Plate Tectonics and Associated hazards

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Plate Movement

Francis Bacon noted the fit of the earth (jigsaw like) in the early 17th century but no one believed the theory as it was believed that continents could not move.

The Theory:

  • Alfred Wegener developed the theory of continental drift, explaining how the world originally was one piece - Pangea 'super continent' but has split to form the individual continents due to continental drift

Evidence:

Geological:

  • fit of South America & Africa
  • deposits from glaciation period found in S America, Antartica & India, formation cannot be explained by present position, must have formed together then moved
  • rock sequences in N.Scotland closely agree with those found in E. Canada- indicates they were laid down in same location.

Biological

  • fossils found in Indian Limestones are similar to fossils in Australia
  • fossil remains of the reptile 'Mesosaurus' found in both S. America & S. Africa- cant have migrated over the sea/unlikely to develop in 2 areas.
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Development of Theory

Wegener's theories didnt explain how continental movement worked, 1940's onwards, evidence accumulated:

  • Discovery of Mid-Atlantic Ridge: ocean crust examined either side suggested sea-floor spreading was occuring
    • alternating polarity of the rocks that form the ocean crust, creates series of magnetic 'stripes' - suggest crust is slowly spreading away from this boundary
    • as we no the world isnt getting bigger, realised plates must be being destroyed somewhere else.
    • Evidence of this was found with the discovery of Oceanic Trenches, where large areas of ocean floor where being pulled downwards.
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Earth's Layers

Originally, before development of Plate Tectonic Theory, earth scientists divided the earth into 3 layers:

  • Crust - lightest layer, (silicon, oxygen, aluminium, potassium & sodium) varies in thickness - beneath ocean only 6-10km/below continents 30-40km (under highest mountains can be up to 70km)
  • Mantle - molten & semi-molten rocks containing lighter elements  (silicon/oxygen)
  • Core - dense rocks containing iron & nickel alloys, divided into a solid inner core & molten outer one, temp of over 5,000 c

Development in research has led to the crust and upper mantle being divided into the Lithosphere and the Asthenosphere.

  • Lithosphere - consists of the crust & the rigid upper section of the mantle (aprox 80-90km thick) Divided up into 7 large plates and a few small ones, plates either continental or oceanic depending on type of material they are made of
  • Asthenosphere - semi-molten layer, on which plates float/move
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How the Plates Move

HOT SPOTS around the core of the Earth generate thermal convection currents within the Asthenosphere

  • causes magma to rise towards crust and then spread before cooling and sinking
  • this circulation of magma alows the plates to move above- 'floating' on denser asthenosphere
  • this is continuos process - new crust being formed along the line of constructive boundaries between plates and older crust being destroyed at destructive boundaries
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Plate Margins: Constructive

CONSTRUCTIVE (Divergent) margins:

  • where two plates move apart
  • in oceanic areas create Mid-Oceanic Ridges
  • in continental areas create Rift Valleys

The space between the diverging plates is filled with basaltic lava upwelling from below 

- constructive margins are therefore some of the youngest parts of Earth's Surface, where new crust is continously created

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Features of Constructive Margins: Oceanic Ridges

Oceanic Ridges are longest continuous uplifted features on the earth's surface, have total length of 60,000km/ some rise 3,000m above ocean floor

Dynamics of each oceanic ridge is influenced by the rate at which the plates seperate:

  • slow divergence rate (10-15mm per yr) produces wide ridge axis and a deep central rift valley with inward facing fault scarps                                E.g. parts of Mid-Atlantic Ridge  
  • intermediate rate (50-90mm per yr)  produces a less well-marked rift with a smoother outline                                                                          E.g. Galapagos Ridge
  • rapid rate (90+ mm per yr) produces a smooth crest and no rift              E.g. East Pacific Rise

Volcanic activity also occurs along ridge:                                             Submarine Volcanoes - sometimes rise above sea level E.g. Surtsey, South of Iceland. These have fairly gentle sides due to low viscosity in basaltic lava, eruptions are frequent but reletively gentle Seismic Activity at ridge:                                                                       Transoform Faults -  occur at right angles to plate boundary                  spreading plates on either side of ridge may spread at different rates, leading to friction which causes faults to form and causes earthquakes  (tend to be shallow focus eqs, originating near the surface)

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Features of Constructive Margins: Rift Valleys

In continental areas, Constructive Margins can cause Rift Valleys:

  • as the plates move apart, the brittle crust fractures due to individual sections moving at different rates
  • fractured areas of the crust drop between parallel faults to form rift valleys

largest of these is the African Rift Valley, extends 4,000km from Mozambique to the Red Sea, from here it extends north into Jordan, with total distance of 5,500km

In some areas, the inward-facing scarps are 600m above the valley floor and are often marked by a series of parrallel step faults.

