Tectonic hazards

Lava flows

• Primary hazards

• Viscosity is determined by the amount of silicon dioxide e.g. Rhytholitic lava is highest viscosity.

• Steep slopes 15m/sec

• Andesitic lava flows like plastic and moves very slowly

• Destroys agricultural land and infrastructure

• e.g. Kilauea volcano in Hawaii destroyed 180 houses been erupting since 1983,covering 78km²

Pyroclastic flows

• Primary hazards

• Mixture of hot rock fragments,lava particles and ash buoyed by hot gases

• Associated with subduction zones

• Move at high speeds

• Most dangerous are those directed laterally when the main crater is blocked by viscous lava and gas pressure builds up and releases through a weak area.-Mount Saint Helens USA in the 1980

• High speed and temperatures mean they destroy everything in their path

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Tephra

• Rock fragments ejected by volcanoes

• Fine ash is carried high in the atmosphere by prevailing winds which means it can cover large distances.

• Finer ashes cover larger distances affecting global weather patterns and are hazards to air crafts.

• Breathing difficulties

• Agricultural production can be reduced causing a loss in economic losses

• Mount St. Helens (1980, USA) — Ejected over 500 million tons of fine ash into the stratosphere affecting Washington and Idhao.

Volcanic gases

• Active volcanoes produce large amounts of water vapour,Carbon dioxide,hydrogen

• Primary hazard

• Rarely reaches lethal level

• Carbon dioxide causes most deaths-colourless,odourless and accumulates in hollows and depression due to density

Lahars

• Mudflows of volcanic material

• Second greatest threat after pyroclastic flows

• Huge amounts of ash and debris produced after eruption mix with water and move rapidly over long distances.

Jokulhlaups

• Glacial outbursts

• Landform modification through erosion and deposition

• Large in volume,including ice,water and debris

• Flooding is the result of glacial failure due to heat from the eruption or collapse of a moraine dam.

How is Basaltic lava formed?

• Melting of mantle minerals(e.g. olivine) from upper zone but sometimes core-mantle boundary.

How is Andestitic lava formed?

Subducted oceanic plate melts and mixes with seawater,lithospheric mantle and continental rocks.

How is Rhyothitic lava formed?

Melting of lithospheric mantle and slabs of previously subducted plates.

Flow characteristics of Basaltic lava?

Thin and runny(low viscosity,gases escape).

Flow characteristics of Andesitic lava

• Slow(intermediate viscosity traps gases).

Flow characteristics of Rhyolitic lava?

• Thick and stiff(high viscosity trap gases).

Eruption energy of Basaltic lava?

• Gentle,effusive

Eruption energy of Andesitic lava?

• Violent,moderately explosive

Eruption energy of Rhyolitic lava?

• Very violent,cataclysmic

Location of Basaltic lava?

• Ocean hot spots

• Mid ocean rigdes

• Shield Volcanoes(e.g. Mauna Loa).

Location of Andesitic lava?

• Composite volcanoes e.g. Chance Peak

• Subduction zones

Location of Rhyolitic lava

• Supervolcanoes(e.g. Taupo) or composite cone volcanoes e.g. Chance Park

Case study-Vatnajokull Glacier Island 1966 MINI CASE STUDY

• Was preceded by a large earthquake 29 September.

• Eruption melted over an overlying ice fissure 4.

• Subsidence cauldron had formed in the overlying ice which was between 400 and 600m thick.

• Steam column 9000 metres high had formed-Wednesday

• Eruptions beneath Icelandic glaciers produced Jokulhlaups.

• Jokulhaups lifted ice dam.

• Damages were US 15 million

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Volcanic case study-Mt Pelee Martinique 1902 MINI CASE STUDY

• Killed 29,025 people

• Lies on destructive margin-magma is highly viscous

• Pyroclastic flows

• Big port Saint-pierre town meant high population density

• No coordinated evacuation of vunerable areas-refugees were crammed into saint-pierre which was believed to be a safe haven.

