Crust: a thin layer of the earth, divided into plates
Mantle: upper - cooler, solid
lower - viscous molten rock
Core: iron and nickel, current generates a magnetic field
less dense more dense
made of granite rocks made of balsatic rocks
(low density materials) (high density materials)
As heat rises from the core, convection currents are realeased in the forms of cells. The currents are strong enough to move tectonic plates.
Flows from core to crust and cools as it nears the earth's surface.
The rise of current decreases, current travels horizontally. Current cools further and descends into inner earth, the temperature increases (cyclical)
Laurasia = Europe, Asia, North America
Gondowanaland = South America, Africa, Antarctica, Australasia
has changed to present days layout due to convection currents.
South America and Africa have seperated. Asia and North America have seperated.
Asia and Europe formed a destructive plate boundary
South America and Africa / Asia/Europe and North America formed a construtive plate margin.
(two plates have been pulled apart)
Continental Drift... proposed by Alfred Wegner, 'all continents once formed pangea'
- Biological - remains of Mesosaurus found in South Africa and Brazil, plants found in India and Antarctica.
- Geological - rocks found in Brazil and South Africa
- Climateological - coal, sandstone, limestone couldn't have formed in Britains prior climate.
Found in oceans, between 2 oceanic plates
Plates are forced apart by basaltic materials which creates a new crust. The crust is pulled apart forming fissures in the rock surface where molten magma reaches the surface.
Found bordering countries, between oceanic AND continental plates.
Plates are pushed together, the oceanic plate is subducted beneath the continental plate as it is more dense.
Energy is released as earthquakes. Rising magma (oceanic) can create volcanoes on continental crust.
Between 2 continental plates.
Continental plates are pushed together, buckling under the crust.
Fold mountains are formed.
Randomly placed which fills gaps between destructive and constructive plates.
Plates slide past one another, creating friction leading to earthquakes.
There is no plate being created, thus no magma is rising to the surface resulting in no volcanoes made.
Earthquakes and Volcanoes
An earthquake is... the vibration of the crust due to moving tectonic plates; can occur along any plate boundary.
Caused when tension is released from within the crust: this point is the focus, above this on the earths surface is the epicentre.
Energy is released in seismic waves, measured by a seisometre on the richter scale.
A volcano is... a lava erupting land form, created when magma rises through a fissure in the earths crust.
Differentiated by: 1) type of lava erupted
2) nature of the eruption
3) type of plate margin formed by
Positives of volcanoes:
- creates new land
- tourism attraction
- makes fertile soil
Greatest range of hazards are at destructive plate boundaries > most explosive and devastating
Volcanic Explosivity Index (VIE) measures volcanic power
Measures - volume of ejecta, height of eruption column, duration of eruption
e.g. Iceland 2010, VEI 2
Viscosity = the stickiness of lava/magma; it's resistance to flow
(determines the nature and power of an eruption and the shape of a volcano)
Factors affecting viscosity...
Temperature: higher temperature, the lower the density, the more easily it flows.
Dissolved Gases: the greater the number of dissolved gases, the more viscous the magma.
Chemistry: higher silica content, the more viscous the lava.
Viscous Magma (Andesitic) Low Viscosity Magma (Basaltic)
- low temperature - high temperature
- high number of dissolved gases - low number of dissolved gases
- higher silica content - lower silica content
Basic Shield Volcano
mostly covered by sea, layers of (mainly) lava + ash
lava: basaltic, from central vent - forming a cone
frequency: less violent, fairly frequent
explositivity: not very explosive
eg Mount Nyiagro, East African Rift Valley
Tectonics: East African, constructive
Date: January 2002
Hazards: poisonous gases, fast lava, earthquakes, could erupt whenever, volcanic activity under lakes
Soc: 120 000 homeless, 100 died, 400 000 evacuated, 12 500 homes destroyed, spread of disease, 14 villages destroyed
Eco: 12 500 homes destroyed, airport destroyed
Env: lava triggered earthquakes, poisonous gases released
Relief: UN sent 260 tonnes of food, TV appeals, $35 million recieved worldwide, measles vaccination
Can have a secondary vent, alternate layers of ash + lava
lava: andesetic, more viscous, slower - narror base + steep sides
explositivity: build up of pressure; explosive. (pyroclastic flows + ash columns)
e.g. Sakarajima, Japan
Date: 1950s onwards
Hazards: Volcanic bombs (3km from crater), pyrocrastic flows (2km long), 30km ash erupts yearly, can cause acid rain
Soc: homes for 7000 people
Eco: tourist attraction, bay is good for the economy
Env: volcanic soil is fertile, lava makes new land
Protection: air crafts measure gas produced, tiltmeters detect when volcano is full of magma, bareholes measure water temperatures, hot springs are monitored, tunnels have seisometers installed, concrete lahar channels divert mud flow, evacuations routes/drills, concrete shelters
measured on the richter scale - the larger the magnitude, the less frequent (due to the pressure build up)
refer to notes for images of building structures and case studies
Earthquakes in LEDCs...
Soc: - high density population, tightly packed Eco: - cost to rebuild
- uneducated - time to pay costs
- rapid disease spread - destroys buisnesses
- lack of training - poorly built
- corrupt government, lack of resources
Env: - dangerous locations
- lack of water sources
Factors affecting impacts...
- magnitude - time of day
- depth of focus - level of preparation
- location of epicentre
In MEDCs: loss of life is low but economic cost is high
In LEDCs: loss of life is high but economic cost is low
Hazard Resistant Buildings (LEDC)
- cross braced frame, resist lateral forces > bamboo is cheap and flexible
- concrete ties walls to foundation, firmly attached
- thatched roof > lightweight and cheap
- walls made of mud and straw absorb energy and wouldnt cause injury
- steel rod foundations extend into the ground > prevent collapsing, liquification and means the house moves with the rods
(refer to notes for diagram)
Tsunamis are... fast moving waves (up to 90km/h) with wavelengths up to 200km, can reach heights of 30m.
Triggered by earthquakes at destructive plate boundaries; continuous, can travels 10s of kms before slowing down or stopping.
1) tectonic: earthquakes displace large amounts of water in short time frames, generating energy
2) build: energy causes a train of oscillatory waves in ever widening circles at speeds of 500mph
3) travel: wavelengths grow, wave periods grow from 5mins to 1 hour
4) approach: they slow as the reach the shore due to friction between the collision and the rising sea bed; as wavelengths shorten, amplitude increases
5) impact: waves collide with shore, suceeding out the flow of water, then continue on their path of destruction.