Tectonic Impacts
1 Lithospheric plates and their motion
describe the characteristics of lithospheric plates
gather and analyse information from secondary sources about the forces driving plate motion identify the relationship between
the general composition of igneous rocks and plate boundary type
outline the motion of plates and distinguish between the three types of plate boundaries (convergent, divergent and conservative)
describe current hypotheses used to explain how convection currents and subduction drive plate motion
Lithospheric Plates
Feature Continental OceanicAverage Density 2.7g/cm*3 3.0g/cm*3Average Thickness 35km 7kmComposition Felsic rocks, sedimentary,
igneous, andesite and graniteMafic rocks, basalt and gabbro
Oceanic crust is composed of four major layers:1) Sediment layer2) Pillow basalt, basaltic breccius3) Sheeted dike, gabbro4) Thin layer of upper mantle material
Igneous rocks and plate boundaries
Location Type of movement Magma formation Lava producedDivergent boundaries Mid – ocean ridge Mafic magma Mafic lave erupts to
form pillow basalt. Forms basalt dykes and gabbro
Continental rift Mafic magma Mafic lava erupts and forms basalt. Felsic lavas forms to produce rhyolite
Convergent boundaries
Oceanic - oceanic Mafic rich magma Eruptions are mafic to intermediate. Early eruptions are mainly mafic
Oceanic – continental Mafic rich magma Eruptions are mainly intermediate. Some mafic magma. Felsic magma. Plutons
Continental collisions Small amounts of felsic magma
None. plutons
Hot spots Under continental crust
Mafic magma Mafic lava produces basalt. Felsic lava form rhyolite
Under oceanic crust Mafic magma Mafic lava erupts
Plate boundaries
Convergent, Divergent and transform Boundaries
- Earthquake focus is the point at which rocks break or move above the epicentre - Subduction is where one plate subducts under another
Convergence (Destructive boundary) – Collision of two plate boundaries usually resulting in subduction. The overriding plate usually becomes folded and volcanic to produce mountain chains
Divergence (Constructive boundary, Extensional boundary – Where two plates separate. The spreading centre is where new crust is formed. The mid ocean ridge is a divergence of multiple plates.
Transform (conservative) – Where two plates move past one another, the plate movement is parallel to the direction of the boundary
Convergent Boundaries
Oceanic – continental convergence
- Summary of features: subduction indicated by trench, intensely folded mountain range, andesitic volcanism and granite magma intrusions, regional and contact metamorphic rocks, shallow to deep focus earthquakes, growth of continental crust
- Example – mountain ranges of the Andes in South America
Oceanic – Oceanic Convergence
- Summary of Features – trench, island arc chain, volcanoes, regional and contact metamorphic rocks
- Example – Mariana Trench in the pacific beneath Japan
Continental – Continental convergence
- Summary of features – intensely folded mountains, regional metamorphism, shallow to medium focus earthquakes, usually no subduction or little, no volcanoes or magma intrusions, no trenches or contact metamorphism
- Example - Himalayas
Divergent Boundaries
- Summary of features – Youngest rocks at boundary, fissure eruptions typical, boundary characterised by an elevated rift valley, little or no metamorphism, shallow focus earthquakes only
- Example – Mid Ocean ridge, marks he divergence of several plates
Transform Boundaries
- Summary of features: Rarely volcanism, shallow focus earthquakes, opposite and parallel movement on either side of the boundary, builds elastic potential energy until it releases in seismic waves
- Example – San Andreas fault
Plate motion
- There are two theories for the movement of plates:o Convection currentso Slab pullo Ridge push
- The accepted theory of plate movement is convection currents- Convection currents occur in all unevenly heated fluids. When part of a liquid is heated it
rises and cools and moves horizontally before it descends.
- It is believed that as the currents move horizontally they push the plates with them- It is now being debated that convection currents alone are not powerful enough to move
crustal plates- The slab pull model suggests that as a plates are subducted or diverge they pull the plate in
the direction of the subduction/divergence due to gravity- The slab pull model has not been proven- The Ridge push model suggests that the driving force of plate tectonics are divergent
boundaries- Suggests that as divergent boundaries are elevated above the rest of the ocean floor they
push the lithospheric plates as they diverge- It is likely that all these forces are contributing to tectonic movements
2 The movement of plates results in mountain building
distinguish between mountain belts formed at divergent and convergent plate boundaries in terms of general rock types and structures, including folding and faulting
gather, process and present information from secondary sources which compares formation, general rock type and structure of mountain belts formed as a result of thermal uplift and rifting with those resulting from different types of plate convergence
Mountain building
Process of formation Example Rock types Structures of mountains
Thermal uplift Blue mountains Any rock type/depends on ocean/continent. No one answer
Folds, faults of all types
Rifting Great dividing range, rift valley
Basaltic, igneous rocks
Plateau, escarpments in the rift valley
Oceanic – oceanic convergence
Hariana trench Regional and contact metamorphic rocks. Andesite magmas
Island arcs and chain
Oceanic – continental convergence
Andes, south America
Regional and contact metamorphic rocks. Granite intrusions
Intensely folded mountain ranges
Continental – continental convergence
Himalayas Regional metamorphic rocks
Intensely folded mountain ranges
- Compression forces can produce folds and faults- Rocks which bend or fold produce arches called anticlines and downfolds called synclines- If the compression forces are large or the rocks brittle, they may snap to produce faults
3 Continents evolve as plate boundaries move and change
outline the main stages involved in the growth of the Australian continent over geological time as a result of plate tectonic processes
summarise the plate tectonic super-cycle
- analyse information from a geological or tectonic map of Australia in terms of age and/or structure of rocks and the pattern of growth of the continent
- present information as a sequence of diagrams to describe the plate tectonic super-cycle concept
Craton – old geologically stable area. No new rock formation/metamorphism occurring.
