Paper 1 - Section B Mixed

Question 1

4a) (i) Define the fluvial terms cavitation and traction. (4 marks)

Answer 1

Cavitation (simple explanation):Cavitation happens when tiny air bubbles in fast-moving river water suddenly burst. When they burst, they create small shockwaves that break bits off the riverbed and riverbanks.These bubbles usually form in very fast, rough water like at waterfalls or rapids.When the bubbles keep bursting over and over, they weaken the rock, making it easier for erosion to happen.Example: Waterfalls, where fast-flowing water creates more bubbles and more cavitation.
Traction (simple explanation):Traction is when big, heavy rocks like boulders or pebbles are pushed or rolled along the bottom of a river by the moving water.This happens when the river is very strong, like during floods or in steep mountain rivers.As these rocks move, they scrape against the riverbed, slowly wearing it down (a process called abrasion).Example: In a flood, large rocks are rolled along the riverbed because the water is flowing very fast.

Question 2

4a) (ii) Briefly describe the conditions required for river beds to be eroded. (3 marks)

Answer 2

High Water Speed and Turbulence (simple explanation):When water flows quickly, it has more energy to pick up and carry rocks and soil.Erosion is much stronger during floods, because the river has more water and moves faster.
Abrasive Materials in the River (simple explanation):Rivers carry things like sand, gravel, and small stones.These materials act like sandpaper, scraping and wearing down the riverbed and banks.The more of these materials there are, the more erosion happens.
Type of Rock in the Riverbed (simple explanation):Some rocks are soft, like clay and shale, and are easy for the river to erode.Hard rocks like granite take much longer to wear away.Limestone can slowly dissolve in the water through a process called solution (a type of chemical erosion).
Steep Slopes (simple explanation):If the river flows down a steep hill, gravity pulls the water faster.This faster flow causes more erosion.
Human Activity (simple explanation):People can change how rivers behave.Cutting down trees (deforestation), building dams, or changing the shape of the river can make the water move faster, which increases erosion.
Example:The Grand Canyon was carved out over millions of years by the Colorado River.The fast-moving water and the large amount of sediment it carried helped create its deep and wide channels.

Question 3

4b) Explain the formation of levées and floodplains. (8 marks)

Answer 3

Levée Formation (simple explanation):
What are levées?Levées are natural walls or raised banks that form along the sides of a river.
How do they form?
Flooding happens: When a river floods, it overflows its banks and spreads water across the land.
Big sediments are dropped first: As the water spreads out and slows down, heavy materials like sand and gravel drop close to the river.
Each flood adds more layers: Every time the river floods, more sediment is added to the riverbank, slowly building up the levee over time.
Example:The Mississippi River in the USA has many natural levees that have been built up by nature, and humans have made them even stronger with artificial walls to stop flooding.
Floodplain Formation (simple explanation):
What is a floodplain?A floodplain is the flat land next to a river that forms from sediment being spread and deposited during floods.
How do they form?
Meanders help shape the land: Rivers bend and curve. They erode (wear away) the outside of bends and drop off sediment on the inside, slowly making the valley wider and flatter.
Flooding spreads sediment: When the river floods, water moves onto the floodplain and slows down, dropping fine materials like silt and clay.
New features form: Sometimes the bends in a river get cut off and form oxbow lakes, which are also part of the floodplain landscape.
Example:The Ganges floodplain in India and Bangladesh is one of the largest in the world. It has very rich soil from all the sediment, which is perfect for farming.

Question 4

6a) (i) Briefly describe the weathering process of pressure release (dilatation). (3 marks)

Answer 4

Pressure Release (Dilatation) – Simple Explanation:
What is it?Pressure release is a type of physical weathering. It happens when rock that was buried deep underground becomes uncovered and starts to crack and break apart.
How does it work?
The top layers get removed: Glaciers, rivers, or wind slowly wear away the rocks above.
The pressure is reduced: Once the weight from above is gone, the rock underneath can expand.
Cracks appear: As the rock expands, it forms cracks called joints, often running parallel to the surface.
Layers peel off: Over time, thin layers of rock peel away like the layers of an onion. This is known as exfoliation, and it often happens in granite.
Example:In Yosemite National Park in the USA, you can see big rounded granite domes. These were shaped by pressure release, where the granite cracked and layers slowly broke off.

Question 5

6a) (ii) Explain how ocean trenches are formed. (4 marks)

Answer 5

Ocean Trenches – Simple Explanation:
What are they?Ocean trenches are very deep valleys in the ocean floor. They form when two tectonic plates crash into each other.
How do they form?
Plates collide: When an oceanic plate hits another plate (either oceanic or continental), the heavier plate sinks underneath. This is called subduction.
Trench forms: As the sinking plate bends downward, it makes a deep trench in the sea floor.
Sediments pile up: Over time, bits of rock and mud collect in the trench, forming a messy wedge called an accretionary wedge.
Earthquakes and volcanoes happen: These places often have strong earthquakes and volcanoes, because the sinking plate melts and causes pressure to build up.
Example:The Mariana Trench in the Pacific Ocean is the deepest ocean trench in the world – over 11,000 metres deep!

Question 6

6b) Explain the movement of material on slopes. (8 marks)

Answer 6

Mass Movement – Simple Explanation
Mass movement is when soil or rock moves downhill because of gravity. It can happen slowly or very suddenly, depending on how steep the slope is and how much water is in the ground.
1. Creep (Very Slow Movement)
This is the slowest type of movement.
It happens when the ground freezes and thaws or gets wet and dries, causing soil to move a little bit each time.
Signs: You might see bent tree trunks or tilted fences on a slope.
2. Flows (Fast and Watery Movement)
Flows happen when the ground is so full of water that it turns into a thick mud and flows downhill.
This can happen after heavy rain or during floods.
Types: Mudflows and debris flows.
Example: In 1999, the Vargas mudslide in Venezuela killed thousands when water-saturated soil and rocks rushed down the mountains.
3. Slides (Sudden, Solid Movement)
A landslide is when a big chunk of rock or soil suddenly slips down a slope as one whole piece.
This usually happens along a surface called a slip plane.
Example: The Vaiont Dam disaster in Italy (1963), where a massive landslide fell into a dam, causing a huge wave and many deaths.
4. Falls (Vertical Drop)
Rockfalls happen when pieces of rock break off from a cliff and fall straight down.
This is usually caused by weathering and gravity.
Example: The White Cliffs of Dover in England often have rockfalls as pieces of chalk break away and drop.

