Plate Tectonics Flashcards
1
Q
what is a volcano?
A
a volcano is formed when magma erupts onto the earth’s surface as lava through the vent in the earth’s crust
2
Q
features of a volcano
A
- lava
- pyroclastic flow
- ash
- lahars
- vent
- secondary cones
- crater
- magma chamber
3
Q
what is lava?
A
Magma that reaches the surface
4
Q
what is pyroclastic flow?
A
Clouds of mixed poisonous gases and ash
5
Q
what is ash?
A
Very fine-grained volcanic material
6
Q
what are lahars?
A
Snow and ice melt and combine with the ash, creating lahars.
7
Q
what is a vent?
A
Central tube through the volcano
8
Q
what are secondary cones?
A
Eruptions from other vents lead to the formation of secondary cones on the sides.
9
Q
what is the crater?
A
bowl-shaped basin at the top of the volcano
10
Q
what is the magma chamber?
A
A large underground pool of magma
11
Q
how do volcanoes form?
A
- 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
12
Q
environmental impacts of volcanoes
A
- pyroclastic flow
- lava flow
- volcanic bombs
- laharas
- earthquakes
- landslides
- tsunami
- acid rain
- ash fallout
13
Q
human impacts of volcanoes
A
- 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
14
Q
opportunities of volcanoes
A
- 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
15
Q
stages of volcanoes
A
- 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
16
Q
what are the two types of volcanoes?
A
- shield volcanoes
- composite volcanoes
16
Q
what is a shield volcano?
A
- 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.
16
Q
how do eruptions occur at constructive boundaries?
A
At constructive boundaries, plates move away from each other; magma rises to fill the gap
16
Q
what is a composite volcano?
A
- 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
16
Q
how do eruptions occur at destructive boundaries?
A
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
17
Q
what is a hotspot?
A
an area of the Earth’s mantle from which hot plumes rise upward, forming volcanoes on the overlying crust
17
Q
how do earthquakes occur?
A
- 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
17
Q
what is an earthquake?
A
a sudden violent shaking of ground followed by a series of vibrations or movements in the earth’s crust
17
Q
what are the features of an earthquake?
A
- focus
- epicentre
- convection currents
- subduction zone
- magnitude
17
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
17
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
18
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
19
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
20
what are the major tectonic plates?
- Nazca
- North American
- South American
- African
- Eurasian
- Indian
- Australian
- Antarctic
- Pacific
21
what is a collision plate boundary?
it occurs when two continental plates move towards each other
e.g. Indo-Australian and the Eurasian plate
22
what is a constructive/divergent plate boundary?
it occurs when two plates move away from each other e.g. North American and Eurasian Plate
23
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
24
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
25
what is the structure of the earth?
- crust
- mantle
- outer core
- inner core
26
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.
27
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
28
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
29
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
30
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
31
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
32
volcano case study: Mt Merapi general facts
- active composite volcano in Java (SE Asia)
- most active volcano in asia
25 Oct - 30 Oct 2010
33
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
34
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
35
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
36
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
