A-Level Geography - Tectonics

structure of the earth (5)

crust, upper mantle, lower mantle, outer core, inner core

2 types of crust

oceanic and continental

What is a mantle? (3)

- largest layer of the earth, beneath the crust,

- flows due to convection currents,

- causes tectonic plates to move, creating earthquakes and volcanoes.

What is the core? (2)

- Centre of the earth,

- convection currents cause the earth's magnetic field.

Convection Current

A current/cycle caused by the hot material rising and cool material sinking within the mantle, causing a loop.

Intraplate

Processes that occur within plates instead of at their borders (e.g., Hotspot).

Magma/mantle plume

A large column of magma (hot rock) that rises up through the mantle to the surface.

slab pull (2)

- An oceanic and continental plate meet, the denser oceanic plate sinks beneath the continental plate,

- this pulls down the rest of the oceanic plate, and the continental plate.

Ridge push (2)

- The lithosphere at divergent boundaries is hotter, causing the rock?plates to rise,

- this then causes the plates to slide away from each other

seafloor spreading (2)

- Process that creates new oceanic crust (from magma rising upwards) at mid ocean ridges as the plates are diverging apart.

- As the earths magnetic field changes polarity, (and therefore alignment of magnetic materials in rock) bands of rock are created

Paleo-magnetism (2)

- The magnetic field of the earth affects the way minerals align,

- The magnetic field of the earth also changes polarity, causing bands of rock to form

plate tectonic theory

the theory that the lithosphere is made up of many tectonic plates that move around

Theory of Continental Drift

Idea that at one point in time there was only one super continent called Pangea, which broke apart and turned into the continents we know today

who discovered that the earths crust was formed over many years of erosion etc.

James Hutton

who discovered the theory of coninental drift

Alfred Wegner

who discovered the sea floor has trenches and mountains due to seafloor spreading (etc)

Harry Hess

who discovered the crust is made up of multiple tectonic plates which move

Dan mackenzie

geological evidence for continental drift (3)

- Jigsaw fit - some continents look like they could fit together,

- tectonic fit - new rock is being formed (e.g: midatlantic ridge) so plates must move,

- geological fit - mountain ranges and craters fit across continents (despite being apart)

biological evidence for continental drift

- fossils - (e.g: mesosaurus) found on coastlines of both South America and Africa, suggesting they were joined

Climatic Evidence for Continental Drift

- Glaciation - areas that show evidence of previous glacial deposits/climates despite not being in the right climate right now (e.g: carniferous limestone in scotland)

The 4 types of plate boundaries

constructive(divergent), destructive(convergent/subduction), collision, conservative.

How does magma plume form islands/volcanoes? (hotspot) (5)

- A column of magma rises up through the mantle, it reaches the lithosphere where it spreads out and pushes the lithosphere up.

- Heat from the plume raises the temperature of the lithosphere allowing the magma to emerge on the surface, creating a volcano (which is fed by the plume).

- However, the plume stays in place while the plate above it moves, the volcano will stop being fed and go extinct.

- A new volcano will form above the hotspot, as the old volcano is eroded.

- Over time this creates a chain of islands (Hawaii)

What happens at divergent (constructive) boundaries?

- plates move apart,

- magma rises up through gap,

- shallow volcanoes start to form,

- small earthquakes also happen.

What do divergent (constructive) boundaries form?

Shield volcanoes and small earthquakes

What do destructive (convergent) boundaries form?

Composite volcanoes, Violent earthquakes

What happens at destructive (convergent) boundaries? (3)

- 2 plates push together (e,g: oceanic and continental),

- denser oceanic plate is subducted,

- as the plate sinks, the magma becomes less dense, it rises as plumes and erupts violently as steam.

What happens at collision boundaries? (2)

- 2 continental plates collide,

- the plates are pushed up (creating mountains),

What do collision boundaries form?

Mountains

What happens at conservative boundaries? (3)

- plates slide past each other,

- they get stuck, and pressure is built up,

- when the pressure is released it creates violent earthquakes.

example of destructive (convergent) boundaries (3)

- O + O - Philippines, Philippine and Eurasian

- O + C - Andes, Nazca and South American

- C + C - Himalayas, Eurasian and Indian

example of conservative boundary

San Andreas Fault

example of constructive (divergent) boundary

Mid-Atlantic Ridge

Subduction zone

The region where a denser oceanic plate collides and descends down into the asthenosphere, below a less dense continental plate.

Benioff zone

The region of seismic activity (where earthquakes occur) typically 10-700 meters below. occur at subduction zones (boundaries where one plate sinks beneath the other).

fault lines

a line on Earth's surface that occurs where there is a break in the crust

focus

The point in the earth where the earthquake starts

different types of focus (3)

- Shallow focus (0-70) - more damage as closer to the surface (most energy),

- Intermediate focus (70-300),

- Deep focus (300-700) - less damage as rocks are more fluid.

