EQ1 Tectonics Flashcards
What was Alfred wegeners theory
Continental drift
Evidence for continental drift
- Truncated geological features
- continents fit together
- paleoclomactic indicators
- fossils found across continents
What are convection currents
Hot rocks heated by mantle rise
Cool rocks sink as more dense
Plate boundary types
Conservative - plates move parallel to one another
Constructive - plates more away from eachother and new land forms where hot magma rises
Destructive- ocean and and plates move towards eachother, oceanic plate subducted as is denser
Collision - two land plates move towards eachother
features at each boundary
Desmuctive - volcano, earthquake, fold mountain
Conservative - earthquakes
Collision - gold mountain, earthquakes
Constructive- volcanoes, fold mountains, earthquakes
What is slab pull?
Gravity acting on dense plates being subducted
What is mantle drag
Friction acting on plates as thick viscous mantle moves underheitnand drags at lithosphere
What is ridge push
Driving force for plate motion that occurs mid ocean ridge
Newer plates less dense so rise to form ridges
Elevation causes gravity to pull them away from older plates
Plates slide down into asthenosphere
What is paleomagnetism
Study of ancient magnetism preserved in rocks
Allow former latitudes to be determined by measuring direction of magnetism in iron bearing minerals
How is paleomagnetism applied in plate tectonics
Sea floor spreading at divergent boundaries
Variations in magnetic field show striped pattern across ocean floor
Confirms newest rock along ridge and older rock progressively further away
What is a hotspot
Extra hot region deep in mantle
What is a mantle plume
Heat rising from hotspot through convectional processes
Facilitates rock melting at base of lithosphere, rises to form volcanos
What is subduction?
Destructive boundary Oceanic lithosphere is recycled into mantle
Difference in subduction angle
Shallow angle results in belt of deformation characteristic see by crustal thickening and mountain building
Steep angle characterised by formation of back arc basins
epicentre and hypocentre
hypocentre- the point within the earth that the rupture starts
epicentre- the point at the surface of the earth above the hypocentre
seismic waves
waves that transmit energy released by an earthquake
secondary impact- soil liquefaction
– Christchurch 2010
surface rock loses strength and become like liquid due to violent shaking
causes buildings to tilt, settle or even collapse
short term impact on delivery of aid, LT impact on recovery costs
secondary impact- lateral spreading
when sloping ground slides across liquefied layer
creates large fissures and cracks in ground surface
secondary impact- quake lakes
landslides block rivers and cause flooding
water collects quickly, flooding huge areas
aftershocks collapse natural dams, sending a torrent of water
secondary impact- landslides/ avalanches
2010 Christchurch, 2010 Nepal
occur when magnitude 4<
slopes weaken and fail, made more likely by heavy rain or fractured rock
around 70% of all earthquake deaths caused by landslides
secondary impact- fire
Kobe Japan 1995, Indonesia 2009
caused by fractured gas mains
hard to out out due to fractured water mains
secondary impact- Tsunamis
Japan 2011
Generated by earthquakes under the ocean displace large amounts of water
secondary impact- comms and infrastructure destroyed
San Fransisco, USA
road and rail links, telephone masts and wifi
hampers rescue efforts, causes injury and loss of life
secondary impact- disease
Indonesia 2004
lack of water and sanitation cause cholera and dysentery to spread quickly
dead bodies add to risk when buried
why do intra-plate earthquakes occur
- reactivation of old fault lines
- subsidence from mining or fracking
- pressure on surface rocks from water in reservoirs
- large manmade explosions
- large avalanches and landslides
what is a megathrust earthquake
after frictional stress has built from plates locked together for some time and failure occurs
what is the benioff zone
where plates converge and one is subducted
different speeds of rock create numerous deep-focused earthquakes
determines position and depth of hypocentre
where to seismic waves originate
Benioff zone
3 ways to measure an earthquake
- Richer scale- vibrations plotted on a seismometer, numbered 0-10
- Moment magnitude scale- moment is product of distance moved and force required to move it
- Mercalli scale- measures damage, based on visual or experienced effects. ranges from unnoticeable shaking to catastrophic damage
Characteristics of P waves
First wave to arrive at seismic recording stations
Compresses and expands land (moves backwards and forwards) in the direction of travel
Characteristics of S waves
Travel through solids
Secondary because Second to arrive at seismic recording stations
Shake the ground side to side perpendicular to the direction of wave travel
Characteristic of Rayleigh waves
Surface waves
Travel in rolling motion like ocean waves
Can travel through solids
Slow moving
Characteristic of a love wave
Surface waves
Travel through solids - not liquids
Horizontal motion that moves surface from side to side perpendicularto direction wave is travelling
What conditions are needed for formation of a volcano
Partially molten rock, magma below surface of the earth.
Rises through natural cracks in crust, or gets safer underground while pressure rises until it erupts explosively
What is tephra
Solid material, ranging from volcanic bombs to ash particles ejected into the atmosphere
What are pyroclastics
Very hot gas charged material, includes gas and tephra
Name some volcanic gases
Carbon dioxide, carbon monoxide, hydrogen sulphide, sulphur dioxide, chlorine
Name primary effects
Tephra, pyroclastic flows, lava, volcanic gases
Name secondary effects
Lahars, flooding, tsunamis, volcanic landslides,
Short term climate change, jokulhlaup
What are lahars
Volcanic mud flows
Why do volcanos cause flooding
Melting of icecaps and glaciers
What is a jokulhlaup
Glacial melting outburst floods
How to volcanos form tsunamis
Caldera forming events (eg Krakatoa) generate giant waves
How to volcanos cause short term climate change
Inject vast amounts of debris into the atmosphere which reduced global temperatures
Difference between dormant, active and extinct
Active = still erupts
Dormant= not currently erupting but supposed to erupt again
Extinct = won’t erupt again
What are the 3 landform characteristics of volcanos
Shield= wide and gentle slopes, runny lava
Stratovolcano= steep sloping side built up over millions of years with compositions, typically more violent
Calderas =large couldron hollow forming after magma chamber empties in volcanic eruption, ground collapses leaving a depression at the surface
What types of eruption are there
Explosive- gas driven eruptions nwhich propel magma and tephra
Effusive- outpouring of lava without significant explosive eruption
What are the three groups of lava
Basaltic
Andesitic
Rhyolitic
How does silica connect affect lava and eruptions
More silica means more gases! More violent, more viscous lava
Features of basalt lava
Fluid
Low silica content
Basic
Hottest lava
Produces shield volcanos- wide with low slopes
Located at divergent margins and hotspots
Effusive
Andesite lava
Viscous
Medium silica content
Medium heat
Produces steep sided cones
Convergent margins
Violent and explosive
Rhyolitic lava
Viscous
Hugh silica content
Lowest heat around 900°C
Produces steep sided cones
Convergent margins
Explosive
How many people have died due to eruptions in the last 300 years
250000
