Physical Geography

WORKBOOK ANSWERS AQA AS/A-level Geography Physical geography

This Answers document provides suggestions for some of the possible answers that might be given for the questions asked in the Workbook. They are not exhaustive and other answers may be acceptable, but they are intended as a guide to give teachers and students feedback.

The answers given to questions within each topic area vary from being directly targeted at knowledge (AO1) and skills (AO3) to more generic answers that fulfil AO2. The levels criteria for the exam-style questions are generic. These generic descriptors are different for each of the three assessment objectives (AO1, AO2 and AO3). The appropriate descriptors for each level of each of the assessment objectives can be found on the AQA website. The notes given for the exam-style questions are suggestions as to what should be included. They are not model answers and do not necessarily include all the material that would be relevant. All your answers in the longer, extended prose-type questions should be supported by examples and case study material. Topic 1 Water and carbon cycles Water and carbon cycles as natural systems

1 One example is the global hydrological cycle: TOPIC 1 Water and carbon cycles

3 One example could be a coastal sediment cell or an ecosystem.

4 The global warming positive feedback system

5 Negative feedback

Following a rise in the use of fossil fuels, global carbon dioxide levels increase. This leads to a global temperature increase which, in turn, results in increased plant growth, meaning that there is an increase in the take-up of carbon dioxide. This has a dampening effect and reduces global temperatures. The water cycle

6 The vast majority of water on Earth (97%) can be found in the oceans. The remaining 3% is fresh water; this consists mostly (almost 4/5ths) of frozen water locked up in ice caps, glaciers and frozen ground as well as groundwater. Only 1% of the freshwater is easily accessible with just over half being found in lakes and freshwater inland seas. The rest is found in the soil, atmosphere biomass and rivers. Although rivers play a big part in human activity and development they only contain about 3/1,000,000s of all the water on Earth.

AQA Geography Workbook Physical geography 2

8 Water can enter a channel by:

 direct precipitation

 overland flow

 soil throughflow

 groundwater flow

 from tributaries

Physical factor How it affects the shape of a storm hydrograph

Impermeable Reduces the rate of percolation into the groundwater, meaning that the underlying rock soil becomes more rapidly saturated. This leads to overland flow. Overland flow is rapid and so water reaches the river more quickly. This gives a flashier hydrograph with steep rising and falling limbs and a shorter lag time.

Steep sides to the Drainage basins with steep sides tend to have flashier hydrographs drainage basin than gently sloped river basins. This is because water flows more quickly on the steep slopes, whether as throughflow or as overland flow, and so gets to the river more quickly.

A period of wet If the drainage basin is already saturated by antecedent rainfall then weather followed by overland flow increases because infiltration capacity has been reached. intense rainfall Since overland flow is the fastest of the transfers, the lag time is reduced. Again, peak discharge is higher, resulting in a flashy hydrograph.

A densely forested Thick vegetation cover in drainage basins will have a significant effect drainage basin on a storm hydrograph. Vegetation intercepts the precipitation, holding the water on its leaves; this slows the movement of rainwater to the ground and so to river channels. Water is also lost due to evaporation and transpiration from vegetation surfaces reducing how much gets to the river. This subdues the storm hydrograph, increasing lag time and reducing peak discharge.

The shape of a Drainage basins that are more circular in shape lead to more flashy drainage basin hydrographs than those that are long and thin because each point in the drainage basin is roughly equidistant from the measuring point on a river.

Human factor How it affects the shape of a storm hydrograph

Deforestation Deforestation reduces interception rates, allowing rainwater to hit the surface directly. The lack of vegetation roots reduces the infiltration rate into the soil. These both lead to rapid overland flow and flashy hydrographs. Deforestation also exposes the soil to greater rates of erosion, which leads to sedimentation in the channel. This reduces the bankfull capacity of a river and can lead to a greater chance of flooding.

Growth of urban Growth of urban areas and other large impermeable surfaces such as areas roads leads to flashy hydrographs. This is exacerbated by the very fact that settlements have been built on floodplains. This urban growth leads to the expansion of built-up, impermeable surfaces such as roads, car parks, shopping centres etc.

Most settlements are designed to transfer water as quickly as possible away from human activity to the nearest river. This is achieved through road camber, building design and drainage systems.

Dam construction in Dam construction will subdue storm hydrographs, reducing the peak

the upper drainage discharge and increasing the lag time. When it rains in the upper part of basin the drainage basin water will flow until it reaches the dam. Here it will be held back and released at a steady rate. Any changes in the storm hydrograph will be as a result of rainfall in the part of the drainage basin between the dam and the gauging station.

Ploughing up of Ploughing breaks up the topsoil and allows greater infiltration, subduing grassland hydrographs. This can be enhanced by contour ploughing. Where furrows are created that run directly downslope they can act as small stream channels and lead to flashier hydrographs. Ploughing wet soils can cause impermeable smears in the subsoil called plough pans. These inhibit percolation, leading to greater surface flows. The carbon cycle

12 a Carbon dioxide is a colourless and odourless gas vital to life on Earth. This naturally occurring chemical compound is composed of a carbon atom covalently double bonded to two oxygen atoms. Carbon dioxide can be found mainly in air, but also in water as a part of the carbon cycle. It plays an important part in vital plant and animal processes, such as photosynthesis and respiration.

b Calcium carbonate, or CaCO3, comprises more than 4% of the Earth’s crust and is found throughout the world. Its most common natural forms are chalk, limestone and marble, produced by the sedimentation of the shells of small fossilised snails, shellfish and coral over millions of years. Although all three forms are identical in chemical terms, they differ in many other respects, including purity, whiteness, thickness and homogeneity. Calcium carbonate is one of the most useful and versatile materials known to humankind.

c Liquid petroleum, along with oil and coal, is classified as a fossil fuel. Fossil fuels are formed when sea plants and animals die, and the remains become buried under several thousand metres of silt, sand or mud. Fossil fuels take millions of years to form and therefore petroleum is also considered to be a non-renewable energy source. It is formed by hydrocarbons (a hydrocarbon is a compound made up of carbon and hydrogen) with the addition of certain other substances, primarily sulphur. Petroleum in its natural form when first collected is usually named crude oil, and can be clear, green or black and may be either thin like gasoline or thick like tar.

14 From 1900 to 1950 the emissions increased slowly, rising by 1,000 million metric tonnes in 50 years. Between 1950 and 2000, they rose more rapidly, rising by 5,250 million metric tonnes. From 2000 onwards the rate of increase grew again, rising by 2,350 million metric tonnes in just 10 years.

Carbon dioxide acts as a greenhouse gas and is increasing so extensively that the Earth’s climate is changing because the temperatures are rising. It is suspected that global warming may cause increases in storm activity as well. Increasing carbon dioxide emissions cause about 50–60% of the global warming.

Exam-style questions (AS) 1 Allow 1 mark for each valid point with additional marks for developed points. (3 marks)

Humans affect the carbon cycle through the exhalation of carbon dioxide, the burning of fossil fuels, deforestation and other poor agricultural practices. Burning fossil fuels and deforestation lead to a disruption in the balance of the carbon cycle.

When a surplus of fossil fuels are burned, a large amount of carbon dioxide is released into the air. Deforestation reduces the amount of vegetation that can reduce the atmosphere’s carbon dioxide levels and creates less habitable soil for new growth. Carbon dioxide builds up due to the overuse of fossil fuels and an increasing lack of vegetation.

2 AO1, AO3: Level 2 (4–6 marks); Level 1 (1–3 marks)

There is one input into the cycle: precipitation. Depending on where this lands, it enters a store. This can be on vegetation surfaces (interception), on the surface or directly into a river channel. The interception store fills until water drips or flows towards the ground. Once on the surface, the water can be stored in puddles for a limited time. Some of this, like the interception storage, can be evaporated back to the atmosphere, but much of it sinks into the soil by infiltration. Water can travel downslope within the soil as throughflow, or it can percolate down into the solid geology below where it becomes groundwater.

If the ground becomes saturated, surface storage remains and the water moves across the surface as overland flow until it reaches a river channel. Once in the channel, water flows towards its base level (usually the sea).

3 AO1, AO2: Level 3 (7–9 marks); Level 2 (4–6 marks); Level 1 (1–3 marks)

The lithosphere: Most of the Earth’s carbon is stored inertly in the Earth’s lithosphere. Much of the carbon stored in the Earth’s mantle was stored there when the Earth formed. Some of it was deposited in the form of organic carbon from the biosphere. It can be removed by humans through the direct extraction of kerogens in the form of fossil fuels. After extraction, fossil fuels are burned to release energy, thus emitting the carbon they store into the atmosphere.

The hydrosphere: Humans affect the oceanic carbon cycle. Current trends in climate change lead to higher ocean temperatures, which limit its ability to absorb carbon on a global scale. It can also have dramatic effects on highly sensitive ecosystems such as coral reefs, thus limiting its ability to absorb carbon on a regional scale as well as reducing oceanic biodiversity globally.

The cryosphere: In 2007 the IPCC concluded that the Antarctic ice sheet is losing ice overall. This loss was estimated to be 24 gigatonnes per year, but the margin of error on that conclusion was high. Globally, mountain glaciers are losing ice mass; one estimate is that approximately 120,000 glaciers around the world are likely to lose their ice in the next century. This melting of ice will put more water into the global water cycle.

Melting of permafrost is likely to release buried carbon dioxide and methane, leading to more atmospheric greenhouse gases.

The biosphere: Over the past several centuries, direct and indirect human-caused land use and land cover change have led to the loss of biodiversity, which lowers ecosystems’ resilience to environmental stresses and decreases their ability to remove carbon from the atmosphere. More directly, it often leads to the release of carbon from terrestrial ecosystems into the atmosphere. Deforestation for agricultural purposes removes forests, which hold large amounts of carbon, and replaces them, generally with agricultural or urban areas. Both of these replacement land cover types store comparatively small amounts of carbon, so that the net product of the process is that more carbon stays in the atmosphere.

The atmosphere: carbon is stored in the atmosphere as both methane (CH4) and carbon dioxide

(CO2); greenhouse gases which absorb and retain heat. Carbon dioxide is released into the

atmosphere through the burning of fossil fuels, deforestation etc. CH4 is released into the atmosphere through animal emissions, decomposition, and the burning of fossil fuels.

The global annual mean concentration of carbon dioxide in the atmosphere has increased by more than 40% since the start of the Industrial Revolution, from 280 ppm in the mid-eighteenth century to 407 ppm as of 2016. The present concentration is the highest in at least the past 800,000 years and probably the highest in the past 20 million years.

4 AO1, AO2: Level 4 (16–20) marks; Level 3 (11–15 marks); Level 2 (6–10 marks); Level 1 (1–5 marks); Level 0: (0 marks)

This depends on the drainage basin you have studied. It is likely that if you have studied an urban drainage basin you will have noted that there are many smooth, sloped impermeable surfaces designed to remove water quickly, leading to a flashy hydrograph which could result in flooding downstream of the urban area.

More rural areas will depend on the land use, shape, steepness etc. of the basin. You will need to describe all the variables and then link them to the hydrograph and flood history.

Exam-style questions (A-level) 5 Allow 1 mark per valid point with extra mark(s) for developed points. (4 marks)

Negative feedback is where the effects of an action are nullified by the subsequent knock-on effects.

An example would be where an increased use of fossil fuels adds greenhouse gases to the atmosphere. This causes the atmosphere to warm up. Globally, more vegetation can grow, meaning more carbon dioxide is absorbed by vegetation. This in turn reduces atmospheric carbon dioxide and dampens down global temperatures.

About 75% of the potential is caused by tropical and temperate afforestation. This is much greater than the boreal afforestation and reflects the speed at which vegetation can grow in warmer areas as well as the total area covered by these vegetation types.

Agroforestry is the growing of both trees and agricultural/horticultural crops on the same piece of land. It is designed to provide tree and other crop products and at the same time protect, conserve, diversify and sustain vital economic, environmental, human and natural resources. Agroforestry is not a permanent solution because it involves the removal of a percentage of the vegetation. It is also not available in the colder regions of the Earth (boreal).

The vast majority of the land surface is predicted to have a greater intensity of precipitation. In the northern hemisphere this seems to be on the western side of the two main landmasses. In the southern hemisphere there is greater intensity in the east of Australia and East Africa, but not South America. The subtropical regions seem to stay mostly the same except for the western fringe of North Africa and Patagonia in southwest South America.

The consequences of this could be flooding in Europe and North America, but drought in desert margins.

8 AO1, AO2: Level 4 (16–20) marks; Level 3: (11–15 marks); Level 2: (6–10 marks); Level 1: (1–5 marks); Level 0: (0 marks)

This depends on the drainage basin you have studied. It is likely that if you have studied an urban drainage basin you will have noted that the many smooth, sloped impermeable surfaces, designed to remove water quickly, lead to a flashy hydrograph which could result in flooding downstream of the urban area. Thus it is dominated by human factors.

More rural areas will also depend on the land use but physical factors such as shape, steepness etc. of the basin will play a larger role. You will need to describe all the variables and then link them to the river regime and the local rainfall patterns.

You need to reach a conclusion which assesses the relative importance of natural variation and human activity. This conclusion must be fully supported by your case study.

Topic 2 Hot desert systems and landscapes 1 They are found straddling the tropics and extend either side of them. They are concentrated along the west coasts of continents such as the Americas, southern Africa and Australia. The Atacama in South America has the most elongated spread, extending along much of the western coastline. The largest continuous expanse is across northern Africa and extending into the Middle East and western Asia. Deserts as natural systems

b Libya, the Sahara desert

c Very low rainfall: 28.5 mm annually with a winter/spring maximum. Very hot summers with daytime temperatures reaching almost 40°C with a big drop at night down to 25°C. Winter temperatures have warm days with a 13°C drop at night, leaving the nights cool.