Volcanic activity also occurs at Rift Valleys: as the two crusts pull apart, the crust thins ADD                                                                                                                         E.g. highest Mt in Africa, Mt Kilimanjaro 

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Plate Margins: Destructive

DESTRUCTIVE (convergent margins): where two plates move together

This can be either:

  • oceanic plate towards oceanic plate
  • continental plate towards continental plate
  • oceanic plate towards continental plate

1) Oceanic/oceanic convergence 

  • When oceanic plates meet, one is forced under the other by the process of subduction
  • Ocean trenches/Island Arcs formed

Example: Pacific plate is being subducted under the Philippine plate. The ocean floor has been pulled down to form the very deep Marianas trench. A line of Volcanic Islands have been formed by upwelling magma from the Benioff Zone

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Plate Margins: Destructive (continued)

2) Continental/Continental Convergence

  • plates forming continental crust have much lower density than underlying layers, so there is little subduction when they meet
  • instead, as plates move together their edges are forced up into fold mountains
  • due to little subduction, there is no volcanic activity
  • due to movement of the plates, shallow-focus earthquakes can be triggered
  • material is also forced downwards to form deep mountain roots

Example: Indo-Australian Plate

  • Indo-Australian plate is being forced northwards into Eurasian plate causing sediment to be forced upwards, forming the Himalayas, uplift is continuing today
  • Himalayan mountain range is 350km wide/ extends for 3,000km & contains higest mountain on earth, Mt Everest  
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Plate Margins: Destructive (continued)

3) Oceanic/Continental Convergence

  • when oceanic & continental plates meet, the denser Oceanic plate is subducted under the less dense Continental plate
  • the downwarping of the oceanic plate forms a very deep trench

Example: of western coast of South America, where the Nazca plate is subducting under the South American plate, forming the Peru-Chile Trench

  • Sediment that has accumulated on the continental shelf on the margin of the continental mass is deformed by folding/faulting
  • This sediment along with the edge of the the continental plate is uplifted to form Fold Mountains,

Example: the formation of the Andes along the Pacific side of S. America

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Plate Margins: Destructive (continued)

Seismicity at an Oceanic/Continental Convergence:

  • As oceanic plate decends, the increase in pressure can trigger major earthquakes, these may be shallow, intermediate or deep focus eqs.

 Volcanicity at an Oceanic/Continental Convergence:

  • the further the rock decends, the hotter the surroundings become
  •  this together with heat produced by increased pressure/friction, begins to melt the oceanic plate into magma in the Benioff Zone
  • as it is less dense than the surrounding asthenosphere, this motlen material begins to rise as plutons of magma, reaching the surface & forming volcano's
  • The andesitic lava (viscous nature, flows easily) creates complex, composite, explosive volcanoes - (contrasts with basaltic gentle eruptions on continental/continental convergence margins)
  • If eruption takes place offshore, a line of volcanic islands 'Island Arcs' can appear

Example: West Indies

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Plate Margins: Conservative

CONSERVATIVE margins:

where two plates slide past eachother, moving in a parallel motion to the plate margin

  • here there is no creation or destruction of crust
  • there is also no subduction and therefore no volcanicity
  • movement of plates alongside eachother creates stresses between the plate edges and causes pressure to builds up
  • in order to realease this pressure and friction, the plates jerk forward
  • this triggers shallow-focus earthquakes

Example: San Fransisco Eq. 1906 & Los Angeles Eq. 1994                              - Occured at the best example of a Conservative margin, the San Andreas fault in California, where the Pacific and North American Plates move parrallel to each other                                                                   - Both plates are moving in same direction, but at different speeds, (Pacific Plate 5-9cm per y) (N. American Plate 2-3cm per y) causing stresses & transform faults occur and consequently earthquakes.

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Hot Spots

HOT SPOTS - provide evidence that Plate Movement does occur

Example: in the case of the Volcanic Hawaiian Islands                                                                                                                       - Hawaiian islands have no connection to any plate boundary and yet are volcanic                                                                                                                                                            - believed this volcanic area is caused by a localised hot spot within the Pacific Plate                                     - a concentration of radioactive elements inside the mantle may cause a hot spot to develop                          - from this, a plume of magma rises into the plate above                                                                                    - where the lava breaks through the surface, active volcano's occur above the hot spot

Evidence for Plate Movement:                                                                                                              - the Hot spot is stationary, and so as the Pacific plate moves over it, a line of volcano's is created                - the volcano directly above the hotspot is active and the rest form a chain of islands of extinct volcanoes                                                                                                                                                             - the oldest volcano's are now reduced to seamounts below the sea level due to marine erosion & subsidence of the crust due to pressure

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Hotspot Summary

Hawaii therefore shows us that                                                                                  - "not all volcanic activity is associated with Plate Margins"

The Hawaii chain of islands is also clear evidence that the Pacific Plate is moving North-West and so acts as further proof that the Earth's crust is moving, as originally suggested by Alfred Wegener.

