content Flashcards
(37 cards)
What causes earthquakes?
Plates don’t fit perfectly, when they move they can become stuck due to friction
Convection currents continue to push the plates causing pressure
Pressure released in a jolting motion causing seismic waves spread through the ground
Features of earthquakes
Focus/Hypocentre - point underground where earthquake originates from
Epicentre - area above ground that is directly above focus
Focal depth - depth at which an earthquake originates
What are the types of seismic waves?
-Travels thru Earth’s interior
-Solids, liquids, gases
-Compressional (moves back + forth like slinky)
-Vibrates in same direction of travel
-4 to 8km/s
-Least destructive
Secondary
-Travels thru Earth’s interior
-Move perpendicular to wave direction
-Only through solids
-More damaging than P waves
Love
-Travel near ground surface
-Slowest
-Only solids
-Most destructive
What are secondary hazards of earthquakes?
Soil liquefaction
-affects poorly compacted sand and silt
-water moisture within soil separates from soil particles rising to surface
-causes soil to behave like liquid causing subside
Landslides
-shaking can weaken or damage cliffs
-unconsolidated material can collapse
Tsunamis
-when oceanic crust is jolted, water above plate is displaced upwards
-water pulled back down due to gravity
-energy transferred into water so it travels like a fast wave with low amplitude
-Sea level decreases closer to coasts
-friction between sea bed and wave cause wave ti slow and gain height (10-100ft)
What causes volcanoes?
Composite volcanoes
-convergent
-subjected plate melts forming magma
-explosive eruptions
-andestic lava, high silica, viscous, gas
Shield volcanoes
-divergent
-magma rises thru gap
-effusive eruptions
-basaltic, low silica, runny, Hugh temp
Hotspots - shield
Primary hazards of volcanoes
Lava flows - streams of lava
Pyroclastuc flows - mixture of hot dense lava, ash, gases which move quickly
Tephra and ash flow - pieces of volcanic rock and ash are blasted into air
Volcanic gases - SO2 and CO released, can travel long distances
What are secondary hazards of volcanoes?
Lahars - Rock, mud and water travelling quickly down sides of volcanoes
Jokulhlaup - snow and ice in glaciers melt after eruption causing sudden flood
Acid rain - SO2 released into atmosphere
What causes tsunamis?
-usually by subduction zones at convergent plate margins
-when oceanic crust is jolted, water above plate is displaced upwards
-water pulled back down due to gravity
-energy transferred into water so it travels like a fast wave with low amplitude
-Sea level decreases closer to coasts
-friction between sea bed and wave cause wave ti slow and gain height (10-100ft)
Where do earthquakes occur?
Typically near plate boundaries
However, some occur in the middle of the plate (intra -plate) because of weaknesses in the crust
Where do volcanoes form?
At plate boundaries (Pacific Ring of Fire)
Some form intraplate due to hotspots
Where do the most powerful earthquakes occur?
Convergent/conservative
Where do tsunamis occur?
Usually in subduction zones
(Pacific Ocean)
How does a volcano form on hotspots?
Mantle plume (rising column of hot solid rock from earths mantle) causing lithosphere to melt above it forming a volcano
What happens at a plate boundary?
Two plates are moving at different speeds and different directions which can cause collisions
What are the type of plate boundaries?
Destructive - move torwards
Constructive - move away
Conservative - move parallel
Types of destructive plate boundaries
Continental + oceanic:
-Denser oceanic subducts below continental
-Leaves ocean trench
-Oceanic crust melted
-Extra magma causes pressure
-Pressurised magma forces through weak areas in continental plate
-Form composite volcanoes
-Fold mountains occur when sediment pushed upwards during subduction
Oceanic + oceanic:
-Heavier plate subducts leaving ocean trench
-Fold mountains occur
-Oceanic crust melted, extra magma causes pressure causing underwater volcanoes to burst
-Lava cools creating new land called island arcs
Continental + Continental:
-Pressure builds
-No subduction of continental crust
-Pile up of continental crust on top of lithosphere due to pressure between plates
-Form fold mountains
Types of constructive plate boundaries
Oceanic + oceanic
-Magma rises between the gap left by separating plates (sea floor spreading)
-Less explosive underwater volcanoes formed as magma rises
Continental - Continental:
-Any land in middle of seperation is forced apart causing rift valley
-Volcanoes form where magma rises/gap fills with water
-Lifted area of rock is hortst, valley is graben
Types of conservative plate boundary
All
-Parallel plates move in different direction/different speeds
-No landform created as no plate destroyed
-Pressure builds up when plates move
-Cause displacement of water on oceanic
-Cause fault lines in continental
What is the evidence for sea floor spreading and plate movement?
Paleomagnetism - study of rocks that show magnetic field of the Earth
As new rock forms and cools the magnetic grains of rock align with the magnetic poles
Poles switch periodically so new rock forming is aligned oppositely to older rock
On ocean floor either side of contructuve plate boundary there is symmetrical hands of rocks with alternating magnetic polarity
What is ridge push?
The slope created when plated move apart is under force of gravity as it has higher elevation
Gravity pushes plates further away widening gap (gravitational sliding)
What is slab pull?
When plate subducts, the plate sinking into mantle pulls the rest of the plate with it causing further subduction
What is mantle convection?
Radioactive elements in the core of the earth decay which produces thermal energy
Causes lower mantle to heat up and rise
As magma cools and becomes more dense it sinks
These are convection currents which push plates
What are the mechanisms by which plates could move?
Mantle convection
Slab pull
What are the two different types of crust
Oceanic - High density, basalt, think, newly created
Continental - low density, mainly granite, thick, old