Question 7

4a) (i) Define the hydrological terms interception and throughfall. (4 marks)

Answer 7

1. Interception (Simple Explanation – 2 marks)
   Definition (1 mark):
   Interception is when rain is caught and held by plants (like leaves and branches) before it hits the ground.

Explanation (1 mark):
Some of this water evaporates back into the air, and some drips down later. How much water is intercepted depends on how thick the plants are and how heavy the rain is.

Example:
The Amazon Rainforest catches a lot of rain on its leaves, so less water reaches the ground right away.

2. Throughfall (Simple Explanation – 2 marks)
   Definition (1 mark):
   Throughfall is when rain gets past the leaves and falls to the ground—either by dripping or falling straight through gaps in the canopy.

Explanation (1 mark):
This usually happens when the plants are already holding as much water as they can or when rain is very heavy.

Example:
In forests, throughfall helps water the soil and nourish plant roots, keeping the ecosystem healthy.

Question 8

4a) (ii) Briefly explain the effect of evaporation in the drainage basin system. (3 marks)

Answer 8

1. Less Water on the Surface
   Evaporation makes water disappear from lakes, rivers, and reservoirs by turning it into water vapour.
   This means water levels go down.
2. Less Water Soaks into the Ground
   When there’s less water on the surface, there’s less water sinking into the ground.
   This lowers the amount of groundwater and reduces the flow of water in rivers during dry times (called base flow).
3. Rivers Have Less Water
   In hot and dry places, like deserts, evaporation is very high.
   This makes river levels fall, especially in areas with little rain.
4. More Water in the Air
   The water that evaporates goes into the air and makes it more humid.
   This can change local weather, sometimes leading to more or less rain depending on other conditions.

Example:
In the Sahel region of Africa, the hot climate causes lots of evaporation.
This leads to water shortages, dry rivers, and droughts, making it hard for people and plants to get enough water.

Question 9

4b) Explain how slopes and soils can affect the shape of a storm hydrograph. (8 marks)

Answer 9

1. Slope Gradient and Hydrograph Shape – Simple Explanation
   Steep Slopes = Flashy Hydrograph
   Water flows quickly down steep hills.

There’s less time for water to soak into the ground.

This leads to:

Short lag time (water reaches the river fast)

Steep rising limb (river level rises quickly)

High peak discharge (lots of water in the river at once = flood risk)

Example: In the Himalayas, steep slopes cause flash floods because rain runs off very quickly.

Gentle Slopes = Subdued Hydrograph
Water flows slowly on flat land.

More water can soak into the soil.

This leads to:

Long lag time (water takes longer to reach the river)

Lower peak discharge (less chance of flooding)

Example: In the Amazon Basin, water moves slowly over flat floodplains, so flooding is gradual.

2. Soil Type and Hydrograph Shape – Simple Explanation
   Impermeable Soils (e.g. Clay) = Flashy Hydrograph
   Water cannot soak in easily.

Most water runs over the surface.

This causes:

Short lag time

High peak discharge (flooding happens quickly)

Example: In urban areas with hard clay soils or pavements, rain causes flash floods because water can’t soak in.

Permeable Soils (e.g. Sand) = Subdued Hydrograph
Water soaks in easily.

Less water flows over the surface.

This causes:

Longer lag time

Lower peak discharge (less water rushing into rivers)

Example: In deserts with sandy soils, water soaks in quickly, so flooding is less likely.

Question 10

6a) (i) Contrast the process of sheetwash with that of rainsplash. (4 marks)

Answer 10

1. Sheetwash (Simple Explanation – 2 marks)
   Definition (1 mark):Sheetwash is when rainwater flows in a thin layer over the ground without forming channels.
   Explanation (1 mark):It happens when the rain is too heavy to soak into the soil, so the water runs over the surface and carries soil downhill. This causes erosion, especially on bare ground.
   Example:Common on deforested slopes or in deserts, where there are no plants to stop the water.
2. Rainsplash (Simple Explanation – 2 marks)
   Definition (1 mark):Rainsplash is when raindrops hit the ground and knock soil particles into the air.
   Explanation (1 mark):On a slope, these soil bits land slightly downhill, so over time this slowly moves soil down the slope and causes erosion.
   Example:Seen on bare farmland or open hillsides with no plant cover.

Question 11

6a) (ii) Briefly explain how ocean ridges are formed. (3 marks)

Answer 11

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.

Question 12

6b) Explain the main differences between the mass movement processes of flows and slides. (8 marks)

Answer 12

1. 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.
2. 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.

Question 13

4a) (i) Describe one way a spring is formed in an area. (3 marks)

Answer 13

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.

Question 14

4a) (ii) Briefly explain why some parts of a river are braided. (4 marks)

Answer 14

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.

1. 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.
2. 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.
3. Unstable Riverbanks
   Banks composed of non-cohesive sediment (e.g., sand and gravel) erode easily, preventing the river from maintaining a single stable channel.

Question 15

4b) Explain the formation of floodplains and river bluffs. (8 marks)

Answer 15

1. 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.
2. 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.

Question 16

6a) (i) Define the weathering terms pressure release (dilatation) and freeze-thaw. (4 marks)

Answer 16

1. 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.
2. 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.

Question 17

6a) (ii) Briefly explain why some rock types are more affected by the weathering process of carbonation. (3 marks)

Answer 17

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.

1. Limestone and Chalk Are Highly Affected
   These rocks contain high amounts of calcium carbonate, making them highly vulnerable to carbonation.
2. Climate Influences Carbonation
   Carbonation is more effective in humid, rainy environments, where more CO₂ dissolves in water, increasing acidity.
3. Example of Affected Rock
   Limestone pavements in Yorkshire, England, show deep cracks (grikes) and blocks (clints) due to carbonation.