Mobile Belts – Areas that are still geologically active, they are unstable
Fold Belt – An area that is greatly folded due to compression forces
Growth of the Australian Continent
- the formation of Australia was west to east- the western parts of Australia are the oldest land forms on the earth- the east coast of Australia formed from a subduction zone, this subduction zone has
since moved eastward and now lies in New Zealand and Tonga
Timeline
- Mount narrayer forms (4.4bya)- Yilgarn block begins to forms (3.5bya)- Crust begins to form, rivers, igneous intrusions (3.4 – 3.09bya)- Yilgarn block forms (3.09 – 2.7bya)- Banded iron formations form, emerging crust, large tectonic forces (2.7 – 2.32bya)- Large crustal areas form in the north coast, west coast and south coast (1.93 –
1.55bya)- Formation of the east coast begins through oceanic – continental convergence, east
coast formed by island arcs from subduction zone (500mya)
Plate tectonic super cycle
- Twice in the earths history continents have joined together and formed a super continent until later it broke apart. This process is cyclic
- There may have been more than two times, however, it is unknown- The super continents:
o Rodinia – broke up around 750myao Pangaea – Broke up around 280mya
- Pangaea separated into Laurasia and Gondwana
Why do the super continents break apart
- When there is a super continent it insulates the mantle resulting in heat build up and eventual expansion
- The continents begin to rise and eventually cracks appear which begin to rift (diverge) apart
- The upwelling of hot material creates an ocean floor
gather, process and present information from secondary sources to chart the location of natural disasters worldwide associated with tectonic activity and use available evidence to assess the patterns in terms of plate tectonics
gather information from secondary sources to identify the technology used to measure crustal movements at collision boundaries and describe how this is used
gather information from secondary sources to present a case study of a natural disaster associated with tectonic activity that includes:– an analysis of the
tectonic movement or process involved
– its distance from the area of disaster
– predictions on the likely recurrence of the tectonic movement or process
– technology available to assist prediction of future events – an investigation of
possible solutions to minimise the disastrous effects of future events
4 Natural disasters are often associated with tectonic activity and environmental conditions caused by this activity may contribute to the problems experienced by people
identify where earthquakes and volcanoes are currently likely to occur based on the plate tectonic model
describe methods used for the prediction of volcanic eruptions and earthquakes
describe the general physical, chemical and biotic characteristics of a volcanic region and explain why people would inhabit such regions of risk
describe hazards associated with earthquakes, including ground motion, tsunamis and collapse of structures
describe hazards associated with volcanoes, including poisonous gas emissions, ash flows, lahars and lava flows and examine the impact of these hazards on the environment, on people and other living things
justify continued research into reliable prediction of volcanic activity and earthquakes
describe and explain the impacts of shock waves (earthquakes) on natural and built environments
distinguish between plate margin and intra-plate earthquakes with reference to the origins of specific earthquakes recorded on the Australian continent
Locations of earthquakes and volcanoes
- Volcanoes can occur on convergent boundaries, divergent boundaries and hotspots- Earthquakes may occur on convergent boundaries, divergent boundaries, transform
boundaries. Intraplate earthquakes are earthquakes which occur on continents not necessarily close to plate boundaries and often occur on faults
- Divergent plate boundaries tend to produce low magnitude and shallow earthquakes- Transform plate boundaries tend to create shallow earthquakes- Convergent plate boundaries then to produce the most destructive earthquakes
which can be shallow
Prediction methods of earthquakes and volcanoes
Earthquakes:
- Little ways to plan or predict earthquakes in long term, more in short term- Seismic Gaps – when no earthquake has occurred along a known fault one is more
likely- Animal behaviour – The strange behaviour of animals is present shortly before a
earthquake this was evident in an earthquake in China in 1975- Wells – Changes in the level of water in local wells- Radon gas – an increase or fluctuation in the amount of radon gas released in deep
wells- Electrical conductivity of rocks – in the area around earthquakes- Seismographs – are able to monitor the small earthquakes that occur before a larger
one- Lasers – uses to measure the change In length of lines across a known fault line- Strainmeters – fitted in boreholes to monitor the build up of force in earthquake
prone regions- Creepmeters – used to measure stretch in their length due to gradual movements
along a fault
- No prediction method is totally successful and mostly it is difficult to inform and move millions of people from a potential earthquake hazard if a short term prediction method is used
Volcanoes:
