Unit 5 - Hazards

AQA A-Level Geography

What are the three official categories of hazards?

Geophysical, Hydrological, Atmospheric

What is a geophysical hazard?

A hazard resulting from tectonic processes.

What is a hydrological hazard?

Hazards caused by disruption of surface and underground water

What is an atmospheric hazard?

Created in the atmosphere by the movement of air and water

What is the proposed biological hazard?

A hazard caused by virus, disease or toxins

How are hazards classified?

By their initial cause

What does the Degg model demonstrate?

A disaster only occurs when a hazardous event overlaps with a vulnerable population

What does vulnerable mean?

Susceptible to human and economic loss

Why is vulnerability a social process?

Because it is socially produced and spatially distributed from HICs to LICs

Fatalism

Accepting that hazards are natural events, that people will die from them, and there is little that can be done. May consider hazards to be ‘God’s Will’.

Fear

People become so afraid of the risk of hazard that they move away from the area.

Prediction

Using technology to try and monitor and estimate when and where hazards might strike in order to reduce risk and be able to provide warnings. This is a form of adaption

Adaption

Understanding that you can prepare for hazards, and that doing things before the hazard strikes can improve chances of survival. Likely to adopt the 3Ps - prediction, prevention and protection.

Mitigation

Taking steps to reduce the long-term risks posed by hazards by putting in place protective measures that enable a place to adjust to the risk posed by hazards

Management

Considering the economic, social and political factors, deciding on acceptable leels of damage, and then putting in place a plan to minimise damage and distruption through a variety of strategies.

Risk sharing / community preparedness

This involves encouraging groups and communities to develop measures such as public education and awareness programmes, evacuation procedures, provision of emergency supplies and taking out of insurance, that are designed to reduce loss of life and property damage.

Hazard Perception

The way in which someone understands or interprets a hazard. People tend to respond to hazards depending on their understanding and interpretation.

Factors affecting hazard perception

* Vulnerabilty
* Education
* Money
* Location
* Media representation
* Infrastructure
* Aid and Management

What does the Park Model show?

The steps that people should take to reduce a hazard, and shows quality of life throughout a hazard and the steps taken to return it to normal

What are the three stages of the Park model?

Pre-disaster, relief, rehabilitation and reconstruction

What are some strengths of the Park Model?

* Has a good structure that allows for a disaster to be looked at in detail
* Allows us to assess the level of success and how quality of life reacts
* We can draw several lines to compare successes
* Looks at quantative data

What are some weaknesses of the Park Model?

* Assumes every hazard has the same effects
* The structure leaves no room for flexibility (e.g. rehabilitation may take longer)
* Can change depending on wealth
* Demonstrates power geometries, response changes based on wealth and privileges

What is the disaster management cycle?

The hazard management cycle illustrates the process by which governments, businesses and society plan for, react to, and recover from a disaster

What are some strengths of the disaster management cycle?\`

* Helps reduce effects of hazards
* Helps people structure their approach to recovery
* Shapes public policies and plans that either modify the causes of the hazard events or mitigate their effects
* Promotes sustainable livelihoods and their protection and recovery duting such events

What are some weaknesses of the disaster management cycle?

* Vague and unspecific, doesn’t have a time scale etc.
* Different forms of the cycle focus on different areas
* Hard to test

What is primordial heat?

Heat trapped inside Earth fom the original rock collisions that formed the planet

What is radiogenic heat?

Heat released by the decay and breakdown of radioactive material inside Earth

What is Continental crust like?

* Between 30-70km thick
* Over 1,500 million years old
* Density of 2.6
* Composed of mainly granie, silicon, aluminium and oxygen

What is Oceanic crust like?

* Between 6-10km thick
* Less than 200 million years old
* Density of 3.0
* Composed of mainly basalt, silicon, magnesium and oxygen

Lithosphere

Made up of the crust and the upper mantle, it is a rigid layer meaning that the lithosphere is a solid that can bend and crack

Asthenosphere

The semi molten layer on which plates float and move, is a plstic layer meaning it is a solid still but can flo due to the effects ofheat and pressure

What is the boundary between the crust and the mantle (or the asthenosphere and the lithosphere)

The Moho

How is the Moho defined?

Defined by the distinctive change in velocity of seismic waves as they pass throug changing densities of rock

What is the core like?

Made of dense rock contaning iron and nickel alloys and divded into a solid inner core and a molten outer one with a temperature of over 5000 c

What is the mantle like?

It is made up of molten and semi molten rocks contining lighter elements such as silicon and oxygen

What is the crust like?

It is extremely light because of the elements present suc as silicon, oxygen, aluminium, potassium and sodium

What are tectonic plates?

The lithosphere is divided into lots of slabs called tectonic plates, which move in relation to each other

Where do tectonic plates meet?

Plate boudaries and plate margins

What is the theory of plate tectonics?

The idea that the lithosphere is divided into many plates

What are convection currents?

