Karteikarten
plate tectonics
Karten in diesem Stapel (50)
- 1what is the earths structure?1) Solid Inner Core
- 1220km in total thickness
- made form iron and nickel
- metal iron does not melt due to the the huge amount of pressure
- 6000 degrees celcius
2) Outer Core
- 2300km in total
- liquid/molten
- made from sulphur, oxygen, iron and nickel
- 4000-6000 degrees celcius
3) Mantle
- 80% of earths total volume
- 2900km thick
- made up of molten and semi- molten rocks, containing lighter elements such as silicon and oxygen
- 1000 degrees celcius
4) Asthenosphere
- This is the upper part of the mantle approximately 80 km deep
- rocks kept in a semi-molten state
- the plate over and floats on here
5) Moho Discontinuity
5) Oceanic Crust
- denser, newer ad thinner
- 6-10 km thick
- made from mainly basalt (originates from cold lava)
- 500 degrees
5) Continental Crust
- older, thicker, less dense, cannot be destroyed to created
- 30-70 km thick
- mainly made from granite, silicon, oxygen, aluminium
-500 degrees
5) Lithosphere
- this is the upper section of the mantle and crust
- about 80-90km thick - 2what is Moho Discontinuity- it separates the mantle from the crust
- it allows the crust to flow without melting
- where seismic waves are modified - 3what are convection currents and how do they occur1) Slow moving plumes of heat
2) generated by radioactive decay within the core
3) Creates thermal currents that rise towards the surface and then cools and sinks again
4) As semi molten rock i the mantle e(asthenosphere) is heated as it becomes less dense than its surroundings and rises
5) As it nears the lithosphere it spreads out carrying the plates above with it
6) As the smell molten rocks cools, it gradually sucks bad down to be re heated
7) The circulatory motion causes the crustal plates to move.
- New crust formed at constructive boundaries
- Older crust being destroyed at destructive boundaries - 4what is continental drift and who came up with it- 1912 Alfred Wegener published his theory of continental drift and that a single continent existed about 300 million years ago (Pangaea).
- He said the the pangaea split into two continents of Laurasia ( north) and Gondwanaland (south)
- Today the contents were formed from further plaiting of theses two mass' - 5geological evidence of continental drift1) The fit of South America and Africa
2) Rock sequences in Northern Scotland are similar to ones in Eastern Canada, perhaps they were laid down under the same conditions in one location.
3) Evidence of glaciation of the late carboniferous period, deposits of which are found in South America, Antarctica and India. Striations are also found on rocks in Brazil and W.Africa which point to similar situation - 6biological evidence of continental drift1) The fossilised remains of a plant which existed when coal was being formed have been located only in India and Antarctica.
2) Fossil remain of reptile Mesosaurus found in both south America and Africa. Unlikely that same reptile developed in both areas or that it could have migrated - 7climatological evidence of continental drift1) Similar glacial deposit are found in Antarctica, Africa, S.America, India and Australia. By fitting these together you can match up the distribution of deposits, suggesting they were once joined together.
2) Large coal deposits that are formed in tropical conditions are found in N.America and parts of Europe, suggesting these regions were once closer to the equator - 8continental fit evidence of continental drift- Continental shelf is the extended perimeter of each continent, this was exposed during glacial periods but is now submerges under relatively shallow sea.
