Natural Hazards

Exam-style Questions

  1. a) Describe the key features found at a destructive plate boundary.

    (6 marks)

    b) Explain why some tropical and subtropical areas experience a greater frequency and risk of tropical cyclones and seismic activity than others.

    (6 marks)

    c) Natural Hazards have a greater impact on LEDC's than MEDC's discuss.

    (12 marks)

    (Marks available: 24)

    Answer

    Answer outline and marking scheme for question: 1

    a) Marks will be given for the following, be careful not to explain any of the features. Begin by saying that plates are moving towards each other at a destructive plate boundary.

    Examples of features created and hazards caused by plate movement are outlined below:

    • Subduction Zones and Ocean Trenches, for example, The Peru - Chile trench
    • Earthquakes
    • Fold Mountains, for example, Andes
    • Volcanoes
    • Island Arcs (such as those found in Japan)

    b) The risk of hazards is increased for the following reasons:

    • High seismic risks are associated with plate boundaries. Due to movement of plate and the generation of heat at subduction zones certain areas are more prone to tectonic activity. The location of volcanoes around the Pacific ring of fire is a good example of this.
    • Areas experiencing little seismic risk / active volcanoes are far removed from plate boundaries.
    • The exception of Hawaii is due to the location of a 'hot spot'.
    • Tropical cyclones need certain conditions for their formation. The presence of high ocean temperatures, and high humidity is limited to areas close to the equator.

    Tropical cyclones are not found along the equator, as the coriolos force is insufficient to allow the spinning motion to develop.

    Tropical cyclones do not occur over land as their main supply of energy (warm water) is removed.

    c) In this answer you need to show that you understand that the term 'impact' can be defined in a variety of ways, and whilst loss of life can be greater in LEDC's, the economic impacts of hazards in MEDC's cannot be underestimated. You need to include examples to illustrate differences and include reference to the following:

    • Population: The higher densities of population in LEDC's (for example, the Mexico City earthquake).
    • Available finances (limiting or allowing enforcement of building legislation codes).
    • Education is the population suitably educated regards steps to take in the event of a hazard.
    • Insurance.
    • Economy: How diverse the economy is of a country hit. Is the country reliant on a cash crop economy? For example, Hurricane Mitch - Nicaragua.
    • Infrastructure: Are the emergency services equipped to cope with the impact of a hazard?
    • Figures to show the impact of a similar strength earthquake in a LEDC and MEDC to help support your answer.

    The question expects you to reach a conclusion based on the evidence you have presented in your answer.

    (Marks available: 24)

  2. a) Define the term mass movement and outline the factors that influence the speed of its movement.

    (6 marks)

    b) Although Mass movements occur naturally their impact increases dramatically as a result of human activity. Discuss with reference to specific examples.

    (15 marks)

    c) The marks for this question will be divided as follows:

    Definition of mass movement = 2 marks.

    Factors influencing movement = 4 marks.

    (4 marks)

    (Marks available: 25)

    Answer

    Answer outline and marking scheme for question: 2

    a) Answer gaining full marks:

    'In its broadest sense mass movement is the movement down slope of any weathered material (regolith) under the influence of gravity.' The type of movement is influenced by:

    • Steepness of slope
    • Type and nature of regolith
    • Type and amount of vegetation
    • Water (precipitation, springs, rivers)
    • Rock structure and type
    • Human activity (type and amount)
    • Climate.

    b) Without examples, or reference to only one the highest available marks for this question is 10. They are vital to show your understanding of the role of human activity in increasing mass movements. It is a good idea to use examples that are from a variety of countries striking a balance between MEDC's and LEDC's.

    Possible examples could include:

    • Aberfan: UK 1966
    • Holbeck Hotel: Scarborough UK
    • Landslides along the Californian Coastline
    • Mass movements linked with volcanic activity (Mt. St. Helens)
    • Mass Movements caused by climatic influences (Hurricane Mitch - Nicaragua)
    • Population pressure increasing likelihood of mass movements due to building on steeper land, for example, Hong Kong and Rio de Janerio.
    • Avalanches (increased risk from skiing industry)

    When talking about impact in this answer you need to show that you understand that 'impact' is a wide-ranging term and address it by examining the following:

    • Loss of life
    • Economic impact
    • Size of the mass movement
    • Impact on buildings, natural vegetation, industry.