* The Earth’s mantle is hottest closest to the core, so parts of the astenosphere begin to heat up, becoming less dense and causing them to rise
* As they move towards to the top, the cool down, becoming less dense and causing them to sink
* These circular movements are called convection current

What do convection currents cause?

They cause drag on the base of tectonic plates, causing them to move

What is slab pull?

* At destructive plate margins, the denser crust is forced under less dese crust
* The sinking of the plate edge pulls the rest of the plate towards the boundary

What is ridge push/gravitational sliding?

* At conservative plae margins, magma rises to the surface and forms new crust which is very hot
* This heats the surrounding roks which expand and rise above the surface of the crust, forming a slope
* The new crust coold and become denser, gravity causes the denser rock to move downslope away from the plate margin
* This puts pressure on the tectonic plates causing them to move apart
* This is also known as gravitational sliding

What is sea floor spreading?

* When plates diverge, magma rises up to fill the gap created, forming new crust
* Over time, this crust is dragged apart and even more new crust forms
* When this happens to a margin under the sea, the sea floor gets wider
* This is known as seafloor spreading
* This creates structures clled mid-ocean ridges

What occurs at a constructive margin?

* Plate are moving apart, diverging
* The mantle is under pressure from the plates above, when they move part this pressure is released
* This causes the mantle to melt and to produce magma'
* This magma is less dense than the plate, so rises to form a volcano and erupt
* The plates dont move in a uniform way, so pressure builds up and creates earthquakes when released

What two landform are produced at a constructive margin?

Ocean ridge and a rift valley

How is an ocean ridge created?

* When two diverging plates are underwater, an ocean ridge forms.
* Underwater volcanoes erupt along mid ocean ridges and they can rise to be above sea level e.g. Iceland was formed by a build up of underwater volcanoes

How is a rift valley created?

* Where plates diverge under land, rising magma causes the continental crust to bulge and fracture, forming fault lines
* As the plates keep diverging, the crut between parallel fautls drops down to form a rift valley
* Volcanos are found along rift valleys

When does a destructive plate margin occur?

When plates move towards each other (converging)

What happens at an oceanic-continental destructive plate margin?

* The more dense oceanic crust is subducted under the less dense continental crust to form a deep sea trech
* Fold moutains also form, they’re made of sediments that have accumulated on the contintental crust, which are folded upwards with the edge of the crust
* Oceanic crust is heated by friction and contact with the upper mantle, turning it into magma'
* Magma is less dense and rises to form volacanoes
* Friction and pressure causes an earthquake

What happens at an oceanic-oceanic destructive plate boundary?

* The denser of the two subducts and forms a deep sea trench, triggering earthquakes and volcanoes
* Volcanic eruptions underwater forms island arcs - a cluster of islands in a curved island e.g. Mariana Islands

What happens at a continental-continental destructive plate boundary?

* Neither is subducted, so there is no volcanoes, but earthquakes occur and fold mountains form

What happens at a conservative plate margins?

* Two plates moving past each other
* as the pates get locked in places, pressure builds up and this causes the plates to jerk ast each other, forming fault lines and earthquakes

What are magma plumes?

Areas of intense volcanic activity not nearany plate boundaries, a magma plume is a vertical column of extra-hot magma that rises up from the mantle

What do magma plumes do?

* Volcanoes form above magma plumes
* The magma plume remains stationary, but the crust above it moves
* Volcanic activity in the parts of the crust that were above the magma plumes decreases
* New volvanoes form in the crust above the magma plume
* This continues and chains of volcanoes form such as the volcanoes that created the islands making up Hawaii

What is continental drift?

The theory that tectnic plates and the land masses on them have moved since the creation of the Earth.

What plates is the Earth made of?

Lithospheric plates

What did the Earth look like in the past?

325 million years ago - Pangaea, a single super continent

150 million years ago - Laurasia and Gondwana, two sper continents

100 million years ago - the super continents split and began to form the continent we are familiar with today

Who was Alfered Wengener and what did he propose?

He propoed the theory of continental drift, that 240 million years ago a supercontinent called Pangaea existed and the plates slowly moved to break this continent apart.

Why were Wengener’s ideas not initially accepted?

Because he was unable to explain how the plates moved.

Who was Arthur Holmes and what did he contribute to Wengener’s ideas?

In 1931, he proposed convection currets that caused the plates to move in these ways

Who was Alexander du Toit and what did he contribute to Wengener’s ideas?

He published maps that included the supercontinent Laurasia

Who was J. Tuzo Wilson and what did he contribute to Wengener’s ideas?

He was the first person to use the term ‘plates’ when referring to the division and pattern between different reigons on Earth’s surface

Who was Marie Tharp and what did she contribute to Wengener’s ideas?

She ws a cartographer in 1947, and she made maps that showed the sea floor an the rift valleys present, she then connected that the epicentres of earthquakes are all found at almost identical places to these rift valleys.

What is some geological evidence for continental drift?

* Rock sequnces in North Scotland and Canada closely match, suggesting they were laid and formed under the same conditions
* Rocks in Brazil and West Africa show similar markings and striations from a late carboniferous glacition, suggesting they used to be side by side.