- Although underwater, continental shelves are part of the continent. The actual boundary of a continent is not its coastline, but the edge of the continental shelf. - 9evidence of sea floor spreading- New crust is comes when plate move apart at constructive plate boundaries
- When this happens at the plate margin under the sea, the SEA FLOOR gets wider, tis is called sea floor spreading
- It forms Mid-ocean ridges
- New oceanic crust is created at The mid atlantic ocean
- The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimeters per year (cm/yr)
- It lies in the Atlantic ocean between N+S America and Africa. There are no ocean trenches destroying these new land being formed on the coats of these continents. Therefore that Atlantic Ocean is exanding - 10Evidence of PalaeomagnetismPalaeomagnetism = study of the history of the Earths magnetic field. Once every 400,000 years the Earths magnetic fires reverse polarity ( the magnetic N and S poles switch)
- As the magma erupts from the mid ocean ridges, magnetic minerals in the molten rock align themselves with the direction of the Earths magnetic field
- The magnetic mineral in the crust that was created in periods of normal polarity are aligned in the opposite direction to those created in periods of reverse polarity
- Creating a series of alternating magnetic stripes along the sea floor. The stripes show that the crust id older the further away from the mid ocean ridge - meaning plates are moving apart - 11constructive plate boundary (oceanic)- Convection currents moving in opposite directions in the mantle move two plates apart. Process called sea floor spreading
- 12tectonic landscapes - Intrusive volcanic landoforms- This is when magma is forced into the rocks that make up the Earths crust, when it could and become solid while still underground
- Weathering and erosion causes these landforms to be exposed.
examples;
1) Batholiths
2) Laccolith
3) Dykes
4) Sills - 13formation of Batholiths1) They are formed deep below the surface when large masses of magma cool and solidify.
2) As the magma cools slowly, large crystals are formed in the rock (granite)
3) Usually dome shaped and can be several hundreds of kilometres in diameter
example: the Isle if Arran in Scotland - 14formation of Lacolith- Smaller injections of magma for a lens shape that is intruded between layers of rock
- This then forces the overlying strata to reach upwards forming a dome
- This feature may be exposed by later weathering and erosion to form a small range of hills
exampls: Eildon Hills on the Scottish Borders. - 15formation of dykes- Vertical intrusions with horizontal cooling cracks.
- They cut accross the bedding planes of the rocks into which they have been intruded.
-Often occur in groups = dyke swarms
example; Scottish islands (mull) - 16formation of sills- Horizontal intrusions with vertical cooling cracks
- Both commonly made up of dolerite (igneous rock)
example: Great Whin Sill - 17tectonic landscapes extrusive volcanic landoforms (minor)- Features formed due to lava escaping onto the ears surface
- The magma here cools much quicker because it comes in contact with air/sea
- As a result igneous rocks tend to be finer grains with smaller crystals e.g Basalt
examples;
1) Geyers
2) Hot springs
3) Boiling mud pools
4) Fumaroles - 18formations of geysers- Occur when water, heated by volcanic activity, explodes onto the surface.
example: Old Faithful, Yellowstone National Park, USA. - 19formatin of hot springs- Area of super heated water at the surface
example:
Rio Hondo, Argentina - 20formation of boiling mud pools- Of surface deposits mixes with heated volcanic water
example:
Iceland - 21formation of fumaroles- It is an opening in a planets crust
- It emits steam and gases such as CO2,SO2,HCL
- The steam is created when superheated water turns to steam as its pressure drops when it emerges from the ground.
- Usually on active volcanoes - 22major forms of extrusive volcanoes list the 6 types of volcanoes1) Fissure
2) Shield
3) Composite
4) Acid/Dome
5) Caldera
6) Ash and acid cinder - 23characteristics of Fissure volcanoesFeatures:
- Occur when an elongated crack in the crust allows lave spill out over a large area
- Typically found around spreading ridges where tensions pulls the plates apart
- Forms lava plateaux which a re flat areas of land created by lava flow
Lava type
- Basaltic
Location
- Rifts/ early constructive margins
Nature of eruption
- Gentle
- Lava flows for long distances and when solidifies surface remains mostly flat
Eg
Antrim lava plateau in Northern Ireland - 24characteristics of Shield volcanoesFeatures:
- Gently sloping sides
- Broad, shallow volcanic cones
- Formed from free flowing lava
- Cover large areas as the runny lava can flow for long distance
- Most have huge craters at their summits
Lava type:
Basaltic
Location:
- Hot spots
- Constructive plate margin
