CAIE AS Level Geography 9696 Core Physical Geography Notes 2021-2022 PDF

ZNOTES.ORG UPDATED TO 2021-22 SYLLABUS CAIE AS LEVEL GEOGRAPHY (9696) SUMMARIZED NOTES ON THE CORE PHYSICAL GEOGRAPHY SYLLABUS CAIE AS LEVEL GEOGRAPHY (9696) Ground Water: water that has percolated into bedrock. Is...

ZNOTES.ORG UPDATED TO 2021-22 SYLLABUS CAIE AS LEVEL GEOGRAPHY (9696) SUMMARIZED NOTES ON THE CORE PHYSICAL GEOGRAPHY SYLLABUS CAIE AS LEVEL GEOGRAPHY (9696) Ground Water: water that has percolated into bedrock. Is a store of freshwater - wells and boreholes can be dug 1. Hydrology and Fluvial below water table to access. Ground Water Recharge: refilling of rock pores as Geomorphology water moves downwards. Occurs when rate of recharge > rate of abstraction. Channel Storage: all water stored in rivers streams and drainage channels. Soil Moisture: water held sub-surface in soil pores. Sandy soils have many large pores, so is permeable, and has quick infiltration rates. Clays are hygroscopic – clay minerals swell when in contact with water, making it impermeable and unstable. SM Deficit: available water is being used up. SM Recharge: precipitation > potential evaporation. Some dry pores refill. SM Surplus: soil is saturated, water cannot enter, so flows over the surface. SM Utilisation: evapotranspiration (and other water uses) > precipitation. Field Capacity: amount of water held once excess has drained away – saturation point. Wilting Point: the range of soil moisture content at which permanent plant wilting occurs. Balance = Precipitation – (run off + evapotranspiration + change in soil moisture). 1.2. Drainage Basin System Outputs Evapotranspiration Evaporation: liquid changes into water vapour, from puddles and streams. Rate of evaporation increases in hot, dry and windy conditions and with larger soil surface area. Transpiration: water is drawn from soil by the plant and leaves the plant as water vapour through the stomata. Potential Evapotranspiration: the amount of evaporation 1.4. Flows that would occur if an unlimited water source were available. Above Ground River Discharge: water that flows into the sea, or that moves in channels (streams/rivers). Water enters the Throughfall: leaves and twigs become saturated so water channel as direct channel precipitation or other flows. drips from them. Precipitation can also fall through gaps Q = AV (Q = Discharge, A = Cross Sectional Area, V in vegetation cover. Stemflow: precipitation is intercepted by vegetation, then = Velocity). Measured in m3/second – Cumecs. runs down the branches and main trunk. Overland Flow: when soil is saturated, or precipitation 1.3. Stores exceeds infiltration rate, surface runoff occurs – where water flows over the surface. Interception: precipitation is caught and stored by Hortonian Flow: shallow, laminar, fast moving water that vegetation before it reaches the ground. causes severe soil erosion when precipitation exceeds the Surface Water: when the infiltration capacity is exceeded, infiltration capacity and depression soil capacity. water builds upon the surface. Channel Flow: movement of water in channels such as Temporary stores: puddles and turloughs. streams and rivers. Permanent stores: lakes and wetlands. WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) Below Ground Soil Storage, Precipitation, QChannel Flow, Evapotranspiration Infiltration: precipitation soaks/is absorbed into soil. Infiltration Capacity: maximum rate that precipitation can be absorbed by soil in given conditions. 1.6. Discharge Relationships Infiltration is inversely proportional to overland runoff. Depends on: rainfall duration, antecedent soil Hydrograph Components moisture, porosity, slope angle, vegetation. A hydrograph plots river discharge against time, and shows Percolation: slow movement of water downwards the river’s regime. Used to understand nature of a drainage through the soil into bedrock under gravity. Fast in basin and factors that affect discharge. Carboniferous Limestone. Rate depends on permeability and porosity of Annual Hydrograph (river regime): to study responses of bedrock. Chalk and sandstones are porous, spaces the river to its environment; highlights seasonal allow water to percolate. characteristics, therefore biggest influencer is climate. Throughflow: water flows through the soil in natural pipes Storm Hydrograph: shows variations of river discharge or percolines. Occurs above bedrock. over a short time period. Includes both discharge and Groundwater: water that has infiltrated the ground, rainfall on the y-axis. entered the phreatic zone and discharged into the Cumecs: cubic metres per second. Unit of discharge. channel. Approach Segment: discharge prior to storm. Phreatic zone: part of an aquifer (permeable rocks Rising Limb: shows quick rise in discharge. and sediments that can hold groundwater or allow it Bank full Discharge: channel full. Any further increase to pass through) below the water table where all in discharge = flood. pores are permanently saturated. Peak Discharge: maximum river discharge. Baseflow: where groundwater seeps into the river’s bed Lag Time: time between max rainfall and max and contributes to discharge. Very slow transfer from discharge. bedrock and very deep throughflow. Takes months/years. Receding Limb: less steep than rising, shows discharge decline after peak discharge. 1.5. Underground Water Stormflow: stream discharge after rainstorm. Quickflow: surface runoff reaches channel quickly. Water table: upper layer of the phreatic zone. It will rise and fall depending on the amount of rainfall percolating downwards, and the amount of baseflow from lower rocks. The aeration zone is seasonally wetted and seasonally dries. Ground water Recharge occurs with: Infiltration (from precipitation) Seepage (through banks/bed of rivers, lakes, puddles and ditches) Leakage and inflow (from adjacent rocks, aquifers) Storm Process Artificially from irrigation, reservoirs Loss occurs with: 1. Rain falls on drainage basin in large amounts. Evapotranspiration (mainly low areas) 2. Overland flow occurs as precipitation > infiltration Natural discharge (seepage and spring flow) rate. Rising limb builds to peak. Leakage and outflow (into aquicludes from 3. After a few hours, overland flow reduces and stops. aquifers) Throughflow then contributes to discharge and stops Artificial abstraction floodwaters going down as quickly as they rose. Aquifers: permeable rocks (sandstone, limestone, chalk) 4. Baseflow takes over – back to pre-flood state. that contain significant quantities of water. Water inside moves slowly and maintains streamflow – by absorbing or 1.7. Drainage Basin Characteristics releasing water in wet/dry periods. Springs: water flow reaches the surface, making a spring. Size and Shape: small basins respond quicker, so lag time Might be substantial enough to become a source. Usually is reduced. River channels in circular basins respond where percolating water reaches an impermeable layer quicker than those in linear ones. or the saturated zone. Drainage Density: low drainage density causes a long lag time, as water only has a few paths to take. Water budget equation: S =P−Q−E WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) A dendritic (tree like pattern) will have a higher effectiveness depends