What is the epicenter?

the point on the surface directly above the focus (where the earthquake begins)

causes of earthquakes

Liquefaction

when saturated rock behaves like a liquid during an earthquake,

this can cause water to rise to the surface,

infrastructure is often impacted by this

landslides

The sudden and rapid movement of a large amount of material down a slope, possibly due to earthquakes, weathering, erosion or saturated silo.

Where do shield volcanoes form?

divergent (constructive) boundaries and hot spots

Features of a shield volcano (4)

- low, gentle sloping sides,

- wide base.

Hazards of a shield volcano (+lava) (4)

- fissures, craters

- frequent but gentle eruptions,

- basaltic, thin, runny lava that flows for a long time,

- low silica/gas content, but the hottest lava.

Where do composite volcanoes form?

Destructive/subduction (convergent) plate boundaries

Features of a composite volcano (3)

- tall, steep slopes,

- narrow base,

- layers of ash and lava.

Hazards at Composite Volcanoes (+ lava) (5)

- pyroclastic flow and lahars,

- ash clouds/fall,

- infrequent, violent, explosive eruptions,

- andesitic/rhyolotic lava is thick and sticky, travels short distances,

- high silica and gas content, but coolest lava.

What is a pyroclastic flow? (3)

- mixture of dense hot rock, lava, ash and gas,

- move extremely fast(100kmph) , at very high temperatures

- primary hazard

What are volcanic gases? (4)

- water vapour, CO2 and sulphur dioxide are released,

- can travel thousands of meters.

- can affect climate change,

- primary hazard.

What are tephra and ash falls? (4)

- pieces of volcanic rock and ash that blast into the air,

- can possibly travel of meters,

- this causes, low visibility, collapses and health risks.

- primary hazard.

Lahars (3)

- a mix of rock, mud and water that moves fast,

- can destroy and submerge easily,

- secondary hazard

Jokulhlaup (3)

- volcanic eruptions heating water in a glacier suddenly realizing large amounts of water and rock,

- this can cause floods,

- secondary hazard

3 types of lava

basaltic, andesitic, rhyolitic

Basaltic lava (temp, content, gas, flow, eruption energy)

Temperature: Hottest (1000-2000)

Contents: high co2, iron and magnesium. low silica, water and aluminium.

Gas: lowest (0.5-2%)

Flow: thin, runny, low viscosity

eruption energy: gentle effusive

Basaltic lava (location, formed by, creates)

Location: ocean hotspots, mid-ocean ridges

formed by: melting of mantle minerals

creates: shield volcanoes, fissure systems, shatter cones

2 types of basaltic lava

Pahoehoe - smooth, billowy

Aa - fragmented, rough, spiky

Andesitic lava (temp, content, gas, flow, eruption energy)

Temperature: (800-100)

Contents: high water and hcl acid, some silica magnesium and iron

Gas: 3-4%

Flow: slow and viscous

eruption energy: violent, moderately explosive

Andesitic lava ( location, formed by, structure)

location: composite cone volcanoes, subduction zones

formed by: subduction of the oceanic plate that then mixes sea water lithospheric mantle and continental rocks

structure: blocky with smooth sides, large angular fragments

Rhyolitic lava (temp, content, gas, flow, eruption energy)

Temperature: Hottest (1000-2000)

Contents: high silica, potassium, sodium, aluminium. low iron/magnesium

Gas: 4 - 6 %

Flow: Thick and stiff

eruption energy: very violent, cataclysmic

Rhyolitic Lava (location, formed by, structure)

location: supervolcanoes

formed by: melting of lithospheric mantle and previously subducted plate

structure: extrusive rock piles up to form lava domes

What is VEI (3)

-Explosivity of an earthquake,

- measure in terms of volume/height ejected, length, observable features

- from 0 - 8, with volume increasing logarithmically

limitations of VEI (3)

- less effective for gentle/effusive volcanoes,

- has a limit,

- doesn't factor in effects on people etc.

what is moment magnitude scale (3)

- measures the amount of energy released at the epicenter,

- does this using size of waves, amount of rock movement and surface area,

- goes from 1+

moment magnitude scale limitations (2)

- doesn't have descriptors,

- doesn't show effects on people.

what is the mercalli intensity scale (4)

- measures the intensity of an earthquakes impacts,

- uses descriptors by witnesses to rank,

- how many feel it, how much breaks

- goes from I - XII (or 1-12)

mercalli intesity scale limitations (5)

- fully qualitative,

- can be biased/wrong due to witness reports,

- has a limit,

- people closer/further from the epicenter will have different opinions

- may be different in place with different infrastructure or development

what is the tsunami intesnity scale (3)

- measures tsunamis based on how destructive/damaging it is,

- does this according humans, nature and infrastructure/buildings,

- from I - XII (1-12)

tsunami intensity scale limitations

- more qualitative than quantitative

- can be subjective,

- has a limit

What is used to measure the SIZE of an earthquake?

