Plate Tectonics Flashcards
What is a Geoid and how is it formed?
Bulging at equator due to centrifugal forces (kids on a roundabout)
What is the oceanic crust?
5-10km, occasionally broken layer of basalt known as ‘Sima’ – Silica and Magnesium
What is the continental crust?
up to 70km, mostly granite known as ‘Sial’ – Silica and Aluminium
Difference between ‘Sial’ and ‘Sima’
‘Sial’ (Conti) is less dense and thicker, found above ‘Sima’ (Ocean)
What is the Lithosphere?
Tectonic plates are formed here
upper-mantle + crust (100km)
What is the Mantle?
(2900km) – great heat and pressure results in liquid dense the deeper you go
Core Characteristics
Core (5000’C) is 4 times denser than crust
Outer Core characteristics
Outer Core – semi-liquid=Iron
Inner Core Characteristics
Inner Core=Iron + Nickel
Convection currents are causes by..?
The heat generated by the core creates convection current
Who and when - Theory of Continental Drift
Alfred Wegner – 1912
6 Things the theory of continental dift is based on:
1) Jigsaw fit of SA and A
2) Matching rock in East Cnd to NW Sco
3) Coal beneath Antarctica
4) Fossils in India matched in Aus
5) Unique Mesosaurus in A + Bra
6) Glacial deposits in Bra match west A
Scientific Community reaction to Theory of Continental Drift
Evidence but no explanation dismissed his theories
Theory - 1950’s?
50s – nuclear submarines – Oceanic Floor Mapping
1962?
Sea floor spreading – youngest rock in the middle of Atlantic, newest in Iceland
Palaomagnitism?
During Polarity every 400,000 years, there were eruptions of magnetite, Symmetrical patterns either side of the Atlantic ridge – confirming sea floor spreading
Explain Convection Currents
Plates are driven by convection currents which rise and spread in the asthenosphere before cooling and sinking back down
Oceanic Crust Contructive Formations
Mid-Ocean Ridge
Faults cut across separating sections of the ridge widening at different rates, creating shallow focus earthquakes
Rift valleys in the middle of ridges
Submarine volcanoes can eventually create volcanic islands
Continental Crust Contructive Formations
Rift Valleys
Lithosphere splits – fractures in parallel faults
Oceanic > Continental Destructive Formations
Denser Oceanic Plate subducts beneath Continental = deep ocean trench
Continental land is uplifted, compressed and folded > chains of fold mountains
Oceanic land is destroyed/melted between 100-700 km (Benioff Zone) due to heat and friction which may also cause deep-focus earthquakes
Turned into magma, oceanic rock is less dense than asthenosphere =rising in faults where the continental plate has buckled, before reaching the surface to form explosive volcanic eruptions
Oceanic > Oceanic Destructive Formations
The faster/ denser plate subducts > deep ocean trench
Rising magma melted in the Benioff zone > volcanic island arcs
Continental > Continental Destructive Formations
Subduction does not occur because continental is not dense enough > High Fold Mountains
Shallow focus earth-quakes can be triggered
Conservative Formations
Crust is not destroyed and no subduction > no volcanic activity + no formation of new crust
Extremely active
Shallow Focus Earthquakes when sticking occurs and stress builds
Contructive Crust and Volcanoes
Oceanic crust is formed by basaltic magma rising from the asthenosphere
Basic submarine volcanoes
Volcanic islands
Destructive Volcanoes
Explosive acid volcanoes where there is subduction
Conservative Volcanoes
No subduction > no Volcanicity
Hot Spots
When radioactive decay at the core is concentrated, it can create localise thermal currents where plumes of magma rise vertically
The hotspot remains stationary, whilst the plate moves resulting in chain islands
Dykes
When magma solidifies in a vertical fissure
Once solidified into igneous rock, it is usually more resistant to erosion, leaving a prominent wall-like feature
Sills
Forms when magma solidifies into horizontal/inclined layers of existing rock
Laccolith
Form where viscous magma forcing into overlying rock strata to arch into a dome
Batholith
Larger scale where often, the other features will feed off of them
Extreme heat/ pressure (metamorphism)= metamorphic aureole
Extrusive Features
Gaseous emissions – steam, carbon monoxide, hydrogen sulphide, sulphur dioxide and chlorine
Solids – ash, dust, glassy cinders
Liquids – lava bombs (tephra/pyroclasts), solidify mid-air
Basic Lava
(basaltic) is low in silica, allowing gas bubbles to move freely – fluid and free-flowing
Acid Lavas
rich in silica – viscous > gas bubbles cannot expand - build up of pressure = violent eruptions
Basic Shield Volcanoes
Mid-ocean ridge, rift valleys and hotspots – direct access to surface
Repeated eruptions
Runny lava forms gentle sloping volcanic cones and shields
Acid Dome Volcanoes
Destructive margins
Viscous lava cannot flow far before cooling = steep convex cones