Question 18

6b) Explain how vegetation and relief affect the type of weathering. (8 marks)

Answer 18

1. 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.
2. 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.

Question 19

4a) (i) Define the fluvial terms helicoidal flow and saltation. (4 marks)

Answer 19

1. 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.
2. 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.

Question 20

4a) (ii) Briefly explain how river bluffs are formed. (3 marks)

Answer 20

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.

Question 21

4b) Explain how a storm hydrograph is affected by the size and shape of a drainage basin. (8 marks)

Answer 21

1. 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.
2. 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.

Question 22

6a) (i) Define the weathering terms carbonation and hydrolysis. (4 marks)

Answer 22

1. 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.
2. 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.

Question 23

6a) (ii) Briefly explain how rock can be weathered by heating and cooling. (3 marks)

Answer 23

1. 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.
2. 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).
3. 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.

Question 24

6b) Explain how two factors affect the type and rate of weathering. (8 marks)

Answer 24

1. 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.
2. 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.

Question 25

4a) (i) Define the fluvial terms solution and throughflow. (4 marks)

Answer 25

1. 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.
2. 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).

Question 26

4a) (ii) Briefly explain how turbulent flow causes erosion in river channels. (3 marks)

Answer 26

1. 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.
2. 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.
3. 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.

Question 27

4b) Explain how water stores in a drainage basin system are affected by changes in land use. (8 marks)

Answer 27

1. 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.
2. 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.
3. 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.
4. 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.

Question 28

6a) (i) Define the weathering terms salt crystal growth and hydration. (4 marks)

Answer 28

1. 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).
2. 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.

Question 29

6a) (ii) Briefly explain how vegetation root action can lead to the weathering of rocks. (3 marks)

Answer 29

1. 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.
2. 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.
3. 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.

Question 30

6b) Explain how rock type affects the type and rate of chemical weathering. (8 marks)

Answer 30

1. 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.
2. 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.
3. 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.
4. 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.

Question 31

4a) (i) Define the fluvial terms laminar flow and evapotranspiration. (4 marks)

Answer 31

1. 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.
2. 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.

Question 32

4a) (ii) Briefly explain why abrasion/corrasion varies along a river channel. (3 marks)

Answer 32

1. Sediment Load and Size (1 mark)
   More sediment = More abrasion.
   Larger, angular particles cause more erosion than smaller, smoother ones.
2. 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.
3. 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.

Question 33

4b) Explain the relationship between riffle and pool sequences in meandering river channels. (8 marks)

Answer 33

1. 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.
2. 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.
3. 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.
4. 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.

Question 34

6a) (i) Contrast continental and oceanic tectonic plates. (4 marks)

Answer 34

1. Composition and Density (2 marks)
   Continental plates: Made of granite (sial - silica & aluminum), less dense.
   Oceanic plates: Made of basalt (sima - silica & magnesium), denser.
2. 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.

Question 35

6a) (ii) Briefly explain the distribution of volcanic island arcs. (3 marks)

Answer 35

1. Location at Subduction Zones (1 mark)
   Volcanic island arcs form above subduction zones, where one oceanic plate sinks beneath another.
2. Formation of Arc-Shaped Chains (1 mark)
   Melting of the subducted plate produces magma, which rises to form volcanic islands in a curved arc.
3. 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.

Question 36

6b) Explain how afforestation and slope grading can reduce mass movements on slopes. (8 marks)

Answer 36

1. 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.
2. 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.

Question 37

4a) (i) Define the fluvial terms cavitation and suspension. (4 marks)

Answer 37

1. 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).
2. 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.

Question 38

4a) (ii) Describe the formation of a point bar within a river. (3 marks)

Answer 38

A point bar (slip-off slope) is a depositional feature found on the inner bend of a meandering river.

1. Reduced Velocity on the Inner Bend (1 mark)
   Water moves more slowly on the inner bend of a meander due to reduced energy levels.
2. Deposition of Sediment (1 mark)
   As the river loses energy, it deposits sediment, forming a gently sloping accumulation of sand and gravel.
3. 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.

Question 39

4b) Explain how a river flood can impact people. (8 marks)

Answer 39

1. 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.
2. 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.
3. 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.
4. 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.

Question 40

6a) (i) Define the weathering terms pressure release (dilatation) and hydrolysis. (4 marks)

Answer 40

1. 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.
2. 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.

Question 41

6a) (ii) Briefly explain the role of water in mass movement. (3 marks)

Answer 41

1. 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.
2. 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.
3. 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.

Question 42

6b) Explain how temperature affects physical weathering processes. (8 marks)

Answer 42

1. 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.
2. 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.
3. 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.
4. 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.

Question 43

4a) (i) Describe two ways that sediment is transported in rivers. (4 marks)

Answer 43

1. 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.
2. 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.

Question 44

4a) (ii) Describe a riffle and pool sequence in a river channel. (3 marks)

Answer 44

1. 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.
2. 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.
3. 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.

Question 45

4b) Explain how a river flood can impact the natural (physical) environment. (8 marks)

Answer 45

1. 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.
2. 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.
3. 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.
4. 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.

Question 46

6a) (i) Describe the characteristics of a mass movement flow. (4 marks)

Answer 46

1. High Water Content and Fluid Motion (1 mark)
   Flows contain large amounts of water, making them move like a liquid.
2. 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.
3. Transport of a Mixture of Debris (1 mark)
   Flows carry rock, soil, and organic material, forming a chaotic, unstructured mass.
4. 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.

Question 47

6a) (ii) Describe the process of a mass movement heave. (3 marks)

Answer 47

1. Expansion and Lifting of Soil Particles (1 mark)
   Heave occurs when individual soil particles are lifted due to wetting, freezing, or thermal expansion.
2. Vertical Movement Followed by Downslope Motion (1 mark)
   As soil dries or thaws, particles settle back down slightly downslope, causing slow mass movement.
3. 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.

