Please enable JavaScript.

Coggle requires JavaScript to display documents.

Tectonics - 3.1.1-5 - Coggle Diagram

- - - - Benioff zone The area where friction is created between colliding tectonic plates, resulting in intermediate and deep earthquakes.
    - - Subduction zones are locations on Earth where the oceanic material of one tectonic plate dives below the material (oceanic or continental) of another tectonic plate into the mantle.
  - - - size - energy released & VEI - volcanic explosive index
      - Moment magnitude scale
    - - return interval - linked to magnitude
      - Low mag - high frequency
      - High mag - less frequent
      - Due to the time for pressure to build
    - - spatial scale
      - high rising ash cam block sunlight
    - - Probability of an event occurring over time and space
      - volcano predictability - seismic waves are unpredictable - once an earthquake occurs the vulnerable population have very little time to evacuate or prepare for impact
    - - length of time the hazard occurs
      - e.g. earthquakes can last 2 min to 8 min depending on the magnitude of the earthquake
    - - time difference between hazard and reaching the vulnerable population
      - Tends to do the greatest amount of damage to people
    - - Destructive plate boundaries have the worst profile as the extremities of rapid speed of onset & the largeness of the magnitude
      - Destructive, conservative and volcanos have similar probability, but volcanoes are very widespread in terms of areal extent and distance effected, while destructive and conservative are more limited.
      - Earthquakes have more extreme levels, while volcanos are generally levelled out, with extremes at hazards, but they are very predictable and rare.
  - - - Destruction of vegetation
      - Changes to drainage patterns by lahars and landslides
      - Reshaping of the landscape by eruption, lahars and landlsides
      - Increased precipitation due to released water vapour
      - Reduction of temperature through ash clouds reducing incoming solar energy
    - - 4.7 million people were affected between 1900 and 2016
      - 15,00 were injured between 1900 and 2016
      - Over 91,00 people were killed by asphyxiation, thermal injuries and trauma from major eruptions between 1900-2016, 80% of deaths were from the 10 deadliest eruptions
    - - Environmental
        
        Emissions of greenhouse gases can add to global warming
        
        Emission of sulphur dioxie increases the risk of acid rain
      - Demographic & social
        
        Poor health from stress-elated ilness or spread of disease
        
        lack of food due to crop damage and lack of clean water
        
        Average of over 15,00 left homeless or displaced every year by volcanic eruptions
      - Economic
        
        Loss or damage to businesses
        
        Cost of clean-up operations, repairs and rebuilding, estimated at US$65 million per year
        
        Financial loss from loss of primary activities such as agriculture and forestry
        
        Economic loss from 1900 to 2016 estimated at US$3.5 billion
        
        Loss of income from the destruction of farmland or business. Financial loss from loss of associated unemployment
    - - Primary
        
        Direct consequence of a volcanic hazrad from the volcano
        
        Primary impacts are immediate and direct
      - Secondary
        
        Indirect consequence - illness and disease due to something volcanic hazards have caused to happen
      - Volcanic hazards can affect a location short term or long term
        
        Depending on the location and its country's economic wealth
        
        LIC
        
        Haiti earthquake
        
        L.I.C's that depend on primary economy and subsistence economy, farming/fishing/quarrying, are impacted very negatively. Governments cannot handle the social panic and control the scale in which a tectonic event has affected. Poorer countries cannot afford or don't have the extra expense to rebuild, reconstruct and help the population in panic. Therefore, the social and demographic aspect post-event, are much more severe, leading to higher death toll from secondary hazards like disease and homelessness. The issue is, L.I.C's have previous long term issues that are higher priority. A poorer country has to contribute it's money into aiding the maximum number of people, this may a cholera outbreak for example.
        
        HIC
        
        Mount Etna volcano
        
        Volcanic hazards vary in the scale of impact due to the wealth of the country the event occurs in.
        
