Unit 8 Exam Questions Flashcards
1
Q
Explain two factors influencing wave height. (6 marks)
A
Wave height is influenced by multiple factors, with the two most significant being:
Fetch Length
Fetch refers to the distance over which the wind blows uninterrupted across the surface of the sea. The longer the fetch, the more energy is transferred from the wind to the water, leading to larger waves. In open ocean environments with extensive fetch, such as the Atlantic Ocean, waves tend to be higher and more powerful compared to those in enclosed seas, like the Mediterranean, where the fetch is shorter.
Wind Speed and Duration
Stronger winds generate more powerful waves by exerting greater frictional force on the water’s surface. Additionally, the longer the wind blows in a consistent direction (duration), the more energy is transferred, further increasing wave height. For example, during storms or hurricanes, where wind speeds exceed 100 km/h, massive waves with heights of over 10 meters can form.
2
Q
Suggest reasons for the differences in beach profile between the summer and winter (6 marks)
A
Wave Energy and Seasonal Variation
In winter, stronger winds generate high-energy waves (destructive waves) that erode the beach, carrying sediment offshore. The steep upper beach profile in winter is due to this erosional action.
In summer, weaker winds produce low-energy waves (constructive waves) that deposit sediment, building up the beach. This results in a wider and more gently sloping profile.
Impact of Wave Type
Winter: Destructive Waves
These waves have a stronger backwash than swash, meaning more sediment is pulled away from the beach than is deposited.
This leads to beach lowering and offshore deposition, forming offshore sandbars.
Summer: Constructive Waves
These waves have a stronger swash than backwash, meaning more sediment is deposited than removed.
As a result, the beach profile is built up and extended.
Sediment Transport and Deposition Patterns
Winter: Strong waves remove material from the beach, leading to offshore sandbars. The profile just offshore becomes less steep as sand accumulates on the seabed.
Summer: Sand that was deposited offshore is returned to the beach, rebuilding the berm (ridge of sediment along the shore).
Effect of Beach Material
Coarse materials such as pebbles or shingle tend to remain on the upper beach, leading to steeper winter profiles.
Finer sand is more easily transported offshore in winter, contributing to a flatter offshore profile.
3
Q
Suggest two reasons for variations in rates of marine deposition. (6 marks)
A
Wave Energy and Coastal Morphology
The type and strength of waves play a major role in deposition rates. Constructive waves (low-energy waves) have a strong swash that pushes sediment up the beach and a weak backwash that leaves it deposited. In contrast, destructive waves (high-energy waves) remove more sediment than they deposit, leading to lower deposition rates.
Sheltered coastlines, such as bays, experience higher deposition because wave refraction reduces wave energy, allowing sediment to accumulate. Exposed coastlines, such as headlands, are subject to stronger wave action, which prevents deposition.
Sediment Supply and Longshore Drift
The rate of deposition depends on the amount of available sediment from rivers, cliffs, and offshore sources. Rivers transport sediment to coastal areas, and cliff erosion provides additional material. Coastlines that receive large amounts of sediment from these sources experience higher deposition rates.
Longshore drift transports sediment along the coast. If sediment transport is interrupted by structures like groynes, deposition increases on the updrift side but decreases on the downdrift side, leading to erosion there.
4
Q
Suggest reasons why the type of hard engineering solutions varies along a stretch of coastline. (7 marks)
A
- Wave Energy and Coastal Exposure
Areas exposed to strong, high-energy waves require robust structures such as sea walls, revetments, and riprap to absorb wave energy and prevent erosion.
Sheltered coastal areas with lower wave energy may use less intrusive solutions like groynes or beach nourishment, which help retain natural sediment. - Coastal Morphology and Sediment Transport
Headlands and steep cliffs experience more wave attack and erosion, requiring hard structures like sea walls and rock revetments.
Bays and estuaries, where waves lose energy, allow for softer solutions such as breakwaters or sand dune stabilization. - The Impact of Longshore Drift
Along coastlines with strong longshore drift, groynes are placed at intervals to trap sediment and prevent beach erosion.
