Paper 1 - Section B Mixed Flashcards
4a) (i) Define the fluvial terms cavitation and traction. (4 marks)
Cavitation:
Cavitation is the process where air bubbles trapped in river water collapse violently, generating shockwaves that erode riverbanks and beds.
These bubbles form in fast-flowing water, especially in turbulent sections like waterfalls or rapids.
The repeated force from the collapse of these bubbles weakens rock surfaces, making them more susceptible to further erosion.
Example: Waterfalls, where high velocity increases turbulence and cavitation.
Traction:
Traction is a process of sediment transport where large, heavy materials such as boulders and pebbles are rolled or dragged along the riverbed due to the force of moving water.
This process occurs when a river has high energy levels, such as during floods or in the upper course of a river where gradients are steep.
Over time, traction contributes to the erosion of the riverbed through abrasion.
Example: During a flood event, large rocks in a riverbed move by rolling along the bottom due to increased water velocity.
4a) (ii) Briefly describe the conditions required for river beds to be eroded. (3 marks)
High Water Velocity and Turbulence:
Faster-moving water has more energy to detach and transport particles.
Erosion is more intense during floods when river discharge increases significantly.
Presence of Abrasive Materials:
Sand, gravel, and pebbles carried by the river act as tools for abrasion, wearing away the riverbed.
More sediment in the water increases the erosive power of the river.
Type of Rock Material in the Riverbed:
Soft rocks like clay and shale are easily eroded compared to hard rocks like granite.
Limestone can dissolve due to chemical erosion (solution).
Steep Gradient of the River Channel:
Steeper slopes increase the gravitational force on water, accelerating flow and enhancing erosion.
Human Activity:
Deforestation, dam construction, and channel modifications can increase river velocity, affecting erosion rates.
Example: The Grand Canyon was formed through millions of years of erosion by the Colorado River, where high velocity and sediment load contributed to its deep channels.
4b) Explain the formation of levées and floodplains. (8 marks)
Levées Formation:
Levées are natural embankments that form along riverbanks due to repeated flood events. Their formation involves:
Flooding and Overbank Flow:
When a river overflows its banks during floods, it carries large amounts of sediment.
Deposition of Heavy Sediments First:
As the water spreads out onto the floodplain, it slows down, causing larger particles (sand and gravel) to settle first near the riverbanks.
Successive Floods Build Up the Levées:
Over time, multiple floods deposit more sediment, raising the height of the levee and reinforcing the embankment.
Example: The levees along the Mississippi River in the USA have been reinforced through artificial embankments to prevent flooding.
Floodplain Formation:
Floodplains are flat areas adjacent to rivers, formed through deposition over long periods. Their formation occurs through:
Lateral Migration of Meanders:
As a river erodes on the outer bend and deposits sediment on the inner bend, it gradually widens and flattens the valley floor.
Deposition During Flooding:
During floods, water spreads over the surrounding land, losing velocity and depositing fine silt and clay, forming fertile alluvial soils.
Formation of Features like Oxbow Lakes:
Erosion and deposition create meanders, and when they are cut off, oxbow lakes form, shaping the floodplain.
Example: The Ganges floodplain in India and Bangladesh, which supports intensive agriculture due to its fertile soil.
6a) (i) Briefly describe the weathering process of pressure release (dilatation). (3 marks)
Pressure release, also known as dilatation, is a physical weathering process that occurs when overlying rock is removed, allowing the underlying rock to expand and crack.
Erosion of Overlying Material:
When glaciers, rivers, or wind erode rock layers above, pressure on the underlying rock decreases.
Expansion and Formation of Joints:
The reduced pressure allows the exposed rock to expand, creating parallel fractures (joints).
Exfoliation (Breaking Away of Rock Layers):
Over time, slabs of rock peel away in layers, especially in granite, where the process is called onion skin weathering.
Example: The granite domes in Yosemite National Park, USA, formed due to exfoliation caused by pressure release.
6a) (ii) Explain how ocean trenches are formed. (4 marks)
Ocean trenches are deep underwater valleys that form at convergent (destructive) plate boundaries due to subduction. The process involves:
Collision of Tectonic Plates:
When an oceanic plate collides with a continental or another oceanic plate, the denser plate subducts (sinks) beneath the lighter plate.
Subduction and Trench Formation:
The sinking plate bends downward, creating a long, deep trench at the point of subduction.
Accumulation of Sediments (Accretionary Wedge):
Over time, sediments accumulate in the trench, forming a wedge of deformed material.
Associated Earthquakes and Volcanism:
Subduction leads to intense earthquakes and the formation of volcanic arcs, such as the Mariana Trench and the Andes mountain range.
Example: The Mariana Trench in the Pacific Ocean, the world’s deepest trench (over 11,000m deep).
6b) Explain the movement of material on slopes. (8 marks)
The movement of material on slopes is controlled by gravity, water content, and slope angle. It occurs through mass movements, which include:
Creep (Slow Movement)
The gradual downhill movement of soil due to freeze-thaw cycles and wetting-drying expansion.
Evidenced by bent tree trunks and tilted fences.
Flows (Fast, Water-Saturated Movements)
Occur when excess water reduces friction, turning soil into a liquid-like flow.
Includes mudflows and debris flows, common after heavy rainfall.
Example: Vargas Mudslide, Venezuela (1999).
Slides (Sudden Movement Along a Plane)
A landslide occurs when a large mass of rock or soil moves as a single unit down a failure surface.
Example: Vaiont Dam Landslide, Italy (1963).
Falls (Vertical Movement of Rock or Debris)
Rocks detach and fall freely due to weathering and gravity.
Example: The White Cliffs of Dover, England.
4a) (i) Define the hydrological terms interception and throughfall. (4 marks)
- Interception (2 marks)
Definition: Interception is the process by which precipitation is captured and stored temporarily by vegetation before reaching the ground. (1 mark)
Explanation: Water may be held on leaves, branches, and stems before either evaporating back into the atmosphere or falling to the ground. The amount of interception depends on vegetation type, density, and precipitation intensity. (1 mark)
Example: Dense forests such as the Amazon Rainforest intercept a significant portion of rainfall, reducing direct surface runoff. - Throughfall (2 marks)
Definition: Throughfall is the process where precipitation passes through or drips off vegetation and reaches the ground. (1 mark)
Explanation: Raindrops may bypass leaves or drip from leaves, branches, and stems when the interception storage capacity is exceeded. This is common in heavy rainfall. (1 mark)
Example: In forests, throughfall contributes to soil moisture and infiltration, supporting tree roots and ecosystem growth.
4a) (ii) Briefly explain the effect of evaporation in the drainage basin system. (3 marks)
Reduces Surface Water Storage
Evaporation removes water from lakes, rivers, and reservoirs, decreasing overall water levels.
Limits Infiltration and Groundwater Recharge
Less surface water leads to lower infiltration rates, reducing groundwater levels and base flow to rivers.
Affects River Discharge
Higher evaporation rates lead to lower river discharge, especially in arid and semi-arid regions where temperatures are high.
Increases Atmospheric Moisture
Water lost from surfaces contributes to humidity, which can influence local rainfall patterns and weather conditions.
Example: In the Sahel region of Africa, high evaporation rates contribute to water scarcity and periodic droughts, reducing river and soil moisture.
4b) Explain how slopes and soils can affect the shape of a storm hydrograph. (8 marks)
- Effect of Slope Gradient on Hydrograph Shape
Steep Slopes → Flashy Hydrograph (Short Lag Time, High Peak Discharge)
Fast water movement downslope increases overland flow, leading to:
Short lag time (water reaches the river quickly).
Steep rising limb (discharge increases rapidly).
High peak discharge (flood risk increases).
Example: Mountainous regions like the Himalayas experience flash floods due to rapid runoff from steep slopes.