Question 48

6b) Explain how rainfall influences the type and rate of weathering. (8 marks)

Answer 48

1. 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.
2. 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.
3. 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.
4. 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.

Question 49

4a) (i) Describe the process of throughflow on slopes. (3 marks)

Answer 49

1. Infiltration of Water (1 mark)
   Rainwater infiltrates the soil surface after precipitation, moving downward due to gravity.
2. 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.
3. 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.

Question 50

4a) (ii) Explain how the type of vegetation affects the shape of a storm hydrograph. (4 marks)

Answer 50

1. 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.
2. 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.
3. 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.
4. 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.

Question 51

4b) Explain the formation of river cliffs and point bars in a meandering river channel. (8 marks)

Answer 51

1. 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.
2. 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.
3. 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.
4. 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.

Question 52

6a) (i) Define the weathering terms hydrolysis and pressure release (dilatation). (4 marks)

Answer 52

1. 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.
2. 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.

Question 53

6a) (ii) Briefly explain how a rock can be weathered by heating and cooling. (3 marks)

Answer 53

1. 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.
2. Formation of Cracks (1 mark)
   Over time, internal stress causes fractures and peeling.
   Granular disintegration occurs when different minerals expand at different rates.
3. 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.

Question 54

6b) Explain how the movement of tectonic plates leads to the formation of ocean trenches and ocean ridges. (8 marks)

Answer 54

1. 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.
2. 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.
3. 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.
4. 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.

Question 55

4a) (i) Define the hydrological terms recharge and infiltration. (4 marks)

Answer 55

1. 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.
2. 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.

Question 56

4a) (ii) Briefly explain how interception is affected by vegetation type. (3 marks)

Answer 56

1. 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.
2. 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.
3. 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.

Question 57

4b) Describe and explain helicoidal patterns of flow and turbulent patterns of flow in river channels. (8 marks)

Answer 57

1. 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.
2. 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.

Question 58

6a) (i) Describe how a rotational slide can affect a slope. (3 marks)

Answer 58

1. Formation of a Back Scar (1 mark)
   As the slope moves, a steep back scarp forms at the top, exposing fresh soil and rock.
2. 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.
3. 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.

Question 59

6a) (ii) Define the terms sheetwash and rills. (4 marks)

Answer 59

1. 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.
2. 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.

Question 60

6b) Explain how the chemical composition of rocks and the physical structure of rocks affect the way they are weathered. (8 marks)

Answer 60

1. 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.
2. 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.

Question 61

4a) (i) Define the hydrological terms evaporation and percolation. (4 marks)

Answer 61

1. 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.
2. 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.

Question 62

4a) (ii) Briefly explain what is meant by a flood recurrence interval. (3 marks)

Answer 62

1. 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.
2. 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.
3. Use in Flood Management (1 mark)
   Helps engineers and planners design flood defences based on historical data and risk assessment.

Question 63

4b) Describe and explain the formation of deltas. (8 marks)

Answer 63

1. 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.
2. 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).
3. 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.
4. 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.

Question 64

6(a)(i) Define the tectonic terms subduction and conservative plate boundary. [4 marks]

Answer 64

Subduction is a process where tectonic plates converge (1 mark), and one plate (usually oceanic) is forced beneath the other into the mantle (1 mark), where it melts in the Benioff zone (1 mark).

A conservative plate boundary is where two plates slide past each other horizontally (1 mark), either in the same or opposite directions at different speeds.

Question 65

6(a)(ii) Briefly describe how fold mountains are formed. [3 marks]

Answer 65

Formed when tectonic plates converge (1 mark), often continental-continental plates.

The pressure causes sediments and crust to buckle and fold (1 mark).

Results in uplift and the formation of fold mountain ranges such as the Himalayas (1 mark).

Question 66

6(b) Explain the role of water in the surface movement of sediment on slopes. [8 marks]

Answer 66

Rainsplash: raindrop impact dislodges soil particles, especially on bare slopes. If on a gradient, particles move downslope.

Sheetwash: occurs when rainfall exceeds infiltration capacity, forming a thin layer of flowing water that erodes and transports sediment.

Rill erosion: surface irregularities channel water, forming narrow rills that deepen with continued flow.

Soil creep: involves wetting and drying, causing soil particles to slowly shift downslope.

Solifluction: in cold climates, saturated soils flow slowly over impermeable layers like permafrost.

Surface mudflows: when intense rainfall saturates fine soils, leading to liquid-like movement of sediment downslope.

Question 67

4a) (i) Define the hydrological terms stemflow and throughflow. (4 marks)

Answer 67

1. 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.
2. 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.

Question 68

4a) (ii) Briefly explain how underground water may form springs. (3 marks)

Answer 68

1. Water Table Intersecting the Surface (1 mark)
   A spring forms where the water table naturally meets the ground surface, allowing groundwater to flow out.
2. 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.
3. 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.

Question 69

4b) Describe and explain how a meander forms. (8 marks)

Answer 69

1. 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.
2. 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.
3. 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.
4. 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.

Question 70

6(a)(i) Define the tectonic terms ocean trench and sea floor spreading. [4 marks]

Answer 70

Ocean trench: A long, narrow, deep depression in the ocean floor, formed where one tectonic plate subducts beneath another at a destructive plate boundary. (2 marks)

Sea floor spreading: The process where oceanic plates move apart (diverge) due to rising convection currents, causing new crust to form at mid-ocean ridges. (2 marks)

Question 71

6(a)(ii) Briefly describe the processes occurring at a conservative plate boundary. [3 marks]

Answer 71

At a conservative boundary, plates slide past one another horizontally. (1 mark)

They may move in opposite directions or at different speeds, causing friction to build up. (1 mark)

This friction is released as earthquakes when the plates suddenly slip. (1 mark)

No crust is created or destroyed, and no major landforms are formed.

Question 72

6(b) Explain why slope processes occur at different rates. [8 marks]

Answer 72

Water content: Increased water adds weight and acts as a lubricant, speeding up processes like flows and slides.