on energy, hardness and density. Increased discharge response, greater flood concentration of particles. risk and reduced lag time. Corrasion: the erosive action of particles carried by the Soil Porosity and Permeability: impermeable surfaces river. cause greater peak flows, due to more overland flow. Solution: the dissolving of rocks (particularly calcium Chalks and gravels allow infiltration and percolation, heavy rocks) by removing chemical ions. Maximum rates whereas clay soils do not. – fast flowing, undersaturated streams pass over soluble Rock Type: impermeable rocks produce a flashier rocks. response, lesser lag times and high peak discharge. Hydraulic Action: direct force of air and water on the Limestone hardly produces a storm hydrograph. rivers banks that causes chunks to break away. Eddies in Slopes: steeper = more overland = short lag and higher the water compress water into bank cracks, and the peak flows. explosion of air bubbles cause the cracks to weaken. Vegetation Type: dense forest vegetation intercepts more, Cavitation: the force of air exploding. With acceleration, so reduced flood response. Opposite in winter. pressure drops in fluids, causing air bubbles to form. Land Use: creation of impermeable surfaces Cavitation is when these bubbles implode and produce (urbanisation) or deforestation increase overland flow. tiny water jets, cutting rock. Increasing drainage density (drains) carries water to rivers Attrition: collision of sediments that wears down both quicker. Peak flow increases, lag time reduces. particles. Produces smaller, rounder particles. Rate of erosion is affected by: amount and weight of load, 1.8. River Channel Processes and velocity, gradient, hardness of geology, pH level and human impacts increasing erosion. Landforms 1.10. Load Transport Channel Processes Traction: large particles that are rolled along the riverbed Bradshaw Model by the force of water. Spend all/most of time on the riverbed. Saltation: gravel and small stones hop along the riverbed, as a fast eddy picks them up, and a slower one causes them to fall back down. Suspension: silts and clays are held up by the water. Gives rivers a cloudy appearance, especially close to the mouth. Solution: dissolved calcareous rocks. Load varies with discharge and velocity. Load is calculated at bank full. Capacity is the greatest amount of load that can be carried. Competence is the diameter of the largest particle that can be transported. 1.11. Hjülstrom Curve Deposition occurs when there is a reduction in energy, often at river mouths, estuaries and deltas. Energy reduces when: gradient reduces, friction increases, load increases, water volume decreases, water flows on the inside of a meander. Sedimentation occurs when sediment is dropped from still water. Flocculation is where charged ions in sea water allow clay particles to group and settle. Flocculation leads to development of mudbanks when water becomes brackish 1.9. Erosion close to the sea. Abrasion: riverbed and bank eroded by the river’s load. It is the mechanical impact produced by debris rubbing on the river’s sides. Abrasion increases with velocity and WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) rotation. Critical erosion velocity: lowest velocity needed to pick up particle of that size - entrainment. Mean settling velocity: velocity needed to drop particles from suspension. Clays have high entrainment value due to their cohesive nature, and gravels due to their weight. Sands are easiest to pick up. Clays remain in suspension if velocity is 0. Velocity for transport is always less than the velocity required to pick up (entrain) the particle. 1.12. River Flow Velocity is affected more by friction than gradient. We can 1.13. Channel Types measure friction with: 2 1 Straight: channel with sinuosity < 1.5. 1 is perfectly Bed roughness: N = R V×S , where R is the hydraulic 3 2 ​ ​ ​ straight. Rare, because thalweg will still move from side to radius, S is channel gradient and V is velocity. Higher the side due to helicoidal flow. Normally artificial. value of N, the rougher the riverbed. Braided: channel is divided by islands or bars. Islands are channel depth × width vegetated, whereas bars are not and are unstable. Hydraulic Radius: (2 x height) + width ​ Formed with steep gradient, coarse material, easily Thalweg is the imaginary line of fastest water velocity down a erodible bank, highly variable discharge. When discharge stream. is reducing (and hence velocity), sediment is plentiful and bars form (coarse then fine sediment). With reduced Laminar: water flows in sheets parallel to riverbed. No discharge, river must split to go around the bar. eddies or meanders. Common on smooth surfaces. Meandering: channel slope, discharge, helicoidal flow and Turbulent: water closest to bed/banks slowed by friction load combine to a situation where lateral erosion causes and is overtaken by thalweg. Turbulence created, and meandering. NOT a result of obstacles. water close to banks eddies towards the banks, water close to the bed eddies towards the bed. Helicoidal: horizontal turbulence produces a corkscrew 1.14. Landforms motion. The thalweg moves both laterally from bank to Meanders: a pronounced bend in the course of a river. bank, but also vertically from surface to bed during one Pools and riffles cause the thalweg to deflect. Where the thalweg is fastest, erosion occurs, and deposition where it is slowest. Over time, this creates a bend in the river. River Cliffs: steep side on the outside of a meander bend where erosion is strongest and downwards. Point Bars: deposits of sediment on the inside of a meander bend, where thalweg is slowest and rising. Oxbow Lakes: erosion with the thalweg causes narrowing of the bend neck, and after a flood event, the neck is breached. Meander cut off with more deposition, creating an oxbow lake. WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) Pools: deep sections develop where erosion dominates Catchment Flow Modifications (high velocity, dominant laminar flow). Riffles: shallower sections of the riverbed where sediment Deforestation: reduced evapotranspiration, increased has been deposited (low velocity, turbulent flow). Steep surface run off, reduced time lag and less surface positive relief gradient compared to the negative gradient storage. Higher peak discharge caused. of the pools. Afforestation: once a fully established forest, Related to helicoidal flow due to regular spacing. afforestation has the opposite effect to deforestation. Different gradients creates variations in subcritical Urbanisation: creation of impermeable surfaces reduces and supercritical flow, causing erosion or deposition. infiltration and increases overland flow. Sewage systems Waterfalls: river spills over gradient change where more and storm drains get water to the main channel much resistant rock is on top of less resistant rock, and quicker than throughflow. Lag times are reduced, and splashback undercuts rocks by processes of abrasion. flood peaks are increased. Building on floodplains Also produced by rejuvenation, where there is a knick reduces the available flood space, so flood waters will rise point. Plunge pool removes support for overhang, so higher. collapses. Causes upstream migration. Grazing: ploughing