Gentle Slopes → Subdued Hydrograph (Long Lag Time, Low Peak Discharge)
Water has more time to infiltrate, leading to:
More throughflow and groundwater recharge.
Longer lag time (slow water movement to the river).
Lower peak discharge (flood risk reduced).
Example: Floodplains of the Amazon Basin experience gradual increases in discharge due to slow infiltration and water movement.
- Effect of Soil Type on Hydrograph Shape
Impermeable Soils (Clay) → Flashy Hydrograph
Low infiltration rate forces water to stay at the surface, increasing overland flow:
Short lag time (water moves quickly to rivers).
High peak discharge (water accumulates rapidly).
Example: Urban areas with compacted clay soils experience flash floods after heavy rainfall due to minimal infiltration.
Permeable Soils (Sandy) → Subdued Hydrograph
High infiltration rate allows water to soak into the ground, reducing surface runoff:
Longer lag time (water reaches the river slowly).
Lower peak discharge (reduced flood risk).
Example: Desert areas with sandy soils have low runoff and a slow hydrological response.
6a) (i) Contrast the process of sheetwash with that of rainsplash. (4 marks)
- Sheetwash (2 marks)
Definition: Sheetwash is the movement of water across a surface as a thin, unchannelized flow, transporting sediment downslope. (1 mark)
Explanation: This occurs when rainfall exceeds infiltration capacity, creating a sheet of moving water that causes erosion on bare slopes. (1 mark)
Example: Sheetwash is common in deforested slopes or desert regions, where there is little vegetation to absorb water. - Rainsplash (2 marks)
Definition: Rainsplash is the dislodging of soil particles by raindrop impact, moving them downslope. (1 mark)
Explanation: When raindrops hit bare soil, they create small craters, lifting particles into the air. On sloped surfaces, more particles are displaced downslope, leading to erosion. (1 mark)
Example: Rainsplash contributes to soil erosion in exposed farmlands and unprotected hillsides.
6a) (ii) Briefly explain how ocean ridges are formed. (3 marks)
Ocean ridges form at divergent plate boundaries, where tectonic plates move apart, allowing magma to rise and create new oceanic crust.
Divergent Plate Movement
Convection currents in the mantle pull two oceanic plates apart.
Magma Rises and Solidifies
As plates separate, magma rises through the gap, cooling and solidifying to form new crust.
Continuous Spreading Forms a Ridge
Over time, repeated volcanic activity builds up an underwater ridge, such as the Mid-Atlantic Ridge.
Example: The Mid-Atlantic Ridge, where the Eurasian Plate and North American Plate are moving apart.
6b) Explain the main differences between the mass movement processes of flows and slides. (8 marks)
- Flows (Wet, Chaotic Movements)
Definition: Flows involve the rapid movement of water-saturated soil, mud, or debris.
Key Features:
Occur in areas with high water content.
Material moves like a liquid, with no clear slip plane.
Internal deformation mixes material, creating chaotic movement.
Example: The Vargas Mudslide (Venezuela, 1999), a debris flow triggered by heavy rainfall. - Slides (Coherent Block Movements)
Definition: Slides occur when a cohesive mass of rock or soil moves downhill along a distinct slip plane.
Key Features:
Movement is relatively slow compared to flows.
Material remains in a single, intact mass.
Often triggered by earthquakes, heavy rain, or undercutting of slopes.
Example: The Vaiont Dam Disaster (Italy, 1963) was a rockslide caused by water saturation.
4a) (i) Describe one way a spring is formed in an area. (3 marks)
Gravity Spring (Unconfined Aquifer)
Water moves through a permeable rock layer (e.g., sandstone) and meets an impermeable rock layer (e.g., clay) that prevents further downward movement. (1 mark)
The water is forced to move laterally, eventually emerging at the surface where the impermeable layer ends, creating a spring at the base of a hill or valley side. (1 mark)
Example: Many natural springs occur in chalk hills, where water is trapped by underlying impermeable clay, such as in the Chiltern Hills, UK. (1 mark)
Alternative Types of Springs
Other ways springs form include:
Artesian Springs (Confined Aquifer): Water under pressure in a confined aquifer is forced to the surface when the pressure is released (e.g., the Great Artesian Basin in Australia).
Fault Springs: Water emerges where fault lines in rock allow groundwater to flow to the surface.
4a) (ii) Briefly explain why some parts of a river are braided. (4 marks)
A braided river consists of multiple interwoven channels separated by islands of deposited sediment. Braiding occurs due to high sediment load, fluctuating discharge, and unstable banks.
- High Sediment Load
Rivers with large amounts of bedload (gravel, sand, and silt) deposit sediment in the channel when velocity decreases.
These deposits create temporary islands (eyots) that force water to split into multiple channels. - Fluctuating Discharge
In rivers with variable flow rates, sediment is deposited during low flow periods and reworked during floods.
Example: Glacial meltwater rivers (e.g., the Brahmaputra River in South Asia) often have braided channels due to seasonal discharge changes. - Unstable Riverbanks
Banks composed of non-cohesive sediment (e.g., sand and gravel) erode easily, preventing the river from maintaining a single stable channel.
4b) Explain the formation of floodplains and river bluffs. (8 marks)
- Formation of Floodplains
Definition: A floodplain is a flat area adjacent to a river that floods periodically, depositing sediment.
Process:
When a river overflows its banks during floods, it deposits fine sediment (alluvium) on the valley floor.
The river loses energy as floodwaters spread out, leading to sequential deposition (larger sediments near the river, finer ones further away).
Repeated floods build up layers of sediment, making the floodplain wider, flatter, and fertile.
Example: The Mississippi River floodplain is one of the largest in the world, supporting extensive agriculture. - Formation of River Bluffs
Definition: River bluffs are steep slopes or cliffs that mark the edge of a floodplain.
Process:
As meanders erode valley sides, steep bluff lines form where the floodplain ends.
These bluffs are composed of older, resistant material, left behind as the river widens its floodplain.
Lateral erosion by the river undercuts the valley sides, forming a steep bluff.
Example: The Missouri River bluffs formed as the river eroded softer sediments, leaving behind resistant rock.
6a) (i) Define the weathering terms pressure release (dilatation) and freeze-thaw. (4 marks)
- Pressure Release (Dilatation) (2 marks)
Definition: Pressure release occurs when overlying rock is removed (e.g., by erosion), allowing the underlying rock to expand. (1 mark)
Process: This expansion creates cracks (joints) parallel to the surface, weakening the rock and making it more susceptible to further weathering. (1 mark)
Example: Granite landscapes in Yosemite National Park, USA, show large exfoliation domes caused by pressure release. - Freeze-Thaw Weathering (2 marks)
Definition: Freeze-thaw occurs when water enters cracks in rocks, freezes, and expands, breaking the rock apart. (1 mark)
Process:
Water seeps into cracks during warm periods and freezes at night.
Since ice expands by 9%, pressure increases, widening the cracks.
Repeated freezing and thawing eventually shatter the rock. (1 mark)
Example: Freeze-thaw is common in mountainous regions such as the Alps and Scottish Highlands.
6a) (ii) Briefly explain why some rock types are more affected by the weathering process of carbonation. (3 marks)
Carbonation is a chemical weathering process where rainwater absorbs carbon dioxide (CO₂) to form carbonic acid, which reacts with calcium carbonate (CaCO₃) in rocks, dissolving them.
- Limestone and Chalk Are Highly Affected
These rocks contain high amounts of calcium carbonate, making them highly vulnerable to carbonation. - Climate Influences Carbonation
Carbonation is more effective in humid, rainy environments, where more CO₂ dissolves in water, increasing acidity. - Example of Affected Rock
Limestone pavements in Yorkshire, England, show deep cracks (grikes) and blocks (clints) due to carbonation.
