Plate Tectonics Flashcards
Evidence for continental drift
Jigsaw fit Geological fit Tectonic fit Glacial deposits Fossil evidence
Types of plate boundaries where volcanoes form
Oceanic oceanic divergent
Continental continental divergent
Oceanic oceanic convergent
Oceanic continental convergent
Type of plate boundaries where ocean ridges form
Oceanic oceanic divergent
Type of plate boundaries where ocean trenches form
Oceanic oceanic convergent
Oceanic continental convergent
Type of plate boundaries where fold mountains form
Oceanic continental convergent
Continental continental convergent
Type of plate boundaries where island arcs form
Oceanic oceanic convergent
Type of plate boundaries where rift valleys form
Continental continental divergent
Hydration melting
Destructive boundary (convergent) Water forced down into mantle Mantle melts at lower temp. As bonds in rock are disrupted my water molecule Liquid mantle = magma which rises up through crust
Decompression melting
Constructive boundary (divergent)
Lower pressure means lower melting point of mantle
Two plates move apart leading to an area of low pressure
Reduction in overlying pressure enable mantle to melt leading to upward movement of magma
No subduction because plate are same density
Evidence for plate tectonics
Theory of Continental Drift 1915 (Alfred Wegener)
Mid oceanic ridges/Sea floor spreading 1962 (Harry Hess)
Paleomagnetism, symmetrical stripes 1963 (Vine and Matthews)
Hotspot theory 1963 and Transform Faults 1965 (John Tuzo Wilson)
Mantle Convection 1966 (Dan McKenzie)
Types of magma and their characteristics
Basaltic: 45-55% silica, 1000-2000C temp, low viscosity, Low gas content
Andesitic: 55-65% silica, 800-1000C temp, medium viscosity, medium gas content
Rhyolitic: 65-75% silica, 650-800C temp, high viscosity, high gas content
6 volcano types by shape
Flood/ Plateau Basalt / Fissure Shield Cinder Cone Composite/ Stratovolcano Volcanic dome/ acid Caldera
Primary volcanic hazards
Lava flows
Pyroclastic flows
Volcanic gases
Ash and tephra fall
Secondary volcanic hazards
Lahars Volcanic landslides Tsunami Flooding Fires
Focus
Location within Earth where underground rock moves and sends out earthquake waves
Epicentre
Location on the surface of the earth directly above focus
Earthquake waves/Seismic waves
Shock waves created at the focus and sent out in all directions
Earthquake
Rapid vibration of earth created by a sudden movement of large sections of rock
Seismograph
A device that reads earthquake waves
Seismogram
The picture drawn by a seismograph indicating earthquake waves
Natural causes of earthquakes
Plate boundaries
Intra plate movement
Isostatic recoil
Quasi-natural / human induced causes of earthquakes
Fracking
Dams
Nuclear testing
Two scales used to measure earthquakes
Richter scale - magnitude determined by logarithm of amplitude of waves recorded by seismograph
Mercalli scale - value assigned to a specific site after assessing damaged caused by an earthquake
Two types of body waves and their characteristics
Body waves: travel through earth itself
P waves (primary): longitudinal waves, push and pull, fastest body wave, average speed 6km/s, travel through both solid and liquid
S waves (secondary): transverse waves, shake side to side, slower, average speed 4km/s, only travel through solid
Two types of surface waves and their characteristics
Love waves: fastest surface wave, side to side, confined to surface of crust, only horizontal motion, shake ground at right angles to direction of movement
Rayleigh waves: rolls along ground like a wave across the ocean, moves ground both up and down and side to side (horizontal and vertical), same direction of motion, most of shaking felt due to these waves
Earthquake hazards
Landslides/ rockfalls Tsunamis Soil liquefaction Ground shaking Lateral spreading / ground displacement Fires
Intrusive volcanic landforms
Batholiths
Sills
Dykes
Extrusive volcanic landforms
Geyser
Fumaroles
Hot springs
Mud pots
Causes of tsunamis
Earthquake - Boxing Day 2004
Volcanic eruption - Krakatoa 1883
Underwater landslide - La Palma theory
Impact of a meteorite
Tsunami
Series of large ocean waves generated in a body of water by an impulsive disturbance that vertically displaces the water column
Characteristics of tsunami
Shallow water waves
Wavelength longer than depth of water travelling through
Rate of waves energy loss inversely related to wavelength
Shallow water, slow down, increased amplitude
Deep ocean, long wavelength, low amplitude
Boxing Day Tsunami causes
26 Dec 2004 Eurasian and Indo-Australian plates Earthquake magnitude 9 240km off coast of Indonesia Speed 800km/h Open ocean less than 1m At shores 15m 20m uplift of sea floor along fault line Wave hit coast within 30mins of earthquake
Impacts of Boxing Day Tsunami
250,000 people died - 14 different countries
8 people killed SA - 8000km away from epicentre
2 million made homeless
Mangrove swamps acted as barrier to reduce energy
Seismic waves caused damage to poorly built homes
Sri Lanka train derailed killed 1000 people
Tourism and fishing reliant countries
Land disputes - lost documents
Boxing Day Tsunami responses
Bodies buried in mass graves to prevent spread of diseases
$7bn by gov’t to help reconstruction
Up to 5million people relocated into temporary refugee camps
Building of homes took longer than expected due to lack of materials
Transport routes hard to rebuild
Short term aid e.g. Water purification tablets, medical supplies
Early tsunami warning system in Indian Ocean installed for $20m
