The earth's crust is made up of large plates. These are called continental plates and oceanic plates.
How many continental plates are there?
There are seven continental plates. These are the North American Plate, South American Plate, African Plate, Indian Australian Plate, Arabian Plate, Eurasian Plate, and the Antarctic Plate. There are more plates, but these are oceanic plates or smaller plates made up of both continental and oceanic materials.
Do continental plates move?
Continental plates are not stationary; they move and they change. The theory regarding the movement of plates in relation to one another is called plate tectonics. It is estimated that the plates move at a rate of one to 10 centimeters per year.
When the plates move, the boundaries between them can cause disturbances in the form of volcanoes and earthquakes. These disturbances are determined by the ways the plates move in relation to one another.
Three types of boundaries
Continental plates are involved in three types of plate movement in relation to each other::
Convergent boundary: A convergent boundary is caused when an oceanic plate slides under a continental plate, creating a trench. Under the surface of the earth, some of the material from the plate and the earth's mantle melts, creating magma, which reappears in a volcano.
Collisional boundary: When two continental plates move towards one another, this results in a collisional boundary. The land then buckles and folds, with some pieces of land going up and some pieces going down, creating a mountain range.
Transform boundary: Sometimes plates will not move over or under one another, rather, they will slide against each other. This is called a transform boundary. The ongoing movement at a transform boundary creates tension between the two plates, and when this tension is released, the result is an earthquake.
If the plates are moving, have the continents changed?
According to the theory of continental drift, the plates have changed over time. The theory was proposed in 1915 by Alfred Wegener. According to the theory, the continental plates once made up an enormous landmass called Pangaea. As the plates started to drift, they broke up into two smaller continents, which are referred to as Laurasia and Gondwanaland. As these two continents broke up, the shape of the continents we see now began to form. The theory of continental drift is supported by similar fossils found on now-separate continents believed to once be connected.
What are some well-known boundaries between plates?
Off the coast of Oregon and Washington, otherwise known as the Pacific Northwest, is the Juan de Fuca Plate. This is an oceanic plate that is sliding under the North American Plate, forming a convergent boundary. This is how the volcanoes in this region were formed.
The San Andreas Fault in California is an example of a transform boundary. The Pacific Plate is moving northwest, while the North American Plate is moving southeast, creating friction between the two plates as they slide against one another. This is the cause of the high number of earthquakes in Southern California.