6b) Explain how vegetation and relief affect the type of weathering. (8 marks)
- Influence of Vegetation on Weathering
a) Biological Weathering
Plant roots grow into rock cracks, exerting pressure and breaking rocks apart (root wedging).
Example: Tree roots breaking pavement or rock slabs in forests.
b) Chemical Weathering
Vegetation produces organic acids (humic acids) that enhance chemical weathering by dissolving minerals.
Example: Tropical rainforest soils experience high chemical weathering rates due to decaying vegetation. - Influence of Relief (Slope and Elevation) on Weathering
a) Steep Slopes Reduce Chemical Weathering
Water quickly drains off steep slopes, reducing chemical reactions.
Example: Rocky mountain slopes in the Himalayas have limited chemical weathering.
b) Shallow Slopes Encourage Weathering
Gentle slopes allow more water to soak into the ground, increasing hydrolysis, carbonation, and oxidation.
Example: Lowland areas in tropical regions experience deep weathering profiles.
c) Freeze-Thaw Weathering at High Altitudes
In cold climates, relief influences freeze-thaw weathering as temperature fluctuations are more extreme.
Example: Glacial regions like the Alps show significant frost-shattered rock fragments.
4a) (i) Define the fluvial terms helicoidal flow and saltation. (4 marks)
- Helicoidal Flow (2 marks)
Definition: Helicoidal flow is a corkscrew-like (spiral) motion of water within a river channel, common in meanders. (1 mark)
Process:
This secondary flow moves from the outer bend of one meander to the inner bend of the next.
It helps in the erosion of river cliffs (outer bends) and deposition on slip-off slopes (inner bends). (1 mark)
Example: The River Thames meanders exhibit helicoidal flow, influencing riverbank erosion and sediment deposition. - Saltation (2 marks)
Definition: Saltation is a type of river sediment transport where small to medium-sized particles (sand, gravel) are lifted and dropped in a bouncing motion along the riverbed. (1 mark)
Process:
The river’s energy is not strong enough to keep particles permanently suspended, but it is sufficient to lift them momentarily before they settle again. (1 mark)
Example: In braided rivers, saltation moves gravel and sand downstream, shaping river channels.
4a) (ii) Briefly explain how river bluffs are formed. (3 marks)
Formation of River Bluffs
River bluffs are steep valley sides that mark the edge of a floodplain, formed by erosion and deposition processes.
Lateral Erosion by Meandering Rivers (1 mark)
The river erodes the outer bends of meanders through hydraulic action and abrasion.
This gradually steepens valley sides, forming bluff lines.
Floodplain Deposition (1 mark)
During floods, sediments are deposited across the floodplain, but the valley sides remain elevated above the floodplain.
River Migration and Bluff Formation (1 mark)
Over time, meander migration widens the floodplain, leaving behind steep river bluffs where erosion has cut into resistant material.
Example
The Missouri River bluffs are steep valley sides formed by continuous lateral erosion and floodplain expansion.
4b) Explain how a storm hydrograph is affected by the size and shape of a drainage basin. (8 marks)
- Effect of Drainage Basin Size
a) Small Drainage Basin → Flashy Hydrograph
Water reaches the river quickly, leading to:
Short lag time (fast response to rainfall).
Steep rising limb (rapid increase in discharge).
Higher peak discharge (flash flooding risk).
Example: The Boscastle flood (UK, 2004) occurred in a small, steep basin, causing a rapid flood event.
b) Large Drainage Basin → Subdued Hydrograph
Water takes longer to reach the main river, leading to:
Longer lag time (delayed peak flow).
Gentler rising limb (gradual increase in discharge).
Lower peak discharge (less flooding risk).
Example: The Amazon River Basin has a large area, leading to slow water movement and a delayed hydrograph response. - Effect of Drainage Basin Shape
a) Circular Drainage Basin → Flashy Hydrograph
All tributaries are equidistant from the main channel, meaning water arrives simultaneously, increasing flood risk.
Example: The Mississippi Basin has areas where circular sub-basins cause localized flooding.
b) Elongated Drainage Basin → Subdued Hydrograph
Water reaches the river at different times, reducing peak discharge.
Example: The River Severn (UK) has an elongated basin, allowing gradual water flow to the main channel.
6a) (i) Define the weathering terms carbonation and hydrolysis. (4 marks)
- Carbonation (2 marks)
Definition: Carbonation is a chemical weathering process in which carbon dioxide (CO₂) in rainwater forms carbonic acid, dissolving rocks rich in calcium carbonate (e.g., limestone). (1 mark)
Process:
CO₂ + H₂O → H₂CO₃ (carbonic acid)
The acid reacts with calcium carbonate in limestone, dissolving it and forming calcium bicarbonate, which is carried away in solution. (1 mark)
Example: Karst landscapes in the Yorkshire Dales (UK) are formed by carbonation. - Hydrolysis (2 marks)
Definition: Hydrolysis is a chemical weathering process where minerals in rock react with water, leading to the breakdown of silicate minerals. (1 mark)
Process:
Feldspar in granite reacts with water, forming kaolinite (clay) and dissolved ions.
This weakens the rock structure, making it more vulnerable to erosion. (1 mark)
Example: Hydrolysis occurs in tropical regions, breaking down granite into kaolin clay.
6a) (ii) Briefly explain how rock can be weathered by heating and cooling. (3 marks)
- Expansion and Contraction of Rock (1 mark)
Rocks expand when heated by the sun during the day and contract when cooled at night.
This repeated thermal stress weakens the rock structure over time. - Formation of Exfoliation Layers (1 mark)
In extreme climates, outer layers peel off due to repeated expansion and contraction.
This process is called onion-skin weathering (exfoliation). - Occurrence in Arid and Semi-Arid Climates (1 mark)
This weathering process is common in desert regions, where high daytime temperatures and cold nights cause extreme temperature changes.
Example: The Sahara Desert experiences thermal stress weathering, leading to rock fragmentation.
6b) Explain how two factors affect the type and rate of weathering. (8 marks)
- Climate (Temperature and Precipitation)
Physical Weathering:
In cold climates, freeze-thaw weathering dominates, breaking rocks through frost action.
Example: The Scottish Highlands experience freeze-thaw weathering in winter.
Chemical Weathering:
In warm, humid climates, chemical weathering (carbonation, hydrolysis) occurs faster.
Example: The Amazon Rainforest has deep weathered soils due to high rainfall and humidity. - Rock Type (Composition and Structure)
Resistant Rocks:
Hard rocks like granite resist weathering, while soft rocks like limestone dissolve easily in acidic water.
Permeable Rocks:
Limestone undergoes carbonation, forming karst landscapes.
Example: The Chalk Cliffs of Dover (UK) erode quickly due to weak calcium carbonate composition.
4a) (i) Define the fluvial terms solution and throughflow. (4 marks)
- Solution (2 marks)
Definition: Solution is a river transport process where dissolved minerals (e.g., calcium carbonate) are carried in the water as an invisible load. (1 mark)
Process:
This occurs when water is slightly acidic, dissolving soluble minerals from rocks like limestone. (1 mark)
Example: In karst landscapes (e.g., the Yorkshire Dales, UK), rivers transport calcium bicarbonate in solution. - Throughflow (2 marks)
Definition: Throughflow is the downslope movement of water within the soil layer, moving parallel to the surface. (1 mark)
Process:
Rainwater infiltrates the soil and moves through pore spaces or cracks toward river channels. (1 mark)
Example: Throughflow is faster in sandy soils (due to larger pores) and slower in clay soils (due to low permeability).
4a) (ii) Briefly explain how turbulent flow causes erosion in river channels. (3 marks)
- Characteristics of Turbulent Flow (1 mark)
Turbulent flow is irregular and chaotic, creating eddies and vortices in the river.
