Tectonics

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  • Created by: Hollyha
  • Created on: 05-05-16 14:00
What was Francis Bacon and Alfred Wegener theory of plate tectonics?
FB = South America and West Africa fit together. AW = supercontinent PANGEA, split into 2 continents LAURASIA in north, GONDWANALAND in south.
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How did the mid-atlantic ridge develop the theory of plate tectonics?
1948 an island in the atlantic noted variation in the depth of ocean, chains of continuous mountains running down centre.
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How did paleomagnetism develop the theory of plate tectonics?
Iron particles in lava erupted on ocean floor and aligned with Earth's magnetic field. Earth's polarity reverses approx every 400,000yrs therefore magnetic stripes are aligned alternately towards north and south poles.
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How did sea floor spreading develop the theory of plate tectonics?
Harry Hess, mid-atlantic ridge and oceanic crust becomes older with distance from the ridge. Mid-oceanic ridges split into segments fractures/faults.
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What is the geological evidence for plate tectonics theory?
Glaciation deposits found in South America, India, Antartica. Striations/layers on rocks in Brazil, west Africa. Rock sequencesin North Scotland are closely matched in East Canada, trends of fold mountains.
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What is the biological evidence for plate tectonics theory?
Brachiopods found in limestone in India and Australia, Mesosaurus fossils found in South America and South Africa. Glossopetoris in coal found in India and Antartica.
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What climate evidence is there for plate tectonics theory?
Coal is formed under warm wet conditions found beneath Antartic ice cap.
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What are the characteristics of the inner core?
Solid, under immense pressure, and rich in iron and nickel.
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What are the characteristics of the outer core?
Semi molten/liquid, rich in iron and nickel, responsible for Earth's magnetic field.
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What are the characteristics of the mantle?
Molten rock, rich in iron and magnesium, rigid near core and semi-molten top layer (ASTHENOSPHERE). Convection currents occur.
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What are the characteristics of the crust?
Crust and upper mantle form LITHOSPHERE. OCEANIC = basaltic rich in silica and magnesium, thinner 6-10km, more dense. CONTINENTAL = rich in silica and aluminium, thicker 30-70km and less dense.
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What are hotspots?
Thermal convection currents, create drag. Radioactive decay (uranium) generates heat, the lower part of the asthenosphere heats up and becomes less dense so it rises to the top of the asthenosphere and cools down becomes denser and sinks.
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How do hotspots form chains of volcanoes (island arcs) like Hawaii?
A magma plume rises form the mantle and volcanoes form above. The plume remains stationary whilst the crust moves above it, volcanic activity that was above hotspot decreases as crust moves over it. New volcanoes form in crust that is now above HS.
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What is a constructive plate boundary? Which type of plates are involved - continental/oceanic?
When 2 plates move apart, either oceanic and oceanic or continental and continental.
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What are the land forms associated with constructive plate boundaries?
MID-OCEANIC RIDGES = diverging plates underwater. RIFT VALLEYS = diverging plates beneath land, magma causes continental crust fracture/fault lines. When crust moves apart parallel faults drop down.
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Why do earthquakes occur at continental plate boundaries?
Don't move apart in uniform way pressure builds up late cracks and creates fault line.
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Why do volcanoes form at continental plate boundaries?
Underwater volcanoes erupt and form volcanic islands (Iceland). there is the Mount Kenya and Mount Kilimanjaro volcano in the East African Rift Valley.
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What is a destructive plate boundary?
When 2 plates move towards each other.
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What land forms are associated with oceanic/continental destructive plate boundary?
DEEP SEA TRENCHES = dense oceanic crust is subducted under less dense continental crust (Peru-Chile trench). YOUNG FOLD MOUNTAINS = sediment gets folded upwards along edge of continental crust.
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Why do earthquakes and volcanoes occur at oceanic/continental destructive plate boundary?
E = plates get stuck at subduction zone, pressure builds up and is released which causes a jerk. V = oceanic crust heated by friction magma less dense and rises.
