The Tectonic jigsaw
The earths crust is divided up into plates
- Plates move very slowly (a few mm per year)
- Plates move at plate boundaries
There are three types of plate boundaries
1) Constructive (Tensional) plate boundaries is where two plates move away from each other. Magma rises from the mantle and new crust is created. eg. Mid-atlantic ridge
2) Destructive (compressional) plate boundaries is where Two plates move towards eachother. Crust is destroyed, Fold mountains, earthquakes and volcanoes are common. eg.West coast of south america
3) Conservative plate boundaries is where plates move sideways again eachother. Material isn`t gained or lost and volcanoes are rare but earthquakes are common eg. The San Andreas fault
Volcanoes and Earthquakes are near plate boundaries
Earthquakes occur at destructive (compressional) or conservative plate boundaries
1) As two plates move towards each other , one can be pushed down under the other one and into the mantle. If this plate gets stuck it causes a lot of strain in the surrounding rocks.
2) When this tension in the rocks is finally released. it produces strong shock waves known as seismic waves. This is called an earthquake
- The shock waves (seismic waves) spread out from the focus- the point where the earthquake starts. Near the foucs the waves are stronger and cause more damage.
- The epicentre is the point on the Earth`s surface immedienty abouve the foucs
The richter scale measures Earthquakes
- Most serious earthquakes are in the range of 5 to 9.
Vocanoes are often (but not always) cone shaped,formed by material from the mantle being forced through an opening in the earths cruth,the vent
A composite volcanoe is made up of lava and ash
1) four different substances can be ejected through the vent
- pieces of rock known as volcanic bombs
- molten rock- known as magam when it`s under the ground and lava reaches the surface
2)once this material has been thrown out at the surface,it cools and hardens,forming the volcano mountain from the mixture of ash and lava.
3) Mount Etna is a famous example of a composite volcano
Sheild and cone volcanoes are made of lava only
1) Shield volcanoes: where the lava is basic and runny. it flows quickly and easily spreading over large areas forming wide, flat feature -eg. Manua Loa
2) Cone volcanoes: where the lava is acid and thicker. it flows more slowly and hardens quickly to form steep-sided features - eg. Mount St. Helens
Tectonic Hazards in LEDCs and MEDCs
Three factors affect how serious the disaster is:
1)Rural / urban areas: Rural areas have fewer people and buildings so the size of the disaster is smaller.
2) Population density: The more people , the more the deaths
3) How prepared countries are: LEDCs have less time, money and expertise to prepare for hazards. MEDCs are better prepared but they still cant stop disasters happening
Surviving Tectonic hazards
Good planning reduces the effects of a Hazard.
- Monitoring helps predict when hazards are coming so people can be warned.
- Families can organise supplies of food and water, dust masks,spare clothes etc...
- Local emergency services such as police , fire birgade and ambulance can be well prepared to deal with any hazard
- information on emergency procedures can be made available to the public
- Disaster plans can be drawn up by local authorities and governments.
People live in earthquake and volcanic zones
1) Volcanic lava and ash make fertile soils so people settle and farm nearby
2) Precious minerals and fossil fuels are found in disaster zones
3)Land is cheap in volcanic and earthquake zones and people feel safer with technolgical advances like 'earthquake proof' houses.