Water moves in multiple directions, increasing its erosive power. - Erosion Through Hydraulic Action and Abrasion (1 mark)
Turbulent water forces air into cracks in riverbanks, leading to hydraulic action.
The swirling motion picks up sediment, which grinds against the riverbed and banks, causing abrasion. - Formation of Potholes (1 mark)
In areas of strong turbulence, pebbles get trapped in depressions and drill into the riverbed, forming potholes.
Example: The Whirlpool Rapids in the Niagara River exhibit intense turbulent erosion.
4b) Explain how water stores in a drainage basin system are affected by changes in land use. (8 marks)
- Impact of Urbanization
Impermeable surfaces (roads, pavements, buildings) prevent infiltration, reducing groundwater storage.
Increased surface runoff leads to faster river discharge, increasing flood risks.
Example: The expansion of London’s urban area has led to reduced groundwater recharge. - Impact of Deforestation
Less interception by vegetation causes more surface runoff and reduced soil moisture storage.
Root water uptake decreases, leading to lower transpiration rates and disrupting the water cycle.
Example: Amazon Rainforest deforestation has reduced regional rainfall and dried out local rivers. - Impact of Agriculture
Irrigation increases soil moisture storage but may deplete groundwater stores if overused.
Plowing breaks up compacted soil, increasing infiltration, but monoculture farming reduces soil organic matter, limiting water retention.
Example: Over-irrigation in California’s Central Valley has led to groundwater depletion and land subsidence. - Impact of Dam Construction and Reservoirs
Dams increase surface water storage, but they reduce downstream river flow, affecting floodplain ecosystems.
Example: The Aswan High Dam (Egypt) reduced sediment deposition on the Nile floodplain, altering natural water storage.
6a) (i) Define the weathering terms salt crystal growth and hydration. (4 marks)
- Salt Crystal Growth (2 marks)
Definition: Salt crystal growth occurs when salty water evaporates, leaving behind salt deposits that expand and break rock apart. (1 mark)
Process:
Water containing dissolved salts (e.g., sodium chloride) seeps into rock pores and cracks.
As water evaporates, salt crystallizes and expands, exerting pressure that weakens the rock structure. (1 mark)
Example: Salt crystal growth is common in hot deserts and coastal areas, such as Death Valley (USA). - Hydration (2 marks)
Definition: Hydration is a chemical weathering process where minerals absorb water molecules, causing them to expand and weaken. (1 mark)
Process:
Certain minerals (e.g., anhydrite) absorb water and convert into hydrated forms (e.g., gypsum), leading to volume increase and rock breakdown. (1 mark)
Example: Hydration affects clay-rich rocks, leading to swelling and landslides in humid regions.
6a) (ii) Briefly explain how vegetation root action can lead to the weathering of rocks. (3 marks)
- Physical Root Action (1 mark)
Tree roots grow into rock cracks, exerting pressure and breaking the rock apart as they expand.
Example: Tree roots breaking concrete pavements in urban areas. - Chemical Root Action (1 mark)
Roots release organic acids, which chemically react with minerals in the rock, weakening it.
Example: Decaying plant material in forests produces humic acid, enhancing rock breakdown. - Enhancement of Freeze-Thaw Weathering (1 mark)
Root expansion creates larger cracks, allowing water infiltration and enhancing freeze-thaw cycles in cold climates.
Example: Vegetation contributes to rock breakdown in mountainous regions like the Alps.
6b) Explain how rock type affects the type and rate of chemical weathering. (8 marks)
- Composition and Mineral Stability
Limestone and chalk (calcium carbonate) undergo carbonation, dissolving in acidic rainwater.
Granite (silicate minerals) undergoes hydrolysis, where feldspar converts to clay.
Example: Karst landscapes in China’s Guilin region are shaped by carbonation. - Rock Permeability and Porosity
Permeable rocks (e.g., sandstone) allow water infiltration, accelerating chemical weathering.
Non-porous rocks (e.g., granite) weather more slowly because water cannot easily enter.
Example: Weathering of porous limestone in the Burren, Ireland. - Joints and Bedding Planes
Rocks with many fractures (e.g., limestone) weather faster due to increased surface area exposure.
Massive, unfractured rocks (e.g., basalt) resist weathering.
Example: The Grand Canyon’s exposed rock layers weather at different rates, shaping cliffs and valleys. - Climate Influence on Rock Type
Tropical climates accelerate chemical weathering of silicate-rich rocks (granite, basalt) due to high temperatures and humidity.
Arid regions experience less chemical weathering, as low water availability slows down reactions.
Example: Tropical hydrolysis of granite in Brazil’s Amazon Basin.
4a) (i) Define the fluvial terms laminar flow and evapotranspiration. (4 marks)
- Laminar Flow (2 marks)
Definition: Laminar flow refers to a smooth and uniform movement of water in parallel layers, with no mixing between layers. (1 mark)
Process:
It occurs in slow-moving water with low turbulence, typically in the lower course of a river or in shallow water. (1 mark)
Example: Glacial meltwater channels sometimes exhibit laminar flow. - Evapotranspiration (2 marks)
Definition: Evapotranspiration is the combined process of evaporation from water surfaces and soil, along with transpiration from vegetation. (1 mark)
Process:
It is a key component of the hydrological cycle, influencing water loss in a drainage basin. (1 mark)
Example: High evapotranspiration rates occur in tropical rainforests due to high temperatures and dense vegetation.
4a) (ii) Briefly explain why abrasion/corrasion varies along a river channel. (3 marks)
- Sediment Load and Size (1 mark)
More sediment = More abrasion.
Larger, angular particles cause more erosion than smaller, smoother ones. - River Velocity and Discharge (1 mark)
Higher river velocity = More kinetic energy, increasing abrasion potential.
In rapids and waterfalls, high-velocity water enhances erosion, while in slower sections (e.g., floodplains), abrasion is minimal. - Rock Type and Resistance (1 mark)
Soft rocks (e.g., sandstone) erode faster due to lower resistance.
Hard rocks (e.g., granite) resist abrasion, slowing erosion rates.
Example: The Niagara River experiences intense abrasion near the waterfall but much less in the calm downstream section.
4b) Explain the relationship between riffle and pool sequences in meandering river channels. (8 marks)
- Formation of Riffles and Pools (2 marks)
Pools (deep sections) form at outer bends of meanders, where fast-moving water erodes the riverbed.
Riffles (shallow sections) form in straight sections between meanders, where reduced velocity causes sediment deposition. - Role of Helicoidal Flow in Erosion and Deposition (2 marks)
Helicoidal flow (spiral current) moves sediment from the outer bend (pool) to the inner bend (riffle).
This continuous erosion and deposition maintain the riffle-pool sequence. - Influence on River Dynamics (2 marks)
Riffle-pool sequences help regulate river energy, ensuring efficient sediment transport.
In flood events, pools store water, while riffles slow the flow, reducing erosion downstream. - Example: The River Severn, UK (2 marks)
The River Severn has riffle-pool sequences in its middle course, maintaining a balanced energy state.
Conclusion: Riffles and pools form a dynamic equilibrium, with erosion in pools and deposition in riffles, shaping meandering rivers.
6a) (i) Contrast continental and oceanic tectonic plates. (4 marks)
- Composition and Density (2 marks)
Continental plates: Made of granite (sial - silica & aluminum), less dense.
Oceanic plates: Made of basalt (sima - silica & magnesium), denser. - Thickness and Age (2 marks)
Continental plates: Thicker (35–70 km) but older (up to 4 billion years).
Oceanic plates: Thinner (5–10 km) but younger (less than 200 million years).
Example:
The Pacific Plate (oceanic) is subducting under the North American Plate (continental) at the Cascadia Subduction Zone.
