Tectonics Flashcards
(18 cards)
How do earthquakes occur
Plates are put under huge stresses due to convection currents, causes rocks to suddenly jolt, forming a brief but violent shaking
How to volcanoes occur
Molten magma is able to escape onto the surface through fractures in the crust
Convection currents
Core heats the mantle
Heated areas of the mantle become less dense and rise
Upon reaching the crust , the magma cools becomes more dense and falls
Forms a convection current/cell
It is these cells which drag the overlying crust
Properties of convergent plate boundaries (O-C)
Andes mountains, Nazca oceanic plate subducted under South American continental plate
Very destructive earthquakes, can lead to tsunamis
Very destructive volcanoes
Properties of convergent plate boundaries (C-C)
Himalayas, formed when Eurasian and Indian continental plates push into each other
Destructive earthquakes, can lead to landsides
Rarely volcanoes
Properties of divergent plate boundaries
Iceland, on mid- Atlantic ridge, formed when Eurasian and North American plates pull apart from one another
Small earthquakes
Little volcanic eruptions, not very damaging
Properties of conservative plate boundaries
San Andreas Fault (USA), formed when Pacific plate and North American plates slid past each other
Destructive earthquakes
No volcanic eruptions
Epicentre
The point on the ground directly above the focus where the seismic waves are the strongest and the most damage occurs
Focus
The point many km below the earths surface where the stress is released
Richter scale
Measures earthquake magnitude Based on information and statistics Measured using a seismometer Has no limit Logarithmic scale
Mercalli scale
Measures earthquake intensity
Based n observation
Classified into 12 grades
Measured using Roman numerals
Cause of Haiti earthquake
13 th Jan 2010
Haiti lies between North American plate and Caribbean plate at a conservative plate boundary
As plates slide past each other, they stick, causing pressure to build
Stress was released (focus), sending out seismic waves which measured 7 on the Richter scale from Leogane (epicentre)
Epicentre located 25 km west of capital (Port-au-Prince)
Effects of Haiti earthquake
People- death toll 230,000, including 6,900 deaths from cholera
- 4000 survivors lost limbs
- 1.5 million made homeless
- 300,000 injuries
Environment - 70% of buildings collapsed, including presidential palace
- 60% of infrastructure destroyed, including port (prevented vital food aid reaching country)
Factors affecting death toll
Time of day
Location of epicentre
Population density
Level of warning
Why people continue to live in areas of volcanic activity
Fertile soil- if land is fertile crops can be grown which provides income for local people eg Mount Vesuvius, Naples (where grapes are grown for the wine production)
Tourist attraction- lots of volcanoes attract tourists which brings income into the local area eg Mount Etna, Sicily
Energy- can provide cheap geo-thermal energy eg Iceland
Why people continue to live in areas of earthquake activity
Raw materials- mineral sulphur found in Java, Mount Ijen, can be mined and sold for profit
Economic reasons- cannot afford to move eg Haiti
Perception of risk- people feel safe there due to the earthquake- proof buildings, so people continue t live there for the economic benefits it provides eg San Francisco, USA (jobs in Apple)
How the effects of volcanic eruptions can be reduced
Defences- Mount Etna erupted in 1993, fire brigade dug ditches and sprayed the lava with cold water, created a wall to prevent anymore lava flowing through lava diversion channels diverted the lava away from homes and businesses
Monitoring- tiltmeters measure bulge, tell us magma might be approaching surface
- geothermal images from space show heat as magma approaches the surface
- gas sampling tells us magma is active below the ground eg radon gas
How the effects of earthquakes can be reduced
Building design- Transamerica pyramid designed to withstand earthquakes, made of flexible steel which sways when the ground shakes, bottom heavy
- automatic shutters to protect windows
Education - In Japan 1st September a drill is held so people know how to react
- train emergency services to deal with injuries