- Seismic activity – Earthquakes provide early warning of a possible volcanic eruption- Geophysical monitoring – prior to an eruption magma moves closer to the surface
this can be monitored by:o Infra red photoso Alterations of magnetic propertieso Gravitational properties of an area
- Topographical monitoring – The shape of the volcano may change prior to an eruption
- Volcanic gases – The amount of gases released may change in particular the rate at which sulphur dioxide is produced
Why people live near volcanoes
- Very fertile soil – new minerals are brought to surface- Born in the area/family- Topographic and orographic rainfall may increase amounts of water in area- 9/10 people living in volcanic areas are in developing nations and are often
uneducated/unaware of volcanic dangers
Earthquake hazards
Earthquake Nature Effect on environment Effect on peopleTsunamis A series of waves
caused by displacement of a large volume of water
Can cause devastating damage on ecosystems and organisms, marine life, trees, land
Can kill large amounts of people in coastal areas. People are swept away and buildings may collapse
Building collapses Due to seismic waves which travel and cause to ground to shake
Can destroy human environment. May pollute the biophysical environment through water and pollutants
Potential loss of life, homes and economic damage
Fire Caused by downed powerlines, explosions. Can spread rapidly through a destroyed city
Can cause damage to human environment, may damage biophysical environment
Potential loss of life, destroys homesEconomic damage
Liquefication Saturated soil looses strength in response to stress. Earthquakes cause water in to soil upwards to the surface
Building can loose support, can cause damage to piping systems
Causes death to people especially if inside a building
Volcano Hazards
Volcanic hazard Nature of the hazard Effect on environment Effect on peoplePoisonous gases Magma contains
dissolved gases which are released into atmosphere
Acid rain has a huge impact on environment. Fertile soils. Destruction of flora/fauna
Respiration illnessPulmonary edimaDeathDizziness/headaches
Pyroclastic flows fast moving superheated rock and gas
Destroys trees and wildlife. Extensive damage to environment close to volcano
Hot gases and high speeds make pyroclastic flows lethal
Lahars Mudflow of debris. Flow composed of pyroclastic, rocky, water
Kills all natural things in its path
17% of volcanic deathsIf fast can kill all in its pathCan destroy homes
Lava flows Generally do not move fast, lava flows from the volcano
Destroys all natural things in its path
Least hazardous people are generally able to avoid lava flows
Tsunamis Series of waves caused by displacement of water
Can destroy the environment and kill wildlife
Can kill thousands of people without warning
Earthquake waves
- Focus – The place often underground where an earthquake starts- Epicentre – A point on the surface of the earth which is directly above the focus of
an earthquake and where earthquake waves reach first- Primary (P) waves – The first seismic wave that reaches a seismograph from an
earthquake; a compression wave. Minor tremors- Secondary (S) waves – The second waves to arrive at a seismograph from a
earthquake; transverse wave. Minor damage- Long (L) (love) (tertiary) waves – An earthquake wave that travels over the surface
of the earth. Destructive waves- Rayleigh waves – waves which travel vertically through ground shaking it
Intraplate and plate marginPlate margin – occur on plate boundaries such as convergence. About 95% of all earthquakes occur on plate marginsIntraplate – Occur on along the edges of crustal plates caused by stresses and strains of the crustal plates moving across the athenosphere
5 Plate tectonics and climate
predict the possible effects of explosive volcanic activity on global and local climates
describe and explain the potential and observed impacts of volcanic eruptions on global temperature and agriculture
identify data, choose resources, gather and analyse secondary data on recent volcanic activity to determine the relationship between the eruption of ash and gas from an explosive volcanic eruption and the subsequent decrease in global temperature
Volcanoes and climate
Short Term:- Volcanoes dust clouds can obscure the sun- Sulfuric acid droplets can absorb the suns radiation- This can cause a solar radiation filter, reducing the amount of sunlight reaching the
earths surface- This can cause a global drop in temperature. (large volcanic eruptions may decrease
global temperature by up to 1c)- Short Term impacts do not last a long time
Long Term:- The large amounts of dust ejected into the atmosphere can produce a global solar
radiation filter, that could potentially in accord with other factors such as changes in the earths orbit and variation in solar activity produce ice ages
Volcanoes and Agriculture
- Effects on local agriculture are large, the blocking of sunlight in conjunction with sulphur dioxide can kill livestock and crops in the local area.
- Furthermore, pyroclastic flows and other volcanic hazards can destroy any immediate agriculture
- This is evident in Iceland in 1783 where the volcano Laki killed 75% of livestock in Iceland and caused a famine killing 25% of the population
- More globally however, the results are less severe. There may be a drop in global temperature which can result in poor harvests