Used to be a supercontinent - pangea.All the plates were joined together.
The plates have drifted apart.
Why do plates move? -
Heat from the core of the earth causes magma to rise towards the surface. Slighlty cooler magma falls to replace it creating convection currents in the mantle. The currents causes friction on the underside of the plates. The dragging effect under the plates causes them to move. This is known as continental drift.
Types of Volcano
Dormant - not errupted recently but likely to errupt again.
Active - is errupting at the moment, has errupted recently.
Extinct - not going to errupt again.
Shield volcano - wide base, runny flowing lava - spreads easily
Strato volcano - made up of layers, sticky lava.
Constructive plate margin - plates move apart. Volcano forms as magma flows up through crust. Magma cools and forms new land - igneous rock.
Example - Iceland is on a constructive plate margin - between North American and Eurasian plates. Iceland is expanding because new land is formed. There are steep escarpments either side of a rift valley. Water is closer to core so gets heated naturally creating a geothermal spring.
Destructive plate margins - plates move together. Oceanic plate subducts under continental plate in subduction zone and land melts into magma - land is destroyed. Land buckles up and forms fold mountains. Oceanic trench formed where plates collide.
Example - Andes mountain range, south America - on a destructive plate margin - fold mountains.
Primary and secondary hazards
Primary hazard - direct result of hazard
Pyroclastic flow- burning clouds of ash and gas.
Tephra - rock from volcanoes
Lahars - ash and gas in a cloud mixed with water to make a flowing cement.
Ash falling on buildings etc.
Secondary hazards - occur because of a change because of hazard
Transport difficulties - railways and roads destroyed
rubble (quakelakes after earthquakes)
occur when plates move passed each other and get stuck, when they move they cause movement.
Where the plates hit each other is the focus, the epicente is the place directly above where the earthquake is strongest.
Earthquakes measured on richter scale
Sichuan Earthquake may 2008
7.9 on richter scale
87,000 people died
rescues were difficult because of aftershocks
secondary hazards created - quakelakes - flooding
why do people live near volcanoes
Geothermal energy - water heated by heat from the earth
volcanic ash fertilises soils - good for farming
companies dig rock - pumice
Toursit attration - B&B's set up there
For the scenery
houses get covered in ash
gases can damage the atmosphere in surrounding area - make it hard to breathe
Erruptions cause problems
Montserrat volcano observatory - sulfur hills
seismographs pick up tremors
GPS detects deformed land
tiltmetres record movements
gas readings monitor sulfur dioxide levels
video cameras monitor appearance
Hazard mapping - dividing the land into areas safe to live, and areas too dangerous for humans
Coping with natural hazards
Short term -
LEDC's (less economically developed countires) are poor and reactive.
evacuate people, search for survivors, temporary camps for survivors, medical supplies
MEDC's (more economically developed countries) are rich and pre-emptive
Spray water from planes to cool lava
earth barriers to channel lava flow
aerial bombing to dissipate the flow
LEDC's - basic warning systems
training peple to cope with disatser, educating people from early ages (california -shake it out preparation drills), new buildings.
New buildings - earthquake proof
Counterbalancing weights on roof
cross bracing to provide extra support
shock absorbers in foundations
cover over areas immediately outside for falling materials
several emergencies stair cases