Geography Paper 3 - Hazardous Earth

What are the three primary layers of earth?

• Core

• Mantle

• Crust

Characteristics of the core?

• Inner core is solid and is 5000km down

• Outer core is liquid and is 2800km

Characteristics of the mantle?

• Asthenosphere 300km down and semi molten

• Lithosphere 100km down rigid layer

Characteristics of the crust?

• Continental crust, 35km thick and granitic

• Oceanic crust, 10km thick and basaltic

What is continental drift and who came up with it?

• Alfred Wagner 1912

• He proposed Pangea which is a single large plate

• This then split into north and south and then split again until continents formed

• People were sceptical because he failed to provide an explanation

Geological evidence for continental drift

• Continents fit together

• Effects of glaciation on continents suggests they were joined

• Mountain chains and rock types that would have joined

Biological evidence for continental drift

• Similar marine and reptile fossils found in adjacent continents

• Fossils from thousands of years ago show few similarities which suggests evolution

What is palaeomagnetism?

Ancient record of changes in rocks

How can technology measure variations in earths magnetic field?

• Lava erupts and cools

• Magnetic iron particles lock into rock

• Magnetic field showed stripes across ocean floor

What is sea floor spreading?

• Lateral movement of new oceanic crust away from the mid ocean ridge

• Moves material across the ocean floor

• Sea floor reaches ocean trench and material subducts

How can age of sea floor be found?

• Ocean drilling investigated ocean sediment on ocean floor

• Revealed spatial pattern of sediment due to sea floor spreading

• Thickest and oldest sediment was nearest to the continents

• But no sediment older than 200 million yrs so ocean crust constantly recycled

How were tectonic plates discovered?

• 1960’s nuclear tests were conducted underground

• They released vast amounts of energy that were picked up by seismometers

• Most earthquakes were shown to be in narrow bands

• This suggested a tectonic plate boundary

What happens at a divergent/constructive plate boundary?

• Plates move apart

• Magmas rises through the asthenosphere and forces its way to surface

What forms at divergent plate boundaries?

• Mid ocean ridges with a combined length of 60,000km

• Mid ocean ridges are broken by transform faults

What are transform faults?

• Large faults in the crust that form at right angles to the mid ocean ridge

Are there volcanoes/earthquakes at divergent boundaries?

• Earthquakes when vast amounts of energy is released

• Volcanoes from seafloor spreading

3 types of spreading ridges and their characteristics?

• Fast spreading form broad and smooth mountains and have no central rift valleys

• Medium spreading form smooth mountain chains and poorly defined valleys

• Slow spreading form steep slopes and clearly defined central rift valleys

What happens when magma eruption is mostly uderwater?

• Cools rapidly forming pillow lavas

• As magma then rises to surface overlying rocks are forced upwards

• Lithosphere is under stress and eventually fractures

What happens at a convergent/destructive plate boundary?

Plates move towards each other

What are the three ways plates can combine?

• Oceanic-Continental

• Continental-Continental

• Oceanic-Oceanic

What happens at the oceanic-continental boundary?

• Denser oceanic plate submerges under the continental

• It causes subduction

What does subduction do?

• Deepens the ocean causing an ocean trench

What is an ocean trench?

An ocean trench is a long narrow depression and the steepest side lies towards the continent

How do mountain chains form at oceanic-continental plate boundaries?

• Layers of rock develop on oceanic plates

• As they converge rock crumples and is lifted along the continental plate

• Magma is also uplifted

• And a mountain chain forms

How do earthquakes form at o-c plate boundaries?

• As oceanic plate descends it comes under immense pressure

• Faulting and fracturing occur in the Benioff zone

• And energy is released resulting in an earthquake

How do volcanoes form at o-c plate boundaries?

• The oceanic plate melts when it subducts

• Because it is less dense than the surroundings it rises towards the surface as magma plutons

• This can cause volcanoes

What happens at oceanic-oceanic plate boundaries?

• The slightly denser one submerges under the other

• As it descends the plate melts and magma rises forming island arcs

What are island arcs?

• Volcanic islands

• E.g. The Antilles formed by North America Plate subducting under the Caribbean plate

What happens at a continental-continental plate?

• Little to no subduction takes place

• Due to similar densities

• Collision of the two plates can they force them upwards resulting in mountain chains

• E.g. African and Eurasian plates have created the Alps

What happens at conservative plate boundaries?

• They slide past each other in a shearing motion

• Friction causes pressure and rocks sometimes fracture causing earthquakes

• E.g. San Andreas fault system

• No volcanoes though

Features of explosive volcanic eruptions?