3 a Earth’s atmosphere moves in general, somewhat predictable patterns that are largely driven by the sun’s rays and the Earth’s rotation.

At the equator, solar heating is intense. Air heated at the equator ascends and is replaced by inrushing air. As the heated air moves upwards, it is gradually cooled. Cool air is capable of holding less moisture within it than warm air. As the air cools, it releases the excess moisture it contains, helping to produce the moist tropics. Higher in the atmosphere, the now cold, dry air rises and moves away from the equator.

At about 30 degree latitudes in both hemispheres (north and south), the air descends. As it does, it warms. As it warms, the air expands, condensation and precipitation are infrequent.

E.g. the Sahara.

b Air descending from mountainous areas warms and dries by compression, little rainfall forms and aridity is the result. E.g. the Atacama desert.

c As an air mass moves over a continent it will lose moisture as precipitation. Equally the air will take up very little moisture due to the low evaporation rates over land surfaces. This means that areas in the centre of continents have very little rainfall simply because the air has become much drier. E.g. the central Sahara.

d Cold air present above cold ocean currents ensures that there is little moisture available to cool and form clouds. The coasts of western, North and South America and Africa display such conditions. Both continents have west coast deserts just a little inland. E.g. the Namib desert.

4 a Ephemerals are plants which have a very short life cycle. They remain in a dry, shrivelled-up state until a rainstorm takes place. As soon as it rains seeds will germinate, flower, fruit and disperse seeds in a very short time. An example is Alyssum alyssoides.

b Xerophytes are plants which are adapted to withstand drought. They include succulents which have developed stomata that shut during the heat of the day and fleshy stems and/or leaves which are able to store water. These include the cacti, agave and euphorbias.

c Phreatophytes are a group of plants which effectively evade drought by having either

 long root systems which enable them to penetrate deep into the earth in search of groundwater

 long roots that spread out close to the surface which are able to tap into dew

An example is the date palm.

d Halophytes are plants that are adapted to salty conditions. These include the saltbush of North America.

Precipitation Potential Aridity index HA/A/N? (mm) (P) evapotranspiration (PET)

200 5,000 0.04 HA

150 2,500 0.06 A

250 1,050 0.24 N

250 2,500 0.1 A

b The main conclusion is that the actual amount of precipitation is not the outstanding factor influencing aridity. The hyper-arid example has more precipitation than the arid. The two places with similar precipitation have different AIs, making one arid and the other not. It is the amount of

water available for plant growth that is important and so potential evapotranspiration (PET) is the dominant factor. Systems and processes

6 High overhead sun, cloudless skies (HP air) and low moisture levels.

7 Cloudless skies lead to rapid heat loss to space. Dry surfaces do not retain as much heat as if they were moist.

8 a Exfoliation results in the breaking, splitting or peeling-off of the outer rock layers. At depth the rock is under considerable pressure. As erosion and weathering occur at the surface, removing surface material, the pressure on rocks lower down is decreased. This creates tension and to relieve this cracks form, running parallel to the surface. As rock is exposed to surface heating and cooling, salt-rich water is drawn to the surface by capillary action. These dissolved salts are deposited in the cracks and together with chemical weathering the cracks are enhanced and thin layers of rock detach from the surface.

b Thermal fracture results from the rapid heating and cooling of rocks in deserts, which is accentuated by the extremes of temperature experienced. With air temperatures during the day rapidly rising to in excess of 40°C the surface layers of rocks can get much hotter, up to 80°C in very exposed locations. At night, temperatures fall very rapidly, generally to below 10°C, but below 0°C in places is not uncommon. This creates a regular rhythm of heating and cooling that also causes the exposed rock to regularly expand during the day and contract at night. This causes weakness, especially along geological lines of weakness (bedding planes, joints etc.) that can lead to cracking.

c In rocks that are either heavily jointed, like granites, or have prominent bedding planes like limestone, the various mechanical processes outlined above can make masses of rock break down into large blocks.

Where rocks have a granular structure, different minerals will heat up and cool down at different rates during the diurnal heating and cooling cycle. This leads to individual particles of rock expanding and contracting at different rates, leading to individual grains being broken off.

9 a Deflation is caused by strong winds removing loose surface material and carrying it away from an area, uncovering the underlying rock structures. An example of one of the deflation hollows is the Qattara depression in Egypt, which is hundreds of square km.

b Abrasion is the process of sand-blasting. Sand and smaller particles are transported close to the surface by wind and driven against rock surfaces, carving them into a variety of shapes.

Ventifacts, rocks smoothed by wind abrasion, are common in deserts. Mushroom rocks have their bases undercut by abrasion to give them their characteristic shape. At a larger scale, yardangs are shaped by abrasion removing bands of soft rock that are lying at a steep angle.

10 Attrition causes desert sediment to become increasingly rounded. This means that the sediment is easily moved by surface creep until it reaches an area of deposition.

11 Saltation is the process whereby sand grains make a series of leaps and bounds across the desert surface. As one lands it disturbs other grains which are then picked up by the wind. It is associated with coarser sands and stormy conditions and only happens very close to the surface.

Arid landscape development in contrasting settings

12 A yardang is a streamlined parallel ridge of rock often described as resembling the upturned keel of a boat. Yardangs are aligned in the direction of prevailing winds and neighbouring yardangs are separated by a wind-scoured groove or trough. They reflect the underlying geology of alternating bands of resistant and less resistant rocks that dip steeply. The streamlined shape, with a rounded upwind face and long tapering ridge downstream, suggests that aeolian erosional processes are the dominant processes of formation.

Zeugen is the term that has come to collectively refer to features such as rock pillars, rock pedestals and rock mushrooms that exhibit considerable undercutting, often due to horizontal layering of resistant and less resistant rock.

14 Bagnold suggested that if a barchan dune formed by gentle winds from one direction moved into an area affected by stronger winds from a secondary direction, then one of its horns would be built up. After the stronger wind stops, the gentle winds would continue to elongate the horn until it came into the path of the other horn of the original barchan. Where these meet, the two sand flows would cause the dune to grow rapidly and develop a leeside slip face which would eventually give rise to a linear seif dune parallel to the resultant direction of the combination of the two sand- moving winds.

15 A wadi is a dry river bed which can be seen cutting across a variety of desert surfaces. Wadis are formed by ephemeral rivers that flow for a short time following intense rainfall. The lack of vegetation and the highly weathered surface layers mean that the rivers are charged with a great deal of sediment; this is deposited when the streams dry up. They vary greatly in size from just a few metres to hundreds of km.

 They tend to have broad, flat bottoms because of the build-up of sediment in them.

 The channels are highly braided, following the deposition of sediment in the channel.

 The sides are steep; the lack of vegetation makes them vulnerable to erosion from the fast-flowing sediment-charged water.

16 When wadis emerge from out of highland areas onto flatter, less confined slopes (a), an alluvial fan is formed (b). If there are several wadis, their alluvial fans coalesce to form bajadas (c).

17 Mesas, buttes and inselbergs are all examples of relic hills which are cut out and isolated by water erosion. Mesas and buttes are typical of areas with horizontally bedded sedimentary rocks. When eroded they are left with a resistant cap rock which determines their shape.

Inselbergs are rounded hills and it is suggested that they were formed during a time when there was a lot more water found in their area. They have then been shaped by present-day desert processes. Desertification

18 The areas at high risk are those on the margins of existing desert. The most extensive area is in the Middle East and central Asia though there are other large areas on the west side of continents (South and North America and southwest Africa).

Those at highest risk are, surprisingly, removed from the main desert areas. One example is the southern part of the Sahel region, which is more at risk than the area closest to the Sahara. This could be because although there may be more rainfall, the population pressure is such that the resources are rapidly becoming depleted.

19 During the course of the twentieth century, the average temperature rose by between 0.3°C and 0.6°C. Analysis of the consequences of this rise has led scientists to believe that temperatures in the drylands will rise by 2°C to 5°C every time the concentration of greenhouse gases doubles, a phenomenon expected to occur during the middle of the twenty-first century.

The general rise in temperature will predictably raise the rate of evapotranspiration, leading to a drop in soil humidity and an increase in the number of droughts. The deterioration in the condition of topsoil, particularly in the drylands, is a consequence of temperature variations, rainfall and soil humidity that exacerbate the process of desertification.

It is very difficult to predict rainfall patterns for any given region under consideration.

20 One-third of the Earth’s land area is subject to some level of desertification with over 10% being highly or very highly vulnerable. This means that unless there is a reversal in the trends, 15 million km2 will become unusable. A large percentage of the world’s population is affected, with 11% in the vulnerable to highly vulnerable classes. It does not match the land area because the more vulnerable the land is, the less dense the population.

Exam style questions (A-level) 1 Allow 1 mark per valid point with extra mark(s) for developed points. (4 marks)

Answer depends on the cause chosen. See question 3.

2 AO1, AO2, AO3: Level 2 (4–6 marks); Level 1 (1–3 marks)

Water, in the form of an exogenous river, has eroded vertically into the desert plain. The sides are steep because there is very little vegetation to hold loose material and reduce the angularity of the edges. There are different angles of slopes depending on the resistance of the rock and the amount of water flowing through the canyon at the time that it was being formed. In order for this to

be so deep, the rate of tectonic uplift of the land surface must have at least matched the rate of vertical erosion of the river, meaning that the river was constantly striving to reach a base level.

3 AO1, AO2, AO3: Level 2 (4–6 marks); Level 1 (1–3 marks)

The answer must only use information from the data. Data that are directly lifted and copied are not worth credit.

4 AO1, AO2: Level 4 (16–20) marks; Level 3 (11–15 marks); Level 2 (6–10 marks; Level 1 (1–5 marks); Level 0 (0 marks)

Since the middle of the twentieth century many countries have experienced significant population growth. As a result, the rate of population growth is often high: between 2% and 3% a year, meaning that, in certain countries, the population will double within the next 20 to 30 years.

Population growth has led to pressure on vulnerable land to support a greater number of people. This means that there has been an increase in four human activities that represent the most immediate causes: overcultivation exhausts the soil, overgrazing removes the vegetation cover that protects it from erosion, deforestation destroys the trees that bind the soil to the land and poorly managed irrigation systems turn croplands salty. Moreover, the lack of education and knowledge, the movement of refugees in the case of war, the unfavourable trade conditions of developing countries and other socioeconomic and political factors enhance the effects of desertification. The causes are multiple and interact in a complex manner.

Due to the lack of alternative survival strategies, farmers tend to relentlessly exploit natural resources (food crops, water for drinking and washing, firewood) to the point that they are overexploited and cannot regenerate naturally. Soil nutrients and organic matter begin to diminish as intensive agriculture removes quantities of nutrients greater than the soil’s natural regeneration capacities. As a consequence, the soil is unable to recover, as it does during fallow periods, resulting in an ever-increasing spiral of environmental degradation and poverty, the principal causes of desertification.

The increase in the demand for firewood is one of the principal causes of desertification. In tropical arid areas, wood is the principal source of domestic energy for cooking and lighting, in both rural and urban populations.

Topic 3 Coastal systems and landscapes Coasts as natural systems

1 Inputs into a coastal system include:

 energy from wind, waves, tides and ocean currents

 sediment either eroded from the local coastal rocks or transported from either offshore or along the coast

 the rock type and structure of the local geology

 sea-level change

Erosional processes such as hydraulic action and abrasion result in erosional coastlines and landscapes as well as eroded material. Attrition alters the eroded material by making it finer and less angular.

Sediment is transported by either water or wind until it reaches a low energy environment where it is deposited.

The outputs from the system are in the form of:

 wave energy dissipated by breaking along the shoreline

 sediment accumulation above high tide level

 sediment moved on to other sediment cells Systems and processes

2 When the wind starts to blow over the sea’s surface there is a certain amount of frictional drag. This energy is transferred to the water and creates ripples. As the wind increases in strength, the ripples get larger until they are large enough to be pushed along by the wind. The movement of the waves is slower than that of the wind and so they increase in size until they become steep enough to break. Swell waves are caused by a combination of wind and atmospheric pressure changes. They travel away from their source areas and reflect the length of time, the wind strength and the distance that the wind has blown over the sea.

5 Constructive waves have a powerful swash compared to the backwash. The swash carries material up the beach in the turbulent water. Because the backwash is so weak, this material is left on the beach. Although they occur on gently sloping beaches, they cause the beach to steepen.

Destructive waves are plunging. They occur on steeply shelving beaches so that the orbits are not greatly disturbed. The force of the breaking wave is directed downwards and so although it seems

powerful, the swash does not go far up the beach and the backwash is strong. Sand and shingle are taken from the beach and moved offshore.

6 Fistral and Tregurran beaches are open to the west, though Tregurran is also open to the SSW, the most dominant wind direction. It is on these beaches where you are most likely to encounter big waves. Harbour beach is sheltered by Towan Head and although it is sheltered, wave refraction will bring waves onto the shore. It would be good for beginners. Crantock beach is sheltered from all but north to northwest winds. If the wind blew from the NW it may have large waves, but at other times small refracted waves would again make this ideal for beginners.

8 The movement of sand and shingle in the nearshore zone by longshore drift has been found to occur in discrete, functionally separate sediment cells. Within these cells the movement of coarser sediment is largely self-contained.

9 One example is Flamborough Head to The Wash (sediment cell 2). It is divided into four sub-cells. The most northerly is Flamborough to the Humber estuary. Most of this consists of boulder clay cliffs to the north and a spit (Spurn Head) to the south. Longshore drift operates, moving sediment from north to south. Sediment leaks out of the sub-cell and crosses the mouth of the Humber to sub-cell 2c, the Lincolnshire coast.