Nature of eruption:
- Not explsive = safe ish
- Gentle, predictable eruptions, low in gas and silica
- Lava flows out of central vent
Eg
- Mauna Loa, largest single mountain in the word, rising over 30,000 feet - 25characteristics of Composite volcanoesFeatures;
- Most common type found on land
- Steep sided conies formed from alternating layers of has and lava
Lava type:
- Andesitic
Location:
- Destructive margins
Nature of eruption:
- Explosive and unpredictable
- Often vent becomes blocked by highly viscous lava and pressure builds up
- Pyroclastic material, ash clouds, volcanic bombs are emitted
- Many little craters on its slope
Eg
- Mt Fuji - 26characteristics of Acid/domeFeatures:
- Very jagged steep sides, this is because the lava is extra viscous so runs slowly and solidifies close to the crater
Lava type:
- Rhyolitic
Location:
- Continental crust
Nature of eruption:
- Very explosive and unpredictable
-Pyroclastic flow and ash couds
Eg:
- Puy de Dome (France) - 27characteristics of CalderaFeatures:
- When the build up of gases becomes extreme and a huge explosion removes the summit of the cone. Surrounding land then collapses into the old magma chamber and leaves enormous carter surrounded by a higher caldera rim
- Caldera may be filled with water to create a lake
Lava type:
- Andesitic/rhyolitic
Location:
- Destructive margins
Nature of eruption
- Very explosive, unpredictable
- Very viscous lava with lots of trapped gas
- Lots of ash
Eg
- Yellowstone - 28characteristic of ash and cinder cone volcanoes -Features:
- Cinder cones are simple volcano which have bowl shaped crater at the summit and steep sides
- Smaller than composite volcanoes
- Formed from ash, cinders and volcanic bombs ejected from the crater
Lava type:
- Basaltic
Location:
- Destructive plate boundaries (west coast of n.America)
- Constructive margins (Iceland)
Nature of eruption :
- During the eruption bliss (cinders) of lava are blown into the air and break into small fragments that fall around the opening of the volcano
- The pile forms an oval shaped small volcano
Eg
- Paricutin (Mexico) - 29characteristics of Basaltic lava1) Low viscosity, hot (1200 c) , runny
2) Lower silica content
3) Takes longer time to cool and solidify so flows longer distances
4) Produces extensive bu gently sloping landforms: lava plateaus (shield volcano)
5) Eruptions are frequent but more gentle
6) Lava and steam are ejected
Location:
- Constructive margins, e.g fissures along Mid-Atlantic Ridge (Heimaey) - 30Features of Basaltic lava/ basic lava- Lava solidifies into smooth folded sheets of rock = pahoehoe
- Pillow lavas
- forms when basaltic lava is extruded under water/ice
- as the lava is extruded the water quickly chills the outer layer
- molten lava beneath the chilled surface eventually breaks through the skin and the process is repeated resulting in a pile of lava pillows - 31characteristics of Andesitic lava1) Viscous, less hot (800c), flows slowly and shorter distances
2) Higher silica content
3) Cools and solidifies quickly
4) Produces steep-sided more localised features ( composite volcanoes)
5) Less frequent eruptions but violent as build up of gases
6) Ash, rocks, gases, steam, lava ejected
Location:
- Destructive margins, where oceanic crust is destroyed e.g. Mt St Helens - 32characteristics of Rhyolitic lava1) Highly viscous lava that can just barely flow
2) less hot
3) Very explosive due to trapped gas bubbles
4) Produces Volcanic domes that eventually is destroyed in a massive explosion as the viscous lava tries to escape - 33hot spots- places where there is volcanic activity occurs, but not close to a plate boundary
- typically away from boundaries
- it is caused by concentration od radioactive elements in the mantle - 34landforms created due to hot spots- active volcano
- atoll
- guyots - 35explain how hot spots cause volcanoes1) caused by a concentration fo radioactive elements in the mantle, the radioactive decay generates very hot temperatures
2) the hot spots heat the lower mantle and create localised thermal currents where hot plumes of magma rise vertically ( thermal plume)
3) These burn through the lithosphere to create volcanic activity on the surface or in the centre of a plate
4) Above a hot spot basaltic shield volcanoes are formed on the crust, they eventually form an island
5) however as the plates move away, they lose their source of magma and are no longer active. They may be eroded by waves ad form flat-topped sea mounts/guyots below sea level
6) A new volcano begins to form, forming a chain
- if lava breaks through to the surface active volcanoes occur above the hot spot - 36what is a Guyots- They are flat topped sea mounts that have sank into deeper colder water where carbonate material no longer accumulates
- 37what is an atoll- A seamount is any submarine mountain of a volcanic or tectonic origin.
