Geo - Tectonic plates Flashcards
tectonic plates
- large slabs of solid rock that floats on the mantle
- constantly move
layers of the earth
- crust
- mantle
- outer core
- inner core
crust
- a layer of sand and rock
- 5-50km thick
mantle
- 2850km thick
- reaches about half distance to the center of the earth
- hot enough to liquify and become slow moving molten rock or magma
outer core
- mass of molten iron
- 2200km thick
- surround the solid inner core
inner core
- mass of iron
- 3870oC
- iron melts at this temp but immense pressure keeps it solid
- 2400km in diameter
movement of plates
convection currents
core heats rock in mantle => hot semi-molten rock becomes less dense than its surrounding and rises => semi-molten rock reaches the crust above => semi-molten rock spreads out carrying the plates above it (conveyor belt) => semi-molten rock cools and sinks back down to be re-heated
2 types of crusts
- oceanic crust
- continental crust
oceanic crust
- 6km (4 miles) thick
- 200 million years old
- made of basalt
- density: 3g/cm
continental crust
- 6 to 47 miles in thickness depending on location
- 1 to 4 billion years old
- made of granite
- density: 2.6g/cm
where do earthquakes happen
- margins / boundaries of tectonic plates
- pacific ring of fire
- hotspots (areas under the crust where magma is hotter than surrounding magma)
pacific ring of fire
- string of tectonic activity
- 90% of all earthquakes
- 75% of all active volcanoes on Earth
4 types of plates boundaries / margins
- constructive boundaries
- conservative boundaries
- destructive boundaries
- destructive boundaries - collision zones
constructive boundaries
plates are moving apart (convection currents) => magma rises from the mantle => magma erupts to surface of earth (accompanied by earthquakes) => magma reaches the surface and cools => solidifies to form new crust of igneous rock => repeated
- new rocks builds up to form a volcano
- constructive boundaries tend to be found under the sea, eg. mid Atlantic
conservative plate boundary
slide in opposite direction / same direction different speed => plates move and create friction and get stuck => pressure builds => pressure releases and sends out huge amounts of energy => causes earthquake
- earthquakes on conservative plates can be destructive bec occurs to earths surface
destructive boundaries
- oceanic plate and continental plate
o.p and c.p collide => o.p forced beneath the c.p (subduction) => results in ocean trench => plate sinks into mantle and melts into magma => pressure builds up beneath earth surface => magma escapes thru weaknesses in rock and rises up thru a composition volcano (stratovolcano)
- volcanic eruptions are often violent with steam, gas and ash
destructive boundaries - collision boundaries
2 continental plates collide => weigh the same so both are forced up => forms fold mountains
- can be very powerful and destructive
- landslides can be triggered by earthquakes
how are volcanoes formed
- rupture in the crust of the earths
- allows hot lava, volcanic ash and gases to escape from a magma chamber below the surface
- volcanoes are most found where tectonic plates are diverging / converging and most are underwater
main features of a volcanoes
- ash cloud
- pyroclastic flow
- crater
- main vent
- lava flow
- magma chamber
- secondary vent
- secondary cone
- volcanic bombs
2 types of volcanoes
- composite volcanoes
- shield volcanoes
composite volcanoes
- found at destructive plate margins
- steep sides
- made up of alternate layers of ash and lava
- doesn’t flow far, sticky acidic lava
- eruptions can be violent
shield volcanoes
- constructive plate margins
- wide base
- gentle sloping sides
- lava is runny, flows a long way, basic (opposite acidic)
- frequent eruptions
- not violent
why do people live near volcanoes
- geothermal energy
- tourism
- mining
- farming
geothermal energy - volcanoes
- energy created by using steam from underground
- steam drives turbines in stations
- energy for domestic and industrial use.
- cheap and environmentally friendly
tourism - volcanoes
- scenery attracts tourists
- creates many jobs for local people (tour guides, restaurants, hotel, gifts shops)
mining - volcanoes
- brings earths riches to the surfaces
- minerals in lava underground can be mined when cooled (gold silver, diamonds, copper, zinc)
- can be dangerous to work in
farming - volcanoes
- soil is mineral-rich and fertile
- ideal for farming
- will produce healthy crops and high yield harvests
soil naturally contains
- potash
- nitrogen
- sulphur
causes of earthquakes
- movement of the tectonic plates
- seismic waves (shock waves like ripples on a pond)
- more damage occurs near the epicenter (directly above the focus)
how do earthquakes happen
plates are constantly moving => friction the plates become stuck => pressure builds => pressure release and sends huge amounts of energy => earths surface shake violently (earthquake)
how are earthquakes measured
seismometers
seismometers
- detects seismic waves
- recorded by a series of zig-zags
- can determine time, location and intensity of an earthquake
Richter scale
- measures the magnitude of a tremor
- scale of 1 to 10
factors of how severely a country is impacted
- geographical location
- level of development - predict / prepare for hazards
- magnitude - scale of the hazard
- natural factor
- population distribution - lower no of deaths
- time
- education - allow more people to survive
- frequency - how often hazard occurs
how do countries reduce the impacts of an earthquakes
3 P’s
1. prediction
2. protection
3. preparation
prediction - 3 p’s
- use of seismometers
- can predict where and when they will happen
protection - 3 p’s
- building adjustments
- rubber shock absorbers
- steel frames
- assembly area
- lightweight roof
- safety glass
preparation - 3 p’s
- earthquake drills
montserrat
location: the Caribbean
area: 12km - 8km
population: 11000
capital: Plymouth
tectonic plates: Caribbean and north American plates, destructive plates
volcano: Soufriere hills volcano, composite
cause of eruption - Montserrat
destructive plates
…
oceanic plate and continental plate
info about eruption - montserrat
- began 18 July 1995
- Plymouth was evacuated bec pyroclastic flows and mudflows began occurring
- built a huge lava dome, lava was sticky and couldn’t flow
- lava dome became unstable and collapsed
- hot fast moving avalanches of lava blocks, gas and dust
- pyroclastic flow travelled down mosquito ghaut
- pyroclastic flow couldnt be controlled by the ghaut and spilled out of it
- killed 19 people, several others were burned
primary effects - montserrat
- 2/3 island was covered in ash
- couldnt aid to people
- ash polluted the air
- over populated the evacuation place
- forest fires & tsunamis caused by pyroclastic flow made more damage
- only airport was closed
- poor sanitation
secondary effects- montserrat
- eruption destroyed two main industries; tourism and farming
- ash covered field killed crops
- farmers had no income
- vegetation was destroyed by acid rain
- polluted lakes and rivers, animal life almost impossible
- population decreased, making it difficult for the country to recover (11,000 ppl to 4,000)
immediate / long term responses- montserrat
- MVO (montserrat volcano observatory) was set up to monitor the volcano / predict eruptions
- scientists prevented progression in island for they believed another eruptions would have wiped out the whole island (no investment went to waste)
- risk map was devised to show residents where it was safe on the island
- 41 million dollars will donated by the British government to help the nation rebuild the island
- 24 thousand was given to individual families as financial aid
why do people still live near the montserrat
- adventure tourism
=> tourists visit ruins and towns which are still buried in ash - geothermal energy
=> plans to increase geothermal energy - volcanic sand
=> exports sand for construction - beaches
=> distinctive ‘black sand’ - poverty
=> no income to move countries
