Tectonics Eq1 Flashcards
What are the 3 belts of tectonic activity
Alpide belt, Pacific belt, mid Atlantic ridge
What are the 4 steps to the formation of a tsunami
- Submarine earthquake or volcano occurs, causes vertical water column displacement
- A wave travels in all directions
- As the wave moves to shallower water, it slows down and gains height
- This can travel great distances across land
Cause of tectonic movement: what is mantle convection
Magma heats in centre of earth, rises to surface, moves and cools, sinks to core again, no longer believed to be main cause
Causes of intra plate earthquakes
Isn’t known fully, may be pre existing weaknesses in plate which reactivates forming seismic waves
Causes of tectonic movement: what is ridge push?
When the magma pushes upwards at a divergent plate boundary, the edge of the plate becomes less dense than the surrounding area, so gravity pulls them apart
Causes of tectonic movement: what is slab pull
When a plate cools and becomes more dense, it becomes heavier than the asthenosphere and subducts. The weight of this pulls the rest of the plate down.
How is disease caused by earthquakes
Illnesses caused by damage to infrastructure and facilities
What are L waves
Seismic love waves - slowest and last to arrive, most damaging
What are p waves
Primary seismic waves - fastest and first to arrive, only damaging in highest magnitude earthquakes
What are s waves
Secondary seismic waves - slower than p waves, more damaging than p waves
What are the secondary hazards of a volcano
- lava flow
- pyroclastic flow
- ash fall
- gas eruption
- wildfire
- lahar
- jokulhlaup
What are the three plate boundaries and what do they mean
Divergent - plates move away from each other
Convergent - plates move towards each other
Conservative - plates move past each other
What evidence of tectonic movement is given by Alfred wegener
- continents fit like puzzle pieces
- glacial deposits in now deserts
- freshwater animal fossils found on opposite sides of the ocean
- plant fossils in Antarctica
- similar rock layers on different continents
What evidence of tectonic movement is given by Harry hess
Palaeomagnetism:
- magma rises through divergent plate boundary
- as it cools down, minerals align with the earth’s magnetic field
- when the magnetic field flips, the cooling minerals align in the opposite direction, stripes can be seen of oppositely aligned rocks
- proves seafloor spreading as new land is being formed, plates can be seen moving apart
What happens at a conservative plate boundary
No volcanoes
What happens at a continental and continental convergent plate boundary
No volcanoes, fold mountains are formed as the plate is pushed up
What happens at a continental and oceanic convergent boundary?
Explosive eruptions due to rhyolite lava, ocean trench
What happens at a divergent plate boundary?
Effusive volcanic eruptions due to basaltic magma, rift valley forms, seafloor spreading occurs
What happens at oceanic and oceanic convergent boundaries
Explosive volcanic eruptions due to rhyolite lava, ocean trench, island arc created
What is a gas eruption
Eruption of carbon dioxide and sulphur dioxide which can poison people
What is a jokulhlaup
Glacial outburst floods caused by volcanic eruptions melting snow and ice from glaciers
What is a lahar
A mixture of water and volcanic rock fragments which flows quickly down a volcano, when a significant rainfall event coincides with eruption
What is a tectonic hazard
An event caused by the movement of tectonic plates which has the potential to threaten human life and property
What is a volcanic hotspot
- Mantle plume = stationary column of abnormally hot rock rising in the mantle
- Pressure creates magma which rises as a volcano
- As the tectonic plates move over the mantle plume, a volcanic island chain forms
What is an avalanche
Mass movement of snow, rock, ice and soil down a mountainside
What is ash fall
Ash from an eruption which settles on surrounding areas
What is basaltic magma
Magma that has a low gas content, a low viscosity and a high temperature
What is continental crust
Less dense, thicker, older
What is crustal fracturing
When the crust causes rock to break and fracture under the stress and strain of seismic stresses
What is lava flow
Lava moving away from a volcano after an eruption
What is liquefaction
When loosely packed waterlogged sediments lose their strength - earthquake
What is oceanic crust
Denser, thinner, younger
What is pyroclastic flow
Dense fast moving flow of volcanic ash, solidified lava pieces
What is rhyolite lava
Lava that has a high gas content, high viscosity and low temperature
What is the benioff zone?
Zone of seismicity where friction causes earthquakes along the subducted plate surface
What is the seismic activity at each plate boundary
Convergent - highest magnitude, frequent
Conservative - high magnitude, frequent
Divergent - high magnitude, frequent
What is the structure of the earth?
- Inner core - solid centre of earth
- Outer core - liquid outer layer of the core which creates magnetic field
- Mantle - solid layer between core and lithosphere
- Asthenosphere - partially melted layer of the earth which allows the plates to move
- Lithosphere - crust and upper mantle fused together
