(pictures may not appear due to no fault of my own! sorry!)
Need to know for the exam:
ï Tectonic Plates/Plate boundaries
ï Distribution of volcanoes/earthquakes
ï Haiti Case Study
ï Living near volcano/earthquake zones
ï Prediction and prevention
ï Managing hazards
ï Richter and Mercalli Scale
1) Tectonic Plates/Plate Boundaries
What are tectonic plates?
The Earth’s crust (the land we live on) is broken into pieces.
Why do the plates move?
The Earth is made up of four layers. The first is the crust, which is the land we live on. The next, the mantle which has the properties of a solid but is liquid and flows. It is made of semi-molten rock. The next two layers are the core made up of the outer core and the inner core. The outer core is liquid and the inner core solid. The inner core is the hottest part of the Earth. Both the outer and inner core are made of nickel and iron.
Heat which rises and falls in the mantle creates convection currents which are generated by radioactive decay in the Earth’s core. As the heat waves rise and hit the tectonic plates they make them move.
How do the plates move?
The point at which two plates meet is known as a plate margin or plate boundary. There are four possible ways in which the plates can move.
Constructive (Divergent) Plate Margin/Boundary:
The plates move apart from one another. By doing so it creates gaps in the crust. This allows the mantle to come through the gaps. This is how volcanoes are caused and more crust created as the mantle solidifies. This plate margin is given the name constructive, because it constructs new crust or divergent, because the plates go in different directions from one another.
Destructive (Convergent) Plate Margin/Boundary:
The thicker, denser oceanic plate (the plate that is underneath the sea) slides beneath the continental plate (the plate that is underneath the ground) and reaches the subduction zone (where one plate sinks beneath another and causes heat, friction and pressure). The oceanic plate melts and is destroyed as it reaches the mantle having been forced down.
When the plates slide past each other friction stores energy in rocks. This energy is released in the form of an earthquake. If the continental plate folds, this causes fold mountains. This is how the Himalayas and the Alps were formed. When the rocks are folding upwards, this is known as anticline. This plate margin is given the name destructive, because one plate is destroyed during the movement or convergent, because the plates move in different directions.
Collision Plate Margin/Boundary:
When continental plates collide head on causes upheaval. Both plates have similar densities so neither of the plates are subducted. A gradual forward movement of each plate creates extreme pressure. Over…