Divergent Boundaries At divergent boundaries in the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates. Share Tweet Email. Why it's so hard to treat pain in infants. This wild African cat has adapted to life in a big city. Animals Wild Cities This wild African cat has adapted to life in a big city Caracals have learned to hunt around the urban edges of Cape Town, though the predator faces many threats, such as getting hit by cars.
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A parallel slope may develop underneath the plate at the base of the lithosphere. These surfaces are zones of weakness that help the plate move away from the ridge. Previous Types of Plate Boundaries. During collision, the crust moves upward, and the crustal material folds, buckles, and breaks Fig.
The Himalayan Mountains were formed by the collision between Indian and Eurasian tectonic plates. Ocean trenches are steep depressions in the seafloor formed at subduction zones where one plate moves downward beneath another Fig. These trenches are deep up to The deepest ocean trench is the Mariana Trench just east of Guam. It is located at the subduction zone where the Pacific plate plunges underneath the edge of the Filipino plate.
Subduction zones are also sites of deepwater earthquakes. Transform faults are found where two tectonic plates move past each other. As the plates slide past one another, there is friction, and great tension can build up before slippage occurs, eventually causing shallow earthquakes. People living near the San Andreas Fault, a transfom fault in California, regularly experience such quakes. Recall that some volcanoes form near plate boundaries, particularly near subduction zones where oceanic crust moves underneath continental crust Fig.
However, some volcanoes form over hot spots in the middle of tectonic plates far away from subduction zones Fig. When magma erupts and flows at the surface, it is called lava. The basalt lava commonly found at hot spots flows like hot, thick syrup and gradually forms shield volcanoes. A shield volcano is shaped like a dome with gently sloping sides. These volcanoes are much less explosive than the composite volcanoes formed at subduction zones.
Some shield volcanoes, such as the islands in the Hawaiian archipelago, began forming on the ocean floor over a hot spot. Each shield volcano grows slowly with repeated eruptions until it reaches the surface of the water to form an island Fig.
Almost all of the mid-Pacific and mid-Atlantic ocean basin islands formed in a similar fashion over volcanic hot spots. Over millions of years as the tectonic plate moves, a volcano that was over the hot spot moves away, ceases to erupt, and becomes extinct Fig. Islands can erode through natural processes such as wind and water flow.
Eventually all that remains of the island is a ring of coral reef. An atoll is a ring-shaped coral reef or group of coral islets that has grown around the rim of an extinct submerged volcano forming a central lagoon Fig. Atoll formation is dependent on erosion of land and growth of coral reefs around the island.
Coral reef atolls can only occur in tropical regions that are optimal for coral growth. The main Hawaiian Islands will all likely become coral atolls millions of years into the future. The older Northwestern Hawaiian Islands, many of which are now atolls, were formed by the same volcanic hot spot as the younger main Hawaiian Islands. This document may be freely reproduced and distributed for non-profit educational purposes.
Skip to main content. Plate boundaries migrate over time and it is unlikely that convection cells within the mantle would migrate with them. The migration of plate boundaries across the surface of the Earth means that they are not firmly fixed into the underlying convective motions of the mantle - from our analysis of real plate motions mantle convection is more likely to be related to the location of hot spots and mantle plumes.
So what, then, drives the plates? An answer to this question may lie in an analysis of the forces acting on plates, both on their undersides and at their boundaries. As you work through this course you will need various resources to help you complete some of the activities. Making the decision to study can be a big step, which is why you'll want a trusted University. Take a look at all Open University courses. If you are new to University-level study, we offer two introductory routes to our qualifications.
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