Subduction

Subduction is a geologic process in which one of the plates in Earth's crust subducts, or slides under, another plate. Subduction is a key part of plate tectonics, which is a scientific theory about how Earth's surface changes. Subduction occurs when one tectonic plate is denser than another. Subduction zones are located in places where two of Earth's plates meet. Scientists believe that subduction is one of the most important forces shaping Earth's crust, and it is responsible for creating mountains, forming volcanoes, and more. Subduction has important effects on all living things on Earth. Although subduction is an important geologic process, the changes it causes occur very slowly.

Plate Tectonics and Subduction

Plate tectonics involves the theory that Earth's crust, or outer layer, is made up of plates that are constantly moving and shifting. A number of different factors cause the plates to move and shift. Subduction is one of the geologic processes that cause the plates to move.

Subduction occurs only in the ocean. This happens because Earth has two different types of plates: continental plates and oceanic plates. Continental plates make up most of Earth's dry land, and oceanic plates are the plates that lie beneath the ocean.

Oceanic plates are comprised of different material from continental plates, and they are denser than continental plates. Because oceanic plates are denser, they can be pushed down. Continental plates are too light to be forced down through subduction. Therefore, when two continental plates meet, they usually crumple and form mountain ranges.

When an oceanic plate meets a continental plate, the denser oceanic plate is often forced under the continental plate, causing subduction. When an oceanic plate is forced under a continental plate, a large trench is formed where the two plates meet. Ocean trenches are the deepest places on Earth's surface, and they can be ten kilometers below the rest of the sea floor. The subduction of an oceanic plate under a continental plate can also cause mountain ranges and volcanoes to form on the continental plate. Subduction also can cause earthquakes on continental and oceanic plates.

Oceanic plates also are affected by subduction when they collide with each other. When two oceanic plates meet, the denser plate can be forced underneath the other plate. A deep-sea trench is formed between two oceanic plates. The plates also can form a string of undersea volcanoes, which may eventually form volcanic islands such as Japan and the Philippines.

Subduction Zones

Subduction zones are areas where subduction takes place. All subduction occurs at convergent plate boundaries. A convergent plate boundary is a place where two plates meet and collide. In subduction, the force of the collision causes the leading edge of one of the plates to slide below the other plate. When one plate slides under another plate, the plate that is forced underneath will begin to melt slightly. The crust and mantle that melt through subduction turn into magma. Sometimes, that magma is forced back up through Earth's crust in the form of a volcano.

Subduction and Other Geologic Processes

Subduction is one of many geologic processes that shape Earth's surface. Subduction and other geologic processes affect one another. Seafloor spreading, which is a process that creates new Earth crust through volcanic activity, is another important geologic process. In the past, scientists believed that subduction was a result of seafloor spreading. They believed that subduction was a passive event that occurred because the new crust created by seafloor spreading pushed plates into each other. However, scientists now believe that the forces associated with subduction are even more powerful than those associated with seafloor spreading. Subduction is now thought of as the most important force in driving the actions of plate tectonics.

Subduction also is important because of the effects it has on Earth's surface. For example, subduction often plays a role in areas where volcanoes form. Many volcanoes, including Mount St. Helens in Washington, occur along subduction zones. These areas commonly have volcanoes because subduction zones form magma.

The volcanoes that form around subduction zones are usually violent, strong volcanoes because the magma in these volcanoes is too stiff to allow gas to release. The gas builds up, and the volcano eventually experiences a fierce explosion, which is what happened when Mount St. Helens violently erupted in 1980.

The volcanoes that form around subduction zones are called convergent-boundary volcanoes because they occur near convergent plate boundaries. The so-called Ring of Fire, which is a ring of volcanoes that formed around the Pacific Ocean, follows the path of convergent plate boundaries and subduction zones.

Effects of Subduction

Subduction affects life on Earth in many ways. It benefits living creatures on Earth. For example, the dry land that is available for plants and animals is made possible in part by the mountains and volcanoes formed by subduction. Subduction also helps create fertile soil in which plants thrive. Nevertheless, subduction can be harmful to plants and animals in other ways. For example, volcanoes and earthquakes can be destructive and even deadly.

The changes that subduction makes to Earth's surface also affect scientific research. Because of plate tectonics (and subduction in particular), large parts of Earth's crust are changed over time. When parts of the crust are pushed down and melted through subduction, any information about climate and magnetic reversals is erased. Because of subduction, it is difficult for scientists to know much about the history of Earth's crust before about 600 million years ago.

Subduction is an important force that is continually changing the face of the earth, but the subduction process occurs very slowly. Earth's plates move only a few centimeters a year, so changes in plate tectonics occur over thousands of years.

Bibliography

"The Continental Slide." PBS. PBS. Web. 26 Dec. 2014. http://www.pbs.org/wgbh/aso/tryit/tectonics/convergent.html

Frisch, Wolfgang, Martin Meschede, and Ronald C. Blakey. Plate Tectonics: Continental Drift and Mountain Building. New York: Springer, 2010. 91–119. Print.

Kious, J. and Robert I. Tilling. This Dynamic Earth: The Story of Plate Tectonics. Washington, DC: U.S. Geological Survey, 1996. 36–69. Print.

"Ocean Trench." National Geographic. National Geographic Society. Web. 26 Dec. 2014. http://education.nationalgeographic.com/education/encyclopedia/ocean-trench/?ar‗a=1

"Seafloor Spreading." National Geographic. National Geographic Society. Web. 26 Dec. 2014. http://education.nationalgeographic.com/education/encyclopedia/seafloor-spreading/?ar‗a=1

"Subduction Zones." Columbia University Earth and Environmental Sciences. Columbia University. Web. 26 Dec. 2014. http://www.columbia.edu/~vjd1/subd‗zone‗basic.htm

"Subduction Zones." National Oceanic and Atmospheric Administration. National Oceanic and Atmospheric Administration. Web. 26 Dec. 2014. http://oceanexplorer.noaa.gov/edu/learning/player/lesson04.html

"Understanding Plate Motions." U.S. Geological Survey. United States Geological Survey. Web. 26 Dec. 2014. http://pubs.usgs.gov/gip/dynamic/understanding.html

van Kedken, Peter E. and Cian R. Wilson. "An Introductory Review of the Thermal Structure of Subduction Zones: I—Motivation and Selected Examples." Progress in Earth and Planetary Science, vol. 10, no. 42, 28 July 2023, doi.org/10.1186/s40645-023-00573-z. Accessed 22 Nov. 2024.