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Volcanicity: Distribution

Most volcanic acticity is associated with plate tectonic processes and is mainly located along margins. Activity is therefore found at the following:

  • Oceanic Ridges - where plates are moving apart e.g. Mid-Atlantic Ridge - Iceland represents a large area formed by volcanic activity
  • Rift Valleys - e.g. The African Rift Valley has a number of volcanoes along it, inclunding Mt Kenya & Mt Kilimanjaro
  • on or near Subduction Zones - The line of volcanoes, or 'ring of fire' that surrounds the Pacific Ocean is associated with plate subduction, this tends to be the most violent of all activity
  • over Hotspots - (only one not associated with plate margins) e.g. the one in the middle of the Pacific Ocean which has created the Hawaiian Islands
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Volcanic Eruptions

There are variations in form, frequency and type of volcanic eruption related to the different kinds of plate margin, emissions & lava

Constructive Plate Margins: 

  • Basaltic magma, Basalt 
  • Low Viscosity, Low Silica content, runny lava  
  • Little Violence, gases escape easily 
  • Mainly lava erupted  
  • Frequent, sometimes continous  
  • Type: Lava Plateau Shield Volcano                                                                              

Destructive Plate Margins: 

  • Acidic Magma, Rhyolite  
  • Very Viscous, High Silica content, slow flowing lava  
  • Potentially explosive, pressure builds up as gasses cant escape  
  • Lava bombs, ash & dust erupted  
  • Infrequent, long dormant periods Type: Acid lava dome Composite Cone
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Intrusive Volcanic Landforms

When Magma is forced to the surface, only a small amount actually reaches the surface, most of the magma is intruded into the crust where it solidifies into a range of features. these are often exposed to the surface by later erosion

1) Batholiths -

  • formed deep below the surface where large masses of magma cool and solidify.
  • As the magma cools slowly, large crystals are formed in the rock e.g. granite.
  • Batholiths are often dome-shaped and exposed by later erosion.
  • Example: Dartmoor & the Isle of Arran (scotland).
  • Batholiths can be several hundred km in diameter.
  • The area surround the Baltholith is altered by the heat/pressure of the intruding magma, forming a Metamorphic Aureole (e.g. limestone can be transformed into marble)
  • Sometimes smaller injections of magma form a lens shape that is intruded between layers of rock, this forces the overlying strata to arch upwards creating a dome - known as a Laccolith, may be exposed by later erosion to form a small range of hills E.g. the Eildon Hills on the Scottish Borders
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Extrusive Volcanic Landforms

2) Dykes -

vertical intrusions with horizontal cooling cracks

cut across the bedding planes of the rocks into which they have been intruded

often occur in groups, known as 'dyke swarms'

E.g. Scottish islands such as Mull & Skye have dyke swarms

3) Sills - horizontal intrusions along the lines of bedding planes

have vertical cooling cracks

E.g. Great Win Sill on the Isle of Arran

Both SILLS and DYKES are commonly made up of Dolerite

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Extrusive volcanic Landforms

Extrusive vulcanic activity involves two forms of lava:

  • Basaltic - formed from magma that is low in silica, more fluid magma, allows gas bubbles to escape preventing sudden explosive activity
  • Andesitic/Rhyolitic - silica-rich magma, very viscous. often solidifies before reaching surface, leads to build up of pressure/gas which causes violent explosion
  • 
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Extrusive volcanic landforms

  • Lava Plateaux - formed from fissure eruptions, free flowing lava, basaltic, flow great distances. Generally flat & featureless E.g. Antrim Lava Plateau in N.Ireland
  • 
  • Basic/Shield Volcanoes - also formed from free flowing lava, gentle sides, cover large area E.g. Mauna Loa, Hawaii
  • Acid/Dome Volcanoes - steep-sided convex cones, consisting of viscous lava (prob rhyolite) E.g. in the Puy region of central France
  • Ash & Cinder Cones - formed from ash, cinders and volcanic bombs ejected from crater, sides are steep & symmetrical E.g. Paricutin, Mexico
  • Composite Cones - classic pyramid shaped volcano, consists of layers of ash & lava (usually andesitic) E.g. Mt Etna, Sicily & Mt Fuji, Japan
  • Caldera's - occur when build up of gases becomes extreme, huge explosion removes top of cone, leaving large hole several km in diameter. may become flooded by the sea - lake may form within. E.g. Krakatoa, Indonesia
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Minor Volcanic Forms

