Tectonic Plates

1. Tectonic Plates

2. The Theory of Tectonic Plates • The theory of plate tectonics is that they move portions of the Earth’s crust, creating different land masses and seas. • The theory is that radioactive energy from the Earth’s core heats up the minerals in the mantle which expand and become less dense. Convection takes place as the minerals rise and fall causing the plates to shift. • Alfred Wegener came up with the theory that continents were moving around the Earth. However he had no evidence to support this and so his ideas were only accepted in the 1950’s when discoveries provided the evidence needed.

3. Evidence to Support the Theory • The evidence found in the 1950’s which meant that Wegener’s theory could be true was mainly that of fossils, varying magnetic fields and new rocks being discovered. • Fossils of similar inheritance were found on opposing sides of the Earth and sea floors were being expanded.

4. Plate Boundaries • Constructive – the plates move apart and create deep sea trenches and expand seas. • Destructive – one plate dips under the other. Usually the continental plate goes over oceanic and can cause mountains and sea trenches. • Conservative – two plates go past each other and can cause earthquakes. • Collision – plates come together and force land upwards causing mountain ranges/volcanoes.

5. Volcanoes • Volcanoes are formed by either constructive or collision plate boundaries. Land is forced up and if there is a magma chamber below, a volcano is made. There are four types of volcano: • Strato Volcanoes – formed by alternating layers of rock and lava. Between eruptions they are so quiet they are often declared extinct. • Shield Volcanoes – they are huge in size and often spurt lava from multiple vents. They can be caused by hot spots far away from plate boundaries. • Cinder Cones – most common form of volcano and have less than impressive eruptions. • Spatter Cones – lava flow is torn by expanding gases and when they fall back to earth, cause small volcanic vents.