increases infiltration, heavy machinery Gorges: a deep, steep sided valley caused by waterfall causes soil compaction, so reduced infiltration, therefore retreat. higher peak discharge. Less evapotranspiration than forested area. Water logging/salination occur with poor drainage. Abstraction: over abstraction causes the drying up of rivers, falling water tables and saltwater intrusion in coastal areas. Channelisation: increases the hydraulic radius of a channel, so shorter lag times and higher flood peaks. Reductions in industrial activity: old springs re-emerge - Potholes: turbulence swirls pebbles around a depression surface water flooding, basements flood, leakage into in the river’s bed. Sides widened and deepened as pebble tunnels, reduced slope stability. erodes the cavity. Initiated by eddying. Water storage: building dams are good for flood/drought Rapids: upper course feature, where gradient is steep, control, irrigation, hydroelectric power. However, they and riverbed is rocky and irregular. Turbulent flow. can lose water, salinization occurs and ground water Bluffs: old floodplains erode leaving terraces. Meanders changes. erode the edge of the terrace, creating a line of steep slopes called bluffs. Floodplains: flat land made up of alluvium next to the 1.16. Causes and Impacts of River river, rise during floods, as fine silt is deposited. Floods Backswamps are sometimes created during flood events. Riverbed can raise if discharge is low, and sediment is Physical Causes deposited. Heavy, persistent rainfall (deep weather depressions) Levees: following a flood event where banks burst, Rapidly melting snow or ice wetted perimeter increases. Increased friction reduces Impermeable soil and bedrock velocity, and coarse material is deposited first around the Coastal storm surges banks, with finer material moving across the flood plain Lack of vegetation causing back swamps. Disaster (natural, or dam failure) Deltas: sediment is deposited where the river meets a Human Causes standing body of water, due to a loss of energy. Clay Urbanisation (impermeable surfaces, storm drains, particles flocculate and deposit. Bottomset beds (fine channel restrictions from bridges) material built out by turbidity currents) form first, then Floodplain developments increase risk foreset beds (coarse material carried seaward by Engineering that obstructs the channel rolling/saltation), then topset beds (fine material built by Mechanised farming and poor/inappropriate farming distributaries). practices. Arcuate Delta: fan shaped. Where longshore drift Impacts occurs. Deaths, damage and disruption Cuspate Delta: pointed, formed by two opposing Death toll higher in LICs. Cost higher in HICs currents. Bird’s Foot Delta: still sea allows each distributary to build in any direction. 1.17. Flood Prediction Recurrence Interval is how often, on average a flood of a 1.15. Human Impact certain size is likely to occur. WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) A 100-year flood is one that is expected to occur every materials have a higher albedo value and therefore 100 years, on average. reflect more radiation energy. Plotting a graph of flood magnitude against Planetary albedo: proportion of insolation scattered recurrence interval can show when a certain size and returned to space by Earth. flood is likely to occur, using a best fit line. Surface/Subsurface Absorption: since darker surfaces Or, look at flood history. absorb more radiation, the energy has potential to be Flood Risk Maps show where the river is likely to flood, transferred to lower layers via conduction. If conduction depending on if flood risk is severe (1-75 years) or is possible, the surface will remain cool as heat is moderate (76-200 years). transferred to the soil/bedrock. Conduction is Areas most at risk are low-lying parts of active encouraged when moisture is present. This heat is floodplains, small basins subject to flash floods, areas released back to the surface at night, offsetting night-time below unsafe dams and low-lying inland shorelines. cooling. Longwave radiation: since the Earth is a cold body, it 1.18. Flood Prevention emits longwave radiation back to space. Longwave radiation is easily absorbed by greenhouse gasses (water Forecasting and Warning: use of weather satellites, have and CO2) and by clouds, which return the heat to the an emergency plan, radio/internet communication, rain surface – called the greenhouse effect. Heat loss is gauges, river discharge gauges. Computer models that greatest on cloudless nights. compare new data with history Loss Sharing: disaster aid and insurance. Hard Engineering: work against natural processes. Construct dams, levees, straighten the channel, reservoirs, build diversion spillways. Normally fixes local problem but causes more up/downstream. Hazard Resistant Design: adjust buildings to reduce losses. Sandbags, seal doors/windows, move off lower floors. Flood gates installed on individual houses. Eg. Yarm, on the River Tees. Land Use Zoning: move/avoid building on flood prone Daytime budget = insolation – (reflected insolation + areas. Allow flooding to happen on floodplain. surface absorption + sensible heat transfers + latent heat Soft Engineering: working with natural processes. Flood transfers + longwave radiation) abatement decreases amount of run-off. Afforestation, Night-time budget = stored energy – (latent heat transfers contour ploughing, remove sediment. Flood diversion + sensible heat transfers + longwave radiation) allows areas to be flooded, not built upon. Appropriate Floodplain Use: working from the channel outwards, appropriate use would be - protected 2.2. Cloud Effects wetlands, rough grazing land (that animals can be removed from), parks and leisure areas, houses, then Day: clouds have a net cooling effect due to their albedo critical buildings such as hospitals furthest away. value, causing insolation to be reflected to space. Cirrus clouds allow insolation to pass through, but not longwave radiation. 2. Atmosphere and Weather Cumulonimbus clouds do not heat or cool well. Low, thick stratus clouds reflect 80% of insolation, keeping Earth’s surface cool. 2.1. Diurnal Energy Budgets Night: thick clouds acts as an insulating layer, absorbing and reradiating longwave radiation which keeps nights Radiation warm. Warm clouds can also emit longwave radiation out to space. Incoming Solar Radiation: shortwave UV insolation is the only energy input. Affected by the amount and type of cloud, the Sun’s angle. 