Solfatara - small volcanic areas without cones, produced by gases escaping to surface E.g around the Bay of Naples, Italy

Geysers - occur when water gets heated by magma, explodes onto surface E.g. Old Faithful, Yellowstone National Park, USA

Hot Springs/Boiling Mud - sometimes the water heated by magma does not escape to surface, this water mixes with surface deposits & boiling mud is formed E.g. very common in Iceland

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Intrusive and extrsive volcanic activity in the UK

Apart from Hot Springs, UK has no current volcanic activity

However, much geological evidence of volcanic activity has been found which occured during the mountain-building periods in history:

  • Granites - other example of intruded rocks found where the top of an exposed batholith is seen. Found in Dartmoor & Bodmin Moor. Weathering/erosion have given distinctive landscape of upland plateaux topped by rock outcrops, known as 'Tors'
  • Dykes & Sills - dyke swarms across the Isle of Arran, Scotland. generally occur as small ridges in the landscape as they are more resistant that surrounding rock. often rivers flow over these, creating high waterfalls E.g. High Force & Cauldron Snout, Pennines
  • Basaltic Flows - can be seen where the Antrim lava Plateau formed in N.Ireland. when lava cooled, vertical cracks in the flow resulted in hexagonal columns. these are exposed to the coast - known as the 'Giants Causeway'
  • Volcanic Plug - from a long extinct volcano forms the site of Edinburgh Castle. Stirling Caste is also built on a Volcanic Plug
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The Impact of Volcanic Activity: Primary

Primary effects:

  • Tephra - solid material of varying size (from volcanic bombs to ash particles) ejected into the atmosphere
  • Pyroclastic Flows - very hot (800c), gas-charged, high velocity flows made up of a mixture of gases & tephra (cloud like)
  • Lava flows
  • Volcanic Gases - Carbon dioxide, carbon Monoxide, hygrogen sulphide, sulphur dioxide and chlorine. E.g. Emissions from Lake Nyos, Cameroon 1986 suffocated 1700 people
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The Impact of Volcanic Activity: Secondary

Secondary Effects:

  • Lahars - volcanic mud flows E.g. those that destroyed the Columbian town of Armero after the eruption of Nevado del Ruiz, 1985
  • 
  • Flooding - melting of glaciers/ice caps due to hot magma can cause severe flooding E.g. the Grimsvotn Glacial burst on Iceland, 1996
  • Tsunamis - giant sea waves generated after violent eruptions E.g. in Krakotoa, 1883, tsunami said to have drowned 36,000 people
  • Volcanic Landslides
  • Climate Change - ejection of vast amounts of volcanic debris into the atmoshphere can reduce global temps - is believed to be a cause of past climate change

Volcanic effects are not hazardous on their own, only become hazardous when they impact upon human & built environments

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Volcanic Case Study: LEDC Mt Nyiragongo, Congo 200

Background:

  • Main crater 250m deep, 2km wide, often contains lava lake
  • 
  • volcano has erupted more than 30 times since records began
  • together with Mt Nyamuragira, its responsible for 40% of Africa's Volcanic eruptions
  • lava is very fluid, known to flow downhill at over 90km per hr.

2002 Eruption:

  • although there had been seismic activity in area, the 2002 eruption was unexpected.
  • 
  • However, warnings of lava flows allowed most people to flee from the effects
  • Large eruption, opening fissure of 13km long on southern flank, lava flowed towards Goma & Lake Kivu
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EFFECTS:

  • lava flows destroyed at least 1/3 of Goma - a town with over 200,000 people
  • commercial centre of the town was destroyed, along with water supplies & many of the medical facilities - including 3 health centres & 1 hospital
  • lava covered the northern third of the runway at Goma airport
  • death toll reached 147
  • estimated that 350,000 fled the area - many over the border to Rwanda, caused problem in providing food/shelter in this small country
  • sulpurous lava entered Lake Kivu, polluting lake - major source of drinking water
  • fear that the increase in temp. of Lake Kivi (from lava) could allow toxic gases to be released from the lake bed
  • several eq's accompanied the eruption - one measuring over 5 on Richter scale. Tremors caused structural damage to buildings
  • thousands required medical attention - first from the effects from smoke/fumes from lava, causing eye irritation & respiratory problems and secondly from diseases from drinking contaminated water
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RESPONSE