- 38what are the primary effects of a volcanic eruption 51) Lava flows – although lava is the greatest perceived threat it rarely moves fast enough to kill people before they are evacuated. However, lava flows that cannot be diverted can cause damage.
2) Pyroclastic flow – Gas builds up under crater when explodes the gas causes the lava to shatter creating particles. As it explodes and breaks this causes the cloud to move down at high speed (700 km/h0 This fast moving cloud of material is known as a Nuee Ardente and can flatten or bury buildings in its path.
3) Poisonous gases – CO2 and CO can spill down a volcano unseen collecting in hollows in valleys causing asphyxiation.
4) Tephra - solid material of varying grain size
5) Death - 39what are the secondary effects of a volcanic eruption1) Shortage of food and clean water due to crops failing and contamination of water systems
2) People are left homeless
3) Infrastructure damaged
4) lahars - volcanic mud flows
5) volcanic landslides
6) Climate change - ash in atmosphere can decrease global temperature
7) Planes can't fly
8) Respiratory problems - 40Why live near volcanoes?1) Buildings materials
- Many igneous rocls make excellent building materials
2) Hydroelectricity
- Rivers flowing on volcanoes can be used to generate this
3) Geothermal energy
4) Metals and precious stones are common in volcanic soil
5) Fertile soil
- This is from the ash
5) Tourism
- Brings money to the local community
- However this may not be a choice, fertile soil = can grow crops = money, but for some the disadvantages outweigh the advantages - 41Why live near volcanoes? Precious minerals- Tin , silver, copper and diamond in magma
- Most of the metallic minerals mined around the world ( copper, gold, silver, lead) are found in rocks below extinct volcanoes
- It is ideal for large commercial mining or small scale local activities - 42Why live near volcanoes? Geothermal energy- Heat energy from the earth
- Completely renewable = reliable
- Heat from underground is used to drive turbines and produces electricity/ heated water used for households
- E.g Iceland and NZ - 43Why live near volcanoes? Fertile soil- Volcanic rocks and ash are rich in minerals that have formed in magma
- Over thousands of years, rocks get weathered and release minerals which get absorbed by the soil - 44Why live near volcanoes? Tourism- Creates jobs in shops, restaurants, hotel and tourist centers
- 45Why live near volcanoes? Volcanic sulphur- Important raw material in many manufacturing processes including pharmaceuticals
- E,.g Chile - 46prediction of earthqaues1) Monitoring ground swelling using sensors, Mt Etna
2) Monitoring temperature close to the volcano (groud water)
3) Measuring the amount of gas produced (in water)
4) Changes in Ph - 47Mitigation of volcanoes - planning undertaken to prepare for hazard events1) Coordinating evacuation policy
2) Setting up exclusion zones
3) Radio announcement
4) Information given t locals
5) Storing food/ resources
6) Planning evacuation centres - 48Prevention of volcanoes1) Building lava channels to divert lava away from homes - Mt Etna
2) Building a lava barrier to prevent lava from flowing too far
3) Pouring cold water breaks up lava and slows it down
4) Can explode the lava ro break them up - 49Adaptation of volcanoes - changes in society makes living near these areas easier1) Building houses with reinforced concrete walls - Mt Etna
2) Waring systems - Iceland
3)Educating people so they understand the risks
4) Hazard insurance
5) Availability of gas masks
6) Text message systems - 50measurement of volcanic explosivityVEI ( Volcanic Explosivity Index)
- A relative measure of the explosiveness of volcanic eruptions
- Volume of product, eruption cloud height and qualitative observations ( "gentle" "mega-colossal") are used to determine explosivity value
- Scale is open ended, but largest volcano recorded in history was magnitude of 8
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- A-Level Geography (plate tectonics yr13) Karteikarten am plate tectonics , erstellt von Hina Nagano am 22/11/2016.
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- Hina Nagano
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