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Tectonic Impacts 1 Lithospheric plates and their motion describe the characteristics of lithospheric plates identify the relationship between the general composition of igneous rocks and plate boundary type gather and analyse information from secondary sources about the forces driving plate motion 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 Average Density Average Thickness Composition Continental 2.7g/cm*3 35km Felsic rocks, sedimentary, igneous, andesite and granite Oceanic crust is composed of four major layers: 1) Sediment layer 2) Pillow basalt, basaltic breccius 3) Sheeted dike, gabbro 4) Thin layer of upper mantle material Oceanic 3.0g/cm*3 7km Mafic rocks, basalt and gabbro Igneous rocks and plate boundaries Location Divergent boundaries Convergent boundaries Hot spots Type of movement Mid – ocean ridge Magma formation Mafic magma Continental rift Mafic magma Oceanic - oceanic Mafic rich magma Oceanic – continental Mafic rich magma Continental collisions Small amounts of felsic magma Mafic magma Under continental crust Under oceanic crust Mafic magma Lava produced Mafic lave erupts to form pillow basalt. Forms basalt dykes and gabbro Mafic lava erupts and forms basalt. Felsic lavas forms to produce rhyolite Eruptions are mafic to intermediate. Early eruptions are mainly mafic Eruptions are mainly intermediate. Some mafic magma. Felsic magma. Plutons None. plutons Mafic lava produces basalt. Felsic lava form rhyolite 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 currents o Slab pull o 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 Thermal uplift Blue mountains Rifting Great dividing range, rift valley Hariana trench Any rock type/depends on ocean/continent. No one answer Basaltic, igneous rocks Oceanic – oceanic convergence Oceanic – continental convergence Andes, south America Continental – continental convergence Himalayas Regional and contact metamorphic rocks. Andesite magmas Regional and contact metamorphic rocks. Granite intrusions Regional metamorphic rocks Structures of mountains Folds, faults of all types Plateau, escarpments in the rift valley Island arcs and chain Intensely folded mountain ranges 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 supercycle - 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 supercycle 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 750mya o 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 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 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 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 photos o Alterations of magnetic properties o 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 Tsunamis Nature A series of waves caused by displacement of a large volume of water Building collapses Due to seismic waves which travel and cause to ground to shake Fire Liquefication Effect on environment Can cause devastating damage on ecosystems and organisms, marine life, trees, land Can destroy human environment. May pollute the biophysical environment through water and pollutants Caused by downed Can cause damage to powerlines, explosions. human environment, Can spread rapidly may damage through a destroyed biophysical city environment Saturated soil looses Building can loose strength in response to support, can cause stress. Earthquakes damage to piping cause water in to soil systems upwards to the surface Effect on people Can kill large amounts of people in coastal areas. People are swept away and buildings may collapse Potential loss of life, homes and economic damage Potential loss of life, destroys homes Economic damage Causes death to people especially if inside a building Volcano Hazards Volcanic hazard Poisonous gases Nature of the hazard Magma contains dissolved gases which are released into atmosphere Pyroclastic flows fast moving superheated rock and gas Lahars Mudflow of debris. Flow composed of pyroclastic, rocky, water Generally do not move fast, lava flows from the volcano Series of waves caused by displacement of water Lava flows Tsunamis Effect on environment Acid rain has a huge impact on environment. Fertile soils. Destruction of flora/fauna Destroys trees and wildlife. Extensive damage to environment close to volcano Kills all natural things in its path Destroys all natural things in its path Can destroy the environment and kill wildlife Effect on people Respiration illness Pulmonary edima Death Dizziness/headaches Hot gases and high speeds make pyroclastic flows lethal 17% of volcanic deaths If fast can kill all in its path Can destroy homes Least hazardous people are generally able to avoid lava flows 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 margin Plate margin – occur on plate boundaries such as convergence. About 95% of all earthquakes occur on plate margins Intraplate – 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