Flashcards
Plate Tectonics - Plate Movement
Cards in this deck (34)
- 1How old is the Earth?4.6 Billion years old
- 2What is the inner core made out of?Iron and nickel.
It is solid
1250km-thick - 3Characteristics of the outer core?Molten
5000 degrees
2200km-thick - 4What are the characteristics of mantle?Semi-solid, asthenosphere is upper mantle
2 900km thick - 5What are the characteristics of the crust?Divided into plates, combined with asthenosphere and lithosphere
80-90km thick - 6What are the characteristics of continental crust?1) Made of older and less dense rocks such as granite.
2) Contains an abundance ofthe minerals aluminium and Silicon. (new name created from these rocks is sial)
3) Generally 35-70km thick and over 1500 million years old - 7What characteristics does the oceanic crust have?1) Made of younger rocks such as ones found along the mid-atlantic ridge.
2) most common rocks are basaltic ones, which are denser
3) 2 main minerals are silicon and magnesium (type of rock is sima)
4) 6-10km thick with an average of 200 million years old - 8What is plate tectonic theory?Alfred Wegener in 1912 proposed the concept of concept of 'continental drift' based on the evidence of the margins of the continents. Calculated 200 mil years ago continents originally joined together forming a large super continent called Pangaea
- 9What evidence is there for Pangea?1) The fit of continents like a jigsaw
2) Rocks on ocean floor are relatively young (sea floor spreading from mid ocean ridge)
3) fossils e.g. mesosaurus found in South America and South Africa
4) similar, age, structure Rock types in NA and mountains in scotland
5) Same age glacial till in south africa, SA india and AUS - 10What is paleomagnetism?When igneous rocks containing magnetic minerals crystallise, the crystals align themselves with the Earth's Magnetic field. The magnetic field periodically reverses polarity. Rocks crystallising during this period do so in the opposite direction. Scientists discovered that there were stripes of 'normal' and reverse polarity.
- 11What did this all show?That the rocks formed at a ridge and moved away from that ridge in both directions (constructive)
- 12How does continental drift occur?Convection currents. Heat rises through the mantle towards the surface from radioactive decay (e.g. uranium) in the core. The current rises to reach its maximum height in the hard uppermost mantle. At these points, the hot mantle rocks melt from the lowering of lithostatic pressure and rises to form new crust at the mid-ocean ridges. The drag at the base of the tectonic plate causes them to move.
- 13What is sea floor spreading?When the above occurs in two oceanic plates
- 14What is a destructive plate margin?Occurs when two tectonic plates are moving towards one another.
e.g. Ocean/continental collision (Nazca beneath South America)
Continental/continental (Indian crash Asia) - 15Seismicity? Vulcanicity?Yes
Yes - 16How are fold mountains formed?1) Sediments accumulate in shallow seas or depressions (GEOSYNCLINES)
2) This creates a sea or lake bed filled with layered sedimentary rocks as compression takes place.
3) Two plates move together because of convection currents in the mantle
4) This starts to crumple the rocks together and form folds which have anticlines and synclines, which are pushed upwards to form fold mountains.
6)The mountains are prone to denudation - 17How are deep sea trenches formed?When an oceanic crust is subducted under a continental crust. Found in a linear pattern.
The pressure can cause earthquakes and magma to heat causing Earthquakes
e.g. marianas trench (11m deep) - 18How are island arcs formed?Form at oceanic - oceanic plate margins where subduction takes place, where one plate is more dense than the other. Volcanoes form where the pressure causes magma to rise from under the ocean. Curved lines of volcanic islands e.g. Mariana islands. Parallel to deep ocean trenches.
- 19What is a constructive (diverging) plate boundary?When two plate boundaries move apart from eachother
- 20Vulcanicity? Seismicity?Yes
Yes - 21How are mid-ocean ridges formed?Long continuous uplifted features on the surfaceof the planet
1) Divergence in 2 plates
2) two plates move apart causing basalitic lava to rise and cool on the sides of the ridge raising its height
3) Gently sloping sides - 22What kind of activity occurs along the ridge?Volcanic activity occurs, forming submarine volcanoes, which sometimes rise above sea level, e.g. Sutsey to the south of Iceland (Iceland itself was formed in this way). These are volcanoes with fairly gentle sides because of the low viscosity of basaltic lava. Eruptions are frequent but relatively gentle.
