Plate Tectonics Flashcards
what is a volcano?
a volcano is formed when magma erupts onto the earth’s surface as lava through the vent in the earth’s crust
features of a volcano
- lava
- pyroclastic flow
- ash
- lahars
- vent
- secondary cones
- crater
- magma chamber
what is lava?
Magma that reaches the surface
what is pyroclastic flow?
Clouds of mixed poisonous gases and ash
what is ash?
Very fine-grained volcanic material
what are lahars?
Snow and ice melt and combine with the ash, creating lahars.
what is a vent?
Central tube through the volcano
what are secondary cones?
Eruptions from other vents lead to the formation of secondary cones on the sides.
what is the crater?
bowl-shaped basin at the top of the volcano
what is the magma chamber?
A large underground pool of magma
how do volcanoes form?
- magma rises through cracks in the earth’s crust
- pressure builds up (inside earth)
- pressure and tension are released → plate movement
- magma explodes to the surface, causing an eruption
- lava cools and forms a new crust
- over time, rock builds up, and new crusts form on top, forming a volcano
environmental impacts of volcanoes
- pyroclastic flow
- lava flow
- volcanic bombs
- laharas
- earthquakes
- landslides
- tsunami
- acid rain
- ash fallout
human impacts of volcanoes
- loss of life and injury
- collapse and destruction of buildings
- transport network damaged
- loss of jobs and businesses
- loss of crops
- power and water supply damaged
opportunities of volcanoes
- fertile soils - cooled lava contains minerals, leading to a high yield of crops
- tourism - many people want to visit the area and study it
- minerals and precious stones - can be sold, providing more work and income
- geothermal energy - the magma gives out heat, which can be used to generate geothermal energy
- creating new land areas - once the lava and ash cool forms new fertile land
stages of volcanoes
- active: has erupted recently and is likely to erupt again
- dormant: has not erupted recently but may in future
- extinct: no evidence to erupt again
what are the two types of volcanoes?
- shield volcanoes
- composite volcanoes
what is a shield volcano?
- basaltic lava
- low in height, gently sloping sides with a broad base
- low silica content (covers long distances)
- frequent eruptions but low in magnitude
- high temperature
- low gas content
There is little build-up pressure.
how do eruptions occur at constructive boundaries?
At constructive boundaries, plates move away from each other; magma rises to fill the gap
what is a composite volcano?
- andesitic lava
- high in height, steep-sided volcanic cones
- high silica content (covers short distance)
- rare eruptions but in high magnitude
- low temperature
- high gas content
- enormous build-up pressure
how do eruptions occur at destructive boundaries?
At the destructive boundary, oceanic crust melts from friction and heat from the mantle, newly formed magma is lighter, so it rises to the surface
what is a hotspot?
an area of the Earth’s mantle from which hot plumes rise upward, forming volcanoes on the overlying crust
how do earthquakes occur?
- tectonic plates move; they strike.
- pressure and tension build up as the plates try to move.
- eventually, they jolt free and pressure and tension are released inside the crust as energy.
- the energy passes through the earth’s crust as waves, an earthquake
what is an earthquake?
a sudden violent shaking of ground followed by a series of vibrations or movements in the earth’s crust
what are the features of an earthquake?
- focus
- epicentre
- convection currents
- subduction zone
- magnitude
what are the effects of earthquakes?
- a large number of deaths
- fires breaking out
- water pipes burst
- water contamination, diseases
- corpses: human & animal
- accessibility difficult
- building damaged/destroyed
- tsunami can follow
- reconstruction costs
how can earthquakes be predicted?
- measure earth tremors, pressure and release of gas
- use maps and facts to find patterns in time/location
- unusual animal behaviour
- seismometer
- richter scale
how can people prepare for an earthquake?
- build earthquake proof buildings
- train emergency services
- set up a warning system
- create an evacuation plan
- emergency food supply
- prepare earthquake kit
features of an earthquake proof building
- computer controlled weights on the top to reduce movement
- ‘birdcage’ interlocking steel frame
- steel frames which can sway with quake movements
- automatic window shatters to prevent falling glass
- open areas for people to assemble when evacuated
- foundations sunk into bedrock avoiding clay
- rubber shock absorbers to absorb earths tremors
what are the major tectonic plates?
