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Publié le 18/05/2020
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Subduction - geography.
Mariana Islands
The Pacific Plate is slowly but constantly expanding westward (see Expanding Oceans Map Trek).
Because the Pacific Plate's oceanic crust is denser than the continentalcrust of Guam and the Mariana Islands—an island arc (see Island Arcs Map Trek) on the Philippine Plate—the Pacific crust plunges beneath the islands in a process calledsubduction.
Along the line where the plates meet, their motion generates frequent, shallow earthquakes (see Earthquake Belts Map Trek), shown in green.
As the Pacificcrust sinks deeper, its motion produces deep earthquakes farther west, shown in brown, and it is melted by Earth's interior heat.
The resultant molten rock is less densethan the surrounding material, so it rises to the surface to form volcanoes (see Volcanoes Map Trek).
Mariana Islands: Physical Features
Where oceanic crust sinks beneath a continental plate through subduction, a deep trench forms on the ocean floor.
The Mariana Trench, just east of Guam and the MarianaIslands, reaches a depth of 11,033 m (36,198 ft)—the lowest point on the surface of Earth's crust.
Indonesia
The crust of the Indian Ocean, which is carried by the Indo-Australian Plate, plunges beneath the islands of Indonesia, on the Eurasian Plate.
Note the pattern of shallowearthquakes near the boundary between the plates, and volcanoes and deeper quakes farther from the boundary, where the ocean crust is melting far below the surface.This pattern is typical of subduction zones, which line the western, northern, and eastern margins of the Pacific Ocean.
Lesser Antilles
Here, the Atlantic Ocean crust, carried by the North American and South American plates, is subducting beneath the Lesser Antilles, on the Caribbean Plate.
Subduction alsooccurs at the eastern edge of the Scotia Plate, just southeast of South America (see Little Plates Map Trek).
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