Where Lincolnshire meets the sea is overwhelmingly flat. In the north of the county, the Humber Head Levels and the reclaimed Lincolnshire Marsh are pretty much at sea level, while in the south the Fens give way to salt marshes.

There are 50 km of sandy beaches along the coast. The rivers Great Eau, Lud, Nene, Steeping, Welland and Witham all drain into the North Sea from Lincolnshire, as well as the Humber. Owing to the combined sediment carried by the Humber and the rivers of the Wash, and to the muddy clay sea floor, the waters off Lincolnshire are usually an opaque brown.

10 The main sources are:

 erosion from cliffs

 silt from rivers AQA Geography Workbook Physical geography 17

 sediment brought along the coast by longshore drift

11 Freeze–thaw weathering is a form of physical or mechanical weathering that induces stress on rocks when water repeatedly seeps into cracks, freezes and expands, eventually causing the rock to break apart. This type of weathering is largely driven by the intensity and frequency of freeze– thaw cycles and the structural properties of the rocks subject to weathering.

On coastlines, this happens above the level reached by waves. Sea water has a lower freezing point than rainwater and so rarely freezes on UK coasts.

The mild winters of southern and western Britain, contributed to by the relative warmth of the sea water (and the North Atlantic Drift) mean that any form of frost action is rare. North Sea coasts are less affected by the warming influences and so frost action is more common.

12 A common type of mechanical weathering found at coasts is salt crystallisation. This is when sea spray wets rock and some of the water soaks into the rocks. When the water evaporates, small amounts of crystalline salt are left behind between the grains of the rock. If this process is repeated, the rock becomes weakened and begins to disintegrate. This granular disintegration means the rock is subject to other weathering and erosion processes.

13 Carbonation is the breakdown of carbonaceous rocks (chalk and limestone) by acidic rainwater. Therefore you need a chalk or limestone coast where there is plenty of rock above the level of the waves. The sea (which is alkaline) does not dissolve limestone except under very special circumstances.

14 An example of slumping has occurred at Overstrand, Norfolk. Slumps happen because of a number of factors. First, marine processes erode and undermine the base of the cliff. Rainwater infiltrates the cliff through unconsolidated boulder clay. The water gathers at the base of the clay where there is a layer of chalk. As more water is added, the clay becomes heavier. A curved slip plane develops and the weight of the saturated clay causes the material to slump along the lubricated slip plane. There is historic evidence of cliff recession as a result of marine erosion and landslides since the late nineteenth century. Cliff retreat has averaged 1.5–2 m per year. A major event in January 1994 resulted in 20 m of recession at the cliff top with debris runout across the beach.

15 In addition to the movements of beach material up and down the foreshore by swash and backwash, material moves along the beach. Sediment is moved along beaches by waves breaking at an angle to the shore. The material is pushed up the beach at an angle to the shore, but when it returns in the backwash, it does so down the steepest gradient, at right angles to the shoreline. Each particle therefore moves in a zigzag fashion.

16 Sand grains bounce or ‘saltate’ slightly above the surface when blown by the wind. With each bounce, the grains usually reach heights of less than 5 cm above the surface, and move horizontally 5–10 cm. The average distance a grain bounces is the width between the crests of two ripples in the sand. Saltation accounts for about 95% of a sand grain’s movement.

Onshore winds will dry out sandy beaches that are exposed at low tide. Sand is blown onshore. In natural circumstances this could produce coastal dunes. Where there is infrastructure along the coastline (roads, railway lines, promenades) then they may be regularly covered by blown sand. This will need to be removed.

Traction involves the ‘rolling’ of sand grains along the beach surface. It occurs with lower wind speeds or coarse sand. Coastal landscape development

17 a The base of the cliffs on this headland is attacked by waves. Waves are concentrated on the headland because of wave refraction. The waves can pick up loose material at the base of the cliffs and hurl it at the cliffs. These chip away and undercut the cliff. The sheer weight of the water in waves hitting the cliff sends hammer-blow shocks through the rock, creating openings along lines of weakness such as joints, faults and bedding planes.

As each wave hits the cliff, air trapped in the cliff is compressed. As the wave recedes, this air expands explosively, again opening up weaknesses.

Where lines are opened up, caves appear. If the cave occurs on a headland, then it can cut through the headland to form an arch.

Constant undercutting of the cliff leads to a notch at the base of the cliffs. If this becomes sufficiently deep, the cliff above becomes unsupported and collapses. This leads to cliff recession and the wave-cut platform.

b Stacks are formed when arches collapse. This happens when:

 undercutting of the sides of the arch continues, making it wider and less well supported

 weathering occurs at the top of the arch, making it become structurally weak

 gravity causes the top of the arch to collapse

18 The main features of a beach

19 One example is the spit at Dawlish Warren:

20 Sand dunes are sometimes found at the top of beaches, above the high tide mark, but not every beach has dunes. For dunes to form there must be a supply of sand, a means of transporting it, and somewhere for it to be deposited more quickly than it is eroded.

At low tide, deposits of sand in the inter-tidal zone (between the high and low tide marks) may be exposed and start to dry. The dry grains of sand can then be transported by the wind (by saltation). If the wind blows towards the land, sand will be transported up the beach and beyond the high tide mark.

When the dried sand reaches the top of the beach it can be trapped by debris such as driftwood, dead seaweed or rocks and pebbles. If the sand is not eroded again it may become colonised by small plants, or trap other windblown debris, increasing its size and thus trapping even more sand.

As the dunes grow in size they are able to catch more of the sand blown across them by the wind. This causes the wind speed to lessen and the sand grains are deposited. Vegetation such as marram grass colonises the dunes. Its long net-like roots hold the sand in place and the stems slow down the wind, allowing deposition.

Most dune areas consist of parallel rows of dunes. They increase in age, height and species diversity inland.

The dunes reach their maximum height where they are fixed. Further inland they become smaller as their source of material is blocked by younger dunes. These become a grey colour from the amount of dead organic matter that is added to the sand.

21 Salt marshes only form in low energy environments where there is shelter from the wind and waves. Depositional landforms such as spits can help provide this shelter. Salt marshes require a large input of sediment, which can arrive from the sea and rivers. The most likely place along a coastline where you will find this sort of sediment input is near a tidal flat. The low gradient of a tidal flat means that any rivers that flow into it will very quickly deposit any sediment they are transporting. At the same time, the periodic flooding of the tidal flat by the tides will deposit even more sediment.

Over time, sediment accumulates and the elevation of the tidal flat increases in a process known as coastal accretion. This reduces the duration of tidal flooding, allowing a small selection of plants to grow on the now developing salt marsh. These plants are halophytic — they love salt — and are capable of surviving underwater for several hours a day. They are often called pioneer species because of their hardy nature, able to live in extreme conditions. These plants, which include species of cordgrass (Spartina) and glasswort (Salicornia), have several adaptations that not only help them thrive in saline environments but also help aid coastal accretion.

The vegetation traps sediment that is too fine to settle out of water in a salt marsh, building up a muddy substrate. At the same time, the roots help stabilise already deposited sediment, aiding coastal accretion. Pioneer species such as Spartina alterniflora are invasive plants that spread rapidly. Once these plants are introduced to a salt marsh, coastal accretion takes place quickly and the elevation of the salt marsh increases greatly. This creates new environments that are submerged by the tide for shorter periods of time, allowing even more species of plants and animals to colonise the salt marsh.

22 Example of a fjord:

Coastal management

23 Depends on the coastline chosen. Hard defences include sea walls, revetments, diodes, groynes, rock armour, offshore reefs etc.

Goals will be based on reduction of damage balanced with the cost of the scheme.

24 Depends on the scheme chosen. Sustainability will depend on cost/benefits, environmental impacts, success (or otherwise) of the scheme.

Weathering weakens rocks and makes them more susceptible to erosion. Arches collapse because the tops are weathered. They are far from the reach of marine processes. Biological weathering can include burrowing into clay cliff which gives access to water and increased mass movement.

This is an area of coastal emergence. There are two raised beaches which indicate three periods when sea level remained static. The oldest surface is at the top of the cliffs. Below that is a raised beach backed by cliffs. This was formed as sea levels dropped and then stayed still for enough time to erode the caves and wave-cut notch. Old beach deposits are strewn on the low-angled surface. The sea level dropped again to its present level, eroding a new cliff into the old platform.

Sea-level change can produce many features along coastlines. We can categorise these features based on how they are formed.

Emergent landforms

Emergent landforms begin to appear towards the end of an ice age and they occur when isostatic rebound takes place faster than a eustatic rise in sea level. Put more simply, the land’s height rises faster than the sea’s. Emergent features are features of coastal erosion that appear to have developed well above the current sea level. In fact, they developed when the sea was at that level and then the sea level changed during an ice age and now they are above sea level.

One such emergent landform is a raised beach. Raised beaches are wave-cut platforms and beaches that are above the current sea level. You can normally find some old cliffs (relic cliffs) too behind these raised beaches with wave-cut notches, arches, stacks etc. along them.

These emergent features no longer experience coastal erosion but they are still weathered, often being weathered biologically, chemically and via freeze–thaw weathering.

Submergent landforms

Submergent landforms are the opposite of emergent landforms. They form when the eustatic rise in sea level takes place faster than the isostatic rebound after an ice age. Basically, the water starts to flood the land and fills up landforms on the land.

One submergent feature is a ria. This is a river valley that has been flooded by the eustatic rise in sea level. Rias are almost exactly like typical river valleys but they have even more water in them. The cross section of a ria is similar to the one you would find for a river in the lower course. The floodplain of the river also gets flooded, altering the cross profile of a ria ever so slightly so that it includes the floodplain.

Another submergent feature is a fjord. Fjords are steeper and deeper variants of rias that are relatively narrow for their size. They have a U-shaped cross profile and are often found in particularly icy sections of the world. They are flooded glacial valleys. In general, fjords are really deep — however, they have a shallow mouth (known as a threshold) as this is where the glacier deposited its load. An example of a fjord is Sognefjord in Norway, which is 1,308 m deep and 205 km long, though its maximum width is only 4.5 km.

The final submergent feature is a Dalmatian coastline. These form in areas of the world where valleys (especially glacial valleys) lie parallel to each other and to the coastline. When the valleys are flooded by the rise in sea level, the tops of the valleys remain above the surface of the sea and appear to be a series of islands that run parallel to the coastline. The best example of a Dalmatian coastline is the one from which they get their name, the Dalmatian coast in Croatia.

4 AO1, AO2: Level 4 (16–20) marks; Level 3 (11–15 marks); Level 2 (6–10 marks); Level 1 (1–5 marks); Level 0 (0 marks)

Depends on the example chosen. Good examples include the Sundarbans of India and Bangladesh. Risks include the increased likelihood of encountering cyclones and coastal flooding. On the plus side there are opportunities for eco-tourism, particularly as this is one of the last places on Earth with wild tigers.

Eustatic sea-level change occurs when the total volume of sea water changes. This can be either because of:

 an interruption of the hydrological cycle, meaning that water is evaporated from the oceans and precipitated on the land where it stays, usually because it falls as snow

Or because:

 volume can change because of thermal expansion/contraction. If the oceans warm up, they will expand and have a greater volume. If they cool, the opposite happens.

6 AO3: Level 2 (4–6 marks); Level 1 (1–3 marks)

Hurlstone shows both a greater amount of sorting and greater roundness. The pebbles have been affected by transport (longshore drift) and attrition from West to East.

b Spearman’s rank

The base of the cliffs on this headland is attacked by waves. Waves are concentrated on the headland because of wave refraction. The waves can pick up loose material at the base of the cliffs and hurl it at the cliffs. These chip away and undercut the cliff. The sheer weight of the water in waves hitting the cliff sends hammer-blow shocks through the rock, creating openings along lines of weakness such as joints, faults and bedding planes.

As each wave hits the cliff, air trapped in the cliff is compressed. As the wave recedes, this air expands explosively, again opening up weaknesses.

Where lines are opened up, caves appear. If the cave occurs on a headland, then it can cut through the headland to form an arch.

Constant undercutting of the cliff leads to a notch at the base of the cliffs. If this becomes sufficiently deep, the cliff above becomes unsupported and collapses. This leads to cliff recession and the wave-cut platform.

8 AO1, AO2: Level 4 (16–20 marks); Level 3 (11–15 marks); Level 2 (6–10 marks); Level 1 (1–5 marks); Level 0 (0 marks)

There are a variety of ways of approaching this question.

One example is that globalisation leads to increasing world trade. In order for this to be enabled there need to be deep-water ports to handle ever-larger ships. These ports take up a lot of land, most of it sterile regarding wildlife and so not very sustainable. Some ports, e.g. Liverpool, do include nature reserves which are usually out of bounds to the general public and so go largely undisturbed.

Another example is the creation of prawn hatcheries in Bangladesh and Myanmar to supply increased demand for luxury foods in NICs. These necessitate the removal of coastal mangrove forests and leave the coastline susceptible to cyclone damage.

Topic 4 Glacial systems and landscapes Glaciers as natural systems

1 Aspect, the direction that a slope is facing, has a major influence. This is further affected by the angle of slope. In the northern hemisphere the sun moves from E to W in the southern sky and so slopes facing SE to SW receive more sunshine and warmth, especially if there are slope angles of 20–40 degrees. Slopes facing NE to NW, conversely, receive little direct sunlight, often only in the early morning or the evening. These are colder. This allows snow to build up.