Soufriere Hills,Montserrat 1997-Volcanic case study MINI CASE STUDY

• Lies on a destructive plate margin

• Highly acidic viscous magma at temperatures of 800+ celsius

• 19 people died-returned to the island prematurely

• Low death toll attributed to monitoring and massive evacuatio programme.

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Nevado del Ruiz,Colombia 1985-Volcanic erruptions MINI CASE STUDY

• Low VEI of 3

• 50m deep lahars-formed when 10% of snow and ice cover was melted by pyroclastic flows.

• 23,000 deaths

Mount St Helens USA 1980-Volcanic erruptions MINI CASE STUDY

• Unexepected lateral blast

• Remote location-limited fatality.

• 57 people killed

• Composite volcano

• Highly viscous lava-trapping gases

Mt Merrapi 2010-Volcanic eruption MINI CASE STUDY

• 473(500) people died

• Zones desiginated where no one lives permanetly

• 9 villages will no longer have new infrastructure-risk of destruction is great

Impacts of Mount Merapi Indonesia 2010

Economic impacts:

• Crop prices e.g. rice fields were damaged and the price increased due to crop damage-mostly affecting Cangkringan and Kemalang.

• Mineral mining increased-the volcano deposited millions of cubic meters of high-quality, easily accessible volcanic materials directly into the surrounding riverbeds and slopes

Social impacts:

• Sulphur dioxide caused irritation to human skin.

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What did Arthur Holmes discover in 1919?

• Mantle was semi-molten

• Meaning convection currents flow in the mantle

What is convection?

• Convection is a mode of heat exchange where hot material rises and cold material sinks.

Primary impacts of Nyriagongo eruption 2002

• The lava flows destroyed crops, and many livestock were killed.-c

• 80 per cent of the airstrips at Goma International Airport were covered in lava.-Goma heavily relies on NGOs.

• The majority of the 200 deaths were caused by carbon monoxide poisoning from the eruption (this continues to be a threat today).

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Secondary impacts of Nyriagongo eruption 2002

• Acid rain fell due to the reaction of volcanic gases in the atmosphere, damaging farmland as it makes the land acidic .Many people in the region are subsistence farmers.

• Social impacts:Overcrowding and poor hygiene conditions led to the spread of cholera in refugee camps.400,000 people displaced.

Factors affecting volcanic eruption Nyiragongo 2002

• Lies on a divergent/constructive plate

• Tectonic spreading of the Kivu rift causes the ground to fracture allowing lava to flow from ground fissures.

• Low amounts of silica making it a basaltic lava flow at speeds of 60km/h

Key facts about Eyjafallajokull 2010

• Iceland lies on the Mid-Atlantic Ridge.

• Constructive plate margin

• Two plates move apart due to ridge push along the Mid-Atlantic Ridge.

Impcts of Eyjafallajokull 2010

• Economic Impact: The airline industry alone lost £130 million a day due to airspace closure, totalling an estimated $1.7 billion.(Tephra)

• Farmers have laid off 5000 workers after flowers and vegetables were left rotting at airports-short shell life

Key facts about Pintubo 1991

• Destructive plate boundary where the Eurasian plate is moving towards the Philippine plate, this creates many subduction zones.

• The subduction of the Eurasian plate beneath the Philippines plate caused the earthquake.

• High population density of 240 people per km², with up to 2,000 people per km² in the megacity of Manila.

Impacts of Pintubo erruption 1991

• Social impact:847 people were killed with 300 by collapsing roofs (due to the number of people who still live below the poverty line). 100 people were killed by lahar mud flows.

Wilson cycle

Describes how continents split apart drift and eventually collide again.

1. Continents begin to pull apart along cracks in the rcust.(Rift causes a new gap called rift valley.)

2. Magma rises along cracks in the crust→forming oceanic crust

3. Widening crack becomes a full oceanic basin

4. As tectonic plates move,the oceanic plate sinks to the subduction zone.

5. This shrinks the basin

6. Volcanic activity,earthquakes and deeo ocean trenches appear.

7. Closing ocean brings contiental plates together.

Hypothesis testing using Paleomagnetism.