6a) (ii) Briefly explain the distribution of volcanic island arcs. (3 marks)
- Location at Subduction Zones (1 mark)
Volcanic island arcs form above subduction zones, where one oceanic plate sinks beneath another. - Formation of Arc-Shaped Chains (1 mark)
Melting of the subducted plate produces magma, which rises to form volcanic islands in a curved arc. - Example: The Pacific Ring of Fire (1 mark)
The Mariana Islands (Philippines) and Aleutian Islands (Alaska) are examples of volcanic island arcs.
Conclusion: Volcanic island arcs occur where two oceanic plates converge, forming chains of active volcanoes.
6b) Explain how afforestation and slope grading can reduce mass movements on slopes. (8 marks)
- Afforestation (Tree Planting) (4 marks)
a) Root Stabilization (1 mark)
Tree roots bind soil particles together, increasing slope cohesion.
b) Reduction of Surface Erosion (1 mark)
Leaves intercept rainfall, reducing surface runoff and soil loss.
c) Water Absorption and Drainage Improvement (1 mark)
Trees absorb water, reducing pore water pressure that triggers landslides.
d) Example: The Himalayas (1 mark)
Afforestation in Nepal has reduced monsoon-triggered landslides. - Slope Grading (Modifying Slope Angle) (4 marks)
a) Reducing Slope Steepness (1 mark)
Flattening steep slopes decreases gravity’s effect, improving stability.
b) Creation of Terraces (1 mark)
Step-like terraces reduce water runoff speed, decreasing erosion.
c) Directing Water Flow (1 mark)
Graded slopes channel excess water safely, preventing oversaturation.
d) Example: Slope Grading in Japan (1 mark)
Japan uses engineered terraces to reduce landslide risks after earthquakes.
Conclusion:
Afforestation improves soil cohesion and reduces runoff, while
Slope grading decreases gravity’s effect and improves water drainage.
4a) (i) Define the fluvial terms cavitation and suspension. (4 marks)
- Cavitation (2 marks)
Definition: Cavitation is an erosional process in which air bubbles trapped in water collapse, creating shockwaves that weaken riverbanks and beds. (1 mark)
Process:
Water forces air into cracks in the riverbank or bed.
The air bubbles suddenly collapse (implode), releasing energy that fractures the rock. (1 mark)
Example: Cavitation is common in high-velocity rivers, waterfalls, and rapids (e.g., Niagara Falls). - Suspension (2 marks)
Definition: Suspension is a river transport process where fine sediment particles (e.g., silt, clay) are carried within the water column without touching the riverbed. (1 mark)
Process:
Small, lightweight particles remain suspended in fast-moving water.
When river velocity decreases, suspended load settles as deposition. (1 mark)
Example: The Amazon River carries large amounts of suspended sediment, giving it a muddy appearance.
4a) (ii) Describe the formation of a point bar within a river. (3 marks)
A point bar (slip-off slope) is a depositional feature found on the inner bend of a meandering river.
- Reduced Velocity on the Inner Bend (1 mark)
Water moves more slowly on the inner bend of a meander due to reduced energy levels. - Deposition of Sediment (1 mark)
As the river loses energy, it deposits sediment, forming a gently sloping accumulation of sand and gravel. - Gradual Growth and Vegetation Colonization (1 mark)
Over time, point bars grow, and vegetation may establish, stabilizing the deposit.
Example: The Mississippi River has well-developed point bars along its meanders.
4b) Explain how a river flood can impact people. (8 marks)
- Loss of Life and Injury (2 marks)
Fast-moving floodwaters can drown people and animals.
Example: The 2010 Pakistan floods killed over 1,700 people due to flash flooding. - Damage to Property and Infrastructure (2 marks)
Floods destroy homes, roads, bridges, and power lines, leading to high repair costs.
Example: The 2019 Venice flood submerged historic buildings, causing extensive damage. - Economic Disruptions (2 marks)
Businesses close due to flood damage, leading to job losses and income reduction.
Agricultural land is submerged, destroying crops and livestock.
Example: The 2011 Thailand floods affected major industries, disrupting global supply chains. - Waterborne Diseases and Food Shortages (2 marks)
Floodwaters contaminate drinking water, leading to cholera and dysentery outbreaks.
Food supplies are disrupted, leading to hunger and malnutrition.
Example: The Bangladesh 1998 floods led to widespread disease outbreaks due to contaminated water.
6a) (i) Define the weathering terms pressure release (dilatation) and hydrolysis. (4 marks)
- Pressure Release (Dilatation) (2 marks)
Definition: Pressure release occurs when overlying rock layers are removed (e.g., by erosion), allowing underlying rock to expand and fracture. (1 mark)
Process:
When overburden is removed, rock expands and cracks, forming joints parallel to the surface. (1 mark)
Example: The exfoliation domes in Yosemite National Park, USA, were formed by pressure release. - Hydrolysis (2 marks)
Definition: Hydrolysis is a chemical weathering process where minerals in rock react with water, leading to decomposition. (1 mark)
Process:
Feldspar in granite reacts with water, forming clay minerals (kaolinite).
This weakens the rock, making it more vulnerable to erosion. (1 mark)
Example: Hydrolysis is common in humid tropical regions like the Amazon Rainforest.
6a) (ii) Briefly explain the role of water in mass movement. (3 marks)
- Increased Pore Water Pressure (1 mark)
Water infiltrates soil and fills pore spaces, reducing friction and cohesion.
This makes slopes unstable and more likely to fail. - Slope Saturation and Weight Increase (1 mark)
Heavy rainfall adds weight to the slope, increasing gravitational force.
Example: The Vargas Mudslide (Venezuela, 1999) was triggered by excessive rainfall. - Water as a Lubricant in Mudflows (1 mark)
In saturated soils, water acts as a lubricant, allowing rapid flow of debris.
Example: Lahars (volcanic mudflows) in Indonesia are triggered by heavy rain mixing with volcanic ash.
6b) Explain how temperature affects physical weathering processes. (8 marks)
- Freeze-Thaw Weathering (Frost Shattering) (2 marks)
Water enters rock cracks, freezes, and expands by 9%, widening the cracks.
Repeated freeze-thaw cycles cause rock disintegration.
Example: Frost shattering is common in the Scottish Highlands. - Thermal Expansion (Exfoliation) (2 marks)
Rocks expand when heated by the sun and contract when cooled at night.
Repeated expansion and contraction cause surface layers to peel off (exfoliation).
Example: The Sahara Desert experiences strong exfoliation due to high temperature fluctuations. - Salt Crystal Growth (2 marks)
In hot, dry climates, water evaporates from rock pores, leaving salt crystals.
Expanding salt crystals exert pressure, causing rock to break apart.
Example: Salt weathering is common in coastal cliffs like the White Cliffs of Dover, UK. - Granular Disintegration (2 marks)
Dark and light minerals absorb heat at different rates, leading to unequal expansion.
This causes rock grains to separate, breaking the rock down.
Example: Granular disintegration affects granite landscapes in tropical regions.
Conclusion: Temperature-driven physical weathering varies by climate, with freeze-thaw dominant in cold regions and exfoliation in deserts.
4a) (i) Describe two ways that sediment is transported in rivers. (4 marks)
- Traction (2 marks)
Definition: Traction is a process where large, heavy sediments such as boulders and pebbles are rolled along the riverbed. (1 mark)
Process:
This occurs in high-energy environments like the upper course or during floods.
The force of fast-moving water pushes rocks along the riverbed. (1 mark)
Example: In mountain streams, large boulders are moved by traction during storms. - Suspension (2 marks)
Definition: Suspension is the transport of fine sediments (silt, clay) that remain lifted within the water column. (1 mark)
Process:
The river’s velocity keeps the fine particles from settling, allowing them to be carried downstream.
When the river slows down, suspended particles settle as deposition. (1 mark)
Example: The Amazon River carries large amounts of sediment in suspension, giving it a muddy appearance.