        Average cause of death
        
        Pyroclastic flows - 27 % Primary hazard
        
        Lahars - 17% - Secondary hazard
        
        Famine and disease - 30% - Secondary hazard
        
        Debris avalanche landslide - 4% - secondary hazard
        
        Tsunamis - 17% - Secondary hazard
  - - - Lava erupts through linear volcano vents. Not explosive. Several M's wide / usually appear as just a crack in the surface. Can create lava fields, ussually found in rift valleys
        
        e.g. Ethiopia Rift Valleys
        
        e.g. Iceland vents
        
        e.g. Hawaii
    - - Low angle profile. Width 20x the height. Most likely form lava flows with high viscosity and low velocity. Basalt composite. Long term eruption / varying formations . Low amount of silicon - so low viscosity. Can ravel long distacnes
        
        e.g. Hawaii
        
        e.g. Iceland
    - - Consist of a cinder - scoria, basalt magma with low density. Lava fountains are driven by bubbles ( gaseous espansion)
        
        e.g. Hawaii - Mauna Kea
        
        e.g. Mexico - Pariwtin
    - - Cone volcanoes, general composite of basalt and silicon, can produce pyroclastic flows and lava flows. Active for long terms, erupt periodically
        
        e.g. Mount Rainer & Mount St Helens Washington
  - - - Rhyolite - high silicon dioxide content creates a light coloured rock
      - Infrequent
      - exolves slowly due to the high viscosity of the lava
      - Silica rich so high viscosity. Thick - partially melted - acidic
      - plates converge, oceanic crust subducts, melts in Benioff zone
      - e.g. Volcan del Fuego Guatemala 2018
      - Convergent/Destructive/Subduction zone
    - - Basalt rock type
      - Frequent
      - exolves fast due to high temperatures. H2O bubbles due to melting ice. Gas release fractures lava creating ash
      - Iron rich - low viscosity - runny
      - Lack of pressure due to plates moving apart
      - Iceland second phase - Eyjafjallajokull April 2010
      - Divergent/constructive
      - Ice is melted by lava - gaseous explosion
    - - Divergent/constructive plate boundary
      - Very frequent
      - Gas - exolves fast due to high temperatures
      - Iron rich low viscosity - runny - liquidated
      - Lack of pressure due to plates moving apart
      - e.g. Iceland - First phase of Eyjafjallajokull march 2010
      - Basalt rock type
  - - - The geological setting of Iceland is highly irregular. It's located on the mid-Atlantic ridge across two major plate boundaries - North American and Eurasian plates - which is diverging an opening of 2cm per year. IN addition, a mantle plume or hotspot is beneath Iceland in which hot magma rises and fault lines release the hot magma into the lithosphere, which results in the progression of volcanic activity in the crust.
      - Iceland is 65 degrees N, has a cool maritime climate with fairly high precipitation. 10% of the Island is covered by glaciers. 50% of the volcanos in Iceland occur near these glaciers at high altitudes where ice covers the land. The result of a volcanic eruption in these areas is the production of lahars and jokulhlaups.
      - 76% of all magma is erupted basalt, 16% of magma is intermediate composition, 5% is silica, 80% of all eruptions are explosive, basaltic explosive activity is due to magma - water interactions
      - E.g. Fagradalfjall - 2021 eruption - deposited lava flows - basalt magma - effusive volcano
      - E.g. Holuhraun - 2014/15 eruption - deposited lava flows - composed of basalt lava - effusive
      - E.g. Eyjafjallajokull - 2010 significant eruption - deposited tephra/lava - intermediate composit of magma - explosive volcano
    - - Located in the Caribbean sea, Montserrat Island is apart of the Leeward Islands (collective of islands - territory's of several country's). The Montserrat volcano is situated in the Soufriere Hills, on an Island stretching 16km in length and 11km wide with 40km of coastline.
      - The Montserrat volcano last erupted in 2012, with significant impacts
        
        Most significatn eruption wsa in 1997, killing 19 people. Effecting the economy - tourism.
        
        The explosive eruption in July 2003 created pyroclastic flows, volcanic dome.
        