2.3. Heat Transfers Around 5% is scattered by atmosphere 24% reflected into space by atmosphere Sensible Heat Transfer 23% absorbed by atmospheric gasses. Convection: thin air layer heated above surface (poor 48% absorbed by Earth’s surface and heats it. conductor), molecules vibrate more, gas is less dense so rises. Air cools, becomes denser and falls, to Reflected Solar Radiation: proportion of energy that is reflected back to the atmosphere is its albedo. Lighter replace rising air. At night, air might sink at night in higher latitudes. Some advection may occur. WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) Conduction: heat transfer between the ground and Temperature patterns: little seasonal variation at the the air when they are in contact. equator, but great variation in mid/high latitudes. A lag Latent Heat Transfer: occurs when water evaporates to time exists between overhead sun and maximum water vapour, or ice melts into water vapour. Heat insolation, as the atmosphere is heated from below, not required to change state is absorbed from the air, leaving above. Coldest period is after winter solstice, as ground less energy to heat the surface. Latent heat of continues to lose heat despite resumed insolation. condensation increases the speed and extent of Greater lag time over ocean due to high specific heat convection. capacity compared to land. Evaporation: water molecules gain enough energy from surrounding air to change state to a gas, and 2.5. Atmospheric Transfers leave the surface. This leaves overall energy less at the surface, so the surface and air cool. Pressure variations: air moves from high to low pressure. Dew: water saturated air comes into contact with an Low/declining pressure systems bring poor weather. object with a temperature cooler than the airs dew Surface pressure: low pressure in equatorial regions, as point. Water vapour condenses into liquid form. warm air rises and leaves the surface. Higher pressures Latent heat is released during condensation, adding seen in polar regions, where cool air descends onto the heat to the ground. surface. Absorbed Energy returned to Earth: greenhouse Surface wind belts: uneven due to seasonal variation in gasses absorb reradiated longwave radiation and insolation. Summer in N. Hemisphere causes cooling in atmosphere warms. southern, hence increasing differences between polar Surface Temperature Changes: during the day, the and equatorial air. Creates stronger high-level westerlies surface is heated by radiation, conduction, and in N. Hemisphere. convection. Surface air moves slow due to friction, is Ocean conveyor belt: cold, salty water sinks from polar heated, and rises as a result of convection. At night, regions and moves towards equator, where warm water ground is cooled by lack of radiation, heat from soil and gives its heat away to the surface winds. More rocks rises to heat the surface. evaporation in North Atlantic, which leaves saltier water behind – denser so sinks and cools. Water is transported 2.4. Global Energy Budgets to Pacific, dilutes, less dense so rises. 2.6. Seasonal Variations Latitudinal Radiation Pattern Temperature Excess: positive radiation budget in the tropics. Occurs Latitude: between the tropics, the angle of Sun is high, because insolation is so concentrated. so greater intensity of insolation is received, and Deficit: negative radiation budget at higher latitudes. hence more heating. Where there is more Insolation has a larger amount of atmosphere to pass atmosphere to pass through, a greater proportion of through, there is more chance of reflection back to space, insolation is lost/scattered/reflected by atmosphere. and rays are less concentrated. Also, the longer the sun shines, the more insolation is Balance: neither regions are getting warmer/colder, received. horizontal transfer from the tropics to higher latitudes Land/Sea distribution compensate to global insolation differences. Land Sea Lower reflectivity, so more Higher reflectivity, so less absorption of radiation (apart absorption of radiation from ice) (especially with low sun) Sun’s rays penetrate deep, Heat confined to near surface convection currents as surface has poor distribute heat to great conductors depths WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) Land Sea This fast-moving air produces jet streams. Air closer to Low specific heat capacity, so High specific heat capacity, so the equator will move slower. In addition, faster moving a set amount of energy raises set amount of energy raises air occurs at high pressure zones, due to centrifugal force land temp by more temp by less – because pressure and Coriolis force work together. Coriolis Force: air masses are deflected due to Earth’s Less water, so less energy Large amounts of energy easterly rotation. Air moving from high pressure to wasted to evaporation used for evaporation low pressure in the N. Hemisphere is deflected to the right, and to the left in the S.Hemisphere acts at right Ocean currents: surface currents caused by prevailing angles to wind direction. winds. Clockwise rotation in N.Hemisphere, and Geostrophic balance: between Coriolis Force and anticlockwise in S.Hemisphere. Water piles into domes pressure gradient, produces resultant wind – and due to Earth’s rotation, water is piled up on western Geostrophic wind. In N. Hemisphere, wind blows anti- edge of ocean basins – return flow is a narrow, fast clockwise around low pressure and clockwise around current (gulf stream). Warm currents from equatorial high pressure. ­ regions raise temps in polar regions. Warm surface Friction: reduces geostrophic force and wind speed, causes low pressure, air moves from high to low, so water so pressure gradient is no longer balanced by the moves from cold to warm; and winds push warm into Coriolis force. Makes air more likely to move to low warm, exposing cold deep water. Process repeats. pressure zones. 2.7. Global Circulation Model 3 Cell Model Hadley Cell: adjacent to ITCZ, where insolation is most intense. Doldrums created (permanent low-pressure belt) due to constant rising of air, trade winds are drawn in. Air subsides around 30°N/S and is deflected right/left depending on hemisphere. Ferrel Cell: not thermally induced, but a result of adjacent cells – creating a ‘cog-like’ system. Air is forced to rise at the polar front, and forced to sink at the high-pressure zone, where it meets the Hadley cell. Altitude: air temperature decreases with altitude, as air is Polar Cell: cold polar air sinks, creating high pressure. thinner, contains less moisture and is therefore less able As the air moves towards the equator, it spreads out, to absorb longwave radiation. pressure reduces, and it rises. Low pressure zone Pressure belts: link between winds and pressure, as created at 50-60°N/S. heating of air causes pressure changes, which puts air in motion thus causing the effect of wind. Pressure changes: air is driven by the pressure gradient – air moves from high to low pressure. Air moves as per the 3-cell model, where high pressure is caused where air sinks to the ground, leaving space for adjacent air at high altitudes to move over and add to the weight of the sinking air mass. Since earth is spinning, winds blow at angles due to the Coriolis force. Rossby waves: ridge and trough wave pattern of fast moving ‘rivers of air’. 3-6 in each hemisphere, and have their course altered by major barriers such as the Andes mountains. Where there is a trough, air converges (low Wind belts: air will move faster closer to the poles, due to pressure system) and at a ridge in the wave, air diverges (high pressure system); as the wind rises over pressure the distance between earths axis of rotation and the air. ridges, conditions at the surface change. WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) Upper westerlies: fast moving winds that result from a -12°C and -30°C, air can only be saturated over ice, so strong north/south temperature (and therefore pressure) water droplets must evaporate. Ice particles grow when gradient and the Coriolis force. Important for mixing the air has a mix of ice and water, as a result of warm and cold air – not included in 3 cell model. sublimation. Water vapour deposits on ice crystals. Jet streams: narrow column of fast-moving air through Precipitation occurs once ice crystals have aggregated the centre of Rossby waves. 