• Form at convergent plate boundaries

• Lava is acidic

• High viscosity

• Lower temperature

• Violent bursts of gas bubbles

• Gas, dust, ash and lava bombs occur

• Strato volcanoes

• Don’t erupt frequently

Features of effusive eruptions?

• Occur at Divergent plate boundaries

• Lava is basaltic

• Low viscosity

• Higher temperature

• Limited explosive force

• Gas and lava flows

• Happen more frequently

• Shield volcanoes

What is a product of an explosive eruption?

• A caldera

How does a caldera form?

• The acidic magma doesn’t flow easily so vents are often filled with solidified magma

• Enormous pressure builds up resulting in an explosive eruption

• This destroys the cone of the volcano and empties magma chamber

• Without support of the magma the sides collapse resulting in a depression known as a caldera

Example of a cladera?

• Krakatoa eruption of 1883 left a 7km wide caldera

2 products of effusive eruptions

• Lava Plateux

• Shield volcanoes

What is a lava plateux?

• Flat elevated platform

• Basic magma erupts and areas are covered by free flowing lava

• This is called flood basalts

• Weathering of the earths surface creates varied relief

What is another word for weathering of the earths surface?

Deundation

How do effusive eruptions cause shield volcanoes?

• Basaltic lava results in gentle sloping sides which can extend for tens of kilometres

• Most occur unseen on ocean floor in mid ocean ridges

What is a hot spot?

• A fixed area of intense volcanic activity where magma from a rising plume reaches the earths surface

What is a super volcano and give an example?

• A volcano that erupts more than 1000km³ of material

• Yellowstone in Wyoming is 75km in diameter

Facts about Yellowstone super volcano?

• Volcanic activity began 2 million years ago

• Since then 2 major eruptions

• It decreased global temperatures due to ash cover over the sun

• There is a hot spot underneath but the probability of eruption is very low

Misconceptions about Yellowstone?

• People say its due an eruption but it has no particular pattern

• People say it will have global implications but it will have little impacts outside of the Yellowstone area

• People say its growing larger but there is no evidence of this

How is volcanic activity measured?

• Volcanic Explosivity Index (VEI)

• Measures magnitude (amount of material erupted)

• Measures intensity (speed at which material erupts)

• 0 (least) to 8 (most)

• Also includes, height material reaches, the duration, volume of erupted material and many qualitative descriptions

What are the 7 hazards of a volcano?

• Lava flows

• Pyroclastic flows

• Tephra

• Eruptions

• Lahars

• Floods

• Tsunamis

How are lava flows a hazard?

• Everything in the lavas path is burned, buried or bulldozed

• Destroys infrastructure, crop, residents

• But rarely lead to fatality and injury

How are pyroclastic flows a hazard?

• 500 degrees + of hot gases and ash

• Rock travels at 100km/hour

• Destroy everything in their path

• Inhalation of gas causes instant death

• e.g. Pompeii AD79

Why is tephra a hazard?

• Material ejected from the air

• Buries farmland

• Disrupts transport

Why are eruptions a hazard?

• Emit a wide range of toxic gases like CO2, CO and SO2

• Can pose deadly threat to humans if inhaled

• When rain and SO2 combine acid rain

Why are lahars a hazard?

• Mud flows of about 50km/hour

• Snow, ice, ash, soil all mix to create a large flow

• Destroy everything in their path

Why are floods a hazard?

• Volcanic eruptions below glaciers can cause rapid melting and floods

• Water accumulates until it finds an exit

• This is known as a jokulhlaup in Iceland

Why are tsunamis a hazard?

• Can cause massive displacement of water resulting in 600km/hour waves

• Can cause drowning

What is an earthquake?

• A release of stress that has built up in the earths crust caused by tension, compression and rock shearing

Where is an earthquakes epicentre?

• A series of seismic waves originates from the focus

• The epicentre is directly above the focus

Where do earthquakes tend to happen although they can anywhere?

• Mid ocean ridges

• Ocean trenches

• Collision zones

• Conservative plate margins

What are the 3 types of seismic waves?

• Primary (P) waves

• Secondary (S) waves

• Surface (L) waves

Characteristics of primary waves?

• Low frequency

• Fast travelling

• Happen everywhere

Characteristics of secondary waves?

• Half the speed of primary

• High frequency

• Cant pass through the outer core as its liquid

Characteristics of surface waves?

• Slowest waves

• Low frequency

• Occur in outer crust

What are characteristics of an earthquake with a shallow depth focus?