Authorities initial response was to issue a 'Red Alert' for Goma & surrounding area - enabled full evacuation to take place (this prompt response was one factor keeping the death rate low)

2 days after eruption, the UN began bringing in humanitarian aid:

  • emergency rations were initially of high-energy foods - biscuits
  • followed by more substantial food aid - maize, beans, cooking oil
  • also set up camps to house displaced people

UN estimated the cost of providing food, blankets, househole utensils, temporary shelter, clean water, sanitation & healthcare to the refugee's at $15 mill

HOWEVER - higher cost will be spent rebuilding Goma's infrastructure, homes & livelihoods

Lava flows destroyed many buisnesses, resulting in a massive increase in unemployment

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Seismicity

As the earths crust is mobile, pressure tends to build up within the rock. When this pressure is suddenly released, earthquakes occur.

  • The point at which the pressure is released within the crust is known as the Focus
  • 
  • The point immediately above this is on the Earth's surface is known as the Epicentre

The depth of the focus influences the characteristic of the earthquake:

Earthquakes are most destructive when they occur near the surface

  • Shallow-focus (0-70km deep) - tend to cause the greatest damage as the pressure released has less distance before it impacts upon the earths surface, therefore the force is stronger when it reaches.
  • Intermediate-focus (70-300km deep)
  • Deep-focus (300-700km deep)
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Seismic Waves

Seismic waves radiate from the focus like ripples in water. There are 3 main types of seismic wave, each travelling at different speeds:

  • Primary (P) waves: travel fastest and are compressional, vibrating parrallel to the direction they are travelling in. Can travel through both solid and liquid
  • 
  • Secondary (S) waves: travel at half the speed of (P) waves and vibrate sideways at right angles to the direction they are travelling in. Cannot travel through liquids
  • Surface (L) waves: travel slowest and near to the ground surface. Some vibrate the ground at right angles to the direction they are travelling in (like S waves) and others have a rolling motion that produces vertical ground movement (often cause of falling buildings)

P & S waves travel through the interior of the Earth and can be recorded on a seismograph - these can be studied - has made it possible to build up a picture of the Earth's interior and to predict future seismic activity

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Earthquake Measurement

1) Richter Scale

  • logarithmic scale that ranks earthquake magnitude from 1-7
  • an event at 7 on the richter scale has an amplitude of seismic waves 10x more than one measured at 6 on the scale
  • the energy released is proportional to the magnitude, so for each unit of increase on the scale, the energy released increases by approx 30 times
  • largest ever recorded was 8.9, recent major e.q Haiti 2010 measured 7 on the scale

2) Mercalli Scale

  • measures the intensity & impact of the event
  • 12-point scale that runs from Level 1 (detected by seismometers but hardly felt - approx 2 on Richter scale) to Level 12 (total destruction with the ground seen to shake - appro 8.5 on Richter Scale)

Seismic records enable earth frequency to be observed and for patterns to be found, which enables future predictions to be madehowever only date back to 1848 when the instrument to record seismic waves was developed

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Distribution of Earthquakes

Vast majority of Eq's. occur along plate boundaries, the most powerful being associated with destructive plate boundaries.

At conservative margins - the boundary is marked by a fault and it is movement along this that produces earthquakes here - most famous is the San Andreas fault in California which represents the boundary between the North American plate and the Pacific plate.

HOWEVER - Some earthquakes occur away from plate boundaries and are associated with the reactivation of old fault lines

Example: 2002 in the UK midlands, eq. measured 4.8 on the Richter Scale . Epicentre located in Dudley, west of Birmingham - believed that the cause was movement along an old fault line known as the Malvern Lineament

It has been suggested that human activity could be the cause of some minor eq's.                                              - An example of this is the building of huge reservoirs where the water puts pressure on the surface rocks, or subsidence of deep mine workings

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Effects/Impacts of Earthquakes

The initial effect of an EQ. is ground shaking.