If longshore drift is interrupted (e.g., by harbors or coastal defenses), breakwaters or artificial sediment replenishment may be needed to compensate for lost sediment supply. - Land Use and Economic Priorities
Urban areas, major roads, and industries (e.g., ports, tourism hotspots) need stronger protections, such as sea walls and rock armor, to minimize damage from storm surges and erosion.
Rural or natural coastlines may rely on managed retreat or beach nourishment, which preserve natural coastal processes while reducing costs. - Cost and Maintenance Considerations
Expensive defenses like sea walls and offshore breakwaters are used in high-value locations due to their long-term effectiveness.
Cheaper solutions, such as groynes and beach nourishment, are preferred in lower-risk areas because they require regular maintenance but are cost-effective.
5
Q
Explain how wave refraction affects the distribution of wave energy. (6 marks)
A
- Wave Refraction at Headlands
As waves approach the coastline, they slow down due to friction with the seabed in shallower water.
Waves bend (refract) around headlands because the water is shallower on the sides of the headland than in deeper offshore areas.
This refraction causes waves to converge (focus) on the headlands, leading to higher wave energy and stronger erosional forces.
This concentrated energy results in the formation of erosional landforms, such as cliffs, caves, arches, stacks, and stumps over time. - Wave Refraction in Bays
In contrast, waves entering a bay experience less friction and maintain higher speeds.
As waves spread out and diverge, the energy is dispersed, reducing erosional forces and encouraging deposition.
This process leads to the formation of depositional landforms such as sandy beaches and spits. - Impact on Coastal Landforms
Erosional Features:
Headlands receive the highest energy, causing cliff retreat and wave-cut notches to form.
Depositional Features:
Bays experience deposition, leading to beach formation.
Over time, beach profiles change seasonally as constructive and destructive waves modify their shape.
6
Q
Suggest how geology can influence the landscape of a coastline.
A
- Influence of Rock Type
Resistant (hard) rocks (e.g., limestone, granite, and sandstone) are more resistant to erosion, forming headlands and steep cliffs.
Less resistant (soft) rocks (e.g., clay, shale, and mudstone) erode more rapidly, leading to the formation of bays and inlets.
If the coastline has alternating layers of hard and soft rock (discordant coastline), the softer rock erodes quickly, forming bays, while the harder rock remains as headlands (e.g., Swanage Bay, UK). - Influence of Rock Structure
Joints and faults create lines of weakness that waves exploit through hydraulic action and abrasion, leading to the formation of caves, arches, stacks, and stumps.
Horizontal rock layers allow for wave-cut platforms to form as cliffs retreat.
Vertically bedded or tilted strata result in steep cliffs, whereas folded strata can produce irregular cliff profiles.
Example: Durdle Door (UK) was formed by wave erosion acting on weakened limestone joints, creating a natural arch. - Influence of Sub-Aerial Processes
Weathering processes such as freeze-thaw, salt crystallization, and biological weathering weaken rock structures, increasing their susceptibility to marine erosion.
Mass movement (e.g., rockfalls and landslides) is more common in soft, weakly consolidated rocks, contributing to cliff retreat.
7
Q
Explain why rates of erosion vary along coastlines. (6 marks)
A
- Wave Energy and Coastal Exposure
Destructive waves (high-energy waves) have a strong backwash, removing sediment and increasing erosion rates.
Constructive waves (low-energy waves) deposit sediment, reducing erosion rates.
Coastlines with a long fetch (distance over which the wind blows) receive more powerful waves, leading to higher erosion (e.g., Atlantic coasts experience greater wave energy than Mediterranean coasts). - Rock Type and Geological Structure
Hard rock (e.g., granite, basalt, limestone) is resistant to erosion, forming cliffs and headlands.
Soft rock (e.g., clay, shale, sandstone) erodes more quickly, forming bays and inlets (e.g., Holderness Coast, UK, erodes at 2m per year due to weak boulder clay).
Faults, joints, and bedding planes create lines of weakness, accelerating erosion through hydraulic action and abrasion. - Coastal Morphology and Sediment Supply
Headlands receive concentrated wave energy, leading to increased erosion.