- Nazca
- North American
- South American
- African
- Eurasian
- Indian
- Australian
- Antarctic
- Pacific
what is a collision plate boundary?
it occurs when two continental plates move towards each other
e.g. Indo-Australian and the Eurasian plate
what is a constructive/divergent plate boundary?
it occurs when two plates move away from each other e.g. North American and Eurasian Plate
what is a conservative/transform plate boundary?
it occurs when two plates slide past each other e.g. North American Plate and the Pacific Plate
what is a destructive/ subduction/convergent plate boundary?
it occurs when an oceanic plate subducts a continental plate e.g. Pacific plate and the Eurasian plate
what is the structure of the earth?
- crust
- mantle
- outer core
- inner core
what are the two types of crust?
- the oceanic crust which is thinner (5-10km) but heavier and denser
- the continental crust which is thicker (25-90km) but is older and less dense
- the oceanic crust is continually being created and destroyed due to plate movement, where it is denser and subducts under the continental crust.
case study: tohuku earthquake general information
- in japan, which is part of the pacific ring of fire, so it is used to tectonic events
- 11 march 2011
- shallow focus: 32km
- magnitude of 9.1
tohuku earthquake 4 causes
- destructive plate boundaries with pacific plate going under north american plate
- epicentre was off the coast, 129km from sendai, so there was limited time to react and evacuate
- caused a tsunami which was given a warning 12 mins after the earthquake and occurred 22 mins after earthquake
- 100’s of aftershocks, including one with magnitude of 7.1, killing 4 people
tohuku earthquake 6 primary impacts
- thousands of buildings collapsed
- 330,000 buildings deemed unsafe
- over 2000 roads and railways collapsed, crushing cars and derailing trains
- 56 bridges collapsed
- people injured by falling objects
- around 18,000 dead
tohuku earthquake 6 secondary impacts
- landslides in Miyagi
- 10m high tsunami
- cost of around $250 billion
- increased dependency ratio
- people made homeless
- food and water contaminated by nuclear waste
tohuku earthquake 4 responses
- Pacific Warning Centre alerted affected countries and most people evacuated coastal areas
- 70,000 people in the exclusion zone were evacuated
- 120,000 people were evacuated later on
- $150 billion was covered by government and insurance companies
volcano case study: Mt Merapi general facts
- active composite volcano in Java (SE Asia)
- most active volcano in asia
25 Oct - 30 Oct 2010
Mt Merapi 5 causes
- destructive plate boundary - indo-australian oceanic plate subducted below eurasian continental plate
- volcanic bombs and heat clouds with temperatures up to 800C spread over a distance of 10km
- pyroclastic flow travelled down 3km of heavily populated mountain sides (over 11,000 people)
- volcanic ash fell up to 30km away and travelled 6km into the sky. Bronggang village was buried under 30cm of ash
- sulphur dioxide blown across indonesia, as far south as Australia
Mt Merapi 6 impacts
- 350,000 people fled their homes
- schools closed
- roads blocked by abandoned vehicles
- vegetable prices increased drastically as the crop yield was significantly reduced
- heavy rain on 4 nov caused lahars, hampering relief efforts
- 353 killed and 577 injured
Mt Merapi 4 short term responses
- 210 evacuation set up in schools, stadiums, etc
- exclusion zone of 20km surrounding the volcano was established
- Indonesian Disaster Management Agency mobilised volunteers to help
- International aid was offered from governments and non-governmental organisations e.g. Red Cross
Mt Merapi 6 long term responses
- 2700 people moved to new and safer housing permanently
- government made money available to farmers to replace livestock
- government set up special task force to help those who were affected by volcano
- ongoing exclusion zone of 2.5km
- dams built in valleys to hold back lahars
- improved prediction measures and improved education on evacuation