10km above surface, around into a large enough snowflake to fall. When falling, ice 250km/h. Two exist in each hemisphere – the polar (30- may melt into rain. 50°N/S) and subtropical (20-30°N/S) jets; both flowing Convectional: land is heated and so air directly above eastward. Jet streams result from differences in becomes less dense, rises and cools. As air rises further, equatorial/sub-tropical air, and sub-tropical/polar air. latent heat is released, powering the ascent. When Greater the difference, stronger the jet stream. condensation occurs, clouds form, precip falls. Result of unstable air, where air parcel cools slower 2.8. Weather Processes and than surrounding air, so has to rise. Frontal: warm air meets cold air. Less dense warm air Phenomena can’t push cool air out of the way, so is forced over the colder air. Warm air rises, cools and condenses, forming a Atmospheric Moisture Processes cloud and therefore rain. Centre of low pressure where two air masses intersect. Evaporation: occurs when vapour pressure of a water Warm front: boundary of advancing warm air mass. surface exceeds that in the atmosphere. Sped up by: low Cold front: boundary of advancing cold air mass. initial air humidity, heat and strong wind. Result of conditional instability in air, where stable air Absolute Humidity: actual amount of water vapour in is forced to rise to where it hits dew point. a given volume of air. Orographic: pressure force strong enough to force air to Relative Humidity = move over a barrier. Air rises, it cools and reaches dew actual moisture content ×100 saturation moisture content at the same temp press ​ point where cloud forms and precipitation falls. Condensation: further cooling below dew point Windward side is called the ‘rain slope’, lee slope named temperature, or when an air mass reaches saturation – ‘rain shadow’ as unsaturated air sinks and warms. Hill fog turns water vapour into a liquid water. When hygroscopic occurs when the forced ascent produces a thin stratiform condensation nuclei are present. cloud. Unstable air (rising temp is warmer than the air Conduction Cooling: leads to condensation when rising into) causes continued rising, instead of falling moist air contacts a cold object. down the lee slope. Radiation Cooling: heat lost to space by longwave Result of conditional instability in air, where stable air radiation from clouds and gases in atmosphere. is forced to rise to where it hits dew point. Expansion Cooling: air rises and expands due to Radiation Cooling: cloudless night, so ground loses heat reduced pressure in atmosphere. Expansion causes a rapidly by returning radiation to space. Little wind temperature drop. present, air remains in contact with valley sides to cool by Freezing: liquid water changes into a solid once conduction, sinks to bottom of valley. Bottom of valley temperature falls below 0°C. has a source of moisture. Ground temperature inversion Melting: the change of state from solid to liquid above occurs and there is warmer air on the sides (heated by 0°C. morning sun, aided by dry ground) than at the bottom. Deposition: transition from water vapour to ice, with no This causes radiation fog and ice to form. intermediate stage. May deposit on surfaces. Frontal inversion: colder, denser air mass descends, Sublimation: transition from ice to water vapour, with no forming warmer air above. Barrier created where the two intermediate stage. Might occur in low humidity. meet that prevents warm air parcels from rising through to the warm air. 2.9. Causes of Precipitation Subsidence inversion: air moving upwards experiences adiabatic cooling, due to pressure decrease. This air falls, Requires hygroscopic condensation nuclei. becomes denser and warms, warm air reaches a cooler Collision Theory: droplets in clouds collide together (after layer of unstable air, and a temperature inversion is rising and falling at different rates based on their size) to created. from a larger droplet. A temperature inversion will dissipate once sun has Coalescence: two droplets combine to form rain. heated the ground long enough to cause cool air above to Aggregation: two ice crystals collide to form snow. warm by conduction processes – allowing warm air to Accretion: ice crystal collects a water droplet, forming rise. hail. Bergeron-Findeisen Theory: air is saturated with ice 2.10. Types of Precipitation before water is added. When air temperature is between WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) Clouds: if a cloud is tall enough to prevent sunlight reaching its base, it could produce precipitation. The base appears dark – such as nimbostratus and cumulonimbus. The latter stretches from sea level to the tropopause, forming an anvil head, because the cold air cannot rise through the warmer atmosphere. A cloud will not produce precipitation if it is thin enough to allow sunlight through, but may form fog if in contact with valley side/mountain top. Greenhouse gasses such as water vapour, carbon dioxide and methane allow shortwave radiation to penetrate, but prevent longwave. This traps radiation inside the atmosphere, causing temperature to rise. Evidence CO2 (315ppm 1950 400+ppm 2020) due to increased fossil fuel burning and deforestation – which increases emissions as well as removing trees that reduce emissions. 5 gigatons of fossil fuels were burnt Rain: liquid water droplets heavy enough to fall to the in 1980 – 1 ton burnt = 4 tons CO2 emitted. ground. Between 0.5mm and 5mm. Drizzle is rainfall less Methane (increases at 0.5-2% per year), cattle than 0.5mm. Varies in amount, intensity, duration. produces 75m tonnes and wetlands 150m tonnes. Hail: raindrops carried to freezing level inside a Methane released as perma-frost melts. cumulonimbus cloud, and freeze. Hailstones then collide CFCs (increases 6% each year) are 10,000x more with supercooled water freezing on impact. Rising and efficient at preventing longwave radiation from falling in the cloud causes repeated melting and freezing penetrating as CO2 (used as refrigerants aerosol until the hailstone is heavy enough to fall. propellants). Also destroys ozone, allowing more Snow: snow crystals form when temp is below freezing, insolation to enter the atmosphere. and water vapour turns solid. Heaviest snowfall occurs Nitrous oxides (increased by 8%) 300x more powerful when warm moist air is forced to rise in orthographic or than CO2, from fertilisers, burning fossil fuels and frontal rainfall, as very cold air contains limited moisture. vegetation. Dew: deposition of water on a surface that occurs in anticyclonic systems. Rapid radiation cooling causes Rising sea levels (3.1mm per year) as a result of ground temperature to hit dew point and thermal expansion and melting glaciers. First 60m of condensation/direct ground precipitation occur. ocean warms by 0.11°C each decade. Ocean acidity (26% acidity increase since 1750). Fog: forms as a result of radiation cooling. When sun Melting ice and