Slope angle: Steeper slopes are more prone to rapid movement (e.g., rockfalls), while gentle slopes favor slow creep.

Vegetation: Stabilizes slopes by binding soil, reducing the rate of movement.

Soil type: Clay soils absorb water and expand, promoting slower, heave-based movements; loose materials encourage faster flow.

Human activity: Deforestation, excavation, or construction can destabilize slopes, increasing movement rates.

Temperature: Freeze–thaw cycles promote heave, increasing movement in cold climates.

Underlying geology: Well-jointed or unconsolidated rock is more likely to move quickly.

Question 73

4(a)(i) Define the fluvial terms traction and abrasion. [4 marks]

Answer 73

Traction is a river transport process where large particles (like boulders and pebbles) are rolled along the river bed by the force of the water. (2 marks)

Abrasion is a type of erosion where the load carried by the river rubs against the bed and banks, wearing them away in a sandpaper-like action. (2 marks)

Question 74

4(a)(ii) Describe the process of suspension within a river channel. [3 marks]

Answer 74

Suspension is a transport process in which fine particles (e.g. clay, silt) are carried within the water column.

These particles are not in contact with the river bed or banks.

The amount carried depends on river velocity and discharge—the faster the river, the more material it can keep suspended.

Question 75

4(b) Explain the formation of river bluffs and levées. [8 marks]

Answer 75

River bluffs form at the edges of a floodplain where the river, through lateral erosion, cuts into the valley sides.

They are often steep and elevated, marking the transition between the floodplain and higher land.

Bluffs form as meanders migrate, eroding the valley sides.

Levées are natural embankments that form alongside river channels.

During a flood, water spreads over the floodplain. The heaviest particles (sand, gravel) are deposited closest to the river, while finer materials are carried further away.

Repeated flooding builds up raised banks—the levées—on both sides of the channel.

Question 76

6(a)(i) Define the weathering terms heating and cooling and vegetation root action. [4 marks]

Answer 76

Heating and cooling: A physical weathering process where rock expands during the day due to heat and contracts at night as temperatures drop. Over time, this causes fractures and rock breakdown. (2 marks)

Vegetation root action: A biological weathering process where plant roots grow into rock cracks, exerting pressure as they grow, which pries the rock apart. (2 marks)

Question 77

6(a)(ii) Briefly explain how sheetwash occurs on slopes. [3 marks]

Answer 77

Sheetwash occurs when intense rainfall exceeds the infiltration capacity of the soil.

On bare or smooth slopes, water cannot soak in and flows as a thin, unchannelled layer across the surface.

This process can transport fine material downhill and is common where vegetation cover is absent or sparse.

Question 78

4(a)(i) Describe the conditions which lead to overland flow on slopes. [3 marks]

Answer 78

High rainfall intensity or sudden snowmelt that exceeds the soil’s infiltration capacity.

Impermeable or saturated ground prevents water from soaking into the soil.

Steep slopes increase runoff as gravity causes water to flow quickly over the surface.

Low vegetation cover means less interception and less water absorption by roots.

Question 79

4(a)(ii) Explain how the shape of a drainage basin affects the shape of a storm hydrograph. [4 marks]

Answer 79

Circular basins tend to have shorter lag times and steeper rising limbs because water reaches the river channel quickly and simultaneously.

Elongated basins have a more gradual hydrograph due to water taking longer to reach the river, resulting in lower peak discharge.

The convergence of tributaries in circular basins increases the speed and volume of discharge.

In elongated basins, discharge is spread over time, giving a more flattened hydrograph.

Question 80

4(b) Explain how the Hjulström curve is used to explain erosion and deposition in a river channel. [8 marks]

Answer 80

The Hjulström curve illustrates the relationship between particle size and the velocity required to erode, transport, and deposit sediment.

Erosion (entrainment):
Larger particles (e.g., gravel) need higher velocities to be lifted.

Fine particles like clay also need high velocity to be eroded because of cohesion.

Transport zone:
Once particles are in motion, they can be transported at lower velocities.

This explains why fine particles remain in suspension even at low flows.

Deposition:
Occurs when velocity drops below the critical threshold.

Larger particles deposit first, followed by smaller ones as flow energy decreases.

Question 81

6(a)(i) Describe the main differences between mass movement processes of flows and slides. [4 marks]

Answer 81

Flows are fluid-like movements of saturated material (e.g., mudflows), while slides involve a cohesive mass moving along a defined slip plane.

Flows have internal deformation, with different parts moving at different speeds; slides move more uniformly as a block.

Flows usually occur in channels and travel long distances; slides occur on slopes and may be more localized.

Slides occur along a shear surface; flows do not have a defined base.

Question 82

6(a)(ii) Briefly explain how rills occur on slopes. [3 marks]

Answer 82

Heavy rainfall or saturated ground causes water to flow over the surface when infiltration capacity is exceeded.

This overland flow becomes concentrated into small channels due to surface irregularities.

These narrow, shallow channels erode the soil, forming rills.

Question 83

6(b) Examine the factors that influence physical weathering in different climates. [8 marks]

Answer 83

Temperature fluctuation is key for processes like freeze–thaw and exfoliation.
In cold climates, freeze–thaw is dominant: water enters cracks, freezes, expands, and breaks the rock.
In hot arid areas, thermal expansion causes outer rock layers to crack and peel (exfoliation).

Moisture availability:
Arid climates with low moisture promote salt crystallization, as evaporating water leaves behind salts that expand and fracture rock.
Humid climates limit physical weathering, as chemical processes dominate instead.

Rock type and structure:
Rocks with joints and bedding planes are more susceptible to physical weathering.
Porous rocks absorb water, promoting freeze–thaw and salt weathering.

Altitude and exposure:
High-altitude areas face frequent freeze–thaw cycles.
Exposed areas receive greater thermal stress.

Question 84

4(a)(i) Briefly explain why precipitation may not always reach a river channel. [3 marks]

Answer 84

Interception by vegetation – precipitation may be caught by leaves and branches, then evaporated or absorbed.