2 Weathering is the process of decomposing and breaking up of rocks in situ. Weathering may be caused by the action of water, air, chemicals, plants or animals. Chemical weathering involves chemical changes in the minerals of the rock, or on the surface of the rock. Mechanical weathering is the process of breaking a large rock into smaller pieces without changing the minerals in the rock. Mechanical weathering may be caused by frost action. Once the rock is weakened by weathering, it may start to be moved by ice or water. When the smaller rock pieces are removed from their original location then it is called erosion.

3 Rock fragments that are embedded in the base of a moving glacier are integral to the process of glacial abrasion. The glacier acts like a giant piece of sandpaper. Abrasion deepens valleys, smooths rock faces and creates striations. Transported rock fragments are eventually deposited either by ice to form various types of moraine or by water to form fluvioglacial deposits. The nature and distribution of cold environments

4 a Glacial areas are those places that are permanently covered by ice. An ice sheet is a mass of glacial land ice extending more than 50,000 km². The two major ice sheets on Earth today cover most of Greenland and Antarctica. During the last ice advance, ice sheets also covered much of North America, northern Europe and Argentina.

b Alpine areas include some ice caps and alpine glaciers. They are usually found in mountainous areas. Ice caps tend to be dome-shaped and are centred over the highest point of an upland area. They flow outwards, covering almost everything in their path and becoming the major source for many glaciers. Ice caps and glaciers occur all over the world in mountainous areas such as the Himalayas, the Rockies, the Andes and the Southern Alps of New Zealand. The Furtwangler Glacier on Kilimanjaro, at 60,000 m², is Africa’s only remaining ice cap. It is melting rapidly and may soon disappear.

c The global extent of the tundra biome accounts for roughly 10% of Earth’s surface. The southern limit of Arctic tundra follows the northern edge of the coniferous forest belt. In North America this line lies above latitude 60°N, while in Eurasia most of it occurs north of 70°N — except in eastern Siberia, where it extends southwards to 60°N in Kamchatka. The northward

bulge of forest in Eurasia is a result of the warmer summers that occur over that large contiguous landmass.

Alpine tundra covers approximately 3% of Earth’s land surface, and it is mostly found in the northern hemisphere. This habitat can be found in mountainous areas worldwide, occurring at high elevations where temperatures are too low and winds are too strong for the growth of trees. The average elevation where alpine tundra occurs is generally higher near the equator than at the poles.

Because nearly all of Antarctica is covered with ice, it lacks a well-developed tundra, though lichens, mosses and at least three species of flowering plants occur in more favourable habitats there.

5 All of Greenland and Iceland were once covered, whereas now Iceland has an ice cap and the southern coastline of Greenland is ice free. In the past all the Canadian Arctic islands were covered in ice, whereas now there are just remnants found on Baffin Island. In North America the ice extended south of the Great Lakes, into what is now the USA. Its furthest extent was in the central eastern part of the continent. In Eurasia two main ice sheets covered all of Scandinavia, extending as far south as southern Britain. There were also isolated ice sheets following a line from the Atlas Mountains to the Pyrenees, the Alps and the Balkans. In central Asia there were isolated ice sheets extending as far south as present-day India and Pakistan.

6 Both climates have extremely low precipitation levels, approximately 100 mm, but Eismitte has a winter maximum and Barrow a late summer maximum. Eismitte is constantly below 0°C, being at its warmest in late summer. The temperatures at Barrow exceed 0°C for approximately 2.5 months from June to August. Eismitte gets much colder than Barrow, going down to −50°C in late winter whereas Barrow only drops to −28°C at more or less the same time.

Systems and processes

9 If precipitation adds more mass to a glacier than melting and sublimation remove, the total volume of the glacier increases. As a result, the glacier grows, extending farther down the valley than it did previously. This is called an advance.

When glaciers melt faster than they are replenished by precipitation, the total volume of ice decreases. The glacier shrinks. This is called a retreat. The glacier is not actually retreating or physically moving up the valley. It just appears to do so, since the glacier does not extend as far down the valley as it did previously.

The rate of melting depends on the temperatures. In the past, as it grew colder, ablation was reduced. If precipitation began to exceed the ablation then advance occurred. Conversely, if it got warmer then melting at the snout would occur and the mass of ice would be reduced, leading to retreat.

10 Warm-based, or temperate, glaciers tend to be found in more temperate maritime locations. Good examples of this include the western coastal mountain ranges of North America, western Norway, southern Iceland, New Zealand and Patagonia (Chile). Here the alpine valley glaciers of the European Alps are included in the warm-based category. These tend to be small valley glaciers typically ranging from hundreds of metres to a few kilometres in width and hundreds of metres to tens of kilometres in length.

Cold-based or polar glaciers by definition are almost all found in areas of high latitude within the Arctic and Antarctic circles, in especially cold areas of Alaska, Canada and Antarctica. Here cold- based glaciers include some very cold valley glaciers but also refer to the much larger glaciers associated with the vast ice caps and ice sheets covering hundreds of km².

Warm-based glaciers are found in places with high winter snowfall rates and spring and summer temperatures high enough to create rapid summer melt rates. The vast amounts of meltwater act

as a lubricant and allow the glacier to be far more mobile than cold glaciers. The faster rates of glacial movement mean that warm-based glaciers are more likely to erode, transport and deposit material. At the surface the thin layer (a few metres) of more recent snow and firn is subject to seasonal temperature fluctuations, so it melts rapidly at around 0°C in the summer melting. This surface layer insulates the layers of ice beneath it. With increasing depth in a glacier the ice is under ever-increasing pressure from the surrounding ice, which has the effect of lowering the melting point of the ice. This is known as the pressure melting point. For example, at the base of a 2,000-m-deep glacier the melting point of the ice is −1.27°C. All ice in a temperate glacier is at or near the melting point because of the warmer atmospheric temperatures, the weight of the ice above, and, as temperate glaciers may be relatively thin, a greater proportion of the ice is influenced by geothermal heat at the bed. Cold glaciers are generally found in places with low precipitation rates, even arid conditions, so receive little new snow each year and accumulation rates are low. There is little or no melting of ice in cold glaciers and so the ice can be very old, with the ice at the base of some Arctic and Antarctic ice sheets dating back around 100,000 years BP.

All ice, except the uppermost surface layers that can be exposed to summer atmospheric temperatures of above 0°C, is below the melting point. There is little meltwater associated with these glaciers as atmospheric and subglacial (geothermal) heat sources are not great enough to reach melting point. Other than limited melting of the surface in summer, the majority of ice loss is due to sublimation and the calving of icebergs/blocks.

Movement in cold-based glaciers is much slower than in temperate glaciers as they are often frozen to their beds, thus most movement is due to internal flow. Much less erosion, transportation and deposition occurs.

11 Frost action or freeze–thaw weathering is a form of physical or mechanical weathering that induces stress on rocks when water repeatedly seeps into cracks, freezes and expands, eventually causing the rock to break apart. This type of weathering is largely driven by the intensity and frequency of freeze–thaw cycles and the structural properties of the rocks subject to weathering.

Freeze–thaw does not occur during periods of intense cold. It is much more common in periglacial conditions where there are daily or seasonal cycles.

Frost action contributes to the development of glacial landforms in several ways:

 It is part of the nivation process that deepens nivation hollows, leading to conditions which may develop into a corrie.

 It weakens rock so that if glaciation occurs, plucking of rock fragments is enabled.

 It steepens the back walls of corries and the sides of arêtes. This could lead to pyramidal peaks.

 It provides material at valley sides for lateral moraine.

 Some of the lateral moraine can reach the base of the glacier and act as tools of abrasion, deepening the floor and forming striations.

12 In periglacial areas the snow melts in summer. However, in locations sheltered from the sun and warming winds, snowbanks may remain all year. Beneath the snow, nivation occurs. Meltwater goes under the snow patch and repeated freeze–thaw cycles cause the regolith to slowly break up. This, and a certain amount of chemical weathering, causes the rock to slowly disintegrate.

Summer meltwater flushes out the remaining debris and the snow slowly ‘eats’ its way into the slope, forming a nivation hollow. No ice movement (and so no erosion) occurs.

13 a Internal deformation: this is the slow creep of ice due to slippage within and between the ice crystals. The rate of internal deformation is greatest at the base of the glacier where pressures are at a maximum. This type of flow can occur in both polar and temperate glaciers.

b Basal sliding involves the sliding of a glacier over its rocky base. The sliding is accomplished in three ways.

Basal slip: when a thin layer of water builds up at the ice–rock interface and the reduction in friction enables the ice to slide forward.

Enhanced basal creep: when ice squeezes up against a large (>1 m wide) bedrock obstacle the increase in pressure causes the ice to plastically deform around the feature.

Regelation flow: when ice presses up against a small obstruction the pressure on the ice is increased to the point that it reaches the pressure melting point. The ice melts and water flows around the obstruction to a zone of lower pressure. The water immediately refreezes.

c Bed deformation: this is movement accomplished by the deformation of soft sediment or weak rock beneath a glacier. It is more effective beneath temperate glaciers, since the underlying sediment and rock will be saturated with water, which in turn reduces the strength of these materials. In contrast, the absence of water at the base of polar glaciers limits the effectiveness of bed deformation, and movement within these cold-based glaciers is mainly by internal deformation.

14 Compressional flow occurs where there is a reduction in the gradient of the valley floor, leading to deceleration and a thickening of the ice mass. At such points ice erosion is at its maximum.

Extensional flow occurs when the valley gradient becomes steeper. The ice accelerates and becomes thinner, leading to reduced erosion.

16 Plucking occurs on the sides and back walls of glaciers. Small amounts of meltwater seep into the rocks. This is facilitated by the rock being previously weakened by weathering. The water freezes in the bedrock, expanding and weakening it. This can go on for some time. Eventually the rock is sufficiently weakened that, as the glacier moves away from the rock, it pulls out fragments with it. These fragments can go on to act as agents of abrasion.

Glacial abrasion is the surface wear achieved by individual pieces of rock material contained within ice or by subglacial sediment sliding over bedrock. Abrasion can involve polishing by silt-sized material; scratching, producing grooves; and striations. It largely occurs at the bottom of warm- based glaciers and deepens/overdeepens valleys and hollows.

17 Glacial meltwater streams are the same as all rivers inasmuch as, when they lose energy, they deposit their load of rocks. With meltwater this can occur in a number of scenarios:

 Rocks are deposited where streams flowing over the surface of a glacier find their way down a moulin (hole in the ice) and fall to the bottom of the glacier. The sudden loss of energy at the base allows the build-up of sediment called a kame.

 Streams within the ice have high energy in summer because of the amount of meltwater and the fact they are contained by the ice. In winter the amount of water falls as there is less melting and material is dropped where the stream bed was. This eventually forms an esker.

 Where a meltwater stream runs out of a glacier at its snout, there is a sudden loss of energy and a mound of material builds up, often being supported by the ice. This is a delta kame.

 If meltwater streams occur along the sides of the glacier, trapped between the rock wall and the ice, linear deposits called kame terraces occur.

 Where meltwater streams reach beyond the immediate environs of the snout, material is dropped in braided streams. These eventually coalesce to form outwash plains.

18 Continuous permafrost extends to below 400 m in the coldest regions (temperatures of −40°C) and gets increasingly shallow as the mean annual temperature increases. At the limit of continuous permafrost, the depth is up to 45 m. The discontinuous permafrost can reach depths of approximately 40 m, whereas the sporadic permafrost does not go below 12 m.

19 First of all, it has nothing to do with the length of time the ground remains frozen. Permafrost is permanently frozen ground. It is the distribution of it that is different. Continuous permafrost has no gaps. Sporadic permafrost has small gaps within a much greater amount of permafrost. These gaps may be found under lakes and rivers. Sporadic permafrost has more unfrozen ground than frozen. It is often found in mountains where there are areas shaded from the sun.

20 Solifluction is the flow of water-saturated regolith down a steep slope. It is common because permafrost is impermeable to water — regolith overlying it may become oversaturated by spring snowmelt and slide downslope under the pull of gravity. If it has been opened and weakened by frost action, it is most susceptible. Movement is at a maximum rate of a few mm per day, eventually producing smooth, gentle, concave slopes. Original stratification of the regolith becomes contorted, if not completely destroyed.

Glaciated landscape development

21 If corries occur back to back, they can form an arête, made steeper by the continuous frost action on the back walls. If three corries occur back to back, then a pyramidal peak can be formed.

22 A river-cut valley will tend to be V-shaped with interlocking spurs. A glaciated valley will have much steeper sides with vertical slopes in areas. There may be truncated spurs. The bottom of the valley will be wide and flat, sometimes with a layer of post-glacial alluvium forming a thin veneer. The glacial valley may have some overdeepened hollows where there are ribbon lakes. The sides of the valley sometimes have talus cones and alluvial fans where post-glacial modifications have changed the shape.

23 Roches moutonnées are landforms found in the bottom of glacial troughs. They are formed from a particularly resistant part of the valley floor. As a glacier flows over the lump of rock, the upstream side is polished by abrasion, with it sometimes having striations scratched into the smooth surface by particularly big rocks in the base of the ice. This process of abrasion is aided by meltwater. The

meltwater is present because the increased pressure of the ice on the upstream side causes the ice to reach its pressure melting point temperature. This water runs over the top of the obstacle, reaching a lower pressure area downstream. Here the water refreezes. This can occur in cracks in the rock and so plucking occurs on the lee slope, causing it to become jagged and steep.

24 Lateral moraines are found deposited along the sides of a glacier and have been formed from material that has dropped onto the glacier from above following frost action on the valley sides.

Medial moraine is simply a line of rock fragments found in the body of the glacier parallel to the flow. They are formed when two glaciers meet and their lateral moraines merge.

Terminal moraines are found at the furthest point reached by a glacier. They are deposited as a ridge parallel to the snout. They are usually the largest of the moraine ridges and represent a location where the glacier stood still for some time, bringing moraine down within the ice.

