Topic 1 - Tectonic processes and hazards

Define a hazard

An event that has the potential to be a threat to human life, property and the environment

What is the OFZ?

What is the CFZ?

- The Oceanic Fracture Zone is a belt of activity through the oceans & along mid-ocean ridges, through Africa

- The Continental Fracture Zone is a belt of activtiy along the mountain ranges from Spain through the Alps, to the Middle East and to the Himalayas

How do convection currents work?

1. Heat from the inner core convects through the mantle to the asthenosphere

2. Hot magma rises due to it becoming less dense with heat

3. Magma is then cooler at the top as it is further away from the core and then becomes more dense, sinking back to the bottom

4. Cooler magma is then reheated and begins to rise again creating a convection current

What are the 4 layers of Earth?

- Crust (Lithosphere) - Uppermost layer, thinnest, least dense & lightest (oceanic crust = 7km thick & continental crust = 70km thick)

- Mantle (Asthenosphere) - A semi-molten layer where convection currents can occur, largely made of silicate rocks & is rich in iron. (Depth of 700-2890km below the crust)

- Outer core - Dense, semi-molten rocks containing iron & nickel alloys (Depth of 2890-5150km below the crust)

- Inner core - Dense & solid due to the extreme pressures from the cores high temperature (Depth of 5150km+ below the crust)

Why is the core so hot?

- Residual heat from formation, kinetic energy from the collision was converted to heat

- Radioactive decay of uranium-238

What happens at a destructive plate boundary with a continental and oceanic plate?

- The denser oceanic plate subducts below the continental, leaving a deep ocean trench

- The oceanic crust is melted as it subducts into the asthenosphere, extra magma is then created causing pressure to build up

- This magma forces through weak areas in the continental plate where explosive & high pressure composite volcanos erupt

- Fold mountains occur when sediment is pushed up during subduction

What happens at a destructive plate boundary with 2 oceanic plates?

- The heavier, older plate subducts leaving an ocean trench and fold mountains

- This built up pressure from the subducting plate entering the asthenosphere and heating up into magma causes underwater volcanoes to burst through

- Lava cools & creates new land called island arcs

What happens at a destructive plate boundary with 2 continental plates?

- Both plates aren't as dense so lots of pressure builds instead when they collide

- This causes a pile up of continental crust on top of the lithosphere due to the pressure between the plates, forming fold mountains e.g the himalayas

What happens at a constructive plate boundary with 2 oceanic plates?

• Magma will rise between the gap left by the 2 plates sperating to form new land

• Underwater volcanoes form as the magma rises

• New land forms on the ocean floor by lava filling the gaps (sea floor spreading)

What is the evidence of seafloor spreading?

• Every time new rock forms, the magnetic grains in the rock switch their alingment with north & south

• There are therefore symmetrical bands of rock with alternating bands of magnetic polarity

What happens at a constructive plate boundary with 2 continental plates?

• Any land in hte middle is forced apart, leaving a rift valley

• Volcanoes form where magma rises

• Eventually the gap (rift valley) will fill with water & seperate from the other island

What is ridge push?

Gravity acting on the slope created when plates move apart, pushing the plaates further away & widening the gap

What is slab pull?

When a plate subducts, the part that is sinking pulls the rest of the plate with it to cause more subduction

What happens at a conservative plate boundary?

• 2 parallel plates move at different speeds & in different directions

• When they rub against eachother, pressure builds up

• For oceanic crust this displaces a lot of water

• For continental crust, fault lkines occur with the ground being cracked

What is the focus & epicentre of an earthquake?

Focus - The point underground where the earthquake originates from

Epicentre - The area directly above the focus on the ground

What are characteristics of primary waves?

• Travel through any state of matter

• Longitudinal

• Vibrates in the direction of travel

• 4-8km/s

What are characteristics of secondary waves?

• Transverse

• Travel only through solids

• 2.5-4km/s

What are characteristics of love waves?

• Near to the surface

• Cause the ground to shift side to side

• Travel 2-4.5km/s

What are characteristics of rayleigh waves?

• Near to the surface

• Cause the ground to shift up & down

• Longitudinal

• 1-5km/s

What seismic waves are the most destructive?