- The severity of this will depend upon  1) magnitude of the earthquake 2) distance from the epicentre 3) local geological conditions

Secondary effects:

  • soil liquefaction - when violently shaken, soils with high water content lose there mechanical strenth and start to behave like liquid
  • Landslides/avalanches - slope failure as a result of ground shaking
  • Effects on people & the built environment - collapsing buildings, destruction of road systems & other forms of communication, destruction of service provision such as gas, water & electricity, fires resulting from ruptured gas pipes & collapsed electricity cables, flooding, disease, food shortages, destruption to local economy. (Some of the effects on humam environment are short term, others are long term and will depend to a large extent on the ability of the area to recover)
  • Tsunamis - giant sea waves generated by displacement of the sea: by shallow-focus underwater earthquakes (most commonly), eq's can also cause them by creating underwater debris slides & large landslides into the sea
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Effects/Impacts of Earthquakes (cont)

The risk to people and the environment is determind by a combination of factors. It is summarised by:

R = M x P/V       

  • R = Risk  
  • M = Size/Scale of earthquake (Magnitude)
  • P = number of people living in affected area (Population)
  • V = Vunerability (i.e. preparedness - building regulations, disaster planning, education, level of development)

Therefore the level of effects felt in each event is different, due to varying influential factors.

These factors can be categorised into Temporal and Spatial factors.

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Predict, Prevent & Protect

PREDICTION

- It is more difficult to predict earthquakes than other natural hazards and due to this they are particularly hazardous.

 However, there are some forms of prediction that can be done:

  • monitoring active earthquake zones, E.g. California & Tokyo Bay, the longer the interval without an earthquake, the higher the probability of one occuring & the greater its magnitude is likely to be
  • monitor release of radon gas
  • monitoring groundwater levels
  • monitoring fault lines
  • magnetic fields
  • animal behaviour

MEDC's tend to spent alot of time/money on prediction which allows authorities time to warrant an evacuation procedure & issue warnings. Due to LEDC's not having sufficient money/equipment, they are often left less prepared and feel the effects more than MEDC's.

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Prevent

PREVENT:

As in the case of most hazards, there is little that can be done to prevent earthquakes from occuring

However: there have been attempts to lubricate the fault line with water and oil, in hope that the plates will slide past eachother rather than julting.

This attempt has been tryed on the San Andreas Fault but made little difference.

It could be said that this may infact increase the possibility of an earthquake, as it is known that injecting high-pressure water into rocks will encourage seismic activity as pressure is hightened (why there is debate about whether geothermal power should be produced near fault lines)

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Protect

The main response to earthquakes is too protect, and this is done by Preparedness.

1) Hazard Resistant Structures

Contrast: 1989 California eq. 7.1 Richter scale, only 63 deaths vs. 2001 Gujarat eq. 7.9, over 20,000 deaths (main contributer to high death toll was insufficient building structures)

 2) Fire Prevention - ‘smart metres’ developed, cuts of electricity/gas in event of earthquake

 3) Land Use Planning -  people/buildings allowed in certain areas and not others, areas at risk of floods after eq. Etc. may be denied planning permission. California, ban on any new big buildings within 40m of fault, schools/hospitals built in low risk areas, should be sufficient open space as safe area away from fires/buildings, services buildings should not be too close to avoid total wipe out of all services -

4) Insurance/Aid - Gujarat; over 1mill recieved some form of aid

5) Education - FEMA objectives: to promote understanding of earthquakes and their effects, to work better to identify risks, to improve earthquake resistant design and construction techniques, to ecourage the use of earthquake safe policies and planning policies. American Red Cross issued list of supplies to Americans should have in case of earthquake (water, canned/high energy foods, clothing/bedding, first aid kit, tools/supplies e.g. torch, radio, can opener, fire extinguisher etc.)

6) Emergency Services - Gujarat; hospitals destroyed, emergency services brought in from other parts of India & overseas

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TSUNAMIS overview

TSUNAMIS: huge waves caused by sea displacement, usually earthquakes

- in the open ocean tsunamis have very long wavelength & low wave height, may go unnotices (can be less than 1m in height)

- as approaches shallow water, wave increases dramatically in height (8-15m)

- Tsunamis travel at speeds up too 800km per hr (some tsunami's take less than a day to travel across pacific)

First warning is often is wave trough in front of tsunami                                     - causes reduction in sea level, known as 'draw down'

Tsunami follows (can be 25m+) usually consists of a number of waves, largest not always first

Around 90% of Tsunamis generated in Pacific Basin, & associated with tectonic activity at surrounding boundaries: most generated at destructive plate bounadries as one subducts under the other, particularly off the Japan-Taiwan island arc which generates (25% of all Tsunami's)                     - Since devastating tsunami of December 2004, area has has 2 more major Tsunami's

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TSUNAMIS

Effects of most tsunami's felt 500-600m inland

When a tsunami reaches land, its effects depend on:

  • height of waves & distance travelled
  • length of the event that caused the tsunami
  • extent to which warnings can be given
  • coastal physical geog. - both ofshore & onshore
  • coastal land use & pop. density