Recessional moraines are similar to terminal moraines but smaller. They are formed when there is an interruption in the retreat of a glacier so that the snout stays in one place for long enough for a low ridge to be formed.

Ground moraines are disorganised piles of rocks of various shapes and sizes and of differing rock types found across the valley floor where a glacier has been.

25 Drumlin shape and measurement:

26 Pro-glacial lakes are formed where the flow of a pre-glacial river is dammed by advancing ice. If the river continues to flow, water will accumulate in between the ice front and surrounding highland. Eventually, the lake will get to a sufficient depth that it overflows through a low point in the surrounding hills (a col). Once the lake begins to overflow, the meltwater stream produced erodes rapidly downwards, making the flow more powerful as it is fed from the lake. Rapid downward erosion leads to a steep-sided gorge called a glacial spillway. Examples of this include Ironbridge Gorge and Kirkham Abbey Gorge.

27 The repeated cycles of freezing and thawing of the active layer can produce a range of landforms collectively referred to as patterned ground. The main process involved is known as frost heave.

Cold penetrates the active layer from above. As the active layer starts to freeze, ice crystals begin to develop. They increase the volume of the soil and cause an upward expansion of the soil surface.

Frost heave is most significant in the fine-grained material and as it is uneven it forms small domes on the surface. Within the fine-grained material there are stones which, because of their lower specific heat capacity, heat up and cool down faster than the surrounding finer material. Cold

penetrating from the surface passes through the stones faster than through the surrounding material. This means that the soil immediately beneath a stone is likely to freeze and expand before other material, pushing the stone upwards until it reaches the surface.

28 Ice wedges begin as small cracks, less than 5 cm across, but over hundreds of years can reach over 10 m wide and extend many metres into the ground. In periglacial landscapes these result from ground contraction due to extreme cold, generally in areas of continuous permafrost.

During the winter the freezing of the soil in the active layer causes the soil to contract. In the following summer the initial small crack is filled with meltwater (called an ice vein when it freezes). The following winter the water freezes and expands, forcing the earth parallel to it up into small ridges. As the temperatures fall even further, contraction of the ground occurs again. This process occurs repeatedly through the cycle of winter and summer, widening and deepening the crack to eventually form the ice wedge. These form polygonal nets. The land within the nets is often lower than that above the sub-surface ice wedge. These depressions become marshy areas or ponds in summer.

29 A pingo is a conical hill typical of the Mackenzie Delta in Canada. It is an ice-cored mound in regions of continuous and discontinuous permafrost. Pingos are true permafrost features as they grow below the active layer where the annual freeze–thaw cycle operates.

The pingos of the Mackenzie Delta are almost all of the hydrostatic variety. Pingos can be up to 70 m high and 600 m in diameter.

Mackenzie Delta pingos often start as thaw lakes in areas of continuous permafrost. The deepest of these lakes (those of more than 3 metres in depth) survive during the winter under an insulating cap of ice, and are underlain by a lens of unfrozen ground due to the thermal insulation of the lake.

During the summer these lakes expand and if they break through the high ground around them, they are often drained very rapidly, sometimes in no more than 24 hours. Once the lake is drained, a layer of permafrost develops on top of the unfrozen talik, so that it is now closed and surrounded by permafrost on all sides. As the permafrost gradually advances, the remaining water in the talik is pressurised due to freezing and expansion of the newly formed ice. This water is then expelled in the direction of least resistance, and it starts to dome up the relatively thin permafrost layer on top of the talik, where it slowly freezes to form the solid ice core of a pingo. As it rises, the ground above it can be cracked by stretching to give a breach in the top of the pingo.

A closed-system pingo

30 Permafrost is insulated from higher surface temperatures because of the layer of snow and/or light-coloured vegetation that has a high albedo and reflects sunlight. If the layer of vegetation is destroyed, or anthropogenic heating penetrates into the permafrost, then this will cause it to melt. If the rocks are solid, or are sands and gravels, this may not make a great deal of difference to the surface. If the rocks below are unconsolidated or are riven by big ice wedges then there will be surface collapse, leading to a series of hollows in the landscape that become full of water. This melting will also release methane gas into the atmosphere. Methane is a powerful greenhouse gas and could lead to increasing the enhanced greenhouse effect.

Supraglacial: Material that falls onto the ice from above is carried on the surface of the ice.

Englacial: Some of the supraglacial moraine along with plucked rocks gets incorporated into the body of the ice.

Subglacial: Rock fragments find their way down to the base of the ice where they are dragged along between the ice and the underlying rock.

The furthest extent was at the mouth of Glacier Bay into Icy Strait in 1760–80. In the next 14 years the ice had retreated approximately 7 km. The retreat continued at approximately 0.5 km per year until 1860. In the Tarr Inlet this speeded up to approximately 1 km per year until 1912, by which time the ice had retreated a total of 95 km.

The retreat in the Muir Inlet was much slower than in the Tarr Inlet in that it was not until 1966 that the ice had retreated 95 km.

The Queen Inlet has seen some advance.

There has been a definite warming since the eighteenth century, leading to retreat. Since the turn of the twentieth century, the retreat is not straightforward and so other factors must have come into play.

Periglaciation means ‘on the fringe of glacial areas’. Thus if ancient periglacial features are found then they must at one time have been close to the ice limits when they were formed. This is true of southern England where, for example, the tors of Dartmoor show that when they were formed the ice front could not have been too far away.

Other, more recent, periglacial landscapes have emerged as the ice has retreated and exposed frozen surfaces. Thus the stone polygons and stripes of the Stiperstones in Shropshire were formed since the last ice advance.

We have to be careful, however. In the 1970s many fossil pingos were mapped in two clusters, one in west Wales and the other in Norfolk. Many of these have now been proven not to be pingos.

4 AO1, AO2: Level 4 (16–20) marks; Level 3: (11–15 marks); Level 2: (6–10 marks); Level 1: (1–5 marks); Level 0: (0 marks)

The answer depends on the examples of globalisation used. For example, oil and gas exploration in N Russia, while Facebook — a media TNC which is driving social and cultural globalisation — has chosen a cold environment in Luleå, Sweden as the site for its newest data-storage facility (called a ‘server farm’). Google also has its own cold-climate data centre in Greenland.

The timber industry in Canada and the USA feeds the demand for building material or wood pulp for paper.

The best way to approach this question is to take two examples and give details of how those two have affected cold environments and then extrapolate from there.

A dynamic equilibrium occurs when a system displays unrepeated average states through time. With glaciers, the inputs are changing all the time. This can be on an hourly scale, but also seasonal, annual etc., thus the mass of ice is changing all the time. It may increase or decrease depending on the balance between the changing inputs and the outputs.

Figure 4.10 shows that the ice melt for 2015 is much greater than the average for 1981–2010. At its peak it is more than twice that of the average and beyond all but 2.2% of previous melts. Figure 4.11 shows that between 1979 and 1994 the melt extent was below average but after 1996 it was above average. The greatest extent was in 2012 when it was 300,000 km2 above average. This did fall in 2013 but then started to rise again.

Figure 4.12 shows that the rate of increase was greatest for 2012, but this was closely followed by 2015. Reasons for this are probably rising global temperatures, and Atlantic weather patterns.

Pre-glacial processes include nivation. The main corrie containing Llyn Cau would not have occurred unless it had originally been deepened by nivation. During glaciation there would have been a corrie glacier. This would have had a huge effect on deepening the hollow and causing the back wall to retreat. At the same time, frost action above the corrie glacier would also have caused retreat. This would have occurred on other corries surrounding the summit to produce the pyramidal peak and radiating arêtes.

The hanging valley would have been carved by the relatively small corrie glacier so that it did not overdeepen it to the level of the main valley glacier below.

Since glacial retreat, frost action has continued on the back wall, causing the creation of the scree slopes.

This depends on the case study chosen. Greenland has new mining opportunities as previously buried deposits are revealed by the ice melt. On the other hand, the fishing industry has taken a hit because the surrounding waters are less saline.

The Inuit of N Canada are struggling as the winter arrives later and the sea freezes later. This stops them being able to hunt and replenish meat stocks for the whole year. On the other hand, AQA Geography Workbook Physical geography 36

the melting of the sea ice has enabled access by sea and so links to the outside world should be greater.

Answers should include at least two challenges faced by a community and at least two opportunities. Describe these, state how they are linked to climate change and then come to a conclusion as to whether people are better or worse off because of the change.

Topic 5 Hazards The concept of hazard in a geographical context

1 The relief phase includes the immediate response, where the focus is on saving lives and property. Teams such as Médecins sans Frontières arrive from outside the immediate area to help with search, rescue and care operations. Urgent medical supplies, rescue equipment, clothing and food may be brought in.

2 The rehabilitation phase may last for several months. It is where efforts are made to restore physical and community structures, at least temporarily.

The reconstruction phase is when permanent changes are introduced to restore the quality of life and economic stability to the pre-disaster level or better. This can also include mitigation and preparedness — reducing vulnerability.

3 Characteristic human responses include:

 Fatalism: people view hazards as natural events that are accepted as inevitable. They stay within a hazardous area, e.g. those living in the shadow of volcanoes. San Salvador volcano, in El Salvador, has more than 500,000 people living within 10 km of its summit.

 Prediction, adjustment/adaptation and mitigation: people see that they can prepare for, and therefore survive, events and so stay within a hazardous area, e.g. those living in San Francisco, California. Building design and regulations have meant that people feel relatively safe despite the fact that they live in an earthquake-prone area.

4 A good example for this would be the way in which responses to tsunamis were handled differently in the Indian and Pacific Ocean basins. There had not been a major tsunami for many years in the Indian Ocean and there was little or no infrastructure to warn surrounding countries. This contrasts with the tsunami warning system in the Pacific Ocean. People too were unaware of the precursor events to a tsunami. Thus when the sea receded below low-tide mark, people ventured onto the shoreline rather than move away.

According to Figure 5.2, several things happen after an event. There is the immediate response followed by recovery. The time taken depends on the location of the event. Following this there has to be the willingness and infrastructure to create systems of prevention, mitigation and preparation. Once these plans are complete, unless there is the political will to maintain watchfulness, human nature tends to make people forget. Once a generation has passed, the collective memory is poor.

Plate tectonics

5 a Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. The crust overlies the solidified and uppermost layer of the mantle. Oceanic crust is the result of erupted mantle material originating from below the plate, cooled and, in most instances, modified chemically by seawater. This occurs mostly at mid-ocean ridges, but also at scattered hot spots, and also in rare but powerful occurrences known as flood basalt eruptions. It is primarily composed of rocks that are rich in iron and magnesium. It is relatively thin, generally less than 10 km thick, and has a mean density of about 2.9 g/cm3. It is also very young, seldom more than 200 million years old.

b The continental crust is the layer of igneous, sedimentary and metamorphic rocks that forms the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is of silica- and aluminium-based minerals. At depth there is a reasonably sharp contrast between the more silica- rich upper continental crust and the lower continental crust, which is more basic in character.

The average density of continental crust is about 2.7 g/cm3, less dense than oceanic crust. At 25– 70 km, continental crust is considerably thicker than oceanic crust. About 40% of Earth’s surface is currently occupied by continental crust. It makes up about 70% of the volume of Earth’s crust.

c The asthenosphere is a zone of the Earth’s mantle lying beneath the crust. It is thought to be much hotter and more fluid than the lithosphere. It extends from about 100 km to about 700 km below Earth’s surface. It is malleable, ‘lubricating’ the undersides of crustal plates.

d The mantle is the second layer of the Earth. It is the largest layer, taking up 84% of the Earth. It is composed of silicates of iron and magnesium, sulphides and oxides of silicon and magnesium. It is about 2,900 km thick. The average temperature of the mantle is 3,000°C. The temperature becomes hotter with depth.

e The core, the Earth’s deepest layer, is a solid iron ball, about 2,400 km in diameter. Although this inner core is white hot, the pressure is so high the iron cannot melt. Scientists believe the core contains sulphur and nickel, plus smaller amounts of other elements. Estimates of its temperature vary, but it is probably somewhere between 5,000 and 7,000°C.

Above the inner core is the outer core, a shell of liquid iron. This layer is cooler but still very hot, perhaps 4,000 to 5,000°C. It too is composed mostly of iron, plus substantial amounts of sulphur and nickel. It creates the Earth’s magnetic field and is about 2,300 km thick.

6 Mantle convection is the theory that there are hot zones deep in the Earth that set off convection currents in the mantle and that it is these currents that drive lithospheric plate movement. The upward limb of the convection cell causes constructive plate boundaries, whereas the downward limbs cause destructive plate boundaries. There has been a lot of debate recently as to both the nature of the convection currents and whether they actually exist at all. Other theories such as ridge push and slab pull are gaining prominence.

7 In the ridge push theory, molten magma that rises at a mid-ocean ridge is very hot and heats the rocks around it. As the asthenosphere and lithosphere at the ridge are heated, they expand and become elevated above the surrounding sea floor. This elevation produces a slope down and away from the ridge. Because the rock that forms from the magma is very hot at first, it is less dense and more buoyant than the rocks farther away from the mid-ocean ridge. However, as the newly formed rock ages and cools, it becomes denser. Gravity then causes this older, denser AQA Geography Workbook Physical geography 39

lithosphere to slide away from the ridge, down the sloping asthenosphere. As the older, denser lithosphere slides away, new molten magma wells up at the mid-ocean ridge, eventually becoming new lithosphere. It is thought that the cooling, subsiding rock exerts a force on spreading lithospheric plates that could help drive their movements. This force is called ridge push.