Evapotranspiration – water may be lost back to the atmosphere before reaching the ground or river.

Infiltration into soil and groundwater – water may seep into permeable soil or rock layers and move away from the channel.

Storage – water may collect in lakes, ponds, or be frozen (as snow or ice), delaying or preventing its entry into the river.

Human use – precipitation may be intercepted by reservoirs or used for domestic/agricultural purposes.

Question 85

4(a)(ii) Outline two factors which influence the formation of a braided channel. [4 marks]

Answer 85

High sediment load
Rivers with a large supply of sediment deposit material when velocity drops, creating eyots (bars) which split the channel.

Variable discharge
Rivers with fluctuating flow (e.g. from glacial melt or seasonal rainfall) deposit sediment during low flows, forming multiple shallow channels.

Question 86

4(b) Describe and explain how soft engineering and hard engineering can be used to prevent river floods. [8 marks]

Answer 86

Soft Engineering:
Floodplain zoning – limits development in high-risk areas, allowing safe overflow during floods.

Afforestation – planting trees increases interception and reduces surface runoff.

Wetland restoration – creates natural water storage areas, slowing flood peaks.

River restoration – returning rivers to natural meanders increases lag time and reduces discharge peaks.

Hard Engineering:
Dams and reservoirs – store water during heavy rainfall, releasing it slowly.

Levees and embankments – increase channel capacity and prevent overflow.

Channel straightening – speeds up water flow away from urban areas.

Diversion spillways or flood relief channels – divert excess water from vulnerable areas.

Question 87

6(a)(i) Define the terms rainsplash and rills. [4 marks]

Answer 87

Rainsplash: When raindrops hit bare soil, the impact dislodges particles, causing them to move a short distance. (2 marks)

Rills: Small, shallow channels formed by flowing water on slopes, especially during heavy rain. They are a form of minor water erosion. (2 marks)

Question 88

6(a)(ii) Briefly explain how afforestation can reduce mass movement on a slope. [3 marks]

Answer 88

Root systems bind soil, increasing cohesion and shear strength.

Trees intercept rainfall, reducing the amount reaching the soil and therefore reducing saturation and pore water pressure.

Water uptake through roots helps reduce overall moisture content and weight of the slope material, decreasing the chance of landslides.

Question 89

6(b) Explain how the type and rate of weathering is influenced by precipitation. [8 marks]

Answer 89

Chemical weathering increases with precipitation:
Water is essential for hydrolysis, carbonation, and solution.
More rainfall = more chemical reactions and faster weathering.

Low precipitation reduces chemical weathering:
In arid areas, limited water means chemical weathering is minimal.

Physical weathering and precipitation:
Precipitation enables freeze–thaw and salt crystallisation.
Requires water entry into rock cracks, then freezing or evaporation.

High rainfall = faster rates:
Sustained rainfall keeps rocks moist, increasing chemical weathering rates.

Too much rainfall in tropical regions can wash away soluble minerals, speeding decomposition and deep weathering.

Question 90

4(a)(i) Describe the main features of a meander. [3 marks]

Answer 90

Asymmetrical cross-section – one side is deeper and faster flowing (outer bend), the other is shallower and slower (inner bend).

River cliff – formed by erosion on the outer bend due to faster current and hydraulic action.

Slip-off slope (point bar) – formed by deposition on the inner bend where flow is slower.

Thalweg – the line of fastest flow follows a helicoidal (spiral) pattern, swinging from side to side.

Winding course – meanders develop as the river erodes laterally across the floodplain.

Question 91

4(a)(ii) Explain two factors which influence the level of a water table. [4 marks]

Answer 91

Precipitation levels – Increased rainfall raises the water table, while dry periods lead to lower levels due to less infiltration.

Evapotranspiration – High rates from vegetation and high temperatures can reduce soil moisture and lower the water table.

Human abstraction – Groundwater pumping for irrigation or industry lowers the water table.

Soil and rock type – Permeable rocks (e.g., chalk, sandstone) allow water to percolate, raising the water table.

Slope gradient – On steep slopes, more water runs off than infiltrates, resulting in a lower water table.

Question 92

4(b) Describe and explain the formation of deltas. [8 marks]

Answer 92

Deltas form where a river meets a standing body of water (e.g., sea/lake), causing a drop in velocity and sediment deposition.

Deposition starts as the river loses energy and begins to lay down coarse material first, followed by finer sediments.

The river channel becomes blocked by sediment, forcing it to split into distributaries.

Over time, this deposition builds a deltaic landform with different parts:

Topset beds: Coarse material, near the river mouth.
Foreset beds: Sloped deposits of finer sediment into deeper water.
Bottomset beds: Finest clays deposited furthest out.

Flocculation: Fine clay particles combine in saltwater and settle more quickly.

Deltas can be:
Arcuate (fan-shaped, e.g., Nile),
Bird’s foot (finger-like, e.g., Mississippi),
Cuspate (pointed, e.g., Tiber).

Question 93

6(a)(i) Describe the processes of sediment movement on a slope. [3 marks]

Answer 93

Falls – Loose material detaches from a steep slope or cliff, falling freely due to gravity.

Creep – Very slow downslope movement of soil, often due to heave (e.g., freeze-thaw expansion).

Flows – Water-saturated soil or debris moves like a liquid (e.g., mudflows or earthflows).

Slides – Large blocks move rapidly along a slip plane (e.g., rockslides).

Rainsplash – Raindrops dislodge particles on exposed surfaces.

Sheetwash – Unchannelled water removes thin layers of soil.

Question 94

6(a)(ii) Explain how modifying a slope with pinning and netting could reduce mass movement. [4 marks]

Answer 94

Pinning – Long metal rods or bolts are drilled into rock surfaces to anchor unstable rock.
This increases shear strength, stabilising the slope.
Reduces the risk of sliding or rockfall by keeping fractured rock in place.

Netting – Steel mesh or wire netting placed over slopes helps to contain loose debris.
Prevents material from falling freely.
Sometimes encourages vegetation growth, which adds further slope stability.