        Soufriere Hills volcano/Montserrat had been passive/inactive for centuries, until 1995 before it became active for 2 decades.
      - Montserrat is a self-govening British overseas territory
        
        Building a new port and main town after being rendered partly uninhabitable by the previous volcanic erputions.
      - Montserrat is situated along the east side of the Caribbean plate where it meets the North American plate boundary and following this the South American plate boundary
  - - - Happen more frequently with smaller magnitudes
      - 90% of Iceland is made up of basalt geology from volcanic activity
      - gases escape easily due to the low pressure composition of the magma
      - Lava flows 1100 degrees Celsius
      - Thin and runny - faster speed of onset
      - Depending on the gradient of the slope, lava flows of thin viscosity can cause a lot of damage
      - Effusive eruption of iron rich magma
    - - Traps gases e.g. CO2 O2 H2 CH4
      - Trapped gases exolved in the magma until the pressure exceeds its strength and the gas molecules explode
      - Explosive eruptions - thick and sticky composition of silicon rich minerals
      - Thick viscosity magma is thicker and flows slower, it also cools down slower, therefore managing it during an eruption if possible is very important.
      - E.g. Montserrat 1995
      - E.g. Pinatubo 1991
      - They happen infrequently with higher magnitudes
      - Can result in pyroclastic flows which are extemely dangerous
      - Silicon rich rock - Rhyolite rock - found at subduction zone in plate boundaries
  - - - Tephra lava - basalt and andesite
      - N.American Plate - Eurasian Plate - The volcano lies on a constructive plate boundary/margin between these plates. The two plates are moving apart due to ridge push along the Mid-Atlantic Ridge. As the plates separate further apart, the magma chmaber beneth filled with
      - Explosive volcano - Primary and secondary volcanic hazards
        
        Eyajafjallajokull volcano exerted lava, composed ofc
        
        Primary - Ash clouds - cancelled over 5000 flights, blocked airspace access over western europe
        
        Secondary - the glacial covered volcano produced secondary hazard lahars, luckily all nearby human settlements were evacuated - 500 to 1000 people - therefore no one was injured or died
        
        lava flows partially melted areas of the glaciers causing avalanches and floods, flowing through the environment, collecting debris
        
        The vulnerable population was safely distanced out of the range of the volcano, leaving empty settlements behind.
        
        Volcanic ash and lava destroyed crop fields and endangered tourists and hikers, tourism rates dropped by 30% in the next 5 years, costing losses of £108 million per year
        
        Released approximately 150,000 tonnes of CO2 each day it was active - around 2 months
        
        Deterioration of water quality - fewer periods of rain
    - - Volcanic eruption in Washington State NW America
        
        , As first earthquakes occurred and then plums of steam and ash was emitted onto the white glacial summit of the mountain. In early May a huge bulge grew up on the northern side of the volcano. In the beginning of May this bulge was growing by 1.5 m a day. Due to such clear indications, by the end of April a 30 km exclusion zone was put around the mountain to keep sightseers away. Eventually at 8.32am on 18 May the volcano exploded violently and a deadly cloud of hot ash, dust and rock was blasted out into the air destroying everything in its path. The shape of the mountain changed completely after the eruption.
      - 80,000 foot plume of ash covered around 100 miles of land and ocean surrounding Mount St Helens
      - $1.9 billion in economic loss - $695 million loss of timber - $92 million loss of agriculture
        
        Forests were obliterated - drainage basins were restructured by lava flows creating new channels in the land
        
        230 square miles of forest were destroyed in minutes
        
        900,000 tons of ash were cleaned up from areas around Washington
        
        57 people died
        
        Most significant eruption in the US
    - - Explosive volcano - Produced pyroclastic flows - arguably the most dangerous primary hazard
      - North American Plate - Caribbean Plate - Atlantic Plate
        
        Soufriere Hills is formed by a convergent plate boundary, where the Atlantic plate is subducting under the Caribbean plate
      - 7000 people were evacuated off the Island to avoid any injuries of death. Nearly 1/2 the Island was abandoned in 2012
        
        Most families fled to England/UK which owns this territory
      - 2/3's inhabitants fled urban areas - airports were closed after evacuations. And imports by plane were halted until the air was safe
      - Thick ash covered vegetation - branches broke and became debris
        
        60% of the Islands forest was obliterated
        
        Lack of photosynthesis with ash clouds blocking the sun meant it took a long time to regrow the forests
    - - Explosive volcano - bursts of gas-charged magma, ash-clouds, lahars and pyroclastic flows caused the most severe damage
        
        Filled in valleys with magma deposition, burning all forest and created a hot blanket in the sky
      - Eurasian plate - Philippine plate
        
