tectonic hazards 1b

Composite / strato volcano

• Forming along convergent plate boundaries

• Tall, steep sided and cone shaped, reaching several thousand meters

• Built from alternating layers of lava and as

• Andesitic magma (viscous with high gas content)

Shield volcano

• Forming along divergent plate boundaries + hot spots

• Low, gently sloped domes with wide bases

• Built from lava, erupting from fissures and the crater

• Basaltic magma (runny with low gas content)

How are strato volcanoes formed?

1. Mantle is heated so it is less dense and will rise

2. Mantle drags plates towards each other by friction

3. Oceanic plate subducts under the continental plate

4. The oceanic plate melts because of friction causing heat and the hot mantle

5. Hot melted plate rises through the continental plate creating a magma chamber for the volcano to form on.

Ocean trenches form in gap between oceanic and continental plate, and so do deep strong earthquakes

Where are strato volcanoes regularly near?

Near oceans because of the oceanic plate

Constructive plate boundary

1. Uplifting mantle drags the two oceanic plates apart

2. Some of the hot mantle rises through fissures and the gap between the two plates

3. Volcano builds up over repeated eruptions releasing lava

Andesitic Lava (strato)

• Higher silica content

• More viscous (sticky and thick)

• Flows slower and less far

• Higher gas concentration

• More explosive and violent (volcanic bombs)

• Less frequent eruptions

Basaltic Lava (shield)

• Less silica content

• Less viscous (runny)

• Flows faster and further before cooling

• Lower gas concentration

• Less explosive and violent (lives rarely lost + crops often destroyed)

• More frequent (potentially continuous) eruptions

What are volcanic hotspots?

Where volcanoes form away from the plate boundaries

When a superheated plume of rock slowly rises through the mantle

After reaching the upper mantle, it melts the asthenosphere and base of the lithosphere

Magma rises through weaknesses in the crust, erupting along the Earth’s surface

Why are the youngest volcanoes above the hot spot?

The oldest is further away from the hotspot because the direction of plate movement is away from the hotspot.

Younger volcanoes at hotspots are…

Larger because newly constructed

Older volcanoes at hotspots are….

Smaller becoming sea mounts due to erosion.

Primary Hazard

Immediate damage

Emergency Response

Immediate response

Secondary Hazard

Knock - on effect

Long-term respone

Putting area back to normal and future preparation

Volcanologist

Someone who works with volcanoes who can monitor them and reduce risks

Tiltmeter / satellite

Ballooning and bulging in the ground, and increase in ground bulging means more likely to erupt

Seismograph / seismometer

Checks for seismic activity such as tremous, and increase in tremours means more likely to erupt

Gas Monitoring

Checking for degassing such as SO2 production, increase in amount of degassing means more likely to erupt

Thermal imaging

Ground temperatures near volcanoes, an increase in temperatures means more likely to erupt

Crust

• Thinnest layer + the only one we interact with

• Oceanic + Continental

Oceanic Crust

Thin (5km-8km), basaltic rock 3g/cm3, denser than continental crust

Continental Crust

Thick (30km-40km), varying to 70km in some mountain belts. Granitic rock so its lighter and less dense than the oceanic crust of 2.7g/cm3

Mantle

• Thickest layer (2900km)

• Temperature from (1000 to 3700 degrees), this heat helps drive convection currents

• Upper and lower mantle

Upper Mantle

• Solid but melting occurs at plate boundaries and hot spots so the mantle flows very slowly (plastic / ductile), semi-molten

Lower Mantle

• Solid because of the high pressure, hotter and denser with depth

Core

• Very hot

• Very dense

• Outer + inner core

• Helps create the magnetic field because of iron + nickel

Outer core

Liquid iron + nickel, 4500-5500 degrees

Inner core

6000 degrees (same as the sun surface temperature), dense + solid ball of iron + nickel, because of the high pressure raising the melting point so they don’t melt

Lithosphere

• Crust + top part of the upper mantle

• Made of peridotite (igneous) mostly solid

• 80km - 100km, thinner under oceans + in volcanically active continental areas

• Broken up into tectonic plates (lithospheric plates), which move or float on the asthenosphere

Asthenosphere

• Denser, mobile layer in the upper mantle

• 100km - 130km deep

• Flows

• Temperature less than 1300 degrees because the pressure is low enough for rocks to slowly flow.