Question 95

6(b) Explain how the type and rate of weathering is influenced by temperature. [8 marks]

Answer 95

Chemical weathering:
Dominant in warm, wet climates (e.g., tropics).
Higher temperatures accelerate chemical processes like hydrolysis, oxidation, carbonation.
More precipitation + high temperatures = deep weathering profiles (e.g., laterites in the Amazon).

Physical weathering:
Freeze–thaw is common in temperate/mountainous areas with temperatures fluctuating around 0°C.
Water enters cracks, freezes, expands, and breaks rock.
In hot deserts, thermal expansion causes daily heating and cooling → exfoliation and granular disintegration.
Salt weathering occurs when evaporating water leaves salt crystals that grow and break rock.

Peltier diagram can illustrate the relationship between temperature, moisture, and weathering type.

Question 96

4(a)(i) Describe how throughflow occurs on slopes. [3 marks]

Answer 96

After infiltration, water enters the soil and moves laterally downslope due to gravity.

Throughflow occurs parallel to the surface, usually in the upper soil layers.

It is more effective in permeable soils (e.g., sandy soils) or on steep slopes, where gravitational pull enhances flow rate.

Question 97

4(a)(ii) Explain how slopes affect the shape of a storm hydrograph. [4 marks]

Answer 97

Steep slopes promote overland flow, reducing infiltration → leads to short lag time and higher peak discharge → “flashy” hydrograph.

Gentle slopes allow more infiltration, slowing water movement → longer lag time and lower peak discharge.

Convex slopes promote faster runoff, concave slopes slow it down.

Vegetated/permeable slopes absorb more water, reducing overland flow.

Question 98

4(b) Describe and explain the formation of gorges. [8 marks]

Answer 98

Gorges are steep-sided valleys formed by vertical erosion of a river. They can form in the following ways:

Waterfall retreat:
A river flows over resistant rock with softer rock beneath → erosion undercuts the soft rock → waterfall retreats upstream via headward erosion.
The retreat leaves behind a steep, narrow gorge.

Rejuvenation:
A river experiences a drop in base level (e.g., due to tectonic uplift or sea-level fall).
This increases vertical erosion → forms a deepened channel, creating a gorge.

Glacial meltwater:
Post-glacial meltwater may cut deep gorges during deglaciation.

Mass movement and rockfalls along the sides may steepen the slopes.

Question 99

6(a)(i) Define the weathering terms heating/cooling and hydration. [4 marks]

Answer 99

Heating/cooling: Also known as thermal expansion. Rocks expand during the day (high temperatures) and contract at night (cooler temperatures). This repeated stress causes fracturing and breakdown of surface layers. (2 marks)

Hydration: A type of chemical weathering where minerals absorb water, causing them to expand. This creates internal pressure and leads to rock disintegration. (2 marks)

Question 100

6(a)(ii) Briefly explain how rockfalls occur on slopes. [3 marks]

Answer 100

Caused by freeze–thaw weathering, where water enters cracks, freezes, expands, and loosens rock.

May also occur due to undercutting by rivers or glaciers, removing support.

Earthquakes or vibrations, steep slopes, or human activity (e.g. quarrying or road construction) can trigger rockfall.

Gravity pulls the detached rocks down rapidly.

Question 101

6(b) Describe and explain the formation of volcanic island arcs. [8 marks]

Answer 101

Volcanic island arcs form at destructive plate boundaries (oceanic-oceanic).

One oceanic plate subducts beneath another due to density differences.

The subducting plate melts due to increasing pressure and temperature → forms magma.

Magma rises through the overlying plate and forms volcanoes.

With repeated eruptions, these build up into chains of volcanic islands, typically curved due to plate movement.

Example: Mariana Islands, Aleutian Islands.

Island arcs often lie parallel to ocean trenches and are seismically active.

Question 102

4(a)(i) Describe the main features of a braided river channel. [3 marks]

Answer 102

Multiple interconnected channels – the river splits into several small, shallow channels that weave around sediment bars.

Eyots (islands) – small temporary or vegetated islands formed by deposition of sediments between the channels.

Shallow and wide river bed – braided channels are typically wide and shallow due to high sediment load and fluctuating discharge.

Question 103

4(a)(ii) Explain two processes of erosion in a river channel. [4 marks]

Answer 103

Hydraulic action – the sheer force of water dislodges and removes particles from the riverbed and banks, especially during high-velocity flows.

Abrasion (Corrasion) – sediment carried by the river is dragged or bounced along the bed and banks, wearing them away like sandpaper.

Question 104

4(b) Explain the formation of river cliffs and point bars. [8 marks]

Answer 104

River Cliffs:
Formed on the outside of meander bends where velocity is highest.
The river’s thalweg (fastest flow) swings to the outside bend.
Hydraulic action and abrasion erode the bank, creating a steep river cliff.
Undercutting may cause the bank to collapse and retreat.

Point Bars (Slip-off Slopes):
Found on the inside of meanders where velocity is lower.
Lower energy leads to deposition of finer sediments like silt and sand.
Over time, the sediments build up to form a gently sloping bar.
Often vegetated and prone to further deposition during floods.

Question 105

6(a)(i) Describe the process of subduction. [3 marks]

Answer 105

Subduction occurs at convergent plate boundaries.

A denser oceanic plate is forced underneath a less dense continental or oceanic plate.

The descending plate is melted in the mantle (Benioff zone), creating magma and deep-sea trenches.

Question 106

6(a)(ii) Explain the weathering process of carbonation. [4 marks]

Answer 106

Carbon dioxide dissolves in rainwater, forming a weak carbonic acid.

This acid reacts with calcium carbonate in rocks such as limestone or chalk.

It forms calcium bicarbonate, which is soluble in water.

The minerals are carried away in solution, gradually weakening and dissolving the rock.

Question 107

6(b) Examine the factors that influence sheetwash and rills on slopes. [8 marks]

Answer 107

Rainfall intensity and amount – Heavy rain overwhelms infiltration, causing overland flow (sheetwash).

