they can erupt more passively with lava flows, or more violently with tephra and ash columns. The accumulation of this material creates a steeply sloped volcano that has alternating layers of lava flows, coarse tephra and fine ash. Composite volcanoes also have another distinguishing characteristic which is the intrusion of lava dikes throughout the volcano. These dikes add strength to the slopes of composite volcanoes so they can usually grow to be several thousand feet above their surroundings. Like cinder cones, composite volcanoes are also cone shaped. Mt. Adams Volcano in Washington state is an example of a composite volcano.
Shield Volcanoes
Shield volcanoes are large volcanoes with broad slopes that form a shape that looks like a shield. This volcanoes are created from the frequent eruption of basaltic lava that can flow easily and for several kilometers down the slopes of the volcano. As the lava flows farther down the volcano's slopes, it cools and becomes more viscous. For this reason, shield volcanoes usually have slightly steeper slopes towards their base than at the summit. Island shield volcanoes, like those in Hawaii, can be misleading in their size since most of the volcano is under water. Mauna Loa, for example, is 13,700 feet above sea level, but if measured from the sea floor this volcano is 32,800 feet high.
Lava Domes
Lava domes form as a result of very viscous lava cooling at the vent before it is able to flow away from the vent. These domes usually occur within the crater of composite volcanoes like Mt. St. Helens. When a composite volcano erupts, much of the upper portion is destroyed during the eruption. Lava domes slowly rebuild the upper portion of the volcano during the later more effusive stages of an eruption. Lava domes are also very hazardous, since the material is unstable and prone to collapse.
Source:
Skinner, Brian J., Porter, Stephen C, and Park, Jeffrey. Dynamic Earth – An Introduction to Physical Geology. NJ: John Wiley and Sons Inc., 2004.
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