Theory of tectonic plates
The Earth's rocky outer crust is not a solid shell; it is broken up into massive slabs of rock called the tectonic plates. These plates drift on top of the soft, underlying layer called mantle. The plates are broadly divided into two groups.
The plates under the oceans are called the oceanic plates and the plates under the continents are called the continental plates. Oceanic plates are denser than the continental plates.
There are about 20 plates along the surface of the earth and they move continuously. Sometimes they just slide past one another. At other times they actually collide with one another.
Plate collisions create landforms like coastal volcanoes, island arcs and mountain chains. When plates move apart, they produce a new ocean floor as magma from the mantle rises up through volcanoes and deposits new rock along the plate boundaries. In some areas plates slide alongside each other, neither creating nor destroying land.
What causes earthquakes?
Plate movement cause a build up of a huge amount of energy. When they spread apart or move past each or under each other, a lot of pressure and energy is released - this produces vibrations, that cause earthquakes. During earthquakes faults are produced by the pressure of the moving rocks. Faults are a giant crack in the rock that makes up the Earth's surface. They usually occur at the plate boundaries. These faults can be pretty long like the San Andreas fault which is 810 miles.
How can you measure the intensity of an earthquake?
A seismograph is an instrument used for recording the intensity (the energy released) and duration of an earthquake. Earthquakes are expressed in the Richter magnitude scale.
How are volcanoes formed ?
Sometimes tectonic plates sink when another one rises above it. The tectonic plate that went under sinks into the Earth's mantel and becomes very hot. It becomes so hot that it melts. This molten rock gradually makes its way to the surface of the earth through a series of cracks (faults). When it reaches the surface of the earth we refer to it as lava. As layer upon layer of lava builds up, a volcano is formed.
Where do earthquakes occur and the volcanoes erupt?
Earthquakes occur near faults and near the edges of plates in the earth's crust. Volcanic eruptions occur wherever a volcano is. Volcanic eruptions can occur when magma from below Earth's surface seeps through a weak spot (fault) in the crust. Volcanoes occur along plate boundaries and along the edges of plates.
Are earthquakes and volcanoes linked?
Volcanoes and earthquakes are strongly related. If you look at a map of earthquakes around the planet and compare it to a map of volcanoes, you'll find that they match closely. Both earthquakes and volcanoes occur at the boundaries of tectonic plates, which make up the Earth's surface. Earthquakes are caused by the release of pressure built up when the plates spread apart or move past or under each other. In slightly more complicated ways, magma is generated at most plate boundaries, and this magma rises to the surface to form volcanoes.
The movement of magma within a volcano causes earthquakes, which are usually small one. Earthquakes are also caused by adjustments of the plates under volcanoes.
Denser: Closely compacted in substance
Stress: Pressure or tension exerted on an object
Energy: A feeling of possessing strength and vitality
Complicated: Make (something) more difficult or confusing by causing it to be more complex
Mantle: The mantle is the layer between the crust and the outer core. Earth’s mantle is a rocky shell about 1,800 miles thick and it consists of about 84% of the earths volume.
Magma: Magma is a mixture of molten or semi-molten rock found beneath the surface of the Earth.