Magma extrudes from the mid-ocean ridge.Contains iron which aligns with the Earth’s magnetic pole and becomes stuck with that alignment when it cools.

How do we prove the Wilson cycle?

• Hypothesis testing using Paleomagnetism.

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  Magma extrudes from the mid-ocean ridge.Contains iron which aligns with the Earth’s magnetic pole and becomes stuck with that alignment when it cools.

Proof of continental drift

• Sea floor spreading

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• Fossils of tropical plants have been found in the Artic Ocean suggesting that they have may have had a warmer climate in the past.

• Geological ecidence for continetal drift-When using Wegner’s map on Pangea these moutains line up into one major range.

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• Glacial evidence-Form and land and move towards he ocean.About 300 million years ago Glaicers covered the Southern hemisphere.The pattern they made makes sense when looking at Wegner’s model.

Ridge Push

• Newly formed plates at the oceanic ridges are warm and so have a higher elevation at the oceanic ridge then the colder,more dense plate material further away;gravity causes the higher plate at the ridge to push away the the lithosphere that lies from the ridge.

What is slab pull?

Older,colder plates sink at subdction zones,because as they cool they become more dense then the underlying mantle due to gravity.Cooler sinking plate pulls the rest of the warmer plate along it.

Constructive(Divergent plates) features?

SEISMIC ACTIVITY:Shallow focus and a low magnitude.

VOLCANIC ACTIVITY:Frequent,gentle

Destructive(convergent:oceanic and oceanic)

• Heavier plate subducts leaving and ocean trench.Fold moutains will occur.

• Built up pressure causes underwater volcanoes burstingthrough oceanic plate.

• Lava vools and creats new land called island arcs.

Destructive(convergent:oceanic and continental)

• Denser oceanic plate is subdcted underneath the continentak.

• The subducted plate froms a deep ocean trench.

• The oceanic crust is melted as it subducts into the asthenosphere.

• Extra magma causes pressure to build up.

• Pressurised mahma forces through weak areas in the continental plate.

• Explosive high pressure volcanoes erupt through the continetal plate know as composite volcanoes.

• Fold moutains occur when sediment is pushed upwards during subduction.

Hot spot theory-1

1.Plume rises-very hot mantle mantle rises beneath the lithosphere.

Pressure falls-decompression melting produces magma beneath the plate.

3.Magma breaks through-magma passes through the crust and builds a volcano across the hot spot

4.The mantle keeps moving-a chain of volcanoes form because the plume stays broadly fixed while the plates move.

The youngest and most active lie directly over the plume.

Hot spot theory 2

1.Plate contains weaknesses-past collisions,rifting and subduction can leave faults and scars in the lithosphere.

2.Some plates are streched-pulling at plate edges can make parts of a plate thinner and vunerable.

3.Old material lies below-previously subducted material may melt more easily when pressure decreases.

4.Magma follows the weak zones-magma rises through the weaknesses and produces volcanoes within the plate.

Explain the causes of intra-plate tectonic hazards-6M

• Occur above a hot spot.

• Mantle plume of unusually hot,buoyant material may rise from near core-mantle boundary.

• Base of lithosphere-fall in pressure causes decompression melting.

• Basaltic magma rises through weakness and forms broad shield volcano

• Hawaiian island lie 3200 km from the nearest plate margin.

• Pacific plate moves north-west over a broadly stationary over hot spot.-kileau volcano remains active.

• Volcanoes became oldee towards the north-west as they move from magma source.

• BecomesCool and becomen denser.

• Stresses reactive ancient weaknesses within a plate.

• Forces generated at distant margins,continuing collision or slab pull-transmitted through rigid plate.

• Stress builds along old faults until friction is overcome.

• Sudden movements release stored strain energy as seismic waves.

• 2001 Gujarat earthquake north-west India.

• Hundred of km away from Indian-Eurasian plate boundary

186+145 =331

331/12 =27.583

= 27.6

5.0

Rejecteion of the null hypothesis as t value is more than critical value at all confidence levels and the acceptance of the alternative hypothesis there is a statistically significant difference in the mean focal depth of the earthquakes at the 99% confidence level.