Geography Paper 1 - Tectonics

Tectonics - Tsunamis, Earthquakes, Volcanoes etc

What occurs at a divergent plate boundary?

Two plates move apart from one another

What occurs at a convergent boundary?

Two plates move towards one another

What happens at a conservative plate boundary?

Two plates move alongside one another

What can occur at a divergent plate boundary?

Magma rises and cools creating new geological features - mid-ocean ridges, rift valleys, volcanoes (often shield) - can also cause relatively small and shallow earthquakes 

Definition of a mid-ocean ridge

underwater mountain ranges formed by seafloor spreading

Definition of a shield volcano

a broad domed volcano with gently sloping sides - basaltic lava

What can occur at convergent plate boundaries between O+O or O+C?

Denser plate subducts beneath the other (oceanic under continental). Can cause earthquakes due to the built up pressure.  As Oceanic crust subducts it releases water which combines with rock to form magma which goes to magma chambers to create volcanoes.

What can occur at convergent plate boundaries between C+C?

At C+C neither can subduct easily so the crust thickens and folds - large mountain ranges.

What can occur at conservative plate boundaries?

The two plates don’t move smoothly due to friction which causes them to get stuck - pressure builds + friction is overcome so plates move. when pressure is released huge amounts of energy are released causing an earthquake.

What is the stratosphere?

The upper mantle layer of the Earth. It is semi-molten and approximately 2000km wide.

How is an intra-plate volcano formed?

Heat from the mantle plume causes melting and thinning of the crust, which leads to volcanic activity at the surface

What is continental crust rich in and how thick is it on average?

Rich in Silica and it is roughly on average 20-70km thick

What is Oceanic crust rich in and how thick is it on average?

Rich in Iron and Magnesium and it is usually 5-10km thick

State of Matter, temperature and depth of the mantle

Solid but Malleable, reaches up to 3500 degrees Celsius and is around 70-2900km deep below the surface

How do convection currents occur and what are they/what do they do?

• Heat from the earths core - core generates heat through radioactive decay and residual heat from the earths formation - rises to the mantle

• As the heat rises it creates convection currents in the mantle - hot magma rises then cools becoming denser so then sinks back down creating a circular motion

• create drag on the overlying tectonic plates causing them to move (divergent, conservative, convergent)

mechanism of slab pull

When subducting oceanic crust sinks down into the mantle it creates a suction like force - pulls the subducting slab further into the mantle. Oceanic crust becomes more dense with age - when more dense than mantle subduction begins 

State of matter, what it contains and temperature of the outer core

Liquid - iron and nickel - 5500 degrees celsius

What does the outer core do?

Carries heat from the inner core to the mantle by convection. Due to iron being a metal as it swirls through the earths magnetic field it creates an electric field.

Depth, state and temperature of the inner core

5150km depth from surface and 6000 degrees Celsius - metals have crystallised due to the pressure creating a solid sphere 

Some different theories about plate tectonics

Fossils - plant and animal fossils were found on the matching coastlines (South america and Africa) → Physically impossible to swim/transport across the vast oceans → evidence they joined along the coasts

Pangea - the remarkable fit of the South American and African continents → believed that the continents were moving and at one time there was a giant super continent → pangea

Palaeomagnetism - When the magnetic patterns of cooled magma were studied, it was discovered that the magnetic patterns were arranged in the direction of the earth’s magnetic field which switch every millions of years. This helps identify the age of the oceanic crust, by studying the youngest rocks at ridges, and proves that the earth did once fit together.

Sea floor spreading - two oceanic plates move away from each other allowing magma from the mantle to rise and form new crust ridges within the ocean resulting in sea floor widening 

Whats the epicentre of a earthquake?

The point of the earths surface that is directly above the hypocentre

Whats the hypocentre of an earthquake?

Where the strain energy of the earthquake stored in the rock is first released

Whats the focal length of an earthquake?

Distance between the hypocentre and the epicentre 

Whats a fault (in terms of an earthquake)?

A fracture in the rocks that make up the earths crust

What are the 3 types of waves?

P waves (primary), S waves (secondary) and L/Q waves (love)

How do primary waves move?

Vibrating parts of the wave move backwards and forwards in the same direction that the wave is travelling 

What do the primary waves do?

they don’t cause any damage and just pulsate up to the surface

How do the secondary waves move?

They move perpendicular to the direction in which the wave is travelling.

What can’t  the secondary waves travel through which primary waves cannot?

Liquid or Gas

What do the secondary waves do?

They travel slower than P-waves however they are the wave that cause the ground to shake 

What do love waves do?

They are a surface wave with a horizontal motion that is perpendicular to the direction the wave is travelling

What are the two main scales that we can rank earthquakes on?

Richter and Mercalli 

How does the Richter scale work?

It is logarithmic → each change between numbers is 10x. 10x stronger/10x more ground shaking. A number between 1-10

How does the Mercalli scale work?

It is based on the effects of the earthquake rather than the physical shaking. It is given a number between 1-12

3 physical factors that can determine the size/strength of an earthquake

The magnitude, The distance from the epicentre, The local geological conditions (how soft is the rock? etc)

What 3 case studies do we use for earthquakes

The 2010 Haiti earthquake,The 2008 China earthquake and the 2011 New Zealand earthquake 

Whats a Natural Hazard?