• 70km down

• Very common

• Release low energy but sometimes can be high

• Occur in cool brittle rock

What are characteristics of an earthquake with a deep depth focus?

• 70-700km down

• Pressure high

• Temperature high

• not very well known as they can explore that far down

How are earthquakes assessed?

• Richter scale made in 1935

• 1(least) to 9(highest recorded) but there is no limit

• Anything under a 2 not usually felt

What affect do earthquakes have on landforms?

• Associate with the formation of mountain chains

• Create large fold mountains

• Rift valleys occur along mid ocean ridges

• Fault scarps form where tension has been from an earthquake

What are the 4 hazards of earthquakes?

• Ground shaking an displacement

• Liquefaction

• Landslides/Avalanches

• Tsunamis

Why is ground shaking/displacement a hazard?

• Its the vertical and horizontal movement of the ground

• Rips apart pipes and railways

• Buildings can better withstand vertical than horizontal displacement

• Disrupts groundwater and can cause it to become contaminated

Why is ground liquefaction a hazard?

• When an earthquake strikes an area with high water content vibrations can cause solid materials to act like liquids

• Materials lose their strength, slopes collapse and places shrink

Why are ground landslides/avalanches a hazard?

• Ground shaking and liquefaction can both cause landslides

• Steeper slopes more vulnerable

• Deforestation and heavy rain also increases vulnerability

• Block transport and rivers

• Can cause flooding

Why are tsunamis a hazard?

• underwater earthquakes displace water

• Wave height increases as they approach the shore

• Tsunamis can spread far inland if no precautions have been taken against them

What is an active volcano?

• One that has erupted in the last glacial period or within the last 10,000 years

What is a dormant volcano?

• One that has not erupted in the past 10,000 years but is expected to erupt again

What is an extinct volcano?

• One that is not expected to erupt again

• There are exceptions though as Yellowstone hasn’t erupted in 70,000 years but is not considered extinct

What are the 5 reasons people choose to live in tectonically active places?

• Fertile soil

• Tourism

• Geothermal energy

• Minerals

• Poverty

Why does fertile soil make people want to stay in an area?

• Fertile soil is produced by weathered lava

• Its possible to grow 2-3 crops on the same piece of land in a year

• Places that rely on agriculture tis brings in more economy and food into the country

Why does tourism make people want to stay in an area?

• Places like Sakurajima is low magnitude eruptions so attracts tourists for sight seeing

• Brings economy into the country

Why does Geothermal energy make people want to stay in an area?

• Japan has had power stations since 1960s

• promotes renewable energy and helps countries progress

• However much of the energy is in conservation sites so can’t be accessed

Why do minerals make people want to stay in an area?

• Minerals produced by earthquakes are used in manufacturing

• Such as sulphur in chemicals

Why does poverty make people want to stay in an area?

• They can’t leave due to travel costs

• Or they can’t pay for education to get a better job somewhere else

• So they must rely on primary industry such as agriculture for a source of income

What does WAPMERR stand for?

• World Association of Planetary Monitoring and Earthquake Risk Reduction

• Formed in 2001

What does physical exposure to hazards depend on?

• Frequency of earthquakes and volcanoes

• Magnitude

• Type of hazard in a particular area

• Number of people that live there

What is a recurrence interval?

• Average time between 2 events of equal magnitude

What is vulnerability?

• Ability of a person or community to withstand a hazard

What is resiliance?

• Rate of recovery from a hazard or event

• It links with effectiveness of measures designed to protect people

What are the 5 stages of disaster response?

1. Modify the cause of the event

2. The even occurs

3. Search and rescue

4. Relief and rehabilitation

5. Nature of recovery and reconstruction

What does the graph for this look like?

How can you mitigate against the event for volcanoes?

• Lava diversion channel

• Spraying lava so it cools

• Slowing the flows by putting obstacles

How can you mitigate against the event for earthquakes?

• nothing can be done

How can you mitigate against vulnerability for volcanoes and earthquakes?

• Education in recognising signs of eruption and what to do along with evacuation drills

• Preparedness as in building shelters and strengthening buildings

• Warning as in using technology to monitor

• Hazard resistant buildings such as steep sloping rooves

How can you mitigate against loses for volcanoes and earthquakes?

• Emergency aid

• Disaster response teams

• Search and Rescue

• Insurance

• Resources for rebuilding

What is aseismic design?

• Buildings being built adjacent so they can sway and bump into each other

• Stepped buildings with a larger bottom on them to offer support

• Excavating weak material so you can build on flat land

• Reinforcements below buildings