How are convection currents formed?

1. Mantle is heated by the hot core making it less dense, rises towards the lithosphere

2. Mantle is pushed within the asthenosphere by more rising mantle under the lithosphere

3. Because it is away from the core. it cools and is denser helping it sink towards the core

4. Mantle is pushed along by more sinking mantle

When convection currents go away from each otherwhat happens?

Creates constructive (divergent) plate boundaries

When convection currents go towards each other what happens?

Creates destructive (convergent) plate boundaries

Why is the inner core so hot?

• Heat is generated in the form of radioactive decay and residual heat

• Radioactive decay occurs because of naturally occurring elements such as uranium releasing heat and rising to the crust

• Residual heat is left over form the formation of the Earth, 4.6 billion years ago

Convergent plate boundaries

• Denser oceanic plate subducts under the continental plate, moving towards each other

• Produces strato volcanoes, the strongest earthquakes and ocean trenches

• An example is the South American (continental) and Nazca (oceanic) creating the Andes in Chile and Peru

Collision plate boundaries

• Two continental plates move towards each other but do not subduct because they have equal densities

• Produces strong earthquakes and zero volcanoes because there is no magma rising. Occasionally makes fold mountains

• An example is the Eurasian and Indian which form the Himalayas

Conservative plate boundaries

• Two plates slide past each other, too and fro at different speeds

• Produces earthquakes but zero volcanoes because there is no magma rising

• An example is the North American and Pacific Plate causing the San Andreas Fault Line

Divergent plate boundaries

• Two oceanic plates moving away from each other

• Produces shield volcanoes, weak earthquakes and a slight ocean ridge because of the uplifting mantle

• An example is the North American and Eurasian plates forming the mid-atlantic ridge

What are Earthquakes?

The intense shaking of the ground caused by seismic waves in the crust

Where do most Earthquakes occur?

Over 90% of Earthquakes occur at convergent plate boundaries where stress is caused by an oceanic plate subducting under a continental plate

What is the focus of the Earthquake?

Point underground where an earthquake starts

What is the epicenter of the Earthquake?

Point on the Earth’s surface directly above the focus

How do Earthquakes form?

Earthquakes happen at tectonic faults when friction prevents plates from moving past each other, pressure builds up behind and a release in this pressure suddenly is a jolt, radiating shockwaves from the epicenter

What is a tectonic fault?

Boundary between two plates where earthquakes occur

How does the magnitude of an earthquake change the risk of an earthquake?

• At a higher magnitude there is more intense shaking

• Higher risk of death a damage

How does population density change the risk of an earthquake?

• The more dense the population, the more people are impacted.

• More high rise buildings therefore there would be more pancaking .

• Increases damage and death toll

How do preparation levels change the risk of an earthquake?

• With more preparation, of monitoring and evacuation, countries can issue evacuation orders.

• Educating through earthquake drills, aseismic building features.

• Decrease damage and death toll

How does the time of day affect risks of an earthquake?

• During night when most people are asleep, they may miss evacuation orders.

• As more people will be in apartment complexes, pancaking will be more likely thus increasing the death toll.

• During day, people are at school or work in office blocks therefore they may have a higher chance of increasing pancaking increasing the death toll.

How do development levels affect risks of an earthquake

• Countries with lower GDPs have poorer building quality and are unable to afford aseismic features so there will be more destruction and death from pancaking.

• Preparation is also less robust, so countries are unable to afford good monitoring and warning systems.

• They are unable to afford preparation drills increasing death toll with an inability to evacuate.

How does the depth of focus affect risk of an earthquake?

• A shallower focus will be more destructive because the energy hasn’t dissipated.

• Increasing damage and death toll.

How does the duration affect the risks of an earthquake?

• The longer the earthquake lasts, the more destructive it will be because more energy can be released and aseismic features may not hold / last the whole earthquake

• Increasing damage and death toll

What is the richter scale?

• It is a scale measuring the pure power of an earthquake in magnitude, represented by the amplitude of the largest wave.

• A seismometer measures the earthquake and shows this on a seismogram

• IT has no upper limit but it’s logarithmic

Why is the richter scale not good for some?