    As the answer stresses the word 'dramatic' do make sure that you show how human activity led to the impact. For example:

    'An example of a mass movement that was increased dramatically as a result of human activity was that which hit the coal mining village of Aberfan, South Wales on 21st October 1966. The landslide which involved over 100 000 cubic metres of colliery waste travelling at speeds over 30 km per hour, killed 144 people, over 100 of whom were school children. The reason for the landslide was a combination of human and physical factors - a build up of rain water inside the waste tip led to its instability, yet human mismanagement proved crucial. The spoil tip was high up on steep valley sides, and despite earlier smaller earth movements the National Coal Board continued to pile waste on the tip'

    (Marks available: 25)

  3. a) Describe the features necessary for hurricane formation.

    (4 marks)

    b) Explain how the formation of hurricanes differs from that of tornadoes.

    (6 marks)

    c) Evaluate the success of a disaster prevention programme for a named area or country you have studied.

    (15 marks)

    (Marks available: 25)

    Answer

    Answer outline and marking scheme for question: 3

    a) Marks will be awarded for mentioning any of the following (award yourself one mark for each):

    • Warm oceans (27 degrees plus) to a depth of 60m
    • Location sufficient to allow Coriolis force
    • Stable and uniform conditions of temp, humidity and pressure.
    • Relative humidity of over 60%
    • Little change in horizontal wind with height
    • Cyclonic spinning of winds in lower troposphere

    b) This question is designed to test that you really do know the differences in formation - not just scale of each. A common mistake at A-Level is to fail to adequately distinguish between each.

    Start your answer by defining each, to demonstrate that you know what each is:

    'Hurricanes are extremely powerful low-pressure systems, and are believed to be responsible for a greater number of deaths than any other natural hazard. They are generated over the Atlantic and Pacific oceans and are most common in autumn when ocean temperatures are at there highest. They can last for up to a week, have wind speeds in excess of 119km per hour and can be 100's of km across. In contrast tornadoes are much smaller, last for a shorter length of time and form over land rather than sea. Both are part of the global energy transfer.'

    The points you need to include are:

    • Different air types meet and due to their different properties do not mix
    • In the USA warm moist air with its origins in the Caribbean meets colder air that has originated in the northern Rockies
    • The need for instability (the two meeting air masses should be conditionally unstable)
    • Low-level air with a relative humidity of over 65%
    • Existence of low-level southerly jet stream in the humid air

    c) Your disaster prevention programme can be for either an MEDC or LEDC, prior to evaluation its success you need to outline its key features - such as:

    • Training and education
    • Land Use Planning
    • Building Codes
    • Communication of information

    In addition, do not forget to include any information that may be relevant to making the programme a success or failure:

    For example: the state of the economy of the country, are they dependent on a cash crop economy?

    What are the available finances to spend on the programme?

    Is their adequate understanding of the programme by the local population - if not why not?

    Is there any evidence to show that the programme has been a success?

    For example: evacuation procedures in the Southeast USA to escape hurricanes, and the use of hurricane shelters. How easily can emergency services reach the injured?

    Does the population know about the potential risk of the area they live in or does population pressure reduce their choices?

    Include the issue of hazard perception, which may reduce the effectiveness of the programme.

    Do, towards the end of your answer relate back to the question. That is deicide if you think the programme has been a success or failure, drawing on the evidence you have presented.

    (Marks available: 25)

  4. Hazards have social, economic and demographical impacts. Examine the main factors that affect these.

    (Marks available: 25)

    Answer

    Answer outline and marking scheme for question: 4

    A full essay answer, so planning is vital, as is a solid, logical structure and appropriate use of geographical terminology. The examiner is looking for understanding that loss of life is the most extreme consequence, but loss of livelihood, community stress, loss of property and businesses are also impacts. You will be expected to demonstrate your knowledge and understanding in the following ways:

    Knowledge

    Factors that affect the impact should begin with the level of development of a country. This should be at a more complex level than simply MEDC's versus LEDC's, by doing this you will put your answer in a higher band. Take each impact in turn: For example, the social impacts could be reduced / increased as a result of religious beliefs. Demographic impacts vary because of both population structure and density. Economic impacts will be linked to levels of development, wealth and insurance. Extra credit will be awarded for mention of ability of country to forecast hazards.