Slope gradient – Steeper slopes increase the speed and volume of surface flow, enhancing erosion and rill formation.

Soil characteristics – Permeable, well-structured soils reduce sheetwash. Compacted or clay soils promote it.

Vegetation cover – Bare slopes experience more sheetwash and rills due to lack of interception and root binding.

Antecedent conditions – Previously saturated soil reduces infiltration, increasing surface runoff.

Surface irregularities – Micro-topography focuses flow into narrow threads, leading to rill erosion.

Human activity – Deforestation, overgrazing, and ploughing increase vulnerability to sheetwash and rills.

Question 108

4(a)(i) Define the hydrological terms infiltration and interception. [4 marks]

Answer 108

Infiltration is the process by which water soaks into the soil from the ground surface (1 mark), usually in a downward direction (1 mark).

Interception is the capture of precipitation by vegetation, such as leaves or branches, before it reaches the ground (1 mark), delaying or reducing the amount of water reaching the surface (1 mark).

Question 109

4(a)(ii) Describe a river levée. [3 marks]

Answer 109

A river levée is a raised bank or ridge running parallel to the river channel (1 mark).

It is formed by deposition of sediments, often during flood events (1 mark).

Coarser materials are typically deposited closer to the river, while finer materials settle farther away (1 mark).

Question 110

4(b) Explain the formation of meanders and oxbow lakes. [8 marks]

Answer 110

Meanders:
Form from initial irregularities in a river’s path, creating alternating riffles and pools.
The thalweg (fastest flow) swings from side to side, causing helicoidal flow.
Erosion occurs on the outer bend (forming river cliffs), and deposition on the inner bend (forming point bars).
This increases the sinuosity of the river channel over time.

Oxbow lakes:
When meanders become very curved, erosion cuts through the narrow neck during flood conditions.
The river adopts a straighter course, and deposition seals off the old bend.
The cut-off meander becomes an oxbow lake.

Question 111

6(a)(i) Define the weathering terms freeze-thaw and pressure release (dilatation). [4 marks]

Answer 111

Freeze-thaw weathering: Water enters cracks in rock (1 mark), freezes and expands (1 mark), exerting pressure which gradually weakens the rock over repeated cycles (1 mark).

Pressure release (dilatation): Happens when overlying rock is removed by erosion (1 mark), leading to expansion of the underlying rock (1 mark), which develops sheeting and joints (1 mark).

Question 112

6(a)(ii) Describe the weathering process of vegetation root action. [3 marks]

Answer 112

Roots grow into cracks or joints in rocks (1 mark).

As they expand, they exert pressure and widen the cracks (1 mark).

Over time, this causes the rock to break apart (1 mark).

Question 113

6(b) Explain how rock type and rock structure affect the rate of weathering. [8 marks]

Answer 113

Rock type:
Rocks with soluble minerals (e.g., limestone) are weathered quickly by chemical weathering such as carbonation.
Granite is more resistant but can still be affected by hydrolysis, especially on feldspar minerals.
Sandstone is porous, promoting mechanical and chemical weathering.

Rock structure:
Rocks with many joints, cracks, and bedding planes provide pathways for water, increasing the rate of weathering.
Massive, unjointed rocks (e.g., basalt) weather more slowly.
Highly jointed rocks (e.g., limestone pavements) weather faster due to greater surface area exposure.

Question 114

4(a)(i) Define the hydrological terms percolation and baseflow. [4 marks]

Answer 114

Percolation is the downward movement of water (1 mark) through the soil and underlying bedrock after infiltration has taken place (1 mark).

Baseflow is the lateral movement of water within the bedrock (1 mark), which discharges into a stream from the groundwater store (1 mark).

Question 115

4(a)(ii) Describe how drainage basin shape affects discharge within drainage basins. [3 marks]

Answer 115

A long, narrow basin produces a slower, more prolonged discharge, with a lower peak and longer lag time.

A rounded or circular basin results in a quicker response to rainfall, producing a shorter lag time and a higher peak discharge.

Shape influences the speed at which water converges into the river channel.

Question 116

4(b) Explain how recurrence intervals can be used in the prediction of flood risk. [8 marks]

Answer 116

Recurrence intervals estimate how often a flood of a specific magnitude might occur, based on past records.

For example, a 1-in-10-year flood has a 10% chance of occurring in any given year.

These predictions help in floodplain management, urban planning, and designing flood defences.

Engineers and planners use recurrence data to design structures that can withstand floods of a given size.

The data allows for risk mapping, identifying high-risk zones.

Recurrence intervals are used for long-term planning rather than day-to-day forecasting.

However, they are based on historical data, so rare floods can still occur unexpectedly.

Climate change and human activity may alter flood frequencies, affecting reliability.

Question 117

6(a)(i) Define the terms subduction and conservative plate boundary. [4 marks]

Answer 117

Subduction is when two tectonic plates converge (1 mark), and the denser oceanic plate is forced beneath the other plate into the mantle (1 mark).

A conservative plate boundary is where two plates slide past each other horizontally (1 mark), either in the same or opposite directions at different speeds (1 mark).

Question 118

6(a)(ii) Briefly explain the formation of volcanic island arcs. [3 marks]

Answer 118

Occurs at convergent boundaries between two oceanic plates (1 mark).

One plate is subducted, melts in the Benioff zone, and forms magma.

Magma rises to the surface, creating a curved chain of volcanic islands (1 mark), e.g. Mariana Islands.

Question 119

6(b) Explain how the strategies of afforestation and grading can be used to reduce mass movements. [8 marks]

Answer 119

Afforestation:
Planting trees increases interception, reducing the amount of water reaching the ground.
Roots bind the soil, increasing slope cohesion and shear strength.
Vegetation also absorbs water, reducing saturation and pore water pressure.
Overall, this reduces the chance of landslides and soil creep.

Grading:
Involves reducing slope steepness by physically altering the slope profile.
Shallower slopes experience less gravitational force, lowering the risk of mass movement.
Slope stability improves, and the rate of erosion is reduced.
Used commonly in construction and road-building projects.