With the slab pull theory, at a subduction boundary, one plate is denser and heavier than the other plate. The denser, heavier plate begins to subduct beneath the plate that is less dense. The edge of the subducting plate is much colder and heavier than the mantle, so it continues to sink, pulling the rest of the plate along with it. The force that the sinking edge of the plate exerts on the rest of the plate is called slab pull. Currently, many scientists consider slab pull to be a much stronger factor than ridge push or mantle convection in driving plate movements.

8 Diagram a shows that a hot spot occurs under a part of the thick continental crust. It causes upward movement of the crust and results in crustal fracturing. This fracturing allows some basaltic lava to reach the surface. This begins to force apart the crust on either side of the hot spot. As the two sections of crust move apart, a series of reverse faults causes collapse of the central area of activity, resulting in a rift valley (diagram b).

The continual creation of new crust forces the two sides of the rift valley apart until eventually oceanic water floods in to form a narrow linear sea (diagram c). The sea eventually widens into an ocean with a central ridge on either side of a rift valley (diagram d).

9 Low-silica lavas are low in viscosity. This means that they are able to flow relatively easily. If the eruption is above the surface of the sea then it results in sheet lavas and shield volcanoes. Under the sea it results in pillow lavas.

10 Earthquakes occur where masses of rock move relative to one another. Movement is not uniform and often the masses become ‘stuck’. This builds up tension within the rocks, which is released when there is movement. This energy release takes the form of an earthquake.

In both these boundaries, an oceanic plate is being subducted. That plate is grinding and getting stuck against either a piece of continental crust or another oceanic plate.

Continued sticking and then release means that earthquakes of varying depths occur, following the downward moving plate into the mantle below.

11 The crustal portion of the subducting slab contains a significant amount of surface water, as well as water contained in hydrated minerals within the seafloor basalt. As the subducting slab descends to greater and greater depths, it progressively encounters greater temperatures and greater pressures, which cause the slab to release water into the mantle wedge overlying the descending plate. Water has the effect of lowering the melting temperature of the mantle, thus causing it to melt. The magma produced by this mechanism varies from basalt to andesite in composition. It rises upwards to produce a linear belt of volcanoes parallel to the oceanic trench. The chain of volcanoes is called an island arc. If the oceanic lithosphere subducts beneath an adjacent plate of continental lithosphere, then a similar belt of volcanoes will be generated on continental crust.

There are a variety of volcanic eruptions. The lava is intermediate between acid and basic. One of the most common types is andesite lava. The eruption varies depending on the amount of gas trapped in the lava.

The huge quantities of seawater taken down with the subducting plate become dissolved within the magma. At a later stage, when the magma rises, the water returns to its gaseous form and

increases the volume of the magma, making the eruptions explosive. This produces phenomena such as pyroclastic flows and ash clouds. Some of the most explosive eruptions ever noted have happened at this type of plate margin. Examples are: Mt St Helens, Mt Pinatubo, Mt Tambora and Krakatoa. The resultant volcanoes range from strato-volcanoes to calderas.

12 Because both plates are of similar densities, neither continental plate could be subducted below the other. This causes the continental crust to thicken due to folding and faulting by compressional forces. The continental crust here is twice the average thickness, at around 75 km. The thickening of the continental crust marked the end of volcanic activity in the region as any magma moving upwards would solidify before it could reach the surface. The Himalayas are still rising by more than 1 cm per year as India continues to move northwards into Asia, which explains the occurrence of shallow focus earthquakes in the region today.

13 At conservative margins, plates slide past each other, so that the relative movement is horizontal. Lithosphere is neither created nor subducted, and while conservative plate margins do not result in volcanic activity, they are the sites of extensive shallow focus earthquakes, occasionally of considerable magnitude. Instead of the plates slipping past each other, they tend to stick. When sufficient pressure builds up, one plate is jerked forward, sending shockwaves to the surface. An example is the San Andreas fault.

14 A few active volcanoes do exist in locations well away from any plate margin. These are volcanic hot spots. The best known example of an oceanic hot spot is the chain of Hawaiian Islands. Iceland is unique in that it is a hot spot but is located on a mid-ocean ridge. As their name suggests, these are points where molten material from the mantle breaks through the rocks of the Earth’s crust to reach the surface. They are caused by convectional plumes of very hot magma in the mantle which burn through the crustal rocks to reach the surface.

The important point to understand is that the plume is stationary. The point where the hot material breaks out of the mantle and onto the surface stays in the same place. However, where it reaches the surface changes with time, because plates move. Above the hot spot a volcano forms and grows and grows until the plate carries it away. Once the volcano has been carried away and no longer sits over its hot spot, it loses its source of magma. A new volcanic cone begins to form on top of the hot spot.

All the Hawaiian islands are volcanic. The nearest land is over 3,000 km away. The islands lie on top of the Pacific plate, which is moving north-westwards by about l0 cm a year. Volcanic activity today only takes place in the southeast corner of the island chain on the big island, called Hawaii. Mauna Loa is a huge volcano. It rises 9,000 m from the floor of the Pacific Ocean to its summit, which is 4,170 m above sea level. At its ocean base, it is over 90 km wide.

The magma comes from the mantle, it is very hot and as it is basalt it has a low viscosity. The activity now seems to be focused increasingly on the southeast part of the island where Kilauea has been active for over 150 years. Volcanic hazards

15 There is a ring of volcanoes around the Pacific Ocean (the Ring of Fire). This shows where subduction is taking place. On the eastern side of the Pacific it is at an ocean/continent boundary and in the west it is an island arc type of boundary. Subduction and melting lead to eruptions. In the centre of the Pacific there are hot-spot volcanoes such as Hawaii. There are some volcanoes in the centre of continents such as the Yellowstone Caldera, which are also found over hot spots. There is a line of volcanoes down the centre of the Atlantic that marks the Mid-Atlantic Ridge, a AQA Geography Workbook Physical geography 41

constructive boundary. It includes Iceland and Tristan da Cunha. Another group can be found in the Great Rift Valley of eastern Africa, a putative constructive plate margin.

16 Answers depend on the examples chosen.

Pyroclastic flows contain a high-density mix of hot lava blocks, pumice, ash and volcanic gas. They move at very high speed down volcanic slopes, typically following valleys. Most pyroclastic flows consist of two parts: a lower (basal) flow of coarse fragments that moves along the ground, and a turbulent cloud of ash that rises above the basal flow. Ash may fall from this cloud over a wide area downwind from the pyroclastic flow.

Pyroclastic flows form in different ways:

 Collapse of eruption column: during a highly explosive eruption, the column ejected upwards into the atmosphere cools and can become too cool and dense to maintain upward momentum.

 ‘Boiling over’ from eruptive vent: during an explosive eruption, material is erupted without forming a high plume and rapidly moves downslope.

 Collapse of lava domes or flows: the fronts of lava flows or domes can become so steep that they collapse due to gravitational force.

With rock fragments ranging in size from ash to boulders that travel across the ground at speeds typically greater than 80 km/h, pyroclastic flows knock down, shatter, bury or carry away nearly all objects and structures in their path. The extreme temperatures of rocks and gas inside pyroclastic flows, generally between 200°C and 700°C, can ignite fires and melt snow and ice.

Pyroclastic flows vary considerably in size and speed, but even relatively small flows that move less than 5 km from a volcano can destroy buildings, forests and farmland. On the margins of pyroclastic flows, death and serious injury to people and animals may result from burns and inhalation of hot ash and gases.

Pyroclastic flows generally follow valleys or other low-lying areas and, depending on the volume of rock debris carried by the flow, they can deposit layers of loose rock fragments to depths ranging from less than 1 m to more than 200 m.

Pyroclastic flows can also lead to secondary hazards, especially flooding and lahars by:

 eroding, melting and mixing with snow and ice, thereby sending a sudden torrent downstream

 damming or blocking streams in volcanic valleys, which may create lakes behind the blockage that eventually overtop and erode the blockage, producing a rush of water and volcanic material downstream

 increasing the rate of stream runoff and erosion during rainstorms due to the creation of an easily eroded landscape with sparse vegetation Seismic hazards

17 The vast majority of earthquakes are found along plate margins, although there are exceptions — e.g. northeast Brazil. Constructive plate margins have shallow earthquakes, caused by rising magma forcing its way to the surface. At destructive margins the earthquakes vary in depth. This is AQA Geography Workbook Physical geography 42

because they are caused by friction along the Benioff zone, which gets increasingly deeper as one moves away from the surface plate boundary. There are many shallow and intermediate depth earthquakes below the collision zone of the Himalayas where there is no subduction. Transform faults result in shallow earthquakes.

18 Answers depend on the hazard chosen.

Earthquake liquefaction or ground failure is a loss of strength that causes otherwise solid soil to behave temporarily as a viscous liquid. The phenomenon occurs in water-saturated unconsolidated soils affected by seismic S waves (secondary waves), which cause ground vibrations during earthquakes. Poorly drained fine-grained soils such as sandy, silty and gravelly soils are the most susceptible to liquefaction. Granular soils are made up of a mix of soil and pore spaces. When an earthquake shock occurs in waterlogged soils, the water-filled pore spaces collapse; this decreases the overall volume of the soil. This process increases the water pressure between individual soil grains, and the grains can then move freely in the watery matrix. This substantially lowers the soil’s resistance to shear stress and causes the mass of soil to take on the characteristics of a liquid. In its liquefied state, soil deforms easily, and heavy objects such as structures can be damaged from the sudden loss of support from below.

19 The seismic gap theory states that, if there have been large earthquakes on an active (but unbroken) fault’s neighbouring faults in the past, then it is the most likely next location for an earthquake. A frequently cited example of a seismic gap being filled was the magnitude 7 Loma Prieta earthquake of 1989. Unfortunately, it is not a precise forecasting tool. There has been a great earthquake expected on the Tokai fault south west of Tokyo for several decades but so far it has not occurred. Storm hazards

20 The main parts of a tropical cyclone are the rain bands, the eye and the eyewall. Air spirals in towards the centre in an anticlockwise pattern in the northern hemisphere (clockwise in the southern hemisphere) and out of the top in the opposite direction. In the very centre of the storm, air sinks, forming an ‘eye’ that is mostly cloud-free.

The eye

The hurricane’s centre is a relatively calm, generally clear area of sinking air and light winds that usually do not exceed 24 km/h and is typically 32–64 km across. An eye will usually develop when the maximum sustained wind speeds go above 119 km/h and is the calmest part of the storm.

At round 119 km/h the strong rotation of air around the cyclone balances inflow to the centre, causing air to ascend about 16–32 km from the centre, forming the eyewall.

The eyewall

The eyewall consists of a ring of tall thunderstorms that produce heavy rains and usually the strongest winds. Changes in the structure of the eye and eyewall can cause changes in the wind speed, which is an indicator of the storm’s intensity. The eye can grow or shrink in size, and double (concentric) eyewalls can form.

In intense tropical cyclones, some of the outer rain bands may organise into an outer ring of thunderstorms that slowly moves inwards and robs the inner eyewall of its needed moisture and momentum. During this phase, the tropical cyclone is weakening.

Eventually the outer eyewall replaces the inner one completely and the storm can be the same intensity as it was previously or, in some cases, even stronger.

Rain bands

These are curved bands of clouds and thunderstorms that trail away from the eyewall in a spiral fashion. These bands are capable of producing heavy bursts of rain and wind, as well as tornadoes. There are sometimes gaps in between spiral rain bands where no rain or wind is found.

If one were to travel between the outer edge of a hurricane to its centre, one would normally progress from light rain and wind, to dry and weak breeze, then back to increasingly heavier rainfall and stronger wind, over and over again, with each period of rainfall and wind being more intense and lasting longer.

21 The most frequent occurrence of tropical cyclones is in the western North Pacific. Tropical cyclones in the western North Pacific and the North Atlantic can have tracks that extend to very high latitudes. Storms following these long tracks generally undergo extratropical transition. The North Indian Ocean (Bay of Bengal and Arabian Sea) is bounded by land to the north and the eastern North Pacific is bounded by cold water to the north. These environmental features limit the lifetimes of storms in these regions.

Southern hemisphere tropical cyclones are generally weaker than storms in the North Pacific and Atlantic basins.

Tropical cyclones do not form very close to the equator and do not ever cross the equator.

22 Early warning systems give people time to move to places of safety. The majority of deaths and injuries during and in the immediate aftermath of a cyclone are caused either by drowning or by being hit by flying debris. Evacuation to concrete shelters raised above the floodwater or inland away from the coast (and the dangers of storm surge) would only be possible if there were time to move people. There are inherent dangers associated with moving large numbers of people but these would be far outweighed by the increased protection. Bangladesh has over 400 cyclone shelters and in 2007 over 3 million people were evacuated to safety before cyclone Sidr reached land. This reduced the immediate death toll (from drowning and trauma) considerably.

23 The best approach is to look at examples of contrasting tropical storms.

In low-lying regions such as Bangladesh tropical cyclones cause storm surges that travel far inland. These destroy homes and poison soils. In mountainous countries such as the Philippines, rainfall, landslides and river flooding play a much bigger role.

Economic development could be exemplified by the contrasting responses to tropical storms from an HIC and an LIC. Fires in nature

Factor Impact on wildfire

Vegetation A wide variety of vegetation catches fire easily. Some has evolved to need wildfire in type order to germinate. Grasses which may wilt during periods of drought are very

susceptible, as are most species of tree.

Fires and natural ecosystems are often closely linked, particularly Mediterranean climate regions and the savannah grasslands. Fire can clear vegetation and aid new seed germination, stimulate the growth of certain plants and rid an area of insects and some parasites.

Some species are pyrophytic in that they can withstand fire through some mechanism such as resistant bark, for example the baobab tree. In Australia, plants such as banksia need fire for their woody fruit to open and thus regenerate.