Bays experience wave refraction, which disperses energy, leading to deposition rather than erosion.
Longshore drift affects erosion rates:
If sediment transport is interrupted (e.g., by groynes), erosion may increase down-drift.
Beaches help protect cliffs from erosion by absorbing wave energy. - Human Activities and Coastal Management
Hard engineering structures (e.g., sea walls, groynes, breakwaters) can alter erosion rates:
Groynes trap sediment, reducing erosion on one side but increasing it further along the coast (e.g., Mappleton, Holderness Coast).
Dredging of offshore sediment for construction or navigation increases erosion by removing natural beach protection.
8
Q
Explain two reasons why the level of risk to coral reefs varies. (6 marks)
A
- Climate Change and Rising Sea Temperatures
Coral reefs thrive within a narrow temperature range (23°C–29°C). Rising sea temperatures due to global warming cause coral bleaching, where corals expel symbiotic algae (zooxanthellae), losing their color and energy source.
Regions with stronger thermal stress (e.g., Great Barrier Reef, Australia) have seen severe coral bleaching events, while reefs near upwelling zones (e.g., Galápagos Islands) may experience cooler water, reducing risk.
Example: The Great Barrier Reef experienced three mass bleaching events (2016, 2017, and 2020) due to record-breaking sea temperatures. - Human Activities and Pollution
Coastal development, agriculture, and tourism introduce sediments, nutrients, and pollutants into the water, leading to eutrophication (excessive algae growth).
Overfishing and destructive fishing methods (e.g., cyanide fishing, dynamite fishing in Southeast Asia) physically damage coral structures and disrupt the food chain.
Marine Protected Areas (MPAs), such as those in Belize and the Maldives, help reduce risks by limiting harmful activities and promoting conservation.
Example: In the Caribbean, reefs near heavily populated coastlines (e.g., Jamaica) experience high levels of pollution and reef degradation, while protected reefs in the Bahamas remain healthier.
9
Q
Suggest how a spit forms. (6 marks)
A
- Longshore Drift and Sediment Transport
Prevailing winds create oblique waves, causing swash (movement of water up the beach) at an angle.
The backwash moves perpendicular to the shoreline due to gravity, leading to a zig-zag movement of sediment along the coast.
Over time, this process transports sediment laterally, forming an elongated feature extending from the shore. - Deposition in a Low-Energy Environment
If the coastline changes direction or the energy of waves decreases (e.g., at a river estuary or bay), deposition occurs as waves lose carrying capacity.
This deposited material gradually builds up above sea level, forming a narrow, elongated spit. - Formation of a Recurved End
Spits often have a hooked or recurved end due to:
Secondary wave directions and tidal currents, which curve the spit’s tip inland.
Seasonal changes in wind direction affecting wave approach.
Example: Spurn Head on the Holderness Coast, UK, exhibits a classic recurved spit formation due to changes in wind and tidal influences. - Stabilization by Vegetation and Dune Formation
Over time, vegetation may grow, stabilizing the spit by trapping more sediment.
Salt marshes or lagoons can form in the sheltered area behind the spit, where water is calmer, allowing fine sediments to accumulate.
10
Q
Suggest reasons for variations of salt weathering. (6 marks)
A
- Influence of Temperature and Evaporation
Salt weathering occurs when salt solutions evaporate, leaving behind salt crystals that expand and exert pressure on rock pores and cracks.
During the summer months, higher temperatures lead to greater evaporation, which results in more salt crystallization and increased weathering rates.
In contrast, cooler winter temperatures slow down evaporation, leading to reduced salt crystal growth and lower weathering rates.
This explains why weathering rates in Fig. 4.1 are consistently higher in summer than in winter. - Wave Action and Salt Deposition
Coastal locations experience constant wave activity, which deposits salt from seawater onto rock surfaces.
During periods of high wave energy (e.g., storms or strong winds), more salt is deposited on the rock, increasing the intensity of weathering.
If storm frequency varies from year to year, it could explain why some years show larger differences in summer and winter weathering rates than others.
