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Tectonics • To review key themes from the tectonics unit. • To link ideas from across the unit to answer exam questions. Exam question Outline how the type of magma effects the shape of extrusive landforms. 7 marks Why is it more hazardous to live near destructive margins than constructive ones? (7) This is about impacts on humans but also requires knowledge of processes taking place at the respective margins. Comments regarding different human perspectives are also relevant. Constructive margins have relatively small land surfaces and so fewer people are directly involved. The processes of sea floor spreading and the development of (largely submarine) volcanic ridges are fairly gentle affairs and, even when hazardous, can be managed (Heimaey, Iceland 1973). Destructive margins have far more violent processes with explosive, more acidic volcanoes. Since many destructive margins are near coasts there are likely to be more people living there and so are also subjected to earthquakes and tsunamis. It is unlikely that candidates will attempt to argue against the statement but any attempt to do so should be assessed in the light of the levels criteria. Level 1 – Generic Descriptor (1 - 3) Basic statements, with general differences or reference to only one type of margin. Level 2 – Generic Descriptor (4 - 6) More detailed comments about both types of margins and understanding of either theory or impacts, probably with exemplars. Level 3 – Generic Descriptor (7) Detailed and knowledgeable comments regarding both margins with an explanation showing understanding of both theory and impact, with exemplars. Total for this question: 15 marks Study Figure 2 which is a diagrammatic section through part of the earth’s crust. Figure 2 (a) Distinguish between intrusive and extrusive volcanic activity. Outline the differences between the intrusive features shown in Figure 2. Intrusive activity takes place beneath the earth.s surface through magma, which cools slowly within the crust, forming large crystals, usually granitic rock, often cracked by large joints and makes up the larger proportion of the earth.s crust. Extrusive activity takes place on the earth.s surface through lava, which cools quickly in air or water, forming small crystals, usually basaltic or andesitic rock and makes up the smaller proportion of the earth.s crust. Each mark is awarded for distinguishing between different features. This can be done by comparison (intrusive activity takes place beneath the earth.s surface, whereas extrusiveactivity takes place on the surface) or comparative (intrusive magma cools slower than extrusive lava) or juxtaposition (as in the 2 paragraphs above). Since part (b) refers specifically to features, there is no credit here for them. (4 marks) Describe the distribution of the earthquakes and attempt to explain the pattern that is shown. Level 1 Basic/simple statements with regard to distribution, mainly names of countries or areas affected by earthquakes. Explanation confined to plate boundaries. (1–4 marks) Level 2 Wider picture seen, such as the ‘Pacific Ring of Fire’. Some reference to the large areas where there are or few recorded instances. More details on plate boundaries such as the activity taking place there which results in earthquakes and activity within fold mountains. Some attempt to explain why some areas are free/relatively free from earthquakes. (5–7 marks). As this question is levels marked, you will receive only Level 1 marks if you describe the distribution in piecemeal form, i.e. simply a list of countries/areas. You must describe a wider pattern to reach Level 2. Similarly, explanations must go deeper than simply stating that the earthquakes are on or near plate boundaries. You could state what is happening to cause earthquakes at specific boundaries (must be those shown on the map, not earthquakes in general) such as on the conservative margin in California. b Describe the effects that a major earthquake can have on the population of an area. (8 marks) Level 1 Simple statements giving nothing more than a list of the effects. (1–4 marks) Level 2 Recognises that effects can be divided into primary and secondary and gives examples of each (accept candidate’s own definition of primary/secondary as long as it is logical). Links are clearly made between primary and secondary hazards, e.g. ground shaking can cause buildings to fall. breaking gas pipes which could lead to fires breaking out. Several effects can be linked together in a chain; another example could be ground shaking resulting in dams cracking, collapsing and leading to flooding downstream. (5–8 marks). To reach the higher mark level, you must do more than write a list of effects. With many hazards it is important to recognise that there are both primary effects and later secondary effects, which may last for a considerable period of time after the event. It is also essential to see that one effect may be the cause of another. If you can link the hazards in this way, your mark will be at the top of the range. Discuss the ways in which people and organisations respond to earthquakes and their effects. (10 marks) In general, they may include: • in inability to leave area, or reluctance preparation in the event of earthquakes - FEMA (USA) • modification of buildings - variety of ways could be described • education to minimise loss of life, including earthquake drills, emergency supplies in the home, posters • fire prevention - smart meters • pre-planning of emergency services • land-use planning to minimise damage and risk. Mark scheme Level 1 – Simple statements of responses which could apply to any earthquake hazard. No specific detail provided. 1-3 marks Level 2 - Specific statements of responses which can be clearly attributed to named areas and/or earthquakes access this level. 4-8 marks Level 3 - Fully developed answer, with good elaboration of more than one response. Rounded answer with full range of responses analysed and/or evaluated. 9-10 marks (c) With reference to examples, discuss the effectiveness of hazard management schemes in areas where earthquakes have taken place. (10 marks) Level 1 (1–4 marks) Identifies several methods of management, but only at a superficial level. Loosely ties management techniques to specific events or areas. Examples used are very thinly developed. Material on effectiveness of schemes is little more than they work or do not work. Level 2 (5–8 marks) Clear identification of schemes and areas in which they are used. Shows, with some details, how effective such schemes can be and why they work Good use of exemplar material. Level 3 (9–10 marks) Clearly links the schemes, the areas in which they operate to their effectiveness in particular situation. Answer contains very good use of exemplar material, with some background to the events and the effectiveness of particular schemes at the time of the event. Figure 1 (Earthquake intensity and number of deaths from 10 earthquakes since 1985) (a) Comment on the information given in Figure 1. (7 marks) Level 1 (1–4 marks) Simple statements as to death toll and size showing some elements of correlation. Some slight indication that the correlation is not strong. Some basic attempts at commentary but with little idea why the correlation not entirely clear. Level 2 (5–7 marks) Shows a clear idea of the strength of the correlation (or lack of it) and offers evidence, particularly in terms of highest size (Mexico City) having lower toll and that of Iran with lower size but high toll. Indicates that size is not the only factor in toll, with evidence from the information given, particularly comparing those events with similar size, i.e. Gujarat, Taiwan and Turkey. Odd one out Batholith – laccolith – fumarole Composite – acid/dome – caldera Oceanic/oceanic – oceanic continental – continental/continental. Dyke – sill – laccolith