Seismometer

What is used the measure the MAGNITUDE of an earthquake?

Richter scale or moment magnitude scale

Tiltimeter

measures tilting or raising of the ground

Seismic waves

The elastic wave/vibration produced by an earthquake.

Types of seismic waves

P wave, S wave, L wave, R wave.

P wave

A longitudinal wave where particles oscillate parallel to the direction of movement.

Aspects of a P Wave

- Longitudinal,

- fastest to reach the surface,

- the least damaging,

- can travel in both solids and liquids.

S wave

A transverse wave where particles oscillate perpendicular to the direction of wave.

Aspects of an S wave

- Transverse,

- slow (reaches the surface after P wave),

- damaging,

- can only travel in solids.

L Wave

A transverse surface wave where the particles oscillate perpendicular (and horizontally) to the direction of the wave.

Aspects of an L wave

- Transverse,

- slowest,

- most damaging,

- moves horizontally on the surface.

natural hazard

Any natural process/event that is a potential threat to human life and property

things that make a disaster(4)

at least one of:

- report of 10+ people killed,

- report of 100+ people affected,

- request for assistance by the national gov.,

- declaration of a state emergency (us).

vulnerability

the susceptibility of a community to a hazard

Hazard resilience

the ability of a community to resist/respond/recover from the effects of a hazard well

goverance

how effectively a place is run and managed

what is administrative governance

policy implementation, on both local and regional scales. this maybe be enforcing building codes and monitoring

general patterns with natural hazards (4)

- overall the amount of water, climate and weather related natural hazards have increased,

- tectonic hazards have stayed the same (unaffected),

- total affected and number of disasters have peaked significantly,

- largest amount of hazards is water related while the least is tectonic and climate.

what is a Multi-Hazard-Zone or disaster hotspot

An area/country that is exposed to a range of different natural hazards and or the hazards occur very regularly.

hazard mitigation vs adaptation (2)

mitigation - avoid/delay/prevent

adaptation - reduce impact

ways to mitigate/adapt to natural hazards (4)

mapping/monitoring/modelling, hazard resistant infrastructure, diverting (lava) and public education/community

how can mapping/modelling/monitoring be used to mitigate/adapt to a natural hazard (6)

- is both mitigation and adaptation,

- mapping of the land, altitude, main features (airports/dense or sparse pop.) etc.

- a computer can then predict what might happen in the event of a hazard,

- this can be used to make escape routes and highlight vulnerable areas.

- it can also be used by aid to prioritize certain areas that need help,

- e.g: GIS, satellite/warning systems and the hazard in Nepal/Haiti

dis/advantages of mapping/modelling/monitoring (4)

- extremely helpful for governments/organisations in seeing what areas need to be prioritized,

___

- not necessarily available to many people (not s useful)

- shown info on what could be done, but doesn't necessarily do anything,

- money and time needed to collect data and map it.

how can hazard resistant buildings be used to mitigate/adapt to a natural hazard (3)

- infrastructure/buildings built to withstand/resist a hazard like an earthquake,

- this can be done through building in mind of shaking (e.g:bridge) or be strengthened/modified(retrofitting),

- e.g: Japan

dis/advantages of hazard resistant buildings

- collapsing buildings make up most of the injury/cost so this is very important,

___

- can be very expensive, especially for protecting a large community,

- skilled engineers are needed

how can diverting (lava) be used to mitigate/adapt to a natural hazard (1)

- diverting hazards such as lava via barriers or channels

dis/advantages of diverting lava (4)

- terrain has to be suitable,

- its hard to predict where lava may flow,

- diverting lava in one area may create problems for another area,

- only for specific circumstances (volcanoes with long lava flows)

how can public/community education be used to mitigate/adapt to a natural hazard (3)

- educating a community of what is a hazard and what to do in case of one,

- practicing drills,

- communities can also help each other, like helping those in need.

dis/advantages of public education (4)

- very effective at reducing loss,

- causes a knock on effect as communities help each other,

- can be very inexpensive in comparison

___

- it may be hard to teach to the amount of people needed.

what is the hazard management cycle

A diagram that displays the different stages of a hazard/disaster, and how a country would react to one

What are the different stages of the management cycle (4)

pre-disaster - preparing for a disaster through mitigation,

(hazard/disaster occurs)

response - short term responses like evacuation/warning and providing immediate assistance such aid,

post-disaster - rebuilding of infrastructure/society and the economy, and new, better, preventative development (leads onto predisaster).

what is deggs model

a natural hazard x a vulnerable population = a disaster