4a) (ii) Describe a riffle and pool sequence in a river channel. (3 marks)
- Riffles (1 mark)
Riffles are shallow, fast-moving sections with coarse sediment (gravel, pebbles).
They form where water velocity is lower, causing deposition of larger materials. - Pools (1 mark)
Pools are deeper, slower-moving sections with fine sediment (silt, sand).
They form where erosion is dominant, typically on the outer bends of meanders. - Connection Between Riffles and Pools (1 mark)
Water moves in a helicoidal flow, transferring sediment from riffles to pools.
This process helps balance the river’s energy and sediment transport.
Example: The River Severn (UK) has well-developed riffle-pool sequences in its middle course.
4b) Explain how a river flood can impact the natural (physical) environment. (8 marks)
- Erosion and River Channel Changes (2 marks)
Fast-moving floodwaters erode riverbanks, widening channels and increasing sediment transport.
Meanders may shift, creating oxbow lakes and new river courses.
Example: The Mississippi River has changed its course multiple times due to erosion during floods. - Deposition of Nutrient-Rich Sediments (2 marks)
Floods spread alluvium (fine silt and clay) over floodplains, making soil fertile.
This supports agriculture but can also bury existing vegetation.
Example: The Nile River’s annual floods enriched Egyptian farmlands for centuries. - Destruction of Natural Habitats (2 marks)
Flooding washes away vegetation, leading to habitat loss for wildlife.
Wetlands can be permanently altered, affecting biodiversity.
Example: The Bangladesh Sundarbans mangrove forests suffer regular flood damage. - Water Contamination and Pollution (2 marks)
Floodwaters carry sewage, chemicals, and debris, contaminating rivers, lakes, and groundwater.
This can harm aquatic ecosystems and kill fish populations.
Example: The 2011 Thailand floods spread industrial pollution into rivers and farmland.
6a) (i) Describe the characteristics of a mass movement flow. (4 marks)
- High Water Content and Fluid Motion (1 mark)
Flows contain large amounts of water, making them move like a liquid. - Variable Speed Depending on Slope (1 mark)
Fast flows (e.g., mudflows) occur on steep slopes.
Slow flows (e.g., solifluction) happen on gentler slopes. - Transport of a Mixture of Debris (1 mark)
Flows carry rock, soil, and organic material, forming a chaotic, unstructured mass. - Distinctive Flow Track and Depositional Lobe (1 mark)
Flows leave behind scar marks on slopes and spread out at the base.
Example: The Vargas mudflows (Venezuela, 1999) killed thousands after heavy rains.
6a) (ii) Describe the process of a mass movement heave. (3 marks)
- Expansion and Lifting of Soil Particles (1 mark)
Heave occurs when individual soil particles are lifted due to wetting, freezing, or thermal expansion. - Vertical Movement Followed by Downslope Motion (1 mark)
As soil dries or thaws, particles settle back down slightly downslope, causing slow mass movement. - Slow and Continuous Process (1 mark)
Heave is a long-term process, leading to gradual downslope movement.
Example: Soil creep in the Scottish Highlands causes fence posts to tilt over time.
6b) Explain how rainfall influences the type and rate of weathering. (8 marks)
- Increased Chemical Weathering in Wet Climates (2 marks)
More rainfall = More chemical weathering (e.g., hydrolysis, carbonation).
Example: Limestone landscapes dissolve due to carbonation in humid regions like the UK. - Freeze-Thaw Weathering in Cold, Wet Areas (2 marks)
In temperate and polar regions, rainfall enters rock cracks and freezes, expanding by 9%.
This widens cracks, breaking rocks apart over time.
Example: Freeze-thaw weathering affects mountainous areas like the Alps. - Salt Weathering in Dry, Occasional Rainfall Areas (2 marks)
In arid regions, rainwater evaporates quickly, leaving salt crystals that expand and fracture rock.
Example: The Atacama Desert experiences salt crystallization weathering. - Increased Biological Weathering in High-Rainfall Areas (2 marks)
More rainfall = More plant and microbial growth, leading to root expansion and acid production.
Example: In tropical rainforests, intense root action weakens rocks, promoting breakdown.
Conclusion: Rainfall accelerates chemical, physical, and biological weathering, shaping landscapes differently based on climate and rock type.
4a) (i) Describe the process of throughflow on slopes. (3 marks)
- Infiltration of Water (1 mark)
Rainwater infiltrates the soil surface after precipitation, moving downward due to gravity. - Lateral Flow of Water Downslope (1 mark)
When the water reaches an impermeable layer (e.g., clay), it moves laterally through the soil pores.
Water moves downslope toward streams and rivers. - Rate and Influence of Soil Type (1 mark)
In permeable soils (e.g., sandy soils), throughflow is faster.
In clayey soils, water moves more slowly, causing temporary waterlogging.
4a) (ii) Explain how the type of vegetation affects the shape of a storm hydrograph. (4 marks)
- Dense Vegetation Increases Lag Time (1 mark)
Interception by leaves slows down rainfall, delaying water reaching the river.
This prolongs lag time, reducing flashy hydrographs. - Root Uptake Reduces Peak Discharge (1 mark)
Roots absorb groundwater, decreasing the volume of water that enters the river.
This results in lower peak discharge. - Deforestation Increases Runoff and Flooding (1 mark)
Without vegetation, water reaches the ground directly, increasing surface runoff.
This shortens lag time and increases peak discharge, creating a flashy hydrograph. - Seasonal Changes in Vegetation (1 mark)
Deciduous trees lose leaves in winter, reducing interception.
Example: In the UK, storm hydrographs show steeper rising limbs in winter due to reduced interception by trees.
4b) Explain the formation of river cliffs and point bars in a meandering river channel. (8 marks)
- Role of Thalweg and Water Velocity (2 marks)
The thalweg (fastest flow path) follows the outer bend, leading to greater erosion.
Slow water on the inner bend deposits material, forming point bars. - Formation of River Cliffs (Outer Bend) (2 marks)
Hydraulic action and abrasion erode the outer bend, forming steep river cliffs.
Undercutting leads to overhanging cliffs, which eventually collapse due to gravity. - Formation of Point Bars (Inner Bend) (2 marks)
Reduced velocity on the inner bend leads to deposition.
Sand and gravel accumulate, forming gently sloping point bars. - Influence of Helicoidal Flow (2 marks)
Helicoidal flow (corkscrew motion) moves eroded sediment from the outer bend to the inner bend.
This maintains the meander shape and point bar formation.
Example: The Mississippi River exhibits well-developed meanders with river cliffs and point bars.
6a) (i) Define the weathering terms hydrolysis and pressure release (dilatation). (4 marks)
- Hydrolysis (2 marks)
Definition: Hydrolysis is a chemical weathering process where minerals react with water, altering their structure. (1 mark)
Process:
Feldspar in granite reacts with water, forming kaolinite (clay minerals).
This weakens the rock, making it more susceptible to erosion. (1 mark)
Example: Hydrolysis is common in tropical rainforests, where high rainfall accelerates chemical weathering. - Pressure Release (Dilatation) (2 marks)
Definition: Pressure release occurs when overlying rock is removed (e.g., through erosion), allowing the underlying rock to expand and fracture. (1 mark)
Process:
When the weight of overlying material is removed, the rock expands, creating parallel joints.
This process can lead to exfoliation (onion-skin weathering). (1 mark)
Example: The granite domes of Yosemite National Park (USA) have formed due to pressure release.
6a) (ii) Briefly explain how a rock can be weathered by heating and cooling. (3 marks)
- Expansion and Contraction (1 mark)
During the day, rocks heat up and expand, while at night, they cool and contract.
This repeated expansion and contraction weakens rock surfaces. - Formation of Cracks (1 mark)
Over time, internal stress causes fractures and peeling.