- 23How do earthquakes occur at mid-ocean ridges?As new crust forsm and spreads, transform faults occur at right angles to the plate boundary. The parts of the spreading plates on either side of these faults may move at differing rates, leading to friction and ultimately to earthquakes. These tend to be shallow-focus earthquakes, originating near the surface.
- 24How are rift valleys formed?Constructive margins in continental areas, brittle crust fractures as it moves apart. Areas of crust drop down between parallel faults to form rift valleys. The largest feature is the African rift valley which extends 4,000km from Mozambique to the Red Sea. In some areas the inward-facing scarpes are 600m above the valley floor and are marked by a series of parallel step faults.
- 25What kind of activity occurs at this area?The area is associated with volcanic activity (e.g the highest mountain in Africa, Mt Kilimanjaro). The crust here is much thinner than in neighbouring areas, suggesting that tension in the lithosphere is causing the plate to thin as it starts to split. The line if the African rift is thought to be an emergent plate boundary, the beginning of a new ocean as eastern Africa splits from the continent.
- 26What is a conservative plate boundary?occur where there are two plates sliding horizontally past one another. Most conservative plate margins are found on the ocean floor. They commonly offset the active spreading ridges, producing zig-zag plate margins, and are generally defined by shallow earthquakes. However, a few occur on land e.g. the San Andreas fault-zone in California.
- 27Explain the location of earthquakes1) Global earthquake maps show most events are concentrated in relatively narrow bands, with large areas between them where there are no earthquakes.
2) The largest-magnitude earthquakes found on Earth occur within the subduction zones of destructive plate boundaries, caused by friction e.g. 2011 Tohoku earthquake, with a magnitude 9.0 - 28What do the narrow belts of earthquakes show?1) The narrow belts of earthquakes show active plate boundaries. The areas between are the rigid plate interiors
2) The narrowest seismic belts (about 20 km wide) are associated with the crests of the mid-ocean ridges. Earthquakes at these boundaries are mostly at a depth of no more than 8 km. Nearly all earthquakes have a magnitude 6<. - 29Explain the location of Volcanoes1) There are well defined island arcs such as in the Aleutians, central and western North and South America correlate with convergin plate margins. Volcanic regions such as the Hawaiian Islands are isolated.
2) A second line of volcanoes follows the constructive plate boundaries of a mid-ocean ridge. Occasionally this volcanic activity reaches the surface in the form of a volcanic island.
3) One final region of substantial volcanic activity is East Africa, the location of a rift valley that scientists believe is the start of a new constructive plate boundary. - 30What is a hotspot?A small area of the Earth’s crust where an unusually high heat flow is associated with volcanic activity.
Approximately 125 hot spots thought to have been active over the past 10 million years most are located well away from plate boundaries - 31How do hotspots form?1) Intense radioactivity in the Earth's interior creates a huge column of upwelling lava, known as a 'plume'.
2) The plume of plastic rock from the anethosphere pushes upwards, pressure drops and the rocks become molten, pushing through the crust above.
3) This lies at a fixed position under the Tectonic Plate. As the plate moves over this “hot spot”, the upwelling lava creates a steady succession of new volcanoes that migrate along with the plate. These domes or plumes of plastic rock can be up to 1,000 km across. - 32How did the Hawaii hotspot formsThe major theory that Geologists believe is that a huge column of upwelling lava, known as a “plume,” lies at a fixed position under the Pacific Plate. As the ocean floor moves over this “hot spot” at five inches a year. Upwelling lava creates a steady succession of new volcanoes that migrate along with the plate, conveyor belt of volcanic islands.
- 33What are the characteristics of the Hawaii islands?Hawaii itself consists of five connected volcanic mountains that were built by this lava plume rising from the mantle. Kilauea, the world’s largest active volcano, is still rumbling because the island has yet to move completely off the hot spot. The Islands get older the further they are in the chain are from Hawaii. About 150 miles to the northwest is Oahu, which burst out of the sea about 3.5 million years ago. Midway, one of the oldest islands in the chain, was formed between 15 and 25 million years ago.
- 34Is there a new island rising?Off the south western coast of the island of Hawaii, beneath the ocean surface, Loihi, the next Hawaiian Island, is forming as the Pacific Plate continues its journey over this hot spot. As it stands today, Loihi rises about 6,000 feet above the sea-floor, which brings it very close to the surface. At its present rate of ascension, scientists predict that Loihi will poke through the surface in one million years.
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- A-Level Geography (A2) Flashcards on Plate Tectonics - Plate Movement, created by Ella Foster on 30/03/2017.
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