There are active volcanoes all over the world and the U.S. is home to many of the world's most active and largest volcanoes. The majority of these volcanoes are situated in the western portion of the continental U.S. and in Alaska. They can be associated with different tectonic regions, which play a large role in the type of volcano that is produced.
Volcanic Regions of the United States
Subduction zones aren't the only kind of tectonic setting that has created volcanic activity in the United States. The U.S. has six major volcanic regions related to tectonics:
- The subduction zone region of the Pacific Northwest, which has created the Cascade Volcano Range, extending from northern California all the way up to southern British Columbia.
- The subduction zone region of the northern Pacific, which has created the Aleutian Arc and the volcanoes of Alaska's Aleutian Island Chain.
- The extensional region of the western interior, which has created a region with a high number of cinder cone volcanic fields.
- The transtensional region at the base of the Sierra Nevada mountain range in California, which has created the Long Valley Caldera.
- The hotspot region within the Pacific Plate, which has created the volcanoes of the Hawaiian Island Chain.
- The hotspot region within the North American plate, which has created Yellowstone Caldera and the world's largest known hydrothermal system.
How Subduction Zones Work
The type of volcano that is created in subduction zones is usually a composite volcano, also known as a stratovolcano. Some of the world's most active volcanoes are situated along subduction zones. This includes the currently active volcanoes of the Cascades Volcano Range and the Aleutian Island Volcano Chain. In subduction zones, two plates converge while one slips below the other. This commonly occurs when one plate is an oceanic plate, such as the Pacific Plate. The ocean crust is saturated with ocean water, making it more dense, and therefore heavier, than a continental plate. When this water mixes with the mantle below the continental plate, it lowers the melting temperature of the buried crust and magma is created. This less buoyant and warmer magma rises and is released through the surface of the overlying continental crust in the form of a volcano.
Subduction of an ocean plate below another ocean plate can also occur, and the results are very similar. In this scenario, the ocean crust sinks below another ocean crust. The process of the water saturated crust creating buoyant magma also occurs, except in this scenario, a volcano island arc is created in the overlying ocean plate.
The Cascades Volcano Range
In the Cascades, the oceanic Juan de Fuca plate is sliding below the continental North American plate. The crust of the Juan de Fuca plate is saturated with ocean water and creates an environment where a volcanic range is produced on the overlying continental plate. This convergence has been occurring for about 36 million years, with the most recent volcanic activity occurring for the past 5 million years. Some of the more active volcanoes of the Cascades include Mt. St. Helens and Mt. Rainier and Mt. Hood.
The Aleutian Island Arc
In the Alaskan Aleutians, the oceanic Pacific plate is being subducted underneath the oceanic portion of the North American plate. This creates an island arc in the northern Pacific Ocean, called the Aleutian Arc. All of these islands are volcanoes and these volcanoes are some of the most explosive in the world. Mt. Cleveland, known for its explosive eruptions, is one volcano in this arc. Recently, Kasatochi Volcano, another Aleutian Arc volcano, produced an ash cloud that was seen by satellites. More than 50 of these island arc volcanoes have been active since about 1760, when historical records of eruptions began.
Related Articles:
Volcano Fields of the United States
Satellites See Kasatochi Eruption
Sources:
USGS Cascades Volcano Observatory – Cascade Range Volcanoes and Volcanics
USGS Alaska Volcano Observatory – About Alaska's Volcanoes
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