Plate Tectonics
Tectonic Plates
The earths crust consists of many huge cracked plates. These plates, known as tectonic plates, are larger than continents! These plates ‘float’ on a layer of semi-liquid rock in the upper mantle called the asthenosphere, which is the layer below the crust (or lithosphere). How many Tectonic Plates are there? The lithosphere is broken up into two types of crust, continental crust and oceanic crust and 15 major tectonic plates. These plates are larger than continents! Where can the boundaries of these boarders be found? The boarder between two tectonic plates is called a boundary. The locations of the 15 major plates boundaries can be found all over the world and seen in the image next to this paragraph. How do these plates explain the occurrences of volcanoes, earthquakes, mountain ranges and rift valleys? At the boundary of two plates, the plates can be either convergent plates, divergent plates or transform plates. A convergent boundary occurs when two plates are pushing toward each other. A divergent boundary marks two boundaries that are moving away from each other. A transform boundary occurs when two plates slide past each other Volcanoes - At some convergent boundaries, an oceanic plate collides with a continental plate. Oceanic crust tends to be denser and thinner than continental crust, the the oceanic crust gets bent and pulled under, or subducted, beneath the light and thick continental crust, this is called a subduction zone. The magma formed by the melting oceanic crust at the subduction zone rises up toward the earths surface and builds up magma chambers, where it feeds and created volcanoes on the overriding plate. Earthquakes - Transform boundaries and the resulting faults produce many earthquakes because edges of tectonic plates are jagged rather than smooth. The edges of tectonic plates are jagged rather than smooth. As the plates grind past each other, the jagged edges strike each other, catch and stick, ‘locking’ the plates in place for a time. Because the plates are locked together without moving, a lot of stress builds up at the fault line. This stress is release in quick bursts when the plates suddenly slip into knew positions. The sudden movement is what we feel as the shaking and trembling of an earthquake. Mountain Ranges - Subduction does not occur when two continental plates collide because the rock making up continental plates is generally lighter and less dense than oceanic rock, it is too light to get pulled under the earth and turned into magma. So when two continental plates collide a mountain range os formed. Rift valleys - Divergent boundaries in the middle of the ocean contribute to seafloor spreading. As plates made of oceanic crust pull apart, a crack in the ocean floor appears. Magma then oozes up from the mantle to fill in the space between the plates, forming a raised ridge called a mid-ocean ridge. The magma also spreads outward, forming a new ocean floor and new oceanic crust. However when two continental plates diverge it is known as a rift. This process creates a rift valley. |