If Tsunami forms thousands of km away, authorities can give early warnings & evacuate area -  Around the Pacific basin, a tsunami warning system is operating        

  - however, such systems did not exist in Indian Ocean when the 2004 Tsunami hit

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Tsunami Case Study: LEDC Indian Ocean Tsunami 2004

Background:

  • pressure building up for some time when Indo-Australian plate subducts beneath Eurasian plate
  • Boxing day December 2004 was slippage along plate 25km beneath Indian Ocean
  • section of sea on Eurasian side rose several metres, generating powerful 9.0 eq. - one of biggest ever

TSUNAMI

  • eq. triggered tsunami that raced across the Indian Ocean devastating islands (Maldives, Andaman & Nicobar Islands) and the coastlines of the countries bordering the ocean - Indonesia, Malaysia, Thailand, Myanmar, India & Sri Lanka
  • some places the wall of water that came ashore was more than 25m high
  • Tsunami warning systems are in place in Pacific basin - no such system had been set up in the Indian Ocean - unexpected
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Effects:

  • 300,000 killed by the waves, tens of thousands injured by force of the waves & debris 
  • many area's affected were tourist destinantions - many deaths were from Europe
  • villages & towns swept away - particulalry Sumatra, nearest land to epicentre
  • destruction of property resulted in millions being made homeless
  • massive damage to tourist infastructure - hotels, restaurants, bars
  • widespread damage to coastal economies - particularly agriculture & fishing - left hundreds of thousands unable to feed themselves. Damage was so severe in areas that coastal economies will be affected for many years
  • many hospitals & clinics washed away/damaged - great deal of medical aid brought in
  • despite huge human cost, estimated that the disaster cost was less than $5bill (contrast with MEDC Northridge - only 57 deaths but cost over $30 bill)

On western side of Indian Ocean, countries did recieve warning - E.g. Kenya reacted quickly, moving thousands of tourists of the beaches to safety

One positive result of the Tsunami is that a warning system is now in place for the countries bordering the Indian Ocean - however; little use to Sumatra as it was so close to epicentre

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Earthquake Case Study: LEDC Gujarat, India 2001

One of most powerful eq's to strike the Indian subcontinent in the last 100yrs

  • centred near small town of Bhuj in Gujarat
  • focus 17km below earth's surface
  • 7.9 on Richter scale
  • shock waves felt from over the border in Pakistan - as a result several were killed
  • also felt on the other side of the subcontinent in Bangladesh & Nepal
  • death toll high - buildings not able to withstand tremors

Effects:

  • death toll just under 20,000 - although experts estimated atleast 30,000
  • over 160,000 were seriously injured
  • over 1mill made homeless
  • approx 345,500 homes were destroyed - from blocks of flats to mud houses
  • over 800,000 buildings suffered some form of damage
  • in Bhuj all 4 hospitals destroyed - made it difficult to deal with the injured. Emergency services had to be brought in from overseas
  • communications severely disrupted & powerlines brought down
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AFTERMATH

One of most disturbing aspects- widespread looting of damaged property authorities struggled to control

In days following - series of aftershocks; most small but all above 5 on the Richter scale - caused considerable amount of damage to already weakened buildings

Rescue teams sent from many parts of the world to save people trapped under buildings

  • Britain sent a team of 69 sponsored by the Department of International Development
  • Indian gov. sent 5,000 troops, 40 military aircraft & 3 naval vessels (floating hospitals)
  • Military people transported medical aid, food, tents & communication equip. by air to worst affected

Authorities feared widespread epidemic of Typhoid & Cholera - however due to prompt action (e.g. spraying disinfectant on collapsed buildings to prevent diseases from rotting bodies) this was avoided - however evidence of widespread diarrhoea evident

Still heavily dependent on agriculture - loss of 20,000 cattle had huge impact

Overall cost of eq estimated at $4-5 bill - suggested that 1 mill+ people recieved some form of aid

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Earthquake Case Study: MEDC Northridge, LA, USA 19

Sine 1933, there have been 5 eq's in Los Angeles area that measured atleast 5.8 on the Richter scale

  • Northridge eq of 1994 occured at 4.30am - early morning occurance one of factors keeping death toll low - people in homes rather than in large office buildings/on roads 
  • result of movement along a previously unknown thrust fault
  • focus at depth of 18.4km
  • ground acceleration (ground shaking) was highest recorded in N. America

Effects:

