Tectonic activity - The Structure of the earth
How do we know what is beneath our feet?
1. We can study the material ejected from volcanoes.
2. We can study earthquake waves to understand the different layers.
Crust - made up of two types of rock, Continential crust (granite) & Oceanic crust (balsalt). The crust is broken up into plates which float on the mantle.
Mantle - a layer of molten rock. temperature increases with depth. ie. some areas are warmer than others. these heat differences set up convectional currents in the mantle ie. it moves.
Core - Inner core and Outer core. made of dense rock - iron & nickel. temperatures in 5000 degrees celcius +. outer core liquid. inner core solid of weight of the earth above.
The Earth's convectional currents
- The earth's core is extremely hot. the core has hot spots. in these areas it heats up the magma. As it is heated it gets lighter and rises.
- Near the surface it cools and gets heavier, then sinks.
- these circular movements are called currents. they keep the magma moving. in effect move the plates as well.
The earth's core is extremely hot due to radioactive processes and reaches temperatures in excess of 5000 degrees celcius. Some parts of the core are warmer than others - hot spots. This heats the magma, causing it to rise - the higher the lower the density.The further away from the core it travels the cooler it gets, as a result the density increases and is forced to come downin a circular motion i.e convectional cell. when it is nearer the core, the process starts again. These convectional currents in the mantle cause the tectonic plates to be pulled apart or force into one another - creating volcanoes.
The crust is broken into several large pieces called plates.
convectional currents cause the plates to move, perhaps by just a cm a year.
Plates move apart, towards each other or side ways past one another.
the place where the plates meet is called a plate margin/ boundary there are 3 main types of margins.
DESTRUCTIVE - towards each other.
CONSTRUCTIVE - apart
CONSERVATIVE - past each other.
DESTRUCTIVE PLATE BOUNDARY / MARGIN
The plates move together because of convectional currents in the mantle. ( continential & oceanic)
The oceanic crust sinks, because it is denser into the subduction zone.
Friction will prevent movement. Pressure will build up. When released energy is given off = EARTHQUAKE.
Heat melts the oceanic crust to form magma. This rises to the surface to form volcanoes.
CONSTRUCTIVE PLATE BOUNDARY / MARGIN
Plates pull apart due to the convectional currents in the mantle.
A "fault" is left in the earth's crust.
Upwelling magma from the mantle rises to fill the crack
CONSERVATIVE PLATE BOUNDARY / MARGIN
Plates slide past each other due to convectional currents in the mantle.
Friction prevents movement , pressure builds up.
Eventually the rocks snap energy is released = earthquake.