For example, 1983 in Fig. 4.1 shows a significant increase in summer weathering, likely due to more intense wave action and salt deposition that year. - Differences in Rock Type and Porosity
Porous rocks (e.g., sandstone, limestone) absorb more saltwater, making them more susceptible to salt crystal growth and mechanical breakdown.
Non-porous rocks (e.g., granite, basalt) are more resistant, leading to lower weathering rates.
If the site being studied has different rock types exposed to salt spray, this could contribute to variation in weathering rates across different years. - Variability in Humidity and Rainfall
Humidity influences salt crystallization. Higher humidity levels in winter may prevent excessive evaporation, reducing salt accumulation.
Rainfall dissolves accumulated salt, washing it away before it can crystallize and exert pressure on rock surfaces.
If some years had wetter winters, this would explain lower weathering rates compared to drier years.
11
Q
Explain two factors that account for the loss of coral cover on reefs. (6 marks)
A
- Climate Change and Coral Bleaching
Rising sea temperatures cause corals to become stressed, leading to coral bleaching. This occurs when corals expel their symbiotic algae (zooxanthellae), which provide them with nutrients and their vibrant color.
If high temperatures persist, corals are unable to recover, leading to reef degradation and mass coral mortality.
Ocean acidification, caused by increased CO₂ absorption, weakens coral skeletons, making them more susceptible to breakage and erosion.
Example: The Great Barrier Reef (Australia) has experienced severe bleaching events in 2016, 2017, and 2020, affecting over 60% of its coral cover. - Human Activities and Pollution
Overfishing and destructive fishing practices (e.g., dynamite fishing, cyanide fishing) physically damage coral reefs and disrupt marine ecosystems.
Coastal development and agriculture increase sediment runoff, which blocks sunlight and prevents coral photosynthesis.
Nutrient pollution from fertilizers leads to eutrophication, where excessive algae growth suffocates corals by blocking sunlight and reducing oxygen levels.
Tourism-related activities, such as boat anchoring and coral collection, also contribute to coral degradation.
Example: In the Caribbean, reefs near heavily populated coastlines, such as those in Jamaica, have suffered significant coral loss due to pollution and unsustainable fishing practices.
12
Q
Explain the formation of coastal saltmarshes. (6 marks)
A
- Sheltered Location and Sediment Deposition
Saltmarshes develop in sheltered environments where wave energy is low, allowing fine-grained sediment (silt and clay) to settle.
Tidal currents transport and deposit these fine sediments in intertidal zones, gradually forming mudflats.
Flocculation, a process where saltwater causes clay particles to clump together, aids in rapid sediment accumulation. - Vegetation Colonization and Stabilization
Once mudflats form, pioneer species like eelgrass and cordgrass (Spartina spp.) colonize the area.
These plants trap additional sediment, raising the land surface and reducing tidal inundation.
Over time, organic matter from decaying vegetation enriches the soil, promoting the growth of more complex plant communities. - Development of Creeks and Tidal Channels
As saltmarshes expand, they develop natural drainage channels (creeks and runnels) to allow tidal water to flow in and out.
These features distribute sediment and nutrients, ensuring the long-term stability of the saltmarsh ecosystem.
13
Q
Explain why the rates of erosion and deposition vary along a stretch of coastline. (6 marks)
A
- Wave Energy and Wave Type
High-energy waves (destructive waves) erode the coastline due to their strong backwash, which removes sediment from the shore.
Low-energy waves (constructive waves) deposit sediment due to their stronger swash, allowing for beach formation and deposition.
Example: Exposed coasts with long fetches, such as the Atlantic-facing coastlines, experience more erosion, while sheltered bays allow for sediment deposition. - Coastal Geology and Rock Resistance
Hard rocks (e.g., granite, basalt) resist erosion, forming headlands, while soft rocks (e.g., clay, sandstone) erode quickly, forming bays.
On discordant coastlines, where bands of soft and hard rock alternate, erosion rates vary significantly due to differences in rock resistance.
