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