Rhyolitic lava is thick and unable to flow
Explosive pyroclastic flows of superheated gases, ash and pumice
Dormant Volcano
Hasn’t erupted within historic times
Extinct Volcano
10,000 years dormant
Composite cones
Alternating eruptions of ash, tephra (incl. lapilli), lava building volcano in layers
Often covered by secondary (parasitic) cones and fissures
Ash and Cinder Cones
Ash, cinder and tephra erupted in the central crater
Steep-sided concave in shape
Calderas
Emptying of the magma chamber allows flanks to cave in creating a vast pit which can be flooded as a sea or lake
Icelandic Volcano
Basaltic
Gentle flow from fissures
Hawaiian
Basaltic
Gentle flow from central vent
Strombolian
Frequent explosive eruptions of tephra and steam
Vulcanian
Thicker basaltic + Andesitic + Rhyolitic
Less frequent, more violent eruption of gas, ash and tephra
Vesuvian
Thicker basaltic + Andesitic + Rhyolitic
Long periods of inactivity
Very violent gas explosion
Peléan
Andesitic + rhyolitic
Very Violent eruption of nuées ardentes
plinian
Rhyolitic
Exeptionally violent eruptions of gases, ash and pumice
Create rainstorms and lahars
Minor extrusive activity
Geysers
Fumaroles
Hot Springs
Boiling Mud
Geysers
Boil from contact with hot rocks
Hot volcanic gases build up pressure until an explosion of water takes place
The vent re-fills and it’s all repeated
Short-lived features
Fumaroles
Low pressure outlets of steam and gas
Solfatara when the gas is sulphurous – leaves yellow deposits
Hot Springs + Boiling Mud
Not under pressure
Not all volcanic
Heated deep below the surface
Dissolved minerals create boiling mud
Surtsey
In 1963
Powerful underwater eruptions led to the birth of a new islandoff the coast of Iceland
As lava erupted onto the seafloor it solidified, eventually formed an island that emerged out of the water
Great African Rift Valley
Constructive plate boundary on two continental plates
Magma plume below
Extends 5000 Km
Shield volcanoes form
Hawaii Hotspot
Shows the movement of the plates since the plume of radioactive decay from the core stays in the same place, so volcanic islands form in the direction of the movement of the plate
The largest island is called Big island and is where there is an active volcano
Then further west smaller islands are areas where the basalt lava rock is older, therefore showing how they used to be above the plume
They get smaller because they are older ad are eroded
To the east of big island is Liohi, an underwater volcano which will eventually form the new island
San Andreas
Shallow focus quakes occur like San Fran 1906,1989 and LA 1994
Where the Pacific and North American late are moving parallel to each other
The same direction but the pacific plate is moving about 3 times faster at 5-9 cm a year
Stresses build up creating transform faults
Himalays
Continental/Continental
Tallest mountain range on earth where the Indian Plate is colliding into the Eurasian Plate
Everest grows 4mm a year, predictions of up to 8 cm shift upwards since the April Nepalese Earthquake 2015
Monserrat
Caribbean plate slips under the South American
Dramatic heat at Benioff zone creates the chain of volcanic islands known as the Lesser Antilles
Andes
Subduction of oceanic Nazca plate below continental South American Plate
The rise of the Andes is down to compression from the Nazca Plate and the Antarctic Plate creating fold mountains
The Peru- Chile Trench is a depression where the Nazca plate is subducting
Nyiragongo general
African rift valley, main crater is 250m deep, containing a lava lake
Frequent! Along with its neighbouring volcano, it is responsible for 40% of Africa’s recorded eruptions
Lava flows, can me as fast as 90km/h
13km fissure was opened up, flowing to Goma and lake Kivu
Stratovolcano 20km from Goma (1,000,000) , just west of Rwanda
$480 GDP Per Capita
Home to The Great African War from 98 to 03
Stratovolcano
Nyiragongo Primary Effects
Lava flows destroyed over 1/3 of Goma; Water, power and medical facilities destroyed including 3 health centres and 1 hospital
Part of the airport was covered
147 Died
Sulphurous lava contaminated Lake Kivu
Medical attention for those effected by smoke and fumes
14 villages destroyed completely
Nyiragongo 2002 secondary effects
Accompanying earthquakes caused structural damage to buildings
Medical attention for diseases spread by contaminated water
Looting homes and a petrol station exploded during looting
220,000 fled to Rwanda to escape lave, making aid difficult
500,000 homeless
Nyiragongo 2002 immediate responses
UN supplied enough food to feed 700,000 for a week
Full evacuation of Goma
Nyiragongo 2002 longer-term responses
Volcanologists monitor Lake Kivu after fears lava, would release large amounts of carbon dioxide and methane
Eyjaffajokull 2010 general
The caldera is 2.5km wide
Constructive plate – North American plate moving west and the Eurasian moving east