Fuel The fuel has to be of sufficient quantity and dry enough to burn. Climate affects the characterist frequency and duration of droughts, during which the vegetation and litter has an ics opportunity to accumulate and dry out. Climate also affects the type of vegetation that will grow in an area and the rate at which litter can be produced.

Climate Wildfires are common in climates that are sufficiently moist to allow the growth of vegetation but feature extended dry, hot periods. Such places include the vegetated areas of Australia and southeast Asia, the veld in southern Africa, the forested areas of the USA and Canada, and the Mediterranean basin. Global warming may increase the intensity and frequency of droughts in many areas, creating more intense and frequent wildfires.

Recent Temperature, relative humidity, precipitation and wind speed independently influence weather wildfire spread rates and intensities. The alignment of multiple weather extremes, conditions such as the co-occurrence of hot, dry and windy conditions, leads to the most severe fires

Fire Important aspects of fire behaviour are as follows: behaviour  Torching: movement of a surface fire up into tree crowns; the precursor to crowning

 Crowning: active fire movement through the tree canopy

 Fire whirl: result of an upward-spinning column of air that carries flames, smoke and embers aloft; whirls often form in heavy fuels on the lee (downwind) side of ridges and, in extreme conditions, can be powerful enough to twist off entire trees

 Spotting: when glowing embers are lofted up and ahead of the main fire front, igniting multiple spot fires that then feed back into the main fire front to create very extreme and dangerous fire conditions

25 In the case of natural fires, lightning is by far the main cause. Climate will affect the frequency of electrical storms, particularly one in which there is hardly any rainfall.

In the USA, arson, escaped debris burns, campfires and engine sparks are the most common types of human-related ignitions. Over the past few decades, several of these ignition sources have become less common. Cigarettes used to frequently provide the spark that would set off a wildfire, but since the early 1970s there has been a 90% reduction on federal lands in this ignition source. The drop is probably related to the fact that fewer people today are smoking than 30 years ago.

26 Answers depend on the example chosen. You need to have a clearly located example. For your example you need to be able to quote a range of impacts (area destroyed, number of trees damaged, houses destroyed etc.). You will also need to have details of the human responses and then some measure of their success.

Similar to other forms of risk management, the management of wildfire risks begins with an assessment of the probability of a wildfire event and the susceptibility of highly valued resources and assets to wildfire. Strategic risk management in the wildfire context involves many complicating factors, including, but not limited to the following:

 Many wildlands are historically predisposed to periodic fire.

 Wildfire is a dynamic ecological process that has contributed to the development of many ecosystems.

 Wildfire is a spatial process: fuel continuity is critical in fire spread, and burned areas may be considerable distances from the ignition point.

 Many communities have developed within or adjacent to fire-prone ecosystems; these communities vary widely in their levels of wildfire exposure and susceptibility.

 Sociopolitical expectations regarding wildland fire management and community fire protection may not be realistic under current and expected future conditions.

2 AO3: Level 2 (4–6 marks); Level 1 (1–3 marks)

Afghanistan: d = −3; d² = 9

Japan: d = 6; d² = 36

RS = 0.358

This falls well out of an acceptable significance level. We can conclude that the chances of there being a correlation between the number of disasters a country experiences and the amount of damage caused is not statistically acceptable. This is almost certainly due to the level of development that each country has attained.

Answers should concentrate on the explosiveness of a volcano, which is linked to the nature of the magma and its tectonic location. This then has to be combined with the proximity of the volcano to human settlement and/or infrastructure.

For example, the eruption of Eyjafjallajökull in Iceland in 2010 occurred under a glacier, but was also an ash eruption. The ash did minor damage to local farms but had a major effect on transatlantic air routes.

Your answer depends on the hazards to which you apply it. Whichever you choose, you should make clear what occurs during the stages of pre-disaster, relief, rehabilitation and reconstruction. Because the question asks you to assess the extent, then it would be best to choose two disasters, one which has followed the model, e.g. Bangladesh and its management of cyclones, and one which has parts absent, e.g. the 2010 Haiti earthquake.

Exam-style questions (A-level) 5 AO2, AO3: Level 2 (4–6 marks); Level 1 (1–3 marks)

There is clear correlation between spring/summer temperatures and wildfire frequency. There are spikes in both temperature and frequency in 1988, 1994, 2000 and 2003.There are dips in frequency when the temperature averages at below 14°C.

The correlation between the timing of spring snowmelt is less clear. In 1975 there is a clear link between the very late snowmelt and fire frequency, as there is in 1993. For much of the rest of the time there is correlation but it almost seems to have a time lag of a year. The higher the temperatures, the earlier the spring melt correlates directly with the length of the fire season.

Your answer depends on the example chosen. You must be able to give details of how the risk was managed and then link it to the damage that was caused.

Plate tectonics is the theory that Earth’s outer shell is divided into several plates that glide over the mantle, the rocky inner layer above the core. The plates act like a hard and rigid shell compared to Earth’s mantle. This strong outer layer is called the lithosphere. The plates move relative to one another and form broadly four different kinds of boundary.

You need to link each of the named features to its appropriate plate boundary and then state how that fits into the theory of plate tectonics.

Your answer depends on the example chosen. A good example might be the Philippines or Los Angeles. You will have to look at each specific hazard in turn, describing the causes and its associated risks. Then you have to account for the fact that although it is a risky environment, people still live there, prepared to take the risks that are presented.

Topic 6 Ecosystems under stress Ecosystems and sustainability

1 Indicator species are used as a way of measuring biodiversity. For example, stoneflies are found in clean, fast-moving streams with a gravel or stone bottom. The presence of stonefly nymphs indicates highly oxygenated (healthy) water. Advantage: easy to measure. Disadvantage: bias towards certain species.

Species richness is one of the most commonly used measures of biodiversity and it refers to the number of different species. Advantage: it has proven to be measurable in practice. It is do-able. Disadvantage: there is a lack of agreement as to what constitutes a species. For example, it is not an adequate method of defining single-cell organisms.

A more recently developed measure of biodiversity is the Living Planet Index (LPI). The LPI measures trends in thousands of vertebrate species populations and provides information on changes in the abundance of the world’s vertebrates. Advantage: it can quickly convey information on which habitats or ecosystems have species that are declining most rapidly. Disadvantage: it relies on secondary data.

2 Going from where the LPI was in 1970, there was a slight increase and then decrease through until 1981. From 1981 onwards there was a steady decrease down to 0.75 by 2001. From 2001 to 2007 there was a very slow increase to 0.77.

Pressure Example(s) of species that has declined

Effects of human The Bengal tiger activity on biodiversity

Habitat loss, alteration The Orangutan in Borneo and fragmentation

Overexploitation of wild The Patagonian toothfish in the Southern Ocean species

Pollution Salmon are harmed by acid deposition finding its way into rivers and reducing the pH

Climate change The polar bear

Invasive species The native white-clawed crayfish has been almost wiped out in England by the introduction of the American signal crayfish by the UK government in 1976

4 A provisioning service is any type of benefit to people that can be extracted from nature. Along with food, other types of provisioning services include:

 drinking water

 timber

 wood fuel, natural gas and oils

 plants that can be made into clothes and other materials

 medicinal benefits

Healthy biodiversity means that we can obtain a range of foodstuffs, timber etc. to suit a variety of needs. Often one species may rely on the presence of another, e.g. food provisioning relies on bees and other similar species to pollinate crops.

Environmental regulation is the benefit provided by ecosystem processes that moderate natural phenomena. Regulating services include:

 pollination

 decomposition

 water purification

 erosion and flood control

 carbon storage and climate regulation

One example would be the maintenance of large, diverse areas of forestry to act as both flood controls and carbon sinks.

A cultural service is a non-material benefit that contributes to the development and cultural advancement of people. A rich biodiversity would aid in creativity born from interactions with nature (music, art, architecture) as well as recreation. Areas with a rich biodiversity play an important role in both physical and mental health. Overall, people living near green spaces like urban parks and nature reserves report better mood and physical health. With regards to mental health specifically, researchers have found a positive association between access to green space and stress relief. Ecosystems and processes

5 All ecosystems consist of the following basic components:

Abiotic components

These include basic inorganic elements and compounds, such as soil, water, oxygen, calcium carbonates, phosphates and a variety of organic compounds (by-products of organic activities or death).

They also include such physical factors and ingredients as moisture, wind currents and solar radiation. Radiant energy of the sun is the only significant energy source for any ecosystem. The amount of non-living components, such as carbon, phosphorus, nitrogen etc. that are present at any given time is known as standing state or standing quantity. AQA Geography Workbook Physical geography 49

Biotic components

These include:

 Producers (autotrophic components): chiefly green plants. They use radiant energy of the sun in the photosynthetic process, whereby carbon dioxide is assimilated and the light energy is converted into chemical energy.

 Consumers: those living members of an ecosystem which consume the food synthesised by producers are called consumers. Under this category are included all kinds of animals that are found in an ecosystem.

 Decomposers or reducers and transformers include fungi and bacteria. They attack the dead remains of producers and consumers and degrade the complex organic substances into simpler compounds. The simple organic matters are then attacked by another kind of bacteria, the transformers, which change these organic compounds into the inorganic forms that are suitable for reuse by producers or green plants.

6 A food chain is a series of organisms interrelated in their feeding habits, the smallest being fed upon by a larger one which in turn feeds a still larger one.

Examples could include:

phytoplankton → zooplankton → fish → seal → killer whale

grass → grasshopper → frog → heron

7 Trophic levels are shown as a pyramid of numbers. This depicts the relationship in terms of the number of producers, herbivores and carnivores at their successive trophic levels. There is a decrease in the number of individuals from the lower to the higher trophic levels. The number pyramid varies from ecosystem to ecosystem.

9 First of all, the succession gets older as you move away from the high-water mark. We assume that the area of oak and ash was, at one time, dominated by the pioneer community of blue-green algae. These pioneers are autotrophs, getting their energy directly from the sun. These are replaced by mosses and liverworts that become established in the thin veneer of weathered

material as well as some biotic content from dead algae. This process continues as the layer of mixed organic and mineral matter becomes a proto-soil, able to retain moisture and provide shelter for seeds. These are followed by flowering plants etc. that begin to out-compete the mosses by shading the ground and using up moisture in the soil. This process continues with larger plants then trees until the vegetation is in a state of dynamic equilibrium with the environment.

10 Stage 1 Open water: There will be microorganisms and plankton floating in the water.

Stage 2 Rooted plants: Over time, sediments will be transported into the pond by streams or rainwater. Large amounts of sediment can be deposited in this way. The water depth will gradually decrease, allowing rooted, submerged plants such as starwort and pondweed to grow. Waterlilies, which are rooted, but with floating leaves, may also become established. The added plant life is accompanied by a variety of invertebrates and fish.

The vegetation traps and holds more and more of the incoming sediment so that the water becomes shallower. Decomposing dead plant and animal matter provides food for detritivores and increases the nutrients in the water. This promotes plant growth.

Stage 3 Swamp stage: By this stage, the water may be too shallow to support fully submerged plants. Instead, emergent plants, such as yellow iris, grow partly in and partly out of the water. These plants tend to have tall, flexible spear-shaped leaves. This allows them to cope with large differences in water level, always having some portion of the leaves above the water for photosynthesis.

Stage 4 Marsh stage: Swamp plants which are adapted to grow in partially submerged conditions will gradually die out as the marsh floor progressively rises above the water level. Some plants such as yellow iris, which grow equally well in swamp or marsh conditions, will continue to grow, while other marsh plants such as water mint become established.

Tree seedlings, such as willow, which favour wet soil conditions, will become well established and begin to grow up.

Stage 5 Carr and woodland stages: The soil is still wet, but no longer completely waterlogged and air is able to enter along root channels. Willow and alder dominate the ground and shade out the lower-lying marsh vegetation. This is replaced by a variety of woodland floor plants, including sedges, rushes, ferns and small flowering herbs, which are adapted to low light levels and flourish in wet conditions.

In drier areas, increasingly aerobic decomposition will accelerate nutrient recycling, increasing the organic and nutrient content of the soil. Tree transpiration will continue to dry out the soil to the point where climax tree species such as oak, beech or ash can become established.

12 In the UK mild weather can delay hedgehogs entering into hibernation or elicit premature awakening, impacting on the creatures’ fat reserves and breeding times and consequently affecting the long-term survival of the species.

Warmer springs have led to earlier nesting for 28 migratory bird species on the east coast of the USA, while northeastern birds that winter in the southern USA are returning north in the spring 13 days earlier than they did in the early twentieth century.

13 Example 1:

Warming in the Himalayas has already occurred at three times the global average. This is prime snow leopard habitat and continued warming will cause their range to shrink as the treeline moves higher up the mountains. This will not only fragment and isolate snow leopard populations, but it will severely affect their prey too — causing some of the alpine pastures that blue sheep and Himalayan tahr (the snow leopard’s main prey) rely on to be replaced by forest.

Example 2:

Recent warming of the seas around the UK has coincided with a northward shift in the distribution of plankton and fish species. This is also the case for dolphin species such as the short-beaked common dolphin and the striped dolphin, which have recently extended their range further north off western Britain and around into the northern North Sea.

14 Example 1:

In the oceans it is thought that climate change could lead to the following:

 Species diversity and abundance will decrease worldwide.

 Microorganisms are expected to increase in number and diversity.

 Primary production (plankton) will increase, but this trend will not continue up the food chain.

 There will be a ‘mismatch’ in food availability — not enough food for animals higher up the food chain — which will impact on commercial fisheries.