    Understanding

    Using a range of examples will show better understanding, and that different factors will affect different areas of the world. Good answers will show that one factor may be important for one hazard, but not for another. (For example, loss of life or property).

    (Marks available: 25)

Earth's Structure

Before starting work on this topic it is vital that you know the structure of the earth, as it underpins a majority of the work related to natural hazards. The diagram below summarises the most important points:

Place the cursor over the various sections of the earth to see what they are called:

Copyright S-cool

Crust

  • Thin, outer-layer of the earth.
  • It is as thin as the skin of an apple is to its flesh.

Mantle

  • Composed mainly of silicate rocks, which contain a lot of magnesium and iron.
  • It extends to a depth of 2900km.
  • Temperatures can reach 5000 degrees Celsius, which generate convection currents.

Core

  • Contains iron and nickel.
  • Situated approximately 6371km below the surface.
  • Temperature is around 5500 degrees Celsius.

S-Cool Revision Summary

Consists of a thin outer layer, the crust.

The mantle is composed mainly of silicate rocks, which contain a lot of magnesium and iron. This is a much thicker part of the earth.

The mantle contains many minerals, particularly iron and nickel.

In the temperatures can reach 5000 degrees Celsius, which generate convection currents.

The core is in the centre of the earth.

Physical hazards include events such as; earthquakes, volcanic explosions, flooding, drought, tropical storms and landslides.

Remember that some of these may trigger other hazards such as tidal waves following earthquakes.

In order for a physical event or process, such as an earthquake to be hazardous there must be the potential for some loss of life.

It is generally felt that that the less developed a country (LEDC) is the more damage, both economically and in terms of loss of life the hazard causes.

The impact of a hazard can be increased by human activity.

Areas vulnerable to tectonic activity are usually found on or near to plate boundaries

The location of continents today of far removed from what it was millions of years ago, when it is believed that all continents were joined to one land mass.

Plate movement is either towards, away, or alongside adjacent plates.

Plate movement can be one of three types:

  1. Convergent (destructive or collision) - Towards each other. For example: The Indian Plate and Eurasian Plate created the Himalayas.

  2. Divergent - Away from each other. For example: North American plate moving away from the Eurasian plate resulting in the mid Atlantic ridge.

  3. Transform or transcurrent - Alongside each other. For example: Earthquakes such as those linked with the San Andreas Fault.

Earthquakes occur because of a slow build up of pressure in the earth's rocks, which is quickly released.

Primary Hazards are hazards due directly to the earthquake itself, and consist of ground movement and shaking.

Earthquakes emit body waves (travel through the earth) and surface waves. It is surface waves that cause most damage as they impact on what is on the surface of the earth

Secondary Hazards are indirect hazards that may result from an earthquake:

Soil Liquefaction - Solid material changed into a liquid state. Damages building foundations, resulting in them sinking.

Landslides - Often as a result of the ground shaking, even if a slope is gentle. Cause burial of people and overrun buildings.

Tsunami (tidal waves) - If the focus of the quake is beneath the sea, tsunami can occur. Ninety percent occur in the Pacific basin. The more movement of the sea floor and the shallower the focus the larger the wave that is created.

Volcanoes occur when magma from the earth's interior is able to make its way to the surface, via a vent.

The shapes of volcanoes that you should be able to recall are:

  1. Fissure: Very gentle slope, found at diverging ocean plates, basaltic lava, can flow over large distances.

  2. Basic / Shield: Have gentle slopes, steeper than fissure due to repeated explosions and subsequent build up of basalt based lava. (Mauna Loa Hawaii)

  3. Cone: Symmetrical in shape, A acid where thick viscous lava, rapidly cools B) Ash / Cinder.

  4. Composite: Very large old volcanoes. Both ash and lava are deposited (Mt. St. Helens)

  5. Crater / Caldera: Form when a very violent eruption occurs after a build up of gas beneath the volcano. Can destroy the magma chamber leaving a large crater.