  • 57 killed, over 1,500 seriously injured
  • 12,500 buildings suffered moderate-serious damage
  • 11 major roads damaged - closed for rebuilding
  • over 11,000 landslides triggered - damaging homes, blocking roads, damaging water lines
  • over 20,000 immediately made homeless
  • 11 hospitals suffered structural damage - unable to serve local area
  • 600 aftershocks - resulted in damage to already weakened buildings
  • days after - 9000 premises had no electricity, 20,000 no gas, 48,500 little or no water
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Earthquake Case Study: MEDC Northridge, LA, USA 19

Damage caused by eq. demonstrated that some types of building structure did not work wellmultistorey wood-frame buildings & those with weak first floors (e.g. parking areas on ground floor)

As California is an area of known seismic acitivity - area building specifications were in place to ensure that new buildings could withstand eq's:

  • School buildings/hospitals, which were required to be reinforced, survived fairly well
  • 
  • The Olive View hospital in Sylmar was destroyed in the1971 San Fernando eq but yet withstood the Northridge event - had been rebuilt to a better standard

As a result of the Northridge eq, the state legislature ordered that all hospitals in California should, by 2005, have eq. proof acute care units & emergency rooms

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Earthquake Case Study: MEDC Market Rasen, Lincolns

Stongest eq. to hit Britain in 25 years

  • occured at 12.56 am
  • 
  • as with all recorded British eq's, no buildings collapsed & no deaths
  • measured 5.2 on Richter Scale
  • focus depth 18.6km
  • epicentre 4km north of Market Rasen
  • tremors felt for hundreds of km
  • several small aftershocks - strongest only 2 on Richter scale

As the British Isle's are not on or near a plate boundary, major eq's are unknown

HOWEVER - tension built up within the plates can be relieved by ground movements at some distance from the boundaries, resulting in minor eq's

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EFFECTS

  • homes were shaken - causing panic & calls to emergency services
  • chimney stacks collapsed - falling onto streets below
  • falling chimney only caused serious injury when it fell on a sleeping man, breaking his pelvis
  • house roofs were damaged - tiles fell off
  • secondary damage to roads/pavements from falling tiles/bricks
  • total cost to insurance companies was estimated at £30 mill
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Case study: Japan Earthquake

Quake happened on a Frriday afternoon, at 5.46 pm, lasting for 6 minutes.

  • quake was centred 130 kilometres to the east of the capital, Sendai.
  • originally reported at a magnitude of 7.9, but later was upgraded to 8.9 and then to a 9.0.
  • fifth largest recorded worldwide since 1900, according to the U.S. Geological Service
  • had 10,000x more energy than the magnitude 6.3 eq in Christchurch, New Zealand
  • Japan is located near a destructive plate boundary, caused as Pacific plate subducts under Eurasian plate
  • due to relatively shallow focus of 20 miles below the Pacific Ocean, combined with a high magnitude, huge tsunami was caused from between 5-12m in height

Japan was very well prepared for the eq as they receive many earthquakes every year - HOWEVER even their level of preparadness could not cope with a tsunami of such scale - tsunami walls protecting coastline villages only 7 metres high, no where near big enough

  • within 10 mins of the eq, warnings of a tsunami were sent out using the Japan earthquake warning system - Text messages, alerts on TV, sirens & police alerted residents. However, people had became desensitised by false alarms - many did not evacuate - became 'complacent'
  • the tsunami warning extended to at least 50 nations and territories, as far as South America
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IMPACT

  • tsunami between 1 - 7.3 meters hit at various places along the coast - 10 meter tsunami seen at the port in Sendai, near the epicentre - tsunami walls not big enough
  • Serious of violent aftershocks continued - one hitting magnitude 7.1, according to the USGS
  • 2 nuclear plants on the Pacific coast in Fukushima were automatically shut down.
  • At Fukushima - tsunami disabled emergency generators required to cool the reactors
  • Over following 3 weeks there was evidence of a partial nuclear meltdown
  • Radiation releases caused large evacuations, concern over food and water supplies, and treatment of nuclear workers - fear of major release of radio active material with widespread health and environmental effects.
  • 2,000 people confirmed dead, 10,000 more people expected, predicted death toll was 18,000 but is probably much higher
  • 530,000 people displaced, staying in 2,500 evacuation centres
  • 24,000 people remained completely isolated/couldnt be reached for days following the event
  • 4,700 destroyed houses, 50,000 damaged houses
  • Economic cost  $235 Billion - exceedingly high (MEDC - lots of economic loss)
  • Japan’s main island moved 2.5 meters and the earth’s rotational speed increased, causing the day to become shorter by 1.8 microseconds

Shows that no matter how much we prepare, the force of nature will always be the influencing factor in determining the outcome

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RESPONSE

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Comments

GeographyBurn

Accidentally 4 starred whikst trying to press 5, amazing resource!

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