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- 1Oceanic - more dense (3g/m3) - darker minerals - thinner (3-15km) - basalt (small crystal) - gabbro (large crystal) - relatively new, oldest rocks 175m.y.o - mafic - simple rock types (igneous)Continental
- less dense (2.7g/m3)
- lighter minerals
- thicker (40-65km)
- granite and andesite
- very old, oldest mineral 4500 m.y.o
- felsic
- complex rock types (metamorphic and igneous) - 2—
- 3Divergent plate boundary M.O.R; - partial melting of asthenosphere produces mafic magma - rises and collects in magma chamber - mafic lavas erupt to form pillow basalts on ocean floor - also cools at depth to form multitudes of basalt dykes, lower in oceanic crust layers of gabbro are producedDiagram;
- 4Divergent plate boundary Continental rift; - same as M.O.R - two types of eruptions - mafic lavas erupt to form basalts, but rising mafic magmas also melt continental crust, causing felsic lavas to erupt to form rhyolitesDiagram;
- 5Convergent plate boundary oceanic-oceanic; - mixing of water with surrounding asthenosphere lowers the melting point to produce mafic-rich magmas - eruptions range from mafic to intermediate - early eruptions are mostly mafic, becoming more intermediate as the island arc growsDiagram;
- 6Convergent plate boundary oceanic-continental; - same as O-O subduction - eruptions predominantly intermediate with some mafic magmas rising magmas altered by melting and then mixing with molten continental crust - heating and hydration of continental crust also cause felsic magmas to develop - usually solidifying at depth to form large masses of plutonsDiagram;
- 7Convergent plate boundary continental-continental; - small amounts of felsic magmas are produced as wet sedimentary material is compressed because of crustal thickening - these felsic magmas solidify before reaching the surface, forming large masses of granite called plutonsDiagram;
- 8Conservative plate boundary;Diagram;
- 9Identify the relation between the general composition of igneous rocks and plate boundary type- divergent zones; new crust material is produced (M.O.R)
- new crust is being produced, same amount has to be destroyed to maintain diameter of the earth
- igneous rocks tell us the geology of the land, the previous geology of the land
- the type of magma/lava depends on the source, amount of melting, and processes that occur in the magma chamber - 10Current hypotheses to explain how the tectonic plates move- convection currents; hot magma in the lithosphere is circulated by heat, continuously moving creating a convection cell
- slab-pull; when both convection currents and gravity drives a subducting plate down, pulling the rest of the plate with it
- ridge- push; involves the M.O.R forcing plates apart as new material rises and accretes to the sides of the plates - 11Distinguish between mountain belts formed at divergent and convergent plate boundariesMountains are formed by folding from compression forces faulting from compressional forces or the rising heated material
- 12Folds occur with compression forces, pressure and heat. They reduce width but increase thickness, creating metamorphic rocksDiagram;
- 13C-C convergentHorizontal pressure folds the rock, shortening width, and increasing height. Rocks are generally felsic, with some mafic material found as ophiolites. Mostly metamorphic rocks, some faulting (reverse) as older continental crust reaches maximum compression. Mountains run parallel to boundary e.g. Himalayas
- 14O-O ConvergentMountains produced by subduction. Very explosive volcanoes- Island Arcs formed parallel to the boundary. Rocks mainly andesite e.g. Japan
- 15Mid-ocean ridgeMountain formed from upwelling of magma as plates move apart, faulting (normal) occurs as plate cools and stretches. Very gentle volcanoes. Mafic rocks, mountains are 2 uninterrupted chains running parallel to each other with a large valley in-between. Transform faults run perpendicular to the ridge axis
- 16Continental riftStretching puts pressure on area and normal faults occur. The plate is stretched and weakened and some molten material can make its way to the surface
- 17Thermal upliftFormed when a hot spot in the mantle occurs. Molten material breaks through the oceanic crust and effusive lava forms e.g. Hawaii
- 18O-C convergentVery explosive volcanoes as high silica content. Mountains intermediate, igneous and metamorphic andesite common. Mountain belt is chain in continental crust running parallel to plate boundary e.g. Andes
- 19Types of volcanoesDiagrams;
- 20The pattern of growth of the Australian continentThe oldest rocks are found in the west of Australia. They are the Yilgarn, Pilbara and Gowler cratons. The youngest rocks are basaltic volcanoes along the crust
- 21Main stages in the growth of the Australian continentOVERALL THE CONTINENT GREW FROM WEST TO EAST
1. Archaean (2500ma); cratons are formed. Yilgarn in South West Australia, Pilbora in West Australia and Gawler in South Australia
2. Orogenesis (products of mountains); joins mountain belts together in the proterozoic (2500ma-550ma) Central Australia becomes cratonised - 223. Phanerozoic (550-250ma) O-O subduction zone in the East produces Island Arc Volcanic chain off the East Coast of the craton. A shallow sea forms. Over time the back arc basin fills with sediments, joining the Island Arc with the craton. Millions of years of weathering and erosion fill the basin4. Australia moves north over hot spot producing hot spot volcanoes (basaltic). This occurred in past (1ma)