Example: The Jurassic Coast (UK) features alternating hard limestone and soft clay, creating distinct headlands and bays. - Longshore Drift and Sediment Transport
Longshore drift moves sediment along the coastline, affecting areas of erosion and deposition.
Coastal features like spits and bars form in areas where drift deposits material.
Obstructions like groynes and breakwaters disrupt sediment flow, increasing deposition in some areas and erosion elsewhere.
Example: On the Holderness Coast (UK), groynes trap sand, increasing deposition, but also causing increased erosion down-drift. - Tidal Currents and Sea-Level Changes
Stronger tidal currents transport sediment offshore, reducing deposition.
Higher sea levels increase erosion, particularly in low-lying coastal areas.
Example: The Mississippi Delta has experienced severe coastal erosion due to rising sea levels and land subsidence. - Human Activity and Coastal Management
Hard engineering structures (e.g., sea walls) prevent erosion locally but reflect wave energy, increasing erosion elsewhere.
Beach nourishment artificially increases deposition rates by adding sediment.
Example: Miami Beach (USA) undergoes regular beach nourishment to counteract erosion.
14
Q
Explain the changes to a wave as it approaches the shore. (6 marks)
A
- Friction with the Seabed Slows the Wave Base
In deep water, waves move in circular orbits with minimal interaction with the seabed.
As waves approach shallower water, the wave base begins to drag against the seabed, causing friction.
This slows down the bottom part of the wave, while the upper part continues moving at its original speed, leading to wave steepening. - Wave Height Increases and Wavelength Decreases
As the base of the wave slows, water at the surface piles up, causing wave height to increase.
Wavelength decreases because the waves become compressed together due to the slower movement of waves closer to shore. - Wave Steepness Increases and the Crest Becomes Unstable
The wave steepens as the crest advances faster than the base.
The wave reaches a point where the ratio of wave height to wavelength exceeds 1:7, making it unstable. - Wave Breaks and Energy is Released
Eventually, the crest of the wave collapses forward, breaking the wave.
The type of breaker depends on the gradient of the seabed:
Spilling waves occur on gently sloping beaches, where the crest spills gradually.
Plunging waves occur on moderately steep beaches, where the wave curls over and crashes down.
Surging waves occur on steep beaches, where the wave slides up the shore without breaking fully. - Swash and Backwash Transport Sediment
After breaking, water rushes up the beach as swash.
The backwash returns to the sea, influencing sediment deposition or erosion depending on the wave type.
15
Q
Explain two factors that might influence rates of erosion along coastlines. (6 marks)
A
- Coastal Geology and Rock Resistance
Hard rocks (e.g., granite, basalt, limestone) resist erosion, forming cliffs, headlands, and wave-cut platforms.
Soft rocks (e.g., clay, shale, sandstone) erode quickly, forming bays, inlets, and retreating shorelines.
Geological structure, such as joints, bedding planes, and faults, also affects erosion rates.
Example: The Holderness Coast (UK), composed mainly of soft boulder clay, experiences one of the highest erosion rates in Europe (~2m per year), while the limestone cliffs of Dorset erode much more slowly. - Wave Energy and Fetch
Wave energy depends on fetch (the distance wind travels over open water)—a longer fetch results in stronger waves and increased erosion.
Destructive waves (high-energy waves) have a strong backwash, removing sediment from the shore and promoting erosion.
Constructive waves (low-energy waves) have a stronger swash, allowing sediment deposition and reducing erosion rates.
Example: The Cornish coastline (UK) experiences strong wave action due to its long fetch from the Atlantic Ocean, leading to severe cliff erosion.
16
Q
Suggest two reasons why coastlines lose or gain land. (6 marks)
A
- Erosion vs. Deposition Balance
Erosion removes land when waves, currents, and tides carry sediment away. This happens in high-energy environments where destructive waves dominate.
Deposition increases land when sediment accumulates in low-energy environments, where constructive waves allow material to settle.