11Km ash plume – fine grained ash
150m Ice cap
$47,000 GDP Per Capita
Sparsely-population, very volcanic, and cold
Strombolian
Eyjaffajokull 2010 Primary effects
Agricultural land damaged, farms hit by ash fall
Roads destroyed
No deaths or injuries
A small number of people had respiratory and irritation issues
Eyjaffajokull 2010 secondary effect
10 million airline passenger stranded abroad with over 100,000 flights cancelled over 8 days
Ash contaminated local water supplies, impacting livestock
Kenya lost $3.5 million as loss in exports
Train industry boosted
Cost $2.6Bn to Europe
Flooding from glacier melt
Flooding up to a year later due the silting up of rivers
Eyjaffajokull 2010 immediate response
People asked to stay indoors because of ash in the air
700 evacuated from flooding
Entirely domestic responses
Eyjaffajokull 2010 long term response
Far more tests on what planes can cope with in terms of ash, very little was known about this at the time
Primary effect of earthquakes
Ground shaking education damage death + injury lahars/avalanches liquefaction power station damge panic fear and hunger
Secondary and long-term effects of Ground shaking
Fire due to broken Gas pipes/power lines
Emergency services hindered
Contaminated water = disease
Secondary and long-term effects of Education damage
Education suspended
Lost generation + poor economic development locally
Secondary and long-term effects of Immediate death and injury
Un-buried bodies lead to more disease
Disability
trauma
Long-term illness
Secondary and long-term effects of Lahars/ Avalanches
Death and injury
Flooding
Loss of farmland and prouction
Disruption to natural drainage basin
Secondary and long-term effects of Liquefaction
Foundations subside = death and injury
Repairs are difficult and expensive
Secondary and long-term effects of Power station damage
Power cuts hinder emergency services
Reconstruction is very expensive
Secondary and long-term effects of panic fear and hunger
disorder and looting
Restoration of trust in neighbours
Explain seismicity
Friction builds up stress in the lithosphere
Once overcome they fracture along cracks called faults
The breaking point is the focus (hypocentre)
Epicentre = point of surface above the focus
What are the seismic shock waves?
Primary/Pressure waves are the fastest – high frequency-Push-travel through mantle and core
Secondary/Shear waves are half as fast – high frequency- shake – travel through mantle but not core
Surface Love waves – slowest – most damage – side to side
Rayleigh waves – radiate in complicated low frequency rolling up and down motion
Two ways of measuring earthquakes
Richter scale = magnitude – logarithmic
Mercalli Scale = intensity of damage – observations
How can you predict an earthquake
Micro quakes Bulging ground Electrical and magnetic changes within rocks Increased argon in soil Animal behaviour
What are the characteristics of a Tsunami
Wave height is less than 1m but can be up to 25m at shore
Wavelength 100-1000km
650-1000kmh
Series of waves, first not always the biggest
Time between each wave = 10-60 minutes
On approaching the coast, the front will slow down allowing the rear to pile up
Nepal April 2015 General
7.8 magnitude and 15km deep – shallow
265 aftershocks a month on, 7.3 magnitude in May, caused further devastation
Maximum of Severe on the Mercalli scale
Landlocked, extremely mountainous country
One of the poorest countries in the world with under $700 GDP per capita
Caused by a sudden thrust along the major fault line where the Indian Plate, is sub ducting underneath the Eurasian Plate
Nepal April 2015 Primary effects
9000 dead, 20,000 injured Thousands of houses destroyed Airport closed for a day Death in churches due to the time of impact and old buildings 700,000 houses destroyed 5000 schools destroyed, 16,000 damaged
Nepal April 2015 Secondary Effects
Avalanche on Everest – killing 19 – bad for tourist industry
Hundreds of thousands homeless
Landslides and aftershock – 200 dead from may aftershock
Trauma, many aftershock
Survivors preyed upon by human traffickers involved in brothels
Sleeping in the streets cold, too scared to go back inside
Displacement of people
Nepal April 2015 Immediate Responses
90% of Nepalese army sent the worst areas
Rainfall, after shock and small airport run-way slowed things down, aid had to be over landed on poor roads from India
Social Media, Drone footage and satellite imaging were used
$350 million donated from the international community
Nepal April 2015 Longer-term responses
Calls for more aid – estimated just 10% of relief came from overseas
Re-building of building sensibly
Calls to build wider run-ways
New Zealand Feb 2011 General
Very shallow- 5 km, 6.3 magnitude, 6 miles from Christchurch
Occurred on a conservative plate margin where the Pacific Plate slid past the Australian Plate in the opposite direction.