glaciers around the world are showing rises, fog lifts, possibly causing smog to form under an inversion layer (cold air trapped by warm air above it). signs of decrease, exposing more land and adding to Fog is common over the sea in autumn and spring. the sea level rise. Arctic ice sheet shrunk by 65% since Steam Fog: localised when cold air blows over warmer 1975. Causes water, and air becomes saturated due to evaporation, Scientific consensus is that fossil fuel burning is resulting condensation causes steam. Advection Fog directly related to the global temperature increase. Winds move towards pole over cold sea, so chilled to This includes the emission of the gasses described. below dew point, forming advection fog. Albedo change: deforestation and urbanisation has resulted in more, much darker surfaces, so the Winds blow over cold ocean current, advection fog ground absorbs more radiation, which is released forms over the current. Air passes from sea onto cold land in winter, causing back to the atmosphere – heating it. advection fog, or hill fog if the air is forced to rise due Arguments against include: orbital eccentricity, axial to relief. Drizzle may fall if thick enough. tilt, axial precession, solar output variations, changes in ocean currents, and increased atmospheric dust from volcanoes. 2.11. The Human Impact El Niño: heats the planet as normal westward surface flow of currents reverses and warm water moves east Enhanced Greenhouse Effect which causes high temperatures and drought in Australia and heavy rainfall in Peru. La Niña produces colder years as a result of cool upwellings off the Peruvian coast. Atmospheric Impacts WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) Sea Levels: 200m people could be displaced, 4 million Tiny specific anomalies: often above canals/rivers. 2 km of land threatened by floods, 200m at risk from Insolation: due to pollution, longwave radiation is flood/droughts. Rise by 2100 is expected to be 26- trapped, and insolation reduced. Warming occurs by 77cm. 570 cities exposed, contamination of drinking the afternoon and mornings are colder than rural water (salt infiltrates groundwater and aquifers), areas. millions of coastline miles under threat. Microclimate Mitigation: London Plane tree. Warming oceans: 50% increase in marine heatwaves Installation of urban forest. Reduces ambient this decade. 1°C fluctuation causes plankton and coral temperatures by 3-5°C by shading and increased to stress and bleach (spit out symbiotic algae and die). evapotranspiration. Air quality improves too – so trees First 700m of ocean absorbs most heat. added to city schools. ‘Living’ roofs are popular. Storm Activity: more frequent and intense hurricanes, tornadoes etc… Floods have causes >500,000 deaths and affected 2.8bn globally, with $8bn in damages in 3. Rocks and Weathering the USA. Agriculture: USA’s grain belt will decrease, China’s 3.1. Plate Tectonics growing season will increase, Northward shift for timber and crop production. 35% drop in African produce if 3°C temperature rise. $10bn in losses in Texas and Oklahoma in a year due to failed crops. Drought: reduced rainfall in Europe and USA will expose 4bn to water shortage risks. Disease: 60 million more people exposed to Malaria, as mosquitos breed faster in the heat. Wildlife: 40% of species will become extinct at +2°C. Tourism: previously undesirable areas may become Nature of Tectonic Plates tourist hotspots, and likewise for desirable places becoming undesirable. Cost: 1 tonne CO2 causes £45 of damage. Solving the effects could cost 5-20% of each country’s GDP, whereas action now may only cost 1% of each GDP. 2.12. Urban Climates Theory Evidence Coastline fit of continents (Africa and South America) Orogenic belt fit (Britain, Norway and Newfoundland) Fossil remains in India match Australian ones. Since these animals couldn’t swim, plates must have been connected. General impacts and causes Glacial deposits (Brazil matches West Africa) Higher temperature: greater surface area to absorb Identical sedimentary sequences along Atlantic heat, low albedo of tarmac (10%) and concrete (20%) coastlines (Africa and South America) so less insolation is reflected (higher specific heat Continental crust: 35-70km thick, > 1500m years old, capacity surfaces), high buildings trap insolation and granite composition, rich in Silicon and Aluminium, less absorb heat, low buildings causes street to collect dense (2.6kgm-3), light colour. heat, more heat for atmosphere due to reduced Oceanic crust: 6-10km thick, < 200m years old, Basalt evapotranspiration, pollutants trap heat. composition, rich in Iron and Magnesium, denser Lower humidity: lack of vegetation so less (2.9kgm-3), dark colour. transpiration, high drainage density removes water, Movement fewer water bodies so less water available to Convection Theory: radioactive decay in Earth’s core evaporate. produces heat. Hot magma rises in convection More intense storms: greater instability of air, hence currents, cools at the surface and sinks as denser. stronger convection above urban areas. Hotspot: lava plume through mantle responsible for Slower winds: wind scattered by buildings. original crust rifting. Outward flow of viscous magma Less snowfall: due to higher temperatures. creates drag force on plates causing movement. Human activity: radiant heat from heating systems and buildings can contribute up to 50%. WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) Ridge push: magma intrusion at ocean spreading Sea floor spreading: creates oceanic crust, explained by ridges, which propels the two plates apart. palaeomagnetism – where lava cools and retains the Slab pull: the force that the sinking (colder and magnetic polarity of Earth at the time of cooling. Slow denser) edge of the plate exerts on the rest of the spreading is a result of the ridge being fed by small, plate. discontinuous magma chambers. Subduction: where denser plate (density similar to 3.2. Types of Plate Boundaries asthenosphere) is pushed into upper mantle. Subduction continues once initiated, driven by the weight of the plate Oceanic constructive: rising convection lifts lithosphere – subducted side remains cooler and therefore denser creating a ridge. Extensional forces cause stretching and than surrounding mantle. a fissure. Fissure opens and exposed magma fills gap, Rate of subduction matches rate of production. then cools and solidifies. MAGMA DOES NOT OVERFLOW Plate dip of 30° to 70° (older crust = steeper). TO FORM TOPOGRAPHIC HIGH. Evidence: surrounding landforms, Beinoff zone, Mid-Atlantic ridge: 0.7-1.4cm per year. disruption of temperature at depth. Continental constructive: as above, but less vigorous pull Beinoff Zone: narrow zone of earthquakes dipping so no clean break. Pulled thin creating fractures, faults away from deep sea trench. Extends to 680km deep. develop and central block slides down creating a rift Deep focus earthquakes occur further from valley which may fill with water. subduction. East-African rift valley: 2cm per year. Fold mountain building (Himalayas) Oceanic/Continental destructive: plates forced together Indo-Australian plate subducts under Eurasian plate. and oceanic plate subducts since denser. In the Benioff Same as collision plate description. Note that no