Example: The Holderness Coast (UK) experiences severe erosion (~2m per year) due to its soft boulder clay, while Spurn Head (a spit) is formed by deposition of sediment carried by longshore drift. - Sea-Level Change and Human Activities
Rising sea levels cause land loss, particularly in low-lying coastal areas, by increasing coastal flooding and submersion.
Coastal engineering (e.g., groynes, seawalls, beach nourishment) affects sediment movement—some areas gain land, while others experience erosion.
Example: Miami Beach (USA) undergoes beach nourishment, increasing land area, while the Maldives loses land due to rising sea levels.
17
Q
Suggest two reasons for variations of erosion rates along a barrier island
A
- Wave Energy, Longshore Drift, and Coastal Morphology
Higher erosion rates are typically found in exposed areas where wave energy is strong, particularly in regions facing a long fetch.
Longshore drift moves sediment along the coastline, leading to variations in erosion and deposition—some areas gain sediment, while others lose it.
Coastal configuration (e.g., headlands, bays) affects wave refraction, influencing where erosion or deposition occurs.
Example: The Holderness Coast (UK) experiences rapid erosion due to longshore drift, while sediment deposition occurs at Spurn Head spit. - Human Activities and Coastal Management
Sea walls, groynes, and breakwaters alter natural sediment movement, reducing erosion in protected areas while increasing it in unprotected zones.
Harbor developments and dredging may disrupt sediment supply, contributing to localized erosion.
Vegetation loss (e.g., mangroves, dune plants) reduces coastal stability, making erosion more severe.
Example: In Lagos, Nigeria, coastal defenses have altered natural sediment transport, leading to uneven erosion rates along the shoreline.
18
Q
Explain the formation of a tombolo
A
- Wave Refraction and Reduced Energy Behind the Island
When waves approach an island, they bend (refract) around it due to the shallower water near the island.
This wave refraction creates a zone of reduced wave energy behind the island, leading to low-energy conditions where sediment can settle. - Longshore Drift and Sediment Deposition
Longshore drift transports sediment along the coastline, moving sand and shingle parallel to the shore.
In areas where wave energy decreases (e.g., behind an island), the transported sediment is deposited, forming a narrow spit extending towards the island. - Formation of a Fully Developed Tombolo
If sediment deposition continues, the spit eventually connects the island to the mainland, forming a permanent or semi-permanent tombolo.
Some tombolos remain permanently above sea level, while others may be submerged at high tide (submerged tombolo).
19
Q
Explain why sand dunes occur on some coastlines. (6 marks)
A
- Availability of Dry Sand
A wide, sandy beach is essential for dune formation, providing a source of sand.
Tidal action and wave movement expose sand to the sun, allowing it to dry.
Example: The Oregon Dunes (USA) formed due to continuous sand deposition and wind transport inland. - Strong and Consistent Onshore Winds
Prevailing onshore winds move dry sand inland, initiating dune formation.
The strength of the wind determines how much sand is transported and deposited.
Example: The Namib Desert coastal dunes are shaped by strong trade winds from the Atlantic Ocean. - Obstacles for Sand Deposition
Sand needs an obstacle (e.g., vegetation, rocks, driftwood) to reduce wind speed and encourage deposition.
Over time, sand accumulates around these obstacles, leading to the growth of dunes.
Example: In Studland Bay, UK, marram grass helps stabilize dunes by trapping windblown sand.
20
Q
Explain the variation between summer and winter beach profiles
A
- Summer Beach Profile (Constructive Waves)
Constructive waves dominate during summer, characterized by low wave energy and a strong swash.
These waves push sand up the beach, forming berms (ridge-like features of deposited sand) at the high tide mark.
The gentle slope of the summer beach is due to deposition exceeding erosion.
Example: The beaches of the Mediterranean expand in summer due to low-energy waves depositing material. - Winter Beach Profile (Destructive Waves)
Destructive waves dominate in winter, characterized by high wave energy and a strong backwash.
These waves erode the upper beach, dragging sediment offshore and forming offshore sandbars.
The beach profile is steeper near the waterline but lower overall, with limited sand above the high tide mark.
Example: The North Sea coastline (UK) experiences significant winter erosion due to storm activity.