What is some biological evience for continental drift?

* Fossilised remains of a plant which existed when coal was being formed have been located only in India and Australia
* Fossil brachipods found in Indian limestone are comparable with similar fossils found in Australia

How has sea floor spreading been evidenced?

* As lava cools into rock, iron particles are algined with the Earth’s magnetic field, these provide a permanent record in the rock of Earth’s polarity
* Earth’s polarity reverses approximately every 4000 years, and scientists then find a series of magnetic rock ‘stripes’ running down the Atlantic

What is a landform?

A feature created by natural processes

What are the two converging plate boundaries?

Destructive and collision

How is a volcano formed?

* Forms at a destructive plate margin
* Can form over ocean ridges where basaltic lava forms shied volcanoes
* Can form on continental boundaries on land
* When they form in a subduction zone the andesitic lava forms from the plate metling in the Benioff zone

How does a volcano form over a hot spot?

Because hot plumes of magma rise and break through to the surface

What is andesitic lava like?

More viscous

What is basaltic lava like?

Less viscous, appears more dark in colour

How do rift valleys form?

* Forms at a constructive plate boundary
* Plates are diverging, crust falls into the gaps in parallel faults between plates, forming a valley
* Volcanoes can form within this
* e.g. East African Ridge Valley

What is a horst?

An area of crust in the middle of a fault that doesn’t fall

How does a mid-ocean ridge form?

* Forms at a constructive boundary
* New sea floor is created from oceanic plates moving apart (sea floor spreading)
* Basaltic lava upwells and creates a ridge at the plate margin
* e.g. Mid Atlantic Ridge

How does an ocean trench form?

* Forms at a destructive boundary
* Dense oceanic crust is subducted under the less dense continental plate
* The continental plate is downwarped
* The area between these two is a subduction zone and this is where the trench forms
* e.g. Marianas Trench

How do island arcs form?

* Form at a destructive plate boundary
* Due to subduction, at the Benioff Zone, friction causes earthquakes
* Sediment on the oceanic plate reacts in the mantle and plutons of melted sediment rise to the surface as they’re less dense than the asthenosphere and break through so form volcanoes
* This forms andesitic lava and strato-volcanoes that form islands
* e.g. Hawaii

How do young fold mountains form?

* At convergent boundaries
* There is little subduction because they are both continental plates
* Sediment on top of the volcano gets folded into mountains as the plate begins to subduct
* As one is slightly subducted beneath the mountains deep mountain roots form
* e.g. Himilayas

What is an accretionary wedge?

Sediment on top of subducting plates that form mountains

What is vulcanicity?

The processes of volcanic activity

What is a volcano?

An opening or vent through which magma, molten rock, ash or volatiles erupts onto the Earth’s surface

What is an active volcano?

One capable of eruption

What is pyroclastic flow (nuée ardente)?

When gas, rock and ash flow down the volcano

What is VEI?

* Volcanic explosivity index
* Classifies volcanoes based on eruption volume and height of the eruption
* One of the greatest eruptions was VEI 7 with Mount Tambora

What is magma?

Molten rock stored under the Earth’s surfaces that contain dissolved volcanic gases

What is lava?

Molten rock that has reached Earth’s surface, and has therefore released some of the dissolved volcanic gases

Where are most volcanoes found?

95% of all volcanoes on Earth form next to a plate boundary

Where do stratovolcanoes form?

At convergent destructive boundaries

How do stratovolcanoes form?

* Sediment on the subducting plate melts after passing the Benioff zone
* The melting point of the asthenosphere is lowered as a result of flux melting
* Plutons of andesitic magma rise because they’re less dense than the asthenosphere
* This goes through the fault lines in plates to erupt
* As the lava is andesitic it doesn’t travel far

What is flux melting?

The addition of water and/or CO2 lowers the melting point of the asthenosphere, forming molten magma. This happens as a result of melting sediment

Why are stratovolcanoes more explosive?

Because the andesitic lava sticks inside the volcanoes and causes a build up of gas

Where do shield volcanoes form?

At divergent boundaries

How do shield volcanoes form?

* As plates part and a rift is formed, magma upwells from the asthenosphere
* As plates move there is a reduction of pressure in the asthenosphere at the divergent boundary, causing decompression melting as the melting point lowers, creating molten magma
* As it is molten it is less dense than the asthenosphere so it rises and erupts
* It is basaltic lava so can flow further before it cools

Why is andesitic magma more viscous than basaltic magma?

Because it has a higher silica content as a result of the melted sediment

How does a caldera form?

A caldera forms from an already existing volcano, when a large, explosive eruption occurs that empties the magma chamber, the roof of the magma chamber can collapse to form a depression

What is a lahar?

A volcanic mudflow; caused when rain mixes with ash

What is a lava flow?

When lava flows out from a volcano; basaltic lava flows further than andesitic

What is a tephra?

The ash produced by a volcanic eruption

What are volatiles/volcanic bombs?

Rocks erupted from a volcano