• Not every are has a seismometer, measuring one area could have different data from a seismometer further away or closer than another seismometer.

What is the moment magnitude scale?

In addition to measuring magnitude, this scale also measures

• area of the fault slipped

• distance of fault moved

• rigidity of solid rock (more rigid, more power)

How do Tsunamis form?

A sudden tectonic upthrust (earthquake) vertically displaces water above. Energy causes waves to progressively move over the ocean in ever widening circles that reach 500mph. The wavelengths continue to large, with frequency varying from 5 minutes to an hour. As the waves approach the coastline, they slow down due to friction with the seabed. The speed decreases but the wavelength shortens and height rises. Waves crash on the shore increasing the height above 5m

How can we manage the risks of a tsunami?

• Evacuating to higher ground with clearly planned routes and emergency shelters

• Monitoring the earthquake and sending out warnings, texts and sirens

• Having mangroves in order to absorb wave energy (roots reduce speed and extent of tsunami

• Flood defences eg. sea walls / dams

• Public education to teach civilians what to do and how to evacuate

Haiti Earthquake background information

• One of the poorest countries

• Transform pb

• 12th January 2010

• 7 magnitude

• Afterschocks 5.5 - 6 mw for days

• Port-au-price was densely populated (2.4mn)

Haiti Earthquake primary impacts

• 250,000 injured

• 316,000 died

• 1.5 million people were displaced

Haiti Earthquake secondary impacts

• 23,500 landslides were triggered

• Docks in port-au-prince experienced liquefaction and the port sank into the ground (limited aid coming in)

• 3m high Tsunami along the bay and 3 died

• Port-au-prince UN peacekeepers caused a cholera outbreak in an evacuation camp and 10,000 people died

Haiti Earthquake short-term response

• Very poor

• Destruction of many hospitals so less patients coould be cured

• Survivors moved to camps with little food, water and sanitation

• Corruption in the government so aid wasn’t spread out equally

Haiti Earthquake long-term response

• 200,000 paid to clear rubble

• ¾ damaged buildings were inspected and repaired but using vulnerable items

• Money abroad was pledged (300 million euros from the EU)

• 235,000 moved from Port-au-prince top local undamaged cities

Haiti Earthquake preparation

• Lower technology Earthquake proof buildings due to lack of development

• GDP/capita of 1172 dollars, very poor

• Only 2 fire stations and had no army at the time

• There hadn’t been an earthquake in 100 years so nobody knew what to do, people ran into homes as thats what they did for hurricanes but it increased the death toll.

Haiti Earthquake prediction

• Unable to predict Earthquakes

Japan Earthquake background information

• 11th March 2011

• Magnitude of 9

• Strongest ever Earthquake in Japans history with aftershocks of 6-7

Japan Earthquake primary impacts

• 130,000 displaced

• 667 - 1479 deaths from Earthquake

• 5000 injured or reported missing

• 2000 roads, 56 bridges and 26 railway lines were damaged / destroyed

• Around 300 billion dollars worth of damage

• Fukushima dam burst , contaminating soil and water.

• Power to fukushima power plant cut so nuclear meltdown as the cooling system failed, releasing much radiation

Japan Earthquake secondary impacts

• Tsunami caused with speeds of 800km/h, waves of 10m and flooded 10km inland. 17,000 deaths with half over 65

• Electricity, water and sewage systems and lines were damaged

Japan Earthquake short term response

• Advanced warnings issued to evacuate tsunami (pacific tsunami warning centre)

• Requested aid from china, india and the USA

• Sent search and rescue teams

• Tens of thousands temporary homes set up in Sendai

• 140,000 evacuated from a 20m radius around fukushima power plant

Japan Earthquake long term response

• Honshu transport and communications partially restored weeks after the tsunami

• 10 year restoration program announced in 2012 but most completed in 2015

• New sea wall built near coastline

Japan Earthquake preparation

• Around 80% of japanese buildings have some sort of aseismic building features

• Emergency services trained to response to EQs

• Locals educated on how to evacuate and respond

• September 1st (National Disaster Prevention Day)

Japan Earthquake prediction

• Earthquakes cannot be predicted