Geology And Geophysics

Types of Volcanoes

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There are four basic types of volcanoes. While there are several that occur in specific locations, like subglacial (under the ice caps) or submarine (on the ocean floor), or size, like super volcanoes, the four basic types that occur are composite, cinder, shield, and lava domes. These either occur separately, or more commonly as part of a compound volcano, or complex volcano.

When one thinks of a volcano, often, it is a composite volcano. This is the type of volcano that is the classic cone shape formed by layers of lava laid down during periods of activity followed by periods of inactivity. These periods of inactivity can last for several hundred years. Some examples are Mt. Saint Helens and Mt. Fuji. The eruptions are usually explosive, causing destruction for miles around. In the case of Mt. Saint Helens, an entire forest was completely devastated, the trees knocked over at ground level.

The next type is called cinder volcanoes. A cinder volcano is generally a cone of lava cinders with a crater in the summit. These cinders are caused as the explosive gases in the magma explode sending out blocks of rock and lava bombs instead of a smooth flow of lava. One of the most famous examples is the one in Paricutin, Mexico, which erupted on a farm, formed a cone approximately 1200 feet tall and eventually, once the gases were burned out, started putting out smooth lava flows. During the nine years it was active, it covered about 100 miles of country side with ash and destroyed the town of San Juan.

The third type is called a shield volcano. These resemble ancient shields, being largely round with a gentle slope to the middle where a vent or vents releases the lava. These types of volcanoes are sometimes found on the sea floor. The lava from these volcanoes is basaltic and doesn't have the viscosity to mound up. Generally, these volcanoes also don't explode outward. The best example of these volcanoes is the Hawaiian Islands. These islands were formed from a chain of shield volcanoes that began on the sea floor. The process continues as the lava is cooled in the oceans, creating new land with every eruption.

The last basic volcano type is a lava dome. A lava dome is created where the lava is very viscous, causing it to mound up and over the vent it comes from, then exploding through again. The lava forms rough domes, sometimes in series along the vent. Sometimes a lava dome occurs in a compound volcano complex, causing a cryptodome. It was a cryptodome that caused the bulge in Mt. Saint Helens that preciptitated the explosion by causing the north side to subside.

Volcanoes are both destructive and creative. While volcanoes can cause great loss of life and property, volcanic soil is some of the most fertile in the world.


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Types of Volcanoes


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