zone, crustal melting occurs, and resultant magma forced magma escapes, so there is little volcanic activity. through cracks – to form volcanoes. Subducting plate Fold mountain building (Andes) drags down crustal material to form an ocean trench. Nazca oceanic plate subducts under continental Juan de Fuca and N.American plate: 3cm per year. South American crust. Oceanic destructive: plates forced together, older plate In addition to normal collision plate process, pieces of subducts as is denser. Forced 100 miles below and melts the Nazca plate scraped off and became part of the – producing magma chambers. Lower density magma accretionary wedge – adding to the mountain range. rises through cracks allowing volcanic eruptions. Partial melting of Nazca plate produces volcanoes. Japanese Arcs: 7-11cm per year. Ocean ridges: occur at divergent boundaries. Ridges are a Collision: powerful collision between two continental series of parallel ridges, with a central double ridge plates. Both densities are lower than the mantle’s, so separated by a ridge valley. As a result of tensions and prevented subduction. Some subduction occurs as stretching a central block may fall. lithosphere breaks free. Crust fragments are trapped in Ocean trenches: found at subduction zones. Long, collision zone, cause deformation. Intense compression narrow, asymmetric (steep side towards land mass) results in folding. depressions in the ocean floor (6000-11000m). Found Himalayan Mountain Range: 5-6cm per year. next to land and island arcs – common in Pacific Ocean Conservative: plates slip past each other with relative Volcanic island arcs: chains of volcanic islands on the horizontal movement (sinistral = left, dextral = right). continental side of an ocean trench. Lithosphere is neither created nor destroyed. Extensive Subducting plate heats up and melts 75 miles deep. earthquakes. Magma formed begins to rise to surface and meets Strike-slip: simple offset. the overriding plate. Material is added to crust – Transform: two divergent boundaries push together. building volcanoes. San Andreas Fault: 3-5cm per year. If upper plate is oceanic, volcanoes pile up until they poke through the surface – forming an island arc. Features: trench outer rise caused by subducting plate, gentle outer slope trench broken by faults, steep inner slope contains fragments of subducting plate. 3.4. Weathering The breakdown of rocks in situ, whereas erosion is the 3.3. Processes and Associated breakdown of material by movement processes. Limestones Landforms and sandstones are least resistant. Physical Processes WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) Produces small, angular fragments of the same rock. Extreme cases result in 1600% expansion, which causes cracking and fractures in the rock. Freeze-thaw: occurs in cold areas where ice forms as Carbonation: acid rain breaks down limestone/chalk. water freezes in cracks in rocks. Carbon dioxide dissolves in rainwater to make a weak Water that collects in crack freezes and expands 10% carbonic (acid rain) Exerts an average pressure of 14kg/cm2, crack forced Calcium carbonate in limestone reacts with carbonic open as this pressure exceeds rock’s resistance acid to form calcium carbonate Ice thaws, parts of the rock breaks free and the water CO2 + H2O ⇋ H2CO3 penetrates deeper. Repeats until rock cut through. Calcium carbonate is soluble and is washed away by Exfoliation: occurs in hot desert with large diurnal energy percolating water, so limestone is removed. range (40°C to below freezing). CaCO3 + H2CO3 Ca(HCO3)2 Rocks heat via conduction, only outer layers expand as rock is a poor heat conductor At night outer layers cool and contract more rapidly 3.6. General Factors Affecting than inner layers, creating stresses Weathering Non-uniform contraction stresses results in outer layers flaking off over time. Climate Salt crystal growth: physical disintegration due to fretting (saltwater penetrating) rock surfaces. Saline solution evaporates, leaving salt crystals A temperature rises, salt expands – exerting a pressure on the rock, causing disintegration Most effective in areas with temperatures around 27°C, where expansion is 300%, with Sodium Sulphate, Magnesium Sulphate and Calcium Chloride. Rates effected by porosity and permeability. Dilation: pressure release process. Overlying rocks are removed by erosion (unloading), or if a glacier load is removed Underlying rocks expand as under reduced pressure Fractures form parallel to the surface, producing pseudo-bedding planes. Deeper down, cracks are less prominent. Most broken = close to surface If horizontal pressure is released, vertical faults develop – common on cliff faces. Vegetation root action: roots can penetrate rocks or Rock Type: some minerals, cements (in sedimentary prevent rocks from forming/settling in a specific place. rocks) are more resistant to weathering than others. Limestone is susceptible to carbonation (CaCO3). 3.5. Chemical Processes Sandstone contains iron, therefore oxidation prone. Quartz is chemically resistant, cannot be chemically Creates altered rock substances. Requires water. weathered. Hydrolysis: acid water breaks down rocks with feldspar Rock Structure: differential resistance along lines of mineral (such as granite). weakness and grains control water movement. Acidic water reacts with feldspar in granite, forming Larger grain results in faster weathering, as there is kaolin, silicic acid and potassium hydroxyl greater void space and high permeability. Acid and hydroxyl are removed, leaving kaolin behind Natural lines of weakness in rock formations allow as the product. Hydroxyl is carbonated and removed water to penetrate – increasing weathering effects. in solution. Rocks can be porous/non-porous (measure of open Feldspar + Water Kaolin + Silicic Acid + Potassium space between grains) and permeable/impermeable Hydroxyl (measure of ease of ability to transmit water). More Hydration: certain minerals absorb water - allowing them permeable = more weathering. to expand and change, producing mechanical and Vegetation: increased organic acid production and carbon chemical stresses. Affects shale/mudstones. dioxide increases carbonation. Physical weathering may Clay minerals (such as Anhydrite) expand as they reduce as temperature are moderated. Roots will absorb water increase biological weathering. Anhydrite forms bonds with water to produce Relief: affects temperatures and exposure. hydrates (Gypsum) – causes 0.5% expansion. Weathered material must be removed to allow the process to continue. If a slope is too steep, water runs WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) away. If too shallow, no material is removed. underlying support, slope loading, lateral pressure, Colder temperature occurs higher, so freeze-thaw is transient stresses. dominant at higher altitudes. Decreased shear strength: weathering effects, Human activity: increased weathering due to increased changes in pore-water pressure, changes of structure, airborne chemical pollutants and acid rain. Vegetation organic effects. removal reduces chemical/biological weathering (fewer Opposition to movement: friction, cohesive forces, organic acids). pivoting, vegetation. 