This ranges from being extremely thick and viscous, to highly fluid. The amount of pyroclastic material also varies. The two types are:

Aa flow - This is a few metres thick, a mix of uneven shaped, sharp edged ash and cinder blocks. It is unstable.

Pahoehoe flow - Is fluid rather than viscous, but does not move quickly. Often the surface layer is static whilst flow continues beneath.

Called by a variety of names: Hurricanes, Typhoons, Cyclones, Willy Willies

Tropical cyclones are generated over the Atlantic and Pacific oceans and are most common in autumn when ocean temperatures are at there highest. There is some evidence to suggest that their frequency and severity is increasing as a result of global warming.

Several basic conditions are necessary for hurricane formation:

  1. Warm oceans with surface temperatures in excess of 27 degrees, and a deep layer of water to 60m

  2. A location between 5degrees north and south of the equator. (Without this the coreolis force is not sufficient to create the spinning motion characteristics of hurricanes.

  3. Relatively stable and uniform atmospheric conditions of temperature, humidity and pressure. In the upper troposphere air drawn in at lower altitudes must be able to escape.

  4. Relative humidity of over 60% to provide sufficient energy to power the hurricane.

  5. Little change of horizontal wind with height.

  6. Existing cyclonic spinning of winds in the lower troposphere.

Most tornado activity (70%) is found in the Great Plains of the USA. They form as a result of intensive convective rainfall systems and are highly unpredictable.

The two meeting air masses are conditionally unstable.

Low level air has a relative humidity of over 65%.

A low level southerly jet stream exists in the humid air.

Mass Movements:

This is where land movement at a range of speeds results in destruction of property and/or loss of life. It is often triggered by human activity. In its broadest sense it is the movement down slope of any weathered material (regolith) under the influence of gravity.

The type of movement that occurs is influenced by:

  1. Angle of slope (steeper is faster)

  2. Nature of regolith

  3. Amount and type of vegetation

  4. Water

  5. Type and structure of rock

  6. Human activity

  7. Climate

Despite their apparent unpredictable nature, attempts have been made to control and influence the amount of damage a hazard causes. Success varies due to issues such as development, frequency and perception.

There is a general belief that often individuals do not perceive themselves to be living in a hazardous area (take Los Angeles, for example), and that it takes experience of a hazard to appreciate the danger.

This then subsides as the time since the hazard increases. In some cases, the advantages of an area may far outweigh the potential disadvantages of the hazard (good fertile soils, favourable climate) and in the case of technologically advanced countries the population may believe they have the technology to manage the hazard.

Hazard Impact:

Obviously this varies depending on the scale, frequency and vulnerability of the population. It is closely tied to wealth, education, health, population and technological advances. (See earlier work on impacts of hazards).

Hazard Prediction:

This is highly complicated and its usefulness is the subject of debate. The main areas covered include forecasting and warning in an attempt to minimise the impact. In the USA hurricane warning systems exist, satellite monitoring equipment, as do posters TV and radio broadcasts informing people of action to take in the event of a hurricane. Seismographs monitor tectonic activity in an attempt to find clues to a large quake.

Hazard Prevention:

Most work regard reducing the impacts of hazards is concentrated in this area as it is considered the most direct and cost effective.

The aim is to reduce the potential impact of hazards by ensuring people are fully prepared should they occur. Hazard prevention exists in a number of ways:

Cities in earthquake zones often use training and education, to ensure that all citizens know what to do in an earthquake situation.

Building Restrictions and Land Use planning - This is far more commonplace in MEDC's where there is a lower density of population and the money available to enforce such codes.

Buildings can be restricted in height, have to conform to a certain design to ensure they have the greatest chance of remaing intact in the event of a hazard.

Problems exist in LEDC's such as the Philippines where housing is vulnerable, due to material being salvaged from homes destroyed in a typhoon in order to rebuild others. There is currently a move towards educating the public on low-cost typhoon resistant housing.

Aid - Often the most contentious issues regards preventing hazards. LEDC's are eager to limit short-term handouts, such as clothes, money, food, and focus on long-term measures that they believe can help a country become more self-dependant and learn to cope with the impacts of hazards for themselves.

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