        It is a subduction-related volcano, formed by the Eurasian Plate sliding under the Philippine Mobile Belt along the Manila Trench to the west. Molten material related to the complex tectonics associated with the subducting slab, rises through the lithosphere and generates the volcanism typical of subduction.
      - impacts
        
        75,000 people were evacuated from the volcanos range - 30km radius away from the volcano
        
        1.2 million homes destroyed from volacnic hazards
        
        Cultural issue - forced Aeta indigenous people to relocated, similar to the Kapampangan people
        
        Damage to crops and vegetation
        
        Destroyed £3 billion of property and infrastructure in 1991
        
        Spent £9 billion restructuring and rebuilding what was damaged/destroyed in the next 10 years
        
        Cooled the earths atmosphere by 0.5 Degrees Celsius for 2 years - sunlight was absorbed by dark ash clouds which hung over the Asian continent - moved by jet streams
      - Nearly 20 million tons of sulfur dioxide were injected into the stratosphere in Pinatubo's 1991 eruptions, and dispersal of this gas cloud around the world caused global temperatures to drop temporarily (1991 through 1993) by about 1°F (0.5°C). The eruptions have dramatically changed the face of central Luzon, home to about 3 million people. About 20,000 indigenous Aeta highlanders, who had lived on the slopes of the volcano, were completely displaced, and most still wait in resettlement camps for the day when they can return home. About 200,000 people who evacuated from the lowlands surrounding Pinatubo before and during the eruptions have returned home but face continuing threats from lahars that have already buried numerous towns and villages. Rice paddies and sugar-cane fields that have not been buried by lahars have recovered; those buried by lahars will be out of use for years to come.
- - - - The Crust
        
        Top of the Lithosphere/thin layer
        
        Continental and oceanic crust
        
        Composed of Basalt and granite rock
        
        8km-65km
      - Mantle
        
        2900km thick / 84% of the Earths volume
        
        Composed of silicon rock, with O2 & Iron
        
        1000-3700 degrees
        
        Brittle, elastic, ductile textures
      - Outer Core
        
        4500-5000 degrees, less pressurised
        
        liquid metal - viscous
        
        Iron & Nickel composition
        
        2200km thick
      - Inner Core
        
        Building pressure and heat, primal heat, compressed
        
        Solid metal sphere comprised of Iron and Nickel
        
        5000-6000 degrees
      - Asthenosphere
        
        The asthenosphere is the denser, weaker layer beneath the lithospheric mantle. It lies between about 100 km and 410km beneath Earth's surface. The temperature and pressure of the asthenosphere are so high that rocks soften and partly melt, becoming semi-molten.
      - Lithosphere
        
        The lithosphere is the rocky outer part of Earth. It is made up of the brittle crust and the top part of the upper mantle. The lithosphere is the coolest and most rigid part of Earth.
      - characteristics
        
        Composition
        
        Physical behaviour
        
        Thickness
  - - - NH - natural hazard
      - VP - vulnerable population
      - NE - Natural event
    - - Atmospheric - Weather
        