3.7. Specific Factors Affecting 3.9. Mass Movement Weathering Heaves (soil creep): slow movement of material where soil particles are heaved to the surface by wetting, Temperature heating and freezing of water. Occurs mainly in winter. Glacial: freeze-thaw is dominant, but number and Particles move perpendicular to the surface (path of duration of cycles is more important than degree of least resistance), and then fall under gravity once ice. Likely slow chemical weathering, but common particle has dried, cooled or water thawed. Net hydration. Alaska 0.04mm/yr. movement is down the slope. Temperate: chemical and biological processes are 1-3mm per year in UK. 10mm per year in rainforest. dominant due to abundance of moisture and Evidence: tension cracks in roads, tilted poles, vegetation. High organic contents, carbonates terracettes, soil piled behind field stone walls. deposited at dry areas. Askrigg 0.5-1.6mm/yr. Talus Creep: slow movement of fragments along a Arid/Semi-Arid: evaporation exceeds precipitation, so scree slope. mechanical processes are dominant. In semi-arid areas thick organic layers lead to leaching and CaCO3 \n accumulation. Egypt 0.0001-2.0mm/yr. Humid tropical: high seasonal rainfall and high temperatures results in significant chemical weathering. Florida 0.005mm/yr. Van’t Hoff’s Law: rate of chemical weathering increases 2-3x for each 10°C temperature rise up to 60°C. Rainfall Slumps: weaker rocks such as clays ‘slump’ with a rotational movement along a curved slip plane. Clay saturates and flows along slip plane. Commonly occurs if the base has been undercut. 3.8. Slope Processes Produces separate, jerky events. Flows: more continuous, smoother form of slump. Occurs Slope Processes in deeply weathered clay, and if particle size is the same or smaller than a grain of sand. Slope: any inclined surface (hill slope) or a slope angle. Mudflows are faster than earthflows (which are Categorising movements deeper and thicker). Higher water content allows flows to occur on shallower slopes. Can occur on saturated toe of a landslide, or as a separate event. Falls: occurs on steep slopes (>40°), with bare rock faces and exposed joints. Initial cause of rocks falling is erosion Slope failure causes or weathering. Increased shear stress: removal of lateral support Rocks detach and fall freely under gravity. If fall is (undercutting/slope steepening), removal of short, a straight scree is produced; otherwise a WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) concave scree is produced. Significantly contribute to the retreat of steep rock faces and providing debris for scree/talus slopes. Slides: when an entire mass of material moves along a slip plane. Can be rock/landslides, or a rotational slide. Material holds its shape until hitting the slope bottom. 3.11. The Human Impact Impact of Human Activities on Stability Excavations: cutting into a slope and leaving loose excavated creates a slope too steep to have stability, and is therefore prone to failure. Excavation at the toe of a slope removes the supporting section of the slope. Waste heaps: highly porous mounds of waste material from quarrying and mining leaves new, unstable steep Conditions: weak rocks, steep slope, active slopes. Slips occur with soil saturation after rainfall. Loading undercutting, intensely cold conditions or sudden change in water content. Buildings: add mass to slope, increase slip likelihood. Landslides: when material moves downslope as a Water: drainage routes disturbed by building result of shear failure. Downward force > resistance. foundations - excess water in soil increases mass and An increase in water content reduces strength will lead to slips (also has lubricating properties). If saturated soils are subjected to an earthquake, (particles pushed apart) and more mass is added. Rockslides: large rock mass slides down slip plane. liquefaction can occur (pressure between particles makes soil act as a liquid). Vegetation removal: deforestation leaves land bare (increased surface runoff, more erosion). If roots die/are removed, material is no longer bound together, and stability is compromised. Traffic vibrations: may trigger mass movements. Footpath trampling: intensified localised erosion. Construction on slopes: uses cut-and-fill technique (as described in excavation). Slip plane: junction between two layers along a bedding line, or the joint between two rock types. Point beneath the surface where shear stress > shear strength. 3.10. Water and Sediment Movement Sheetwash: occurs when the soil’s infiltration capacity is EROSION PROCESSES: can be increased by the removal of exceeded by precipitation rate. Hortonian flow. vegetation, ploughing up and down slopes (creating water Surface wash: unchanneled (sheet like) flow of water over channels and rills) and destruction of the soil structure soil’s surface. Some high/low velocity sections may (through overgrazing/growing, allowing organic develop. Transports material dislodged by rain splash, by deterioration). eroding a uniform layer of soil. Produces rills. Rills: shallow channels that carry water and sediment 3.12. Strategies to Modify Slopes for a short period of time. Common in agricultural lands after harvesting (bare land) and after Pinning: rock bolts, dowel bars and ground anchors compaction of the soil by heavy machinery. installed to hold loose rock into stable rock below. Rain splash: raindrops have an erosive effect. This effect Ground anchors penetrate deeper, through different rock is most prominent on slopes with inclines between 33° strengths. and 45° at the start of a rainfall even, when the soil is Netting: metal mesh nets attached to slope surface, loose. prevents loose rocks falling onto road/rails below. 5° slope: 60% of movement is downwards. 25° slope: 95% of movement is downwards. WWW.ZNOTES.ORG CAIE AS LEVEL GEOGRAPHY (9696) Grading: process of reducing the slope angle (by Shotcrete: loose surfaces sprayed with concrete to excavation) to reduce the risk of movement. Material prevent loose rocks from falling. must be transported away, so costs can be high. Afforestation: adding vegetation increases the interception, so less surface runoff and erosion occur. Reduces mudflows. More roots hold the soil bound. Reduced infiltration means the slope has less mass. Gabions: metal mesh boxes used to stabilise the toe of a landslip. Drainage: excess water adds mass to slope and lubricates it. Trenches dug (filled with permeable aggregate) to quickly remove water from a slope. Grouting: permeable rocks injected with cement to increase strength and reduce pore water capacity. WWW.ZNOTES.ORG CAIE AS LEVEL Geography (9696) Copyright 2022 by ZNotes These notes have been created by Reuben Allan for the 2021-22 syllabus This website and its content is copyright of ZNotes Foundation - © ZNotes Foundation 2022. All rights reserved. The document contains images and excerpts of text from educational resources available on the internet and printed books. If you are the owner of such media, test or visual, utilized in this document and do not accept its usage then we urge you to contact us and we would immediately replace said media. No part of this document may be copied or re-uploaded to another website without the express, written permission of the copyright owner. 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