Granular disintegration occurs when different minerals expand at different rates. - Occurrence in Deserts and High Mountains (1 mark)
Most effective in arid areas with large temperature fluctuations.
Example: In the Sahara Desert, rocks break apart due to intense daytime heating and rapid cooling at night.
6b) Explain how the movement of tectonic plates leads to the formation of ocean trenches and ocean ridges. (8 marks)
- Formation of Ocean Trenches (Convergent Boundaries) (2 marks)
At subduction zones, an oceanic plate sinks beneath another plate, forming a deep trench.
Example: The Mariana Trench (Pacific Plate subducting beneath the Mariana Plate) is the deepest ocean trench. - Process of Subduction (2 marks)
The denser oceanic plate bends downward, forming a deep-sea trench.
As it sinks, it melts, creating volcanic arcs behind the trench. - Formation of Ocean Ridges (Divergent Boundaries) (2 marks)
At mid-ocean ridges, plates move apart, allowing magma to rise and solidify as new crust.
Example: The Mid-Atlantic Ridge is formed by the separation of the North American and Eurasian Plates. - Role of Sea-Floor Spreading (2 marks)
As magma emerges at the ridge, new crust forms, pushing older crust away.
Magnetic striping in ocean rocks confirms this process.
4a) (i) Define the hydrological terms recharge and infiltration. (4 marks)
- Recharge (2 marks)
Definition: Recharge is the process by which groundwater is replenished by water percolating from the surface. (1 mark)
Process:
Occurs when rainwater or surface water infiltrates into the soil and reaches the water table.
Recharge rates depend on soil permeability, precipitation, and human activities. (1 mark)
Example: The Great Artesian Basin in Australia is recharged by rainfall infiltration through sandstone layers. - Infiltration (2 marks)
Definition: Infiltration is the movement of water from the ground surface into the soil. (1 mark)
Process:
Water enters pores in the soil due to gravity and capillary action.
Infiltration rate depends on soil type, vegetation, and saturation levels. (1 mark)
Example: Sandy soils have higher infiltration rates than clayey soils due to larger pore spaces.
4a) (ii) Briefly explain how interception is affected by vegetation type. (3 marks)
- Dense Vegetation Increases Interception (1 mark)
Forests and woodlands intercept more rainfall due to thick canopies.
Example: Rainforests intercept 30–50% of rainfall, slowing water movement. - Deciduous vs. Evergreen Differences (1 mark)
Evergreen trees (e.g., conifers) have higher interception year-round, as they retain leaves in winter.
Deciduous trees shed leaves in winter, reducing interception in colder months. - Short and Sparse Vegetation Has Low Interception (1 mark)
Grasslands and crops intercept less rain, allowing more direct infiltration and runoff.
Example: In agricultural areas, short crops intercept less than 10% of rainfall.
4b) Describe and explain helicoidal patterns of flow and turbulent patterns of flow in river channels. (8 marks)
- Helicoidal Flow (4 marks)
a) Definition and Process (2 marks)
Helicoidal flow is a corkscrew-like motion of water within a meandering river.
Water moves from the outer bend to the inner bend along the riverbed, then returns to the outer bend near the surface.
b) Role in River Processes (2 marks)
Transports sediment from river cliffs to point bars, maintaining meander shape.
Example: The River Severn (UK) exhibits helicoidal flow, moving material downstream in meanders. - Turbulent Flow (4 marks)
a) Definition and Process (2 marks)
Turbulent flow occurs when water moves chaotically, with swirls and eddies.
Caused by bed roughness, obstacles, and high velocity.
b) Effects on River Dynamics (2 marks)
Increases erosion through hydraulic action and abrasion.
More turbulence = Greater sediment transport and deeper channels.
Example: The Colorado River’s turbulent flow deepens the Grand Canyon through intense erosion.
6a) (i) Describe how a rotational slide can affect a slope. (3 marks)
- Formation of a Back Scar (1 mark)
As the slope moves, a steep back scarp forms at the top, exposing fresh soil and rock. - Downward and Rotational Movement (1 mark)
The slope material rotates and moves downslope as a single unit.
The failure surface is curved rather than straight. - Creation of a Toe Feature (1 mark)
At the base, displaced material accumulates as a bulging toe.
Example: The Holbeck Hall Landslide (UK, 1993) resulted in a large rotational slump along the coastline.
6a) (ii) Define the terms sheetwash and rills. (4 marks)
- Sheetwash (2 marks)
Definition: Sheetwash is the thin, unconfined movement of water across a surface, carrying soil and sediment. (1 mark)
Process:
Occurs during heavy rain, when water moves downslope in a thin layer.
Causes erosion, transporting fine particles across the landscape. (1 mark)
Example: Common in deforested slopes and overgrazed land. - Rills (2 marks)
Definition: Rills are small, narrow channels formed by running water on a slope. (1 mark)
Process:
Form when sheetwash becomes concentrated into small streams.
Rills widen and deepen into gullies if erosion continues. (1 mark)
Example: Rill erosion is common in over-cultivated farmlands.
6b) Explain how the chemical composition of rocks and the physical structure of rocks affect the way they are weathered. (8 marks)
- Chemical Composition Influencing Weathering (4 marks)
a) Carbonate Rocks and Carbonation (2 marks)
Limestone (CaCO₃) dissolves in carbonic acid (rainwater mixed with CO₂).
Forms karst landscapes with caves and sinkholes.
Example: The Yorkshire Dales in the UK have limestone pavement formations.
b) Silicate Rocks and Hydrolysis (2 marks)
Feldspar in granite reacts with water, breaking down into clay minerals.
Leads to the gradual breakdown of granite over time.
Example: Hydrolysis occurs in humid, tropical regions like the Amazon Basin. - Physical Structure Influencing Weathering (4 marks)
a) Joints and Bedding Planes (2 marks)
Highly jointed rocks weather faster because water can enter cracks more easily.
Granite has few joints, making it resistant to weathering, while limestone has many joints, increasing vulnerability.
b) Porosity and Permeability (2 marks)
Porous rocks (e.g., sandstone) absorb water, increasing chemical weathering.
Impermeable rocks (e.g., basalt) resist weathering, breaking down mainly through physical processes.
Example: Sandstone weathers quickly in wet climates due to high porosity.
4a) (i) Define the hydrological terms evaporation and percolation. (4 marks)
- Evaporation (2 marks)
Definition: Evaporation is the process by which water changes from liquid to gas (water vapour) due to heat from the sun. (1 mark)
Process:
Occurs from water bodies (oceans, lakes, rivers) and wet surfaces (soil, vegetation).
Influenced by temperature, humidity, and wind speed. (1 mark)
Example: High evaporation rates occur in deserts due to intense solar radiation. - Percolation (2 marks)
Definition: Percolation is the downward movement of water through soil and permeable rock layers into the groundwater zone. (1 mark)
Process:
Occurs after infiltration, where water moves deeper underground.
Depends on soil porosity and permeability. (1 mark)
Example: In limestone landscapes, percolation allows water to reach underground caves and aquifers.
4a) (ii) Briefly explain what is meant by a flood recurrence interval. (3 marks)
- Definition of Recurrence Interval (1 mark)
The flood recurrence interval is the estimated time between floods of a certain magnitude occurring in a specific location. - Probability of Flood Occurrence (1 mark)
A 100-year flood does not mean it happens exactly every 100 years, but there is a 1% chance of it occurring in any given year. - Use in Flood Management (1 mark)
Helps engineers and planners design flood defences based on historical data and risk assessment.
4b) Describe and explain the formation of deltas. (8 marks)
- Conditions Necessary for Delta Formation (2 marks)
High sediment load: Rivers must carry and deposit large amounts of silt, clay, and sand.
