S-Cool Revision Summary
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:
Convergent (destructive or collision) - Towards each other. For example: The Indian Plate and Eurasian Plate created the Himalayas.
Divergent - Away from each other. For example: North American plate moving away from the Eurasian plate resulting in the mid Atlantic ridge.
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:
Fissure: Very gentle slope, found at diverging ocean plates, basaltic lava, can flow over large distances.
Basic / Shield: Have gentle slopes, steeper than fissure due to repeated explosions and subsequent build up of basalt based lava. (Mauna Loa Hawaii)
Cone: Symmetrical in shape, A acid where thick viscous lava, rapidly cools B) Ash / Cinder.
Composite: Very large old volcanoes. Both ash and lava are deposited (Mt. St. Helens)
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:
Warm oceans with surface temperatures in excess of 27 degrees, and a deep layer of water to 60m
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.
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.
Relative humidity of over 60% to provide sufficient energy to power the hurricane.
Little change of horizontal wind with height.
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.
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:
Angle of slope (steeper is faster)
Nature of regolith
Amount and type of vegetation
Type and structure of rock
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.
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).
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.
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.