S-waves & L-waves as they have large amplitudes but are at different speeds to have a delayed impact

What is soil liquefaction?

• Water moisture within the soil separates from the soil & rises to the surface

• This causes soil to behave like a liquid

What are landslides?

• Unconsolidated material or loose rocks collapsing

How is a tsunami formed?

• When an oceanic crust is jolted, all the water above gets displaced upwards

• This water then gets pulled back down due to gravity, causing it to act like a wave

• The wave travels fast but with low amplitude

• As the sea level decreases there is friction between the sea bed & waves

• This causes the waves to slow down & gain height

What makes a country vulnerable to a tsunami?

• High population density

• Little coastal defences

• Long duration

• Large wave amplitude & long fetch

• Slow gradient

• Small beach

Primary hazards from a volcano:

• Lava flows

• Pyroclastic flows (mixture of rock,lava,ash & gases moving across the surface)

• Tephra (volcanic rock) and ash flows blasted into the air to land on buildings

• Volcanic gases (sulphur dioxide & carbon monoxide)

Secondary haards from a volcano:

Lahars

• Rock,mud & water traveling down the sides of volcanoes

• Occur when the heat of the eruptio causes snow & ice to melt or when there is heavy rainfall

Jokulhaup

• Snow & ice in glaciers melt after an eruption causing sudden floods

Acid rain

• Sulpfur dioxide in the atmosphere

What is a disaster?

A serious disruption of the functioning of a community involving human, material, economic & environmental losses that exceeds the ability of the affacted community to cope using its own resources

What is the hazard risk equation?

What is Degg’s model? & What does it show?

A hazard becomes a disaster if it is met by a vulnerable population

What is the Park Model? & What does it show?

Shows the importance of recovery & compares different events

• Curve A = Small impact on QoL & a short response time as QoL improves quickly after a few months

• Curve B = Medium impact on QoL as reconstruction takes longer but mitigation improves QoL so the community has improved

• Curve C = Major impact on QoL as a slow reconstruction phase means even year slater QoL has not returned to pre-disaster levels

What is the PAR model? & What does it show?

Analyses factors that make a population vulnerable to a hazard going from countrywide, to county, to individual

• Root causes - Caused by underlying economic, demographic, political processes

• Dynamic processes - Local economic/political factors

• Unsafe conditions - Physical conditions that affect an individual

What is a hazard profile?

A description of a hazard that outlines its physical characteristics & important figures about the hazard

What is VEI?

The volcanic explosivity index measures the relative explosiveness of a volcanic eruption based on the height of ejected material & duration of the eruption. It ranges from 0 to 8 logarithmically

What is the Modified Mercalli Scale?

Measures the destructiveness of an earthquake subjectively, the scale varies from I to XII and only measures physical impacts like furniture moving or houses collapsing

What is the moment magnitude scale?

Measures the amount of energy released in an earthquake from 0-9

What is the richter scale?

Measures the amplitude of the waves produced during an earthquake & is logarithmic from 1-10

What is the hazard management cycle?

• Preparedness - Being ready for an event to occur (public awareness & training)

• Response - Immediate action taken after an event (evacuation & medical assistance)

• Recovery - Long-term responses (reconstruction)

• Mitigation - Strategies to lessen effects of another hazard (warning signals & observatories)

How can volcanoes be predicted?

• Small earthquakes around the time

• Changes to the top surface of a volcano swelling up

• Changes to the gradient of the volcano as it swells up

How does modify the event work for an earthquake, tsunami & volcano

Earthquake

• More public buildings to shelter people

• Infrastructure is reinforced

• Private homes are improved

Tsunami

• Tsunami walls but only up to a certain amplitude

• Replanting coasts with mangroves & a large beach

Volcano

• Diverting lava flows

• Reinforcing house roofs

What are the 3 different approaches to managing a tectonic hazard & reducing its impact?

• Modify the event

• Modify the vulnerability

• Modify the loss

How does corruption affect the vulnerability of an area?

• Money may not be directed towards hazard preparedness

• Inequality can lead to more deaths

• Lack of transparency can affect foreign aid