Low-energy environment: Weak tides and currents prevent sediment removal, allowing accumulation. - Deposition and Land Growth (2 marks)
As the river slows down upon entering the sea, its carrying capacity decreases, depositing sediment in layers.
Fine silt and clay settle furthest (prodelta), while coarser sand settles closer to the shore (delta plain). - Delta Types Based on Water Movement (2 marks)
Arcuate Delta (e.g., Nile Delta) – Formed by balanced wave action and sediment deposition.
Bird’s Foot Delta (e.g., Mississippi Delta) – Formed where river deposition dominates over tides.
Estuarine Delta (e.g., Seine Delta) – Formed in river estuaries with tidal mixing. - Role of Vegetation and Human Activity (2 marks)
Mangroves and plants trap sediments, stabilizing deltas.
Human activities (dam construction, deforestation) disrupt sediment supply, leading to delta shrinkage.
5a) (i) Briefly describe how albedo affects what happens to incoming (shortwave) solar radiation. (3 marks)
- High Albedo = More Reflection (1 mark)
Bright surfaces (e.g., ice, snow, clouds) reflect more shortwave solar radiation.
Example: The Antarctic ice sheet has an albedo of 80-90%, meaning most sunlight is reflected. - Low Albedo = More Absorption (1 mark)
Dark surfaces (e.g., oceans, forests) absorb more solar radiation, increasing surface heating.
Example: Urban areas with dark asphalt roads absorb heat, contributing to the urban heat island effect. - Influence on Climate and Energy Balance (1 mark)
High-albedo regions stay cooler, while low-albedo regions warm up more.
Example: The loss of Arctic ice reduces albedo, accelerating global warming.
5a) (ii) Describe two ways longwave radiation is prevented from leaving the Earth’s atmosphere. (4 marks)
- Greenhouse Gas Absorption (2 marks)
Greenhouse gases (CO₂, methane, water vapour) absorb outgoing longwave radiation and re-radiate it back to Earth.
Example: The burning of fossil fuels increases CO₂, trapping more heat in the atmosphere. - Cloud Cover and Atmospheric Reflection (2 marks)
Clouds trap outgoing longwave radiation, preventing heat loss at night.
Example: Tropical regions with dense cloud cover stay warmer at night due to trapped heat.
5b) Explain how the distribution of land and sea influences seasonal variations in temperature. (8 marks)
- Land Heats and Cools Faster than Water (2 marks)
Land has a lower specific heat capacity than water, meaning it heats up and cools down more quickly.
Example: Siberia experiences extreme winter cold and summer heat due to rapid temperature changes on land. - Water Stores and Releases Heat More Slowly (2 marks)
Oceans absorb heat during summer and release it in winter, moderating temperatures.
Example: The UK has milder winters than Russia due to the Gulf Stream warming the Atlantic Ocean. - Continental vs. Maritime Climates (2 marks)
Inland (continental) areas have extreme seasonal variations, while coastal (maritime) areas have milder seasons.
Example: New York (coastal) has milder winters than Chicago (inland), despite being at similar latitudes. - Influence of Ocean Currents on Temperature (2 marks)
Warm ocean currents (e.g., Gulf Stream) raise coastal temperatures.
Cold currents (e.g., California Current) cool coastal regions.
4a) (i) Define the hydrological terms stemflow and throughflow. (4 marks)
- Stemflow (2 marks)
Definition: Stemflow is the process where intercepted rainfall runs down the stems and branches of plants before reaching the ground. (1 mark)
Process:
Water is first intercepted by leaves and branches before flowing down stems.
Smooth-barked trees enhance stemflow, while rough-barked trees reduce it. (1 mark)
Example: Tropical rainforests have high stemflow due to dense vegetation cover. - Throughflow (2 marks)
Definition: Throughflow is the horizontal movement of water through the soil towards a river channel. (1 mark)
Process:
Water infiltrates the soil and moves laterally due to gravity.
Throughflow speed depends on soil porosity and permeability. (1 mark)
Example: In hilly areas, throughflow contributes to stream baseflow during dry seasons.
4a) (ii) Briefly explain how underground water may form springs. (3 marks)
- Water Table Intersecting the Surface (1 mark)
A spring forms where the water table naturally meets the ground surface, allowing groundwater to flow out. - Permeable and Impermeable Rock Layers (1 mark)
Water percolates through permeable rock (e.g., sandstone) and is blocked by an impermeable layer (e.g., clay).
This forces water to emerge at faults or slopes. - Types of Springs (1 mark)
Artesian springs occur in confined aquifers, where pressure forces water to the surface.
Example: The Chad Basin (Africa) has artesian wells due to water trapped under pressure.
4b) Describe and explain how a meander forms. (8 marks)
- Initial Irregularities and Helicoidal Flow (2 marks)
Minor channel irregularities cause uneven water flow, leading to erosion on one side and deposition on the other.
Helicoidal flow (corkscrew motion) moves sediment from outer to inner bends, enhancing meander formation. - Erosion at the Outer Bend (River Cliff Formation) (2 marks)
Faster water velocity on the outer bend leads to erosion through hydraulic action and abrasion.
Undercutting creates steep river cliffs, increasing meander curvature. - Deposition at the Inner Bend (Slip-off Slope Formation) (2 marks)
Slower water on the inner bend leads to deposition, forming a gentle slip-off slope (point bar).
Sediment accumulates over time, extending the meander curve. - Continuous Migration of Meanders (2 marks)
As erosion and deposition continue, meanders migrate laterally and downstream.
Over time, meanders may form oxbow lakes when two bends meet.
Example: The Mississippi River has well-developed meanders that constantly shift due to sediment transport.
5a) (i) Define the atmospheric terms convection and wind belts. (4 marks)
- Convection (2 marks)
Definition: Convection is the vertical movement of warm air rising and cooler air sinking due to temperature differences. (1 mark)
Process:
Sun heats the Earth’s surface, warming air above it.
Warm air expands, becomes less dense, and rises, creating convection currents. (1 mark)
Example: Tropical convection creates thunderstorms in the Amazon Rainforest. - Wind Belts (2 marks)
Definition: Wind belts are large-scale patterns of moving air caused by atmospheric circulation and Earth’s rotation. (1 mark)
Process:
Air moves from high to low-pressure areas, creating prevailing winds.
Trade winds, westerlies, and polar easterlies are major wind belts. (1 mark)
Example: The Northeast Trade Winds blow from 30°N towards the Equator.
5a) (ii) Briefly describe how solar radiation may be reflected. (3 marks)
- Reflection by Clouds (1 mark)
Clouds reflect 20–30% of incoming solar radiation, preventing some heat from reaching the surface. - High Albedo Surfaces (1 mark)
Snow and ice reflect up to 80% of solar radiation, reducing warming.
Example: The Antarctic ice sheet reflects most incoming sunlight. - Atmospheric Scattering (1 mark)
Dust and gas molecules scatter solar radiation in different directions.
Example: Volcanic eruptions release ash that reflects sunlight, causing cooling.
5b) Explain how human activity can affect the temperature of an urban area. (8 marks)
- Urban Heat Island (UHI) Effect (2 marks)
Cities absorb and retain more heat than rural areas, leading to higher temperatures.
Example: London is 2–4°C warmer than surrounding countryside due to UHI effects. - Reduced Albedo from Dark Surfaces (2 marks)
Concrete and asphalt absorb more heat due to their low albedo.
Example: City roads heat up faster than rural grasslands. - Heat from Human Activities (2 marks)
Industry, vehicles, and air conditioning release excess heat, warming urban areas.
Example: New York’s high energy consumption raises city temperatures. - Limited Vegetation and Evapotranspiration (2 marks)
Less vegetation reduces cooling through evapotranspiration.
Example: Green roofs and urban parks help reduce UHI effects.