Example 2:

Declines in the duration and extent of sea ice in the Arctic caused by climate warming leads to declines in the abundance of ice algae, which thrive in nutrient-rich pockets in the ice. These algae are eaten by zooplankton, which are in turn eaten by Arctic cod, an important food source for many marine mammals, including seals. Seals are eaten by polar bears. Hence, declines in ice algae can contribute to declines in polar bear populations.

15 Climate change and shifts in ecological conditions could support the spread of pathogens, parasites and diseases, with potentially serious effects on human health, agriculture and fisheries. For example, the oyster parasite, Perkinsus marinus, is capable of causing large oyster die-offs. This parasite has extended its range northwards from Chesapeake Bay to Maine in the USA, a 500-km expansion tied to above-average winter temperatures.

Oysters provide supporting ecosystem services, along with provisioning, regulating and cultural services. Oysters influence nutrient cycling, water filtration, habitat structure, biodiversity and food- web dynamics.

16 Golden toad (Bufo periglenes), along with the Monteverde harlequin frog (Atelopus varius), also of Central America. The golden toad is among the very small number of species whose recent extinction has been attributed with medium confidence to climate change. Last seen in 1989, the golden frog lived in mountaintop cloud forests that have disappeared due to drought and other climatic changes. Biomes

17 a Tropical rainforests are mostly distributed between the latitudes 10° north and 10° south of the equator. They are found in:

 the Amazon river basin of South America, with more than half of it in Brazil; this area holds about one-third of the world’s remaining equatorial forests

 the equatorial part of Africa, including large parts of the Republic of Congo, the Central African Republic and Gabon

 the Guinea coast of Africa in isolated pockets stretching from Liberia to Cameroon

 SE Asia and Oceania, for example, Malaysia, Indonesia and Papua New Guinea

b Savanna grassland is to be found in:

 northern-central Australia, straddling the tropic of Capricorn

 the Cerrado grasslands of southern Brazil and the Llanos of Colombia and Venezuela

 parts of India and Pakistan straddling the tropic of Cancer

 sub-Saharan Africa, both north and south of the equator; in East Africa, in the upland areas, these grasslands are found right on the equator

18 The equatorial climate has no seasons. It is hot and wet all year round. The average temperatures rarely go below 24°C or rise above 28°C. There is a low diurnal range of temperature; during the daytime it might reach above 30°C, but the nights remain very warm. The high temperatures are because the sun is high in the sky all year round. They are, though, moderated by the presence of cloud.

The pattern of rainfall in the rainforest varies during the day. In the morning, skies are generally clear, though there may be a low mist. Evapotranspiration is rapid as the sun beats down on the humid forest and the low-pressure conditions allow this air to be rapidly uplifted.

As the air rises it cools and water vapour condenses into clouds. These clouds continue to build until they become towering, grey, cumulonimbus clouds in the early afternoon. In the middle of the afternoon, heavy rain, often with thunder and lightning, returns the previously uplifted moisture back to ground level. The cycle begins again and the day ends as it started, with clear skies.

20 The hot, damp conditions on the forest floor allow for the rapid decomposition of dead plant material, which in turn provides plentiful nutrients that are easily absorbed by plant roots. However, as these nutrients are in high demand from the rainforest’s many fast-growing plants, they do not remain in the soil for long and stay close to the surface of the soil. If vegetation is removed, the soils quickly become infertile and vulnerable to erosion.

21 The vegetation has developed and adapted to the physical conditions of the rainforest in a number of ways:

 Leaves have drip tips and waxy surfaces. Others have jagged edges and holes in the leaves. All these allow the excess rainfall to be easily shed. This discourages growth of bacteria and fungi on the leaf surface.

 The trees grow rapidly upwards towards the light. This results in tall slender trunks with few branches. All the leaves are concentrated in the umbrella-like crowns where they can absorb sunlight and photosynthesise. Flexible trunks and buttresses help hold them up because the roots themselves are so shallow.

 Most of the minerals needed by the trees are close to the surface of the soil and so the roots do not penetrate deep into the soil but spread outwards, just below the forest floor.

 Climbing vines such as lianas are found throughout the rainforest. They have thick, woody stems and come in various lengths (up to 1,000 m) and varying shapes. They begin life on the forest floor but depend on trees for support as they climb upwards towards the sunlight. They attach themselves to trees with sucker roots, or tendrils wind themselves round a tree’s trunk.

 Because the forest floor is so dark there are many epiphytic plants that grow on branches, trunks and even the leaves of the trees.

 Epiphytic orchids have aerial roots that cling to the host plant, absorb minerals and absorb water from the atmosphere.

22 a Studies have revealed that there is a strong relationship between population growth and deforestation/loss in biodiversity in Central America, East and West Africa and South Asia, but a much less clear association in Amazonia (South America) and Central Africa.

From the deforestation studies to date, a few generalisations can be made. At extremely low population densities (less than one to two persons per square kilometre), it is possible to maintain large amounts of forest intact in areas where the population can be sustained, primarily through the harvesting of non-timber forest products rather than by agriculture. However, even in sparsely inhabited areas, external forces such as demand for timber or cattle in other parts of the country or world can lead to deforestation that is not closely related to local population growth. This has been the case in parts of the Brazilian Amazon.

b Human activity and development in the tropical rainforest has led to massive amounts of forest land being converted into other human uses such as mining or agriculture. Overexploitation of the rainforest’s natural resource is a highly damaging impact that humans have on the rainforest, for example the rainforest is being used up at an exceptional rate for mining purposes: oil, gold and iron ore are being mined at a massive rate.

Other developments include the construction of roads and, more recently, bridges. These will open up hitherto unreachable areas and spread the loss of biodiversity.

c As agriculturally based population density increases in and near forested areas, the strongest relationship between population growth and loss in biodiversity occurs where forests are cleared to provide more areas for subsistence farming. The poorer the soil quality, the lower the agricultural production per hectare, and the more land per capita is likely to be cleared. In Central America, population density and loss of forest cover are closely related at many scales: at the regional and national level, and in local areas inside and near forest reserves.

More recently, there has been a domino effect of deforestation as single-crop farming of soya beans, rice and corn has grown to meet strong worldwide demand. Soya bean cultivation tends mainly to take over grazing land and thus moves herds closer to the forest.

23 The typical climate is a tropical wet and dry climate that shows seasonal variations in wind direction, precipitation and temperature. It is transitional between the equatorial rainforests, where rain can be expected all year, and the hot deserts, which have minimal precipitation. Variations occur with increasing distance from the equator. Ninety per cent of the annual precipitation falls within the wet season and, although the sun is higher in the sky, the rain clouds reflect insolation back out of the atmosphere and reduce the temperatures. During the dry season, with lack of cloud, heating can be intense and temperatures high.

25 A typical soil moisture budget for the savanna is one where precipitation is greater than potential evapotranspiration in the wet season (summer), whereas the reverse is true in the dry season (winter). There are four distinct periods that can be seen in the soil moisture budget for this area:

 Soil moisture recharge occurs at the start of the rainy season when precipitation first becomes greater than evapotranspiration. Rainwater begins to fill the empty pores in the soil. When they are full the soil is said to have reached its field capacity.

 Soil moisture surplus occurs late in the wet season. When the soil becomes saturated rainwater has difficulty infiltrating the ground. This causes surface runoff and explains the high river levels and flooding.

 Soil moisture utilisation occurs when the rainy season begins to come to an end and the dry season starts. Evapotranspiration begins to exceed precipitation. There is more water evaporating from the ground surface and being transpired by plants than is falling as rain. Water is also drawn up the soil by capillary action and this leads to further evapotranspiration.

 Soil moisture deficit occurs when the soil moisture is used up and there is a water deficit.

Plants can only survive by being drought resistant or through irrigation. This period lasts until precipitation again becomes greater than evapotranspiration the following wet season.

26 During the dry season, plants die back and litter builds up which, if not destroyed by fire, forms a thin layer of humus. This low level of nutrients is further reduced by aerobic bacteria, which are particularly active in areas with a long wet season and where the temperature remains above 25°C for substantial periods of time. The activity of these bacteria under such conditions occurs at a rate above that of plant growth, thus breaking down plant matter faster than it is produced. During the wet season leaching removes nutrients from the soil and that can result in a hard crust forming that hinders plant growth. Biomass varies seasonally, with elephant grasses growing up to 2 m high in the wet season.

27 Plants of the savanna have evolved to survive long periods of drought. They have long tap roots that can reach the deep water table, thick bark to resist annual fires, trunks that can store water, and leaves that drop off during the winter to conserve water. The grasses have adaptations that discourage animals from grazing on them; some grasses are too sharp or bitter-tasting for some animals, but not others, to eat. Many grasses grow from the bottom up, so that the growth tissue AQA Geography Workbook Physical geography 56

does not get damaged by grazers. Many plants of the savanna also have storage organs like bulbs and corms for making it though the dry season. Ecosystems in the British Isles over time

28 This depends on the ecosystem chosen. Examples could include sand dunes, a pond etc. In your description you will need to identify the main components of the ecosystem, both abiotic and biotic. You should be able to describe a simple food web, identifying the trophic level of the species named.

29 This again depends on the example chosen. There is no limit to the scale of the ecosystem, so you could choose a local ecosystem or a more regional one. Regional ecosystems could include the South Downs, the machair of coastal Scotland, the blanket bog of northwest Scotland. Marine ecosystems

Environmental Ideal conditions for coral Comment factor development

Water 26–27°C Reef-building corals require warm water conditions to temperature survive. Different corals living in different regions can withstand various temperature fluctuations.

If the water gets too warm then coral expels the symbiotic algae and is likely to die if the water does not cool down.

Water salinity Coral reefs develop best Corals need saltwater to survive and require a certain where the salinity of the sea balance in the ratio of salt to water. This is why corals water is between 34 and 37 do not live in areas where rivers drain fresh water into parts per 1,000. the ocean.

Clearness of Clear water away from silty Most reef-building corals contain photosynthetic water estuaries algae, called zooxanthellae, which live in their tissues. The corals and algae have a unique relationship. The coral provides the algae with a protected environment and compounds they need for photosynthesis. In return, the algae produce oxygen and help the coral to remove wastes. Most importantly, zooxanthellae supply the coral with food. The algae need light in order to produce food via photosynthesis.

Water depth Coral reefs can be found at Corals must stay submerged, otherwise they dry out. depths exceeding 91 m but The shallow depth allows sunlight to penetrate, reef-building corals enabling the zooxanthellae algae to photosynthesise. generally grow best at depths shallower than 70 m.

Water Corals develop best on Breaking waves oxygenate the water. Unfortunately, turbulence windward-facing coasts. tropical storms and powerful waves can also destroy coral.

31 a Taking 1960 as a base level, between 1960 and 1963 the temperatures rose slightly but then fell to a minimum of −0.33 in 1964, 1972 and 1976. These low temperatures brought the running 10-year mean to below 1960 levels between 1960 and 1979. There were some fluctuations above and below the 1960 level until 1986 when the temperature stayed above it. Once again there were fluctuations but the 10-year mean shows a steady rise in temperatures to +0.7.

b Warmer water temperatures brought on by climate change stress corals because they are very sensitive to changes in temperature. If water temperatures stay higher than usual for many weeks, the zooxanthellae they depend on for some of their food leave their tissue. Without zooxanthellae, corals turn white because zooxanthellae give corals their colour. White, unhealthy corals are called ‘bleached’. Bleached corals are weak and less able to combat disease.

32 For example:

Onshore development such as bauxite mining is particularly important for the local economy. This type of activity also releases large quantities of particulate matter (sediment) that choke nearby coral reefs.

Coastal developments such as tourist hotels in countries that do not have a well-developed infrastructure are creating problems for the satisfactory treatment of sewage. Coastal hotels each have their own disposal systems but much waste is discharged into the sea after little treatment.

Excess nutrients are discharged to the marine environment through fertilisers from agriculture. These nutrients may lead to eutrophication which could lead to algal blooms. Local ecosystems

33 This depends on the ecosystem chosen. Suitable examples could be sand dunes, a pond, an area of parkland. It is best to keep it quite small.

Exam-style questions (A-level) 1 AO2, AO3: Level 2 (4–6 marks); Level 1 (1–3 marks)

Temperature anomalies are much greater in the northern hemisphere (but on land) and yet most of the stress appears to be in the southern hemisphere. This could be simply because there is more ocean in the southern hemisphere and so more opportunities for coral growth.

In the northern hemisphere in the Caribbean Sea there are positive temperature anomalies and yet the stress levels are below Watch level. On the other hand, there are positive temperature anomalies in the eastern Pacific offshore of Central America and these are matched by Alert level 1. In the northern Indian Ocean there is very little warming and yet there are areas of high alert.

In the southern hemisphere the same confused pattern occurs. For example, off the coast of SE Australia the temperature anomaly is low and yet the alert levels are high, whereas the sea off the coast of NW Australia has been warmed and the alert level is also high.

The conclusion is that there seems to be little correlation.

Plant succession is the evolution of plant communities at a site over time — from pioneer species to climax vegetation. At each stage of the succession the plant community alters the soil and microclimate, allowing the establishment of another group of species.

The rest of the answer depends on the example you have chosen but you must show how each stage develops from the last. You must also show how at the final stage all the components of the biome are in balance.

Depends on the ecosystem you have chosen. Suitable habitats could be a pond, coastal dunes, a patch of wasteland, a routeway etc.

The two biomes must be tropical rainforest and savanna. The best way to approach this question is to integrate the two biomes throughout your answer. Thus you might start with how population change affects tropical rainforest and then contrast it with how it is affecting savanna. You need to support your answer with examples. For example, large parts of the Amazon basin are being put under commercial soya bean production. It is an extensive system, taking up large areas and clearing whole swathes of forest. Bean production in Kenya, although mainly commercial, is much more intensive and so environmental damage is, so far, not very great.