The tectonic plates move because they are floating on the liquid mantle of the earth. This mantle in turn also moves due to convection currents that cause hot rock to rise, give off a little heat, and then fall. This phenomenon of the liquid mantle generates eddies of liquid rock under the crust of the earth, which move to the plates (BBC, 2011).
Tectonic plates are subterranean layers that move, float and sometimes fracture, and whose movement and collision can trigger phenomena of continental drift, earthquakes, the birth of volcanoes, the formation of mountains and ocean trenches.
Tectonic plate map.
The depth of the liquid mantle makes its study difficult, for which reason the nature of its behavior has not yet been fully determined. However, it is believed that the movements of tectonic plates are caused in response to sudden stresses and not by underlying temperature changes.
The process of formation of plate tectonics or plate tectonics can take hundreds of billions of years to complete. This process does not occur uniformly, since small pieces of plate can join with each other, generating shocks on the earth's surface that vary in intensity and duration (Briney, 2016).
Apart from the convection process there is another variable that makes the plates move and that is gravity. This force causes the tectonic plates to move a few centimeters each year, causing the plates to have become enormously distant from each other over the passage of millions of years (EOS, 2017).
Convection currents
The mantle is a liquid material but dense enough for tectonic plates to float in it. Many geologists think that the reason why the knob flows is because there is a phenomenon known as convection currents that has the ability to move the tectonic layers (Engel, 2012).
Convection currents are generated when the hottest part of the mantle rises, cools, and re-submerges. By repeating this process several times, the necessary movement is generated to displace the tectonic plates, which have freedom of movement depending on the force with which the convection currents agitate the mantle.
The linear movement of the plates can be explained by the way in which the convection process forms units of fluid mass or cells that in turn move in different directions as seen in the following graph:
Convection cells are constantly changing and behave within the parameters of a chaotic system, which allows the generation of different unpredictable geographical phenomena.
Some scholars compare this phenomenon to the movement of a child playing in a bathtub full of toys. In this way, the land surface can join and separate several times in an indeterminate period of time (Jaeger, 2003).
Subduction process
If a plate located under the oceanic lithosphere meets another plate, the dense oceanic lithosphere submerges under the other plate sinking into the mantle: this phenomenon is known as the subduction process (USGS, 2014).
As if it were a tablecloth, the sinking oceanic lithosphere drags the rest of the tectonic plate, causing its movement and a violent shaking in the earth's crust.
This process causes the separation of the oceanic lithosphere in various directions, giving rise to ocean baskets, where a new, warm and light oceanic crust can be created.
Subduction zones are places where the Earth's lithosphere sinks. These zones exist in the convergent zones of plate boundaries, where one plate of the oceanic lithosphere converges with another plate.
During this process there is a descending plate and another that is superimposed on the descending plate. This process causes one of the plates to tilt at an angle between 25 and 40 degrees from the earth's surface.
Continental drift
The theory of continental drift explains how the continents changed their position on the earth's surface.
This theory was raised in 1912 by Alfred Wegener, a geophysicist and meteorologist who explained the phenomenon of continental drift based on the similarity of the fossils of animals, plants and various rock formations found on different continents (Yount, 2009).
It is believed that the continents were once united in the manner of Pangea (a super continent more than 300 million years old) and that they subsequently separated and displaced to the positions that we know today.
These displacements were caused by the movements of the tectonic plates that took place over millions of years.
The curious thing about the theory of continental drift is that it was initially discarded and endorsed decades later with the help of new discoveries and technological advances in the field of geology.
Movement speed
Today it is possible to track the speed of the movement of tectonic plates thanks to the magnetic bands located on the bottom of the ocean floor.
They can record variations in the Earth's magnetic field, allowing scientists to calculate the average speed with which the plates are moving apart. This speed can vary enormously depending on the plate.
The plate located in the Cordillera del Artíco has the slowest rate of speed (less than 2.5 cm / year), while that of the East Pacific, near Easter Island, in the South Pacific, 3,400 km to the west Chile, has the fastest movement rate (more than 15 cm / year).
The speed of movement can also be obtained from geological mapping studies that allow us to know the age of the rocks, their composition and structure.
These data allow us to identify if one plate boundary coincides with another and the rock formations are the same. By measuring the distance between the formations, an estimate can be given of the speed with which the plates have moved in a given period of time.
References
- (2011). BBC. Retrieved from Changes to the Earth and its atmosphere: bbc.co.uk.
- Briney, A. (2016). About Education. Retrieved from Plate Tectonics: geography.about.com.
- Engel, J. (2012, 3 7). Quora. Retrieved from Why do tectonic plates move ?: quora.com.
- (2017). Earth Observatory of Singapore. Retrieved from Why do tectonic plates move ?: earthobservatory.sg.
- Jaeger, P. (Director). (2003). Causes of Tectonic Plate Movement.
- (2014, 9 15). US Geological Survey. Retrieved from Understanding plate motions: usgs.gov.
- Yount, L. (2009). Alfred Wegener: Creator of the Continental Drift Theory. New York: Chelsea House Publishers.