- 23Diagram of main stages in the growth of the Australian continentdiagram;
- 24Plate tectonic super-cycleContinents break up into smaller pieces which then accrete back together to form SUPERCONTINENTS, which then break up again. This is known as the 'Wilson' cycle and involves the closing and opening of oceans. As the plates move, new material can be added to the continental margins. The cycle takes anywhere up to 350ma to complete. Past land masses have included Pangea (250ma), Sturtia (720ma) and Rhodinia (1120ma)
- 25Plate Tectonic Super-cycleDiagram;
- 26Where do most earthquakes and volcanoes occurActive volcanoes and earthquakes are not randomly distributed, most occur at plate boundaries. Some occur at hot-spots. We can predict the general areas that most future volcanoes or earthquakes will occur- plate boundaries, or as a plate moves over a hot spot. Every type of plate boundary ca produce an earthquake. C-C convergent and conservative boundaries are the only ones NOT to produce volcanoes
- 27Physical, chemical and biotic characteristics of a volcanic areaHAZARD VS BENEFIT
- many hazards
-benefit of living has to overweigh cost/risk
-moving has to be more difficult/money/time than cost/risk
-most volcanoes are safe in between eruptions
-people think they are predictable - 28POPULATIONS ON VOLCANOES-500 million people live on or close to volcanoes
- some major cities near volcanoes;
Mt Etna, Mt Rainier, Mt Loa, Mt Merapi, Sakurajima - 29SOIL and MINERALS-igneous rock and ash produces fertile soil when weathered
-generally takes thousands of years
-soil builds up forming soils full of minerals
-used for farming
MINERALS
-igneous rocks comprised of minerals
-some are very useful (zinc, tin etc)
- hot gasses bring some minerals like sulfur to the surface, where they condense
- locals collect and sell it - 30RAINFALL and GEOTHERMAL ENERGY-produce rain-shadow
-good for agriculture
GEOTHERMAL ENERGY
-use heat energy from earth (steam)
-not used directly in houses (unpredictable)
- used for commercial turbines for electricity or heat water
- can pump cool water down and extract steam - 31BIODIVERSITY and AESTHETICS-more natural resources
-stronger population of plants/animals due to natural selection pressures
-further increase soil with organic matter
AESTHETICS
- pretty to look at and live near
-tourism - 32TOURISM-volcanic eruptions (explosive or gentle)
-hot springs/baths
-mud pools
-steam vents
-geysers (Old Faithful in US)
- waterfalls
-climbing/hiking
-skiing
-biodiversity - 33FAMILY HISTORY and WHERE ELSE TO GO?-many generations of farms, villages
-often no eruption in living memory
-assume they will be safe or happy to take risk
-nowhere else to go
-cost or relocating and setting up new livelihoods
-spiritual/cultural connection
-benefits outweigh risk - 34POISONOUS GAS EMISSIONS (ACID RAIN)Sulfur dioxide (SO2), sulfur trioxide (SO3), Hydrochloric acid (HCL), carbon monoxide (CO), hydrogen sulfide (H2S), carbon dioxide (CO2). EOP; suffocation as CO2 is more dense than air sits lower in valleys. Acid vapours can irritate eyes, lungs and skin. EOE; acids can dissolve in water and chemically weather rocks and other buildings. EOOLT; acids dissolve in rainwater, killing plants. Some can be ingested by animals. Livestock can suffocate if in valleys
- 35ASH FLOWSFine particles of ash, dust and aerosols that enter the atmosphere and can settle on Earth. EOP; knocks down and burns everything in its path. Can't be outrun. Burns, suffocation, respiratory issues, death. EOE; knocks down and burns everything. Starts fires, clogs machinery, layer of ash reflects sunlight so climate change. EOOLT; layer of ash hardens on contact, preventing seeds from germinating
- 36LAHARMud flows, contains tiny sediments as well as huge boulders. Very rapid. EOP; increased sediments covers land, housed and agricultural land washes houses and people away, death. EOE; erodes rocks by direct impact, melts ice/snow if present. Landslides, blocks tributaries, floods. EOOLT; destroys vegetation, increases sediments reduces photosynthesis
- 37LAVA FLOWSMolten rock escaping from a volcano, can be effusive or part of pyroclastic flow. EOP; burns, destroys property. EOE; destroys property, stops services (power, water etc.), melts snow/ice, dams/rivers causing flooding. EOOLT; burns, covers land in new rock, no new growth
- 38VAN techniqueMessages are sent to a satelite about the earth's movement. Just before and earthquake occurs (roughly 30 minutes) the earth sends out electromagnetic signals that are picked up by the satelite
- 392 colour laser geodimeterOn either side of a volcano, a laser is set, it has two colours helping with precision. The device measures any movement that occurs, which could help to warn if an eruption is going to occur
- 40Earthquakes A sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within the earth's crust (FORCES, FAULTS and FRICTION)Different results of earthquakes;
- 41Earthquakes and plate boundariesDiagram;
- 42Seismic Waves- P-waves; fast (compressional like a slinky)
- S-wave; intermediate
- Surface waves; slow - 43IMPACT OF EARTHQUAKES;NATURAL;
-faults
- mountians
-displaced streams
-crevices
-movement of water in bays
-landslides - 44IMPACT OF EARTHQUAKES ON BUILT ENVIRONMENT-collapse buildings
-break sewerage, pipes
-roads
-power lines
-damage vehicles
-kills people and animals
-waste dumps and underground storage
-fires from ruptured gas lines
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