Types of Plate Boundaries

Plate tectonics is the scientific theory that describes the large-scale motion of seven tectonic plates that make up the Earth's lithosphere. The lithosphere is the rigid outer shell of the Earth, composed of the crust and upper mantle. The plates move slowly over the Earth's asthenosphere, a viscous layer of the upper mantle that allows the plates to slide over it.

Types of Plate Boundaries
Types of Plate Boundaries

There Are Three Main Types of Plate Boundaries

Divergent Plate Boundaries

Divergent plate boundaries are where two plates move away from each other. when plates diverge, spreading centers form creating new oceanic crust. Examples include mid-ocean ridges in world's ocean basins. Spreading centers occur where continents are pulling apart. Examples include the Africa rift zones, Red Sea basin, Iceland, and North America's Great Basin region including the Gulf of California.

Divergent plate boundaries are associated with a variety of geological features, including:

  • Mid-ocean ridges:  Mid-ocean ridges are underwater mountain ranges that run through the  middle of all the major oceans. They are formed by the rising of hot  mantle material at divergent plate boundaries.

  • Rift valleys: Rift  valleys are long, narrow valleys that form when two plates begin to move  apart. They are often found on land, but they can also form underwater.

  • Transform faults: Transform faults are faults that connect mid-ocean ridges. They allow the plates to slide past each other horizontally.

Spreading center

Spreading centerA linear area where new crust forms where two crustal plates are moving apart, such as along a mid-oceanic ridge. Spreading centers are typically seismically active regions in ocean basins and may be regions of active or frequent volcanism.

Convergent Plate Boundaries

Convergent plate boundaries are where two plates move towards each other. This type of boundary can be found at subduction zones, where one plate slides beneath another, and at collision zones, where two plates collide head-on.

When continents collide... mountains belts form - examples include the Himalayas, Alps, and ancient Appalachian Mountains when the ancient continent of Pangaea formed. - examples include the Andes Mountains, Aleutian Islands, Japan, Philippines, Indonesia, the ancient Sierra Nevada and modern Cascades Range.

Convergent plate boundaries are associated with a variety of geological features, including:

  • Volcanoes: Volcanoes  are formed at convergent plate boundaries, where the subducting plate  melts and releases water and other volatile substances. These substances  rise to the surface and trigger the eruption of volcanoes.

  • Mountain ranges:  Mountain ranges are formed at convergent plate boundaries, where two  plates collide head-on and the crust is crumpled and pushed upwards.

  • Oceanic trenches: Oceanic trenches are deep, narrow depressions in the ocean floor that are formed at subduction zones.

Subduction Zone

Subduction zonea plate boundary along which one plate of the Earth’s outer shell descends (subducts) at an angle beneath another. A subduction zone is usually marked by a deep trench on the sea floor. An example is the Cascadia Subduction Zone offshore of Washington, Oregon, and northern California. Most tsunamis are generated by subduction-zone-related earthquakes. 

Transform Plate Boundaries

Transform plate boundaries are where two plates slide past each other horizontally. This type of boundary is found at fault lines, such as the San Andreas Fault in California. when plates slide past each other creating fault systems along plate margins. Examples include the San Andreas Fault and major faults in Pakistan, Turkey, and along the Jordan River/Dead Sea. 

Transform plate boundaries are associated with earthquakes. As the plates slide past each other, they can get stuck and pressure builds up. When the pressure is released, the plates can slip suddenly, causing an earthquake.

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