THE RESTLESS EARTH
Crust – The outer layer of the earth
Plate – A section of the earth’s crust
Plate Boundary – The boundary where two plates meet
Mantle – The dense, mostly solid layer between the outer core and the crust
Convection Currents – The circular currents of heat in the mantle
Subduction – The sinking of oceanic crust at a destructive margin
Collision – The meeting of two plates of continental crust that come together and buckle
Destructive Plate Margin – Where two plates are moving towards each other
Constructive Plate Margin – Where two plates are moving apart and magma rises
Conservative Plate Margin – Where two plates slide past each other along a fault and jerk
Fold Mountains – Large mountain ranges formed by crumpled rock layers forced together
Ocean Trenches – Deep Ocean sections where an oceanic plate sinks below a continental
Composite Volcano – A steep-sided volcano made of lava and ash
Shield Volcano – A broad-sided volcano mainly made of lava
Supervolcano – A massive volcano that erupts at least 1,000km³ of material
The Structure of the Earth
The earth is made of four main layers (inner core, outer core, mantle and crust).The crust is split into plates of varying sizes and at plate margins it may move, determined by the convection currents in the layer of mantle below. In some cases platesare moving apart (destructive plate margin) and sometimes they are moving together (constructive plate margin).
The main areas of land are made up of continental crust, which is 35-70km thick, very old, cannot be renewed or destroyed and is relatively light. The ocean floor is made of oceanic crust, which is 6-10km thick, very young, can be renewed or destroyed, and is relatively heavy and so can sink.
Types of Plate Margin
There are two types of Destructive plate margins – Subduction (where the dense oceanic crust sinks below the lighter continental crust and is melted to form magma under high pressure) and Collision (where two continental plates collide rather than one sinking beneath the other). In Subduction, the oceanic crust melts in the Subduction Zone. Energy is released by the movement, and may be felt on the surface as an earthquake, which the molten magma may rise up and cause a volcanic eruption. A deep ocean trench is also formed. The continental crust is crumpled upwards into Fold Mountains.
At a Constructive plate margin the plates are moving apart and this happens mostly under the ocean. The gap left is filled by magma rising up from the mantle below to form volcanoes. Some of these volcanoes have grown large enough to become volcanic islands such as Hawaii and Iceland.
At a Conservative plate margin the plates slide past each other. The line of weakness where the two plates meet is called a fault. Pressure builds up until the plates jerk past each other and cause an earthquake. The land around it becomes crumpled and ridged,…