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What land forms are associated with oceanic/oceanic destructive plate boundary?
DEEP SEA TRENCHES = the denser oceanic crust is subducted under the other oceanic crust. ISLAND ARCS = volcanic eruptions underwater (Hawaii).
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Why do earthquakes and volcanoes occur at oceanic/oceanic destructive plate boundary?
They are both triggered by deep sea trenches.
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What land forms are associated with continental/continental destructive plate boundary?
FOLD MOUNTAINS = converging continental plats fold crust upwards (Himalayas).
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hy do earthquakes occur at continental/continental destructive plate boundary?
Pressure builds up and is released suddenly.
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What are conservative plate boundaries?
When 2 plates move past each other.
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What land forms are associated with conservative plate boundary?
LOW RIDGES
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Why do earthquakes occur at conservative plate boundary?
The 2 plates lock together and pressure builds up, they jerk when energy is released (San Andreas Fault)
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What is a fissure eruption?
Form at constructive boundaries, long linear vents several km long few m wide, flat surface, low viscosity basaltic lava flows long distances (Lake fissure system Iceland).
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What is a basic shield volcano?
Form at constructive boundaries, low viscosity basaltic free flowing lava, gentle sides cover large area. Mauna Loa Hawaii.
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What is an acid dome volcano?
Formed at destructive boundaries, high viscosity andesitic/rhyolite quick solidifying lava, steep sided. Mt Pelee.
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What is a caldera?
Formed at destructive plate boundaries, andesitic/rhyolitic lava, ash and cinders. Central part collapses when magma chamber empties, wide circular crater several km across, Krakatoa Indonesia.
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What are composite cone volcanoes?
Layers of ash and lava, steep sided, symmetrical cone, plug, subsidiary cones and vents.
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What is a solfatara?
Small volcanic areas that release gases. Bay of Naples Italy.
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What is a geyser?
Type of hot spring, hot water and steam explodes to surface in a fountain. Groundwater gets heated to above boiling point by magma, the hot water is pressurised and gets forced through cracks. Old Faithful Yellowstone National Park.
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What are boiling mud hot springs?
Have high mineral content as hot water holds a lot of dissolved solids. Heated water mixes with surface deposits to form boiling mud. Blue Lagoon Iceland.
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What is basaltic lava?
Released at constructive plate boundaries, low viscosity and flows easily.
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What is andesitic lava?
Released at destructive plate boundaries, medium viscosity, violent eruptions.
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What is rhyolitic lava?
Released at destructive boundaries, high viscosity, violent eruptions.
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What is a batholith?
INTRUSIVE VOLCANIC ACTIVITY = Igneous rock, magma cools and solidifies, large crystals - cool slowly. Dome shaped can be exposed by erosion. The area around the the batholith that altered by heat and pressure is the METAMORPHIC AUREOLE.
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What is a laccolith?
INTRUSIVE VOLCANIC ACTIVITY = smaller injection of magma between layers of rock, the layers above a forced upwards into a small dome. Eldon Hill Scotland.
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What is a dyke?
INTRUSIVE VOLCANIC ACTIVITY = small vertical magma plumes, form across bedding planes, have horizontal cooling cracks. Form dyke swarms. Scottish Islands - Mull Skye.
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What are sills?
INTRUSIVE VOLCANIC ACTIVITY = small vertical magma plumes, form along bedding planes and have vertical cooling cracks. Great whin-sill.
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What are the primary impacts of volcanic activity?
TEPHRA= solid material, vary from ash particles to volcanic bombs, PYROCLASTIC FLOWS = very hot gas charged high velocity flows, gases and tephra, LAVA FLOWS, VOLCANIC GASES = CO2, from lake Nyos Cameroon suffocated 1,700 people, CO, HS, SO2, Cl.
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What are the secondary impacts of volcanic activity?
LAHARS = volcanic mudflows, FLOODING = melting glaciers and ice caps, Grimsvotn glacier Iceland, TSUNAMIS = caldera forming events 1883 Krakatoa, VOLCANIC LANDSLIDES, CLIMATE CHANGE = ejection of volcanic debris into atmosphere reduce global temps. .