It was the aftershock from a larger earthquake in 2010 but the impacts were more severe
$42,000 GDP per capita
New Zealand Feb 2011 Primary Effects
181 killed, 2000, injured
Hundreds of kilometres of water and sewage piper were damaged
Over half of the city buildings were damaged
Moderate amount of liquefaction
An iceberg of 20 football fields broke off
80% without electricity
New Zealand Feb 2011 Secondary Effects
Businesses put out of action causing losses of income and jobs
Schools sharing classrooms due to damage elsewhere
Difficult to get around due to transport destroyed
Trauma, due to aftershocks, injury and death
Tourism loss because they couldn’t host rugby world cup matches
New Zealand Feb 2011 Immediate Responses
Chemical toiles provided for 30,000
International aid of around $7 million and aid workers
300 Australian police arrived
Earthquake commission assessed all buildings to ensure they were safe
New Zealand Feb 2011 Long term responses
Red Cross provide grants to families with children under 5 years
Water and sewage all restored fully by august
Roads and housed cleared of silt from liquefaction, 80% clear by August
How do japan earthquake proof buildings
Rolling weights on roof to counter-act shock waves
Panels of marble and glass flexibly anchored to steel structure
Bird cage like interlocking steel frame
Reinforced latticework foundations deep in bedrock
Rubber shock absorbers
How does japan prepare for earthquakes
Earthquake proof buildings
Education – everyone knows what to do – practice drills
Every one has an emergency survival kit
You cant buy a phone without overriding warning software
Warnings seconds before impact are simultaneously across all media
Large network of seismometers
Prediction- micro quakes, bulging, electrical and magnetic changes with rocks, in creased argon gas content in soil and curious animal behaviours
10m sea wall to prevent the effect of a Tsunami
Indian Ocean Tsunami 2004 Secondary Effects
500,000 into refugee camps in just one region of Indonesia
Economies like fishing, agriculture and tourism ruined
44% of one region of Indonesia lost their livelihoods
£226m damage to the Thai fishing industry
Water supplies contaminated
Inequality increases
Indian Ocean Tsunami 2004 Immediate Responses
Relief efforts with more than 160 aid agencies
Foreign military troops
Indian Ocean Tsunami 2004 General
Second biggest earthquake in history – 9.3
240Km of the coast of Sumatra
Cause – the release of stress along a 1000km thrust fault
Indian plate moved downwards by 15m, forcing the ocean floor above the thrust fault
8 aftershocks followed
Warning were slow - with nothing on the media in Thailand until an hour after the first wave
Indian Ocean Tsunami 2004 Primary Effects
290,000 died, thousands missing
Vegetation + top soil removed up to 800m in land
Infrastructure destroyed
Coastal settlements devastated
Indian Ocean Tsunami 2004 Longer-term responses
Reconstruction- still thousands in tents a year on
Aid was delayed by rebel group Tamil tigers in Sri Lanka
Underclasses ignored by the government
A UN group set up a warning system but it relies on the countries own alerts – tourist areas with sirens, rural communities with radio warning
More education on awareness with drills and plans
Areas at more risk were mapped
Japan March 2011 Tsunami General
9.0 – 10m waves
100km from Sendai
500 km segment of the North American Plate dragged down my sub ducting pacific plate, moving upwards 10m
10 waves 1km apart
Japan March 2011 Tsunami Primary Effects
Weaker buildings collapsed
Flooded 500 square metres
25,000 dead or missing
Japan March 2011 Tsunami Secondary Effects
500,000 homeless
Some homes without water or electricity, petrol had to rationed
700 aftershock traumatised people
Explosions and leaks at Fukushima nuclear plant panicked the whole world, with stock markets plummeting
Japan March 2011 Tsunami Immediate Responses
Helicopter rescues on roofs 100,000 soldiers Many countries offered aid Fukushima exclusion zone No reports of looting
Japan March 2011 Tsunami Long Term Responses
Level of sea defence increased
Government borrowing even more increased, resulting in austerity and tensions
Trauma, illness and disablement