        Cyclone/Typhoon/Hurricane
        
        Floods - rainfall
        
        Drought
        
        Monsoon
      - Geomorphic
        
        Sinkhole
        
        Landslides/Avalanche
      - Tectonic
        
        Earthquakes
        
        Tsunami
        
        Volcanos
        
        Caused by DEEP EARTH processes
      - Space
        
        Meteor strike
        
        Solar flare
  - - - Slab pull occurs where older, denser tectonic plates sink into the mantle at subduction zones. As these older sections of plates sink, newer and less dense sections of plate are pulled along behind. Sinking in one place leads to plates moving apart in other places.
    - - As plates separate, new, hotter sediment is extruded into the gap between plates. The elevated temperatures lower the density of the recently deposited sediment, it floats/pushed upwards into the mantle, forming ridges.
      - Heat rises through the mesosphere through the asthenosphere creating a hotspot plume. This melts the mantle, making it ductile and more liquid. Reaches the crust and spread outwards (expansion)
      - Intrusion of magma to an oceanic ridge. Rises through partially melted, then it travels upwards and get cooler.
    - - The release of pressure on the rock in the gap between the plates causes it to partially melt, increase in volume and extrude through.
      - The extruded rock cools down forming a ridge at the plate boundary, e.g. Mid Atlantic Ridge. Occasionally, the ridge breaks the surface of the ocean and creates a volacno.
      - The convection current pushes the N.A plate & Eurasian plate apart i na process called ridge push.
      - The cool rock is compressed by the weight of the water above it, New ocean floor is formed.
      - A plume of hot rock rises through the asthenosphere creating a convection current.
      - The process continues so that the newest ocean floor is closest to the reidge and the oldest if the furthest away.
  - - - N. American Plate
      - Pacific plate
      - Eurasian plate
      - S. American Plate
      - African Plate
      - Nazca Plate
      - Caribbean Plate
      - Indian Plate
      - Australian Plate
      - Philippine Plate
      - Arabian Plate
      - Scotia Plate
    - - Mariana Trench
      - Mid Atlantic ridge
  - - - As the oceanic crust subducts it also starts to melt due to friction in a location called the Benioff Zone. This melting produces granite or andesitic magma which is quite viscous.
      - Subduction zones typically occur a long distance away from divergent margins. This means the plate and associated convection current have started to cool
      - As the oceanic lithosphere descends the increase in pressure which puts both plates under stress and strain. (stress is the force exerted on the plates, strain is the distance the plates move because of this force). The stress can cause the continental crust to fold under too.
      - When the stress caused by the subduction is too great. The contact gives way and the continental crust snaps back into position or the oceanic crust thrusts into the mantle. This releases energy in the form of seismic waves which radiate out from the point the rock gave way (focus). The energy travels through crust and the ground at the surface shakes - often a major earthquake is triggered such as on the 24th December 2004 at 9.3 on the magnitude scale, in the Indian ocean causing a tsunami.
    - - the convergence of the two pates pushes up the crust and has caused the formation of the Tibetan Plateau and surrounding fold mountains (Himalayas)
      - Shallow focus earthquakes are common along tis type of boundary such as the 2005 Kashmir earthquake which was recorded at 7.6 om the moment magnitude scale.
      - At collision zones two or more plates are moving towards each other. The Indo-Autralian Plate is currently moving towards the Eurasian Plate at a rate of 5.8cm/year
      - Long term change of continental push
    - - Rift Valleys
        
        Where continental plates diverge, mountain ridges are formed at the plate margins as hot magma forces the crust to buldge.
        
        As plates move apart the brittle crust fragments forming parallel faults
        
        Areas of crust slowly subside between the faults to form a rift valley between rift mountains
        
        The East African Rift Valley, 3000km long, as a result of the African Plate spreading/splitting into two and moving apart - 7cm/year
        
        Volcanic activity can occur along the plate margin, e.g. Mt Kilimanjaro in Tasmania, which lies on the eastern edge of the East African Rift Valley
    - - Both plates in a locked position under stress, as one moves faster. Eventually, the faster plate will strike and slip further forward, creating a quake on a shallow level in the crust.
      - Boundary of two continental plates moving in the same direction at different speeds. Plate ridges/edges are rough not smooth, therefore, while the plates move they get stuck, and gradually creep forward while the stress and pressure builds. Until the plate strikes forward ( strike & slip movement) releasing an energy waves, causing and earthquake.
      - Energy is released in the form of seismic waves which radiate out from the focus. The ground shakes and the resultant earthquakes can be of very high magnitude.
      - E.G. Loma Prieta earthquake 1989 - 6.9 magnitude.
      - Stress becomes too great for the strength of the contact between the two plates and they jolt past each other. The plates slide past each other in either the same direction or the opposite directions at different speeds.
      - The San Andreas fault is the North American plate moving slower than the Pacific plate, but they're both moving northwards.
    - - Hotspots punch a hole through the (pacific - Hawaii) plate. Magma is hot, it melts through the lithosphere from the mantle asthenosphere. Considering the plates are always moving - very long term, - the hotspot plume is dragged with plate.
      - As the volcano moves away from the hotspot magma ceases to build up and the volcano becomes extinct.
      - Eventually the volcano is eroded/weathered into a sea mount
      - As Island chain occurs as a result of this movement.
    - - Natural hotspots, cracks in the lithosphere, from stress in the plate. Heat is allowed to rise up from the asthenosphere.
      - Geothermal activity int eh crust