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When do impacts become hazards?
When they impact on human and built environments, killing, collapsing, agriculture.
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What is the activity of earthquakes?
Tension builds up at all 3 types of plate boundary, plates jerk past each other and seismic waves spread out from focus.
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What is the focus?
Point underneath the surface where the earthquake originates from. SHALLOW = 0-70km deep greatest damage, INTERMEDIATE = 70-300km deep, DEEP = 300-700km deep.
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What is the epicentre?
Point on Earth's surface above the focus, where the earthquake is first felt.
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What are primary/P waves?
FAST COMPRESSIONAL = travel through solids and liquids, push and pull earth in same direction as wave is travelling.
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What is secondary/S waves?
Travel through solids, move through earth 90degrees to direction of travel, cause lot of damage = SHEARING EFFECT.
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What are surface waves/L waves?
Slower than S+P waves. RAYLEIGH WAVES = move through solids and liquids in a rolling motion. LONE WAVES = travel through solids from side to side.
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What is the distribution of earthquakes?
The most powerful occur at destructive boundaries. Occur along fault line on conservative boundaries San Andreas Fault California. Reactivation of old fault lines, subsidence due to mining, pressure on surface rocks form water in reservoirs.
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What are seismometers used for?
Measure magnitude (strength), duration and direction (horizontal/vertical) of vibrations.
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What does the Richter scale measure?
MAGNITUDE = logarithmic earthquake of magnitude 5 is 10 times greater than an earthquake of magnitude 4. 30 times more energy released than previous value.
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What does the mercalli scale measure?
IMPACTS = using observations (reports/photos). Between 1 (only detected by instruments) and 12 (causes total destruction)..
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What are the secondary effects of an earthquake?
LANDSLIDES/AVALANCHES, PEOPLE/ENVIRONMENT = collapsing buildings/destruction to roads, gas pipes, water pipes, electricity lines, disease, flooding. TSUNAMIS.
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What are the characteristics of tsunamis in the open ocean?
They have long wavelengths (200km) low wave height/amplitude (1m) travel at high speeds (over 700km/h).
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When a tsunami reaches the land, its characteristics depend on?
Height of the waves and distance they have travelled, length of the earthquake/event, coastal physical geography - offshore/coastal area, coastal land use and population density.
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What are the characteristics of tsunamis closer to land?
The water is shallower so wave becomes compressed + energy is more concentrated, wavelength decreases (
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Explain the causes of tsunamis?
Giant sea waves generated by shallow-focus underwater earthquakes, volcanic eruptions, underwater debris landslides into sea. This causes vertical displacement of the sea bed and large volumes of water.
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How can tectonic hazards be managed by using predictions?
EARTHQUAKES: small tremors, cracks, warning system, where based on past E. VOLCANOES: tiny earthquakes, bulges. TSUNAMIS: earthquake/tsunami detection systems.
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How can tectonic hazards be managed by using building techniques?
EARTHQUAKES: strong materials reinforced concrete absorb energy, construction laws. VOLCANOES: strengthened not collapsed by ash, divert lava/barriers. TSUNAMIS: raised open foundations, concrete, Tsunami walls Hokkaido Japan.
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How can tectonic hazards be managed by using planning and education?
Avoid areas at risk, train emergency services/FEMA USA, evacuation routes Oregon USA provide maps, government/organisations educate people Japan/drills.
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Card 2

Front

How did the mid-atlantic ridge develop the theory of plate tectonics?

Back

1948 an island in the atlantic noted variation in the depth of ocean, chains of continuous mountains running down centre.

Card 3

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How did paleomagnetism develop the theory of plate tectonics?

Back

Preview of the front of card 3

Card 4

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How did sea floor spreading develop the theory of plate tectonics?

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Card 5

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What is the geological evidence for plate tectonics theory?

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