A natural or human-made event with the potential to cause harm 

Whats a Natural Disaster?

The point at which a hazard becomes devastating because it intersects with a vulnerable population

Whats liquefaction?

Process by which water-saturated material can temporarily lose normal strength and behave like a liquid under pressure of strong shaking. This can cause buildings to settle tilt and eventually collapse

What does the UN suggest a catastrophic event (mega-disaster) is?

Over 2000 deaths, Over 200,000 made homeless, the GDP of a country is decreased by at least 5%, dependence on aid from abroad for a year or more after the event 

What is the hazard-risk equation?

Hazard(H) X Vulnerability(V) / Capacity to cope (C)

What does the Hazard part mean in the Hazard-Risk equation?

All to do with the actual disaster → For example, Magnitude, How long it lasts and time of day

What does the Vulnerability part mean in the Hazard-Risk equation?

To do with Human Factors. Eg. Level of development, Emergency services, population density 

What does the Capacity to Cope part mean in the Hazard-Risk equation?

It is based of the idea of how the country/area can withstand the hazard → generally lower in developing countries

What does resilience stand for (in this context)

The ability to protect lives, livelihoods and infrastructure from destructive and to restore areas after a natural hazard has occurred 

What are the 5 different types of vulnerability?

Physical, Social, Economic, Knowledge, Environmental 

Whats a physical vulnerability?

When people live in hazard prone areas with buildings that offer little to no protection

Whats an economic vulnerability?

When people risk losing their jobs, assets (eg. houses) and money

Whats a social vulnerability?

When a household or community is unable to support the disadvantaged people within it

Whats a knowledge vulnerability?

People lack education or training and there are no warning/evacuation systems in place

Whats an environmental hazard?

Where the area that people are living in has increased in hazard risk because of population pressure forcing people into riskier areas 

What does the PAR model do?

It shows how root causes, dynamic pressures and unsafe conditions combine with a natural hazard to create a disaster.

What are the 3 parts in the PAR model that increase the effects?

Root causes, Dynamic pressures, Unsafe conditions 

What does Root causes in the PAR model mean?

Low access to resources, Limited influence in decision making, Poor governance and a weak economic system

What does Dynamic Pressures in The PAR model mean?

Lack of education, training and investment, rapid population change and urbanisation 

What does Unsafe conditions in the PAR model mean?

Poor construction standards, unsafe infrastructure, poverty, lack of social safety net 

What is on the right hand side of the PAR model?

The natural hazard → eg. an earthquake, a volcano, a hurricane etc

What is in the middle of the PAR model?

Risk = Hazard x Vulnerability 

How does the Spearmans’s rank work?

It gives you a number in between 0-1. You rank things from 1 (small→large). Then you work out the difference between the two different ranks then sqaure them. Then use the formula to work out the correlation coefficient. 

Why is Spearman’s rank used?

to measure the strength and direction of a relationship between two variables, especially when the data is ordinal or non-normally distributed

Whats the Benioff zone?

An area of seismicity corresponding with the slab being thrust downwards in a subduction zone. 

3 ways that tsunamis can occur?

Earthquakes, Landslides and Volcanoes 

How are tsunamis created?

By water column displacement → the movement of a large volume of ocean water

mostly undersea plate movements where part of the seabed is thrust upwards (or downwards) very quickly, or by explosive volcanic eruptions on a volcanic island, or underwater landslides such as at continental shelf edges. 

What two case studies do we use for Tsunamis?

Boxing day Tsunami (2004) and Japan Tsunami (2011)

Why are hazard profiles helpful?

They help compare across hazards → normally hard because they have different impacts on society and have varying spatial and temporal distributions 

How is hazard profiling done?

You have a table like thing with multiple different rows based on different rank-able things such as magnitude, speed of onset and frequency. You then put dots between the two sides (each side labelled with one extreme beforehand) depending on where it fits on the spectrum. Then you can join up the dots for the full effect 

4 types of volcanoes

Shield volcanoes → Large, broad slopes - fluid lava flow

Composite volcanoes → Steep, explosive

Lava domes → Small, steep

Cinder cones → Smallest, single vent, erupts cinders, ash and rocks 

What are pyroclastic flows?

A fast moving, avalanche of hot gas, ash and volcanic debris that flows down a volcano’s slopes

What are the effects of pyroclastic flows?

Instant death through extreme heat and suffocation, destroying everything in their path with hot gas and rock, burying landscapes under thick deposits, and creating secondary hazards like flooding and lahars 

Whats Tephra?

Its used to describe the rock fragments and other particles ejected from a volcano 

What are some effects of Tephra?

• Fine, sharp ash particles can cause eye irritation, respiratory problems and chronic conditions such as bronchitis.

• Ash loading can collapse roofs, damage electrical systems, and contaminate water supplies.

• Some tephra has acid coatings that can react with rain damaging vegetation and corroding materials. 

What are ash clouds?

A massive cloud of fine volcanic ash, rock fragments and gas that is ejected into the atmosphere during a violet volcanic eruption

What are some effects of ash clouds?

• widespread disruption to aviation due to engine damage and sensor failure

• serious health problems from inhalation causing respiratory issues like asthma

• significant infrastructure damage to buildings roads and power systems