Coastal Landforms | Geography for GCSE/IGCSE - Year 11 PDF Download

Erosional Landforms

• Cliffs are formations of steep or gently sloping rocks, their profiles influenced by geological characteristics and surrounding topography.
• The angle of a cliff face is determined by geological factors and the intensity of wave erosion at its base, where high-energy waves are more destructive than low-energy ones.
• Many cliffs feature a 'knick-point' near the high-water mark, known as the 'wave-cut notch,' formed by wave undercutting.
• Abrasion, corrosion, and hydraulic action further erode the notch, extending it backward into the cliff.
• As undercutting persists, the cliff above becomes unsupported and unstable, eventually leading to collapse.
• The backwash of waves removes the eroded material, leaving behind a wave-cut platform.
• This process repeats, causing the cliff to continue retreating, resulting in coastal erosion.

The process of cliff retreat and wave-cut platform formation:

Headlands and bay

• These features are typically located in regions where layers of durable (hard) and less durable (soft) rocks alternate, creating a discordant coastline.Initially, erosion targets the less durable rock, such as clay, carving out a bay.
• A bay refers to a sea inlet where the land curves inward, often featuring a beach.
• Meanwhile, the more resilient rock, like limestone, remains projecting outward into the sea, forming a headland.
  
• A headland typically features cliffs along its sides, projects out to sea, is usually longer than it is wide, and consists of resistant rock.
• A bay usually has a wide, open entrance from the sea, a roughly semi-circular shape extending into the coastline, land that is lower than the surrounding headlands, and may or may not have a beach.

Caves, arches and stacks

• When waves approach the shore, their velocity decreases as they encounter the seabed.
• This alters the wave direction, causing the crests to align parallel to the coastline, a phenomenon known as wave refraction.
• Refraction concentrates erosive forces on all sides of the headland.
• Weaknesses in the headland are exploited by hydraulic action, abrasion, and corrosion.
• As cracks widen, abrasion begins to erode the forming cave.
• The cave expands over time, eventually breaking through the headland to create an arch.
• Erosion continues to widen and thin the arch's base, both from below by wave action and from above by weathering.
• Ultimately, the arch's roof collapses, leaving a solitary rock column known as a stack.
• The stack is undercut at its base by wave action and weathering from above until it crumbles, forming a stump.

Depositional Landforms

Beach

• Beaches typically form in protected areas like bays.
• Deposition takes place via constructive wave action, where the swash is stronger than the backwash.
• Beach formation commonly occurs during calmer summer months.
• Occasionally, strong winds may carry offshore sand onto the shore.
• This blown sand can accumulate and create sand dunes in the beach's backshore.

Spit

• A spit is an elongated strip of sand or shingle extending from the shoreline into the sea.
• Spit formation is triggered by changes in coastline shape or the presence of a river mouth, preventing a spit from forming across the estuary.
• The shape of a spit, including whether it has a curved end, depends on wind and current directions.
• A notable example is Spurn Point, which spans three and a half miles across the Humber Estuary in northeast England.

Formation Stages

• Sediment is transported by longshore drift along the coastline.
• When the coastline changes direction, shallow, sheltered areas facilitate sediment deposition.
• Increased friction leads to further deposition.
• Over time, a spit gradually builds up to sea level and extends.
• Changes in wind direction can alter wave patterns, resulting in a hooked end for the spit.
• The area behind the spit becomes sheltered, allowing for the deposition of silts that form salt marshes or mud flats.

Bar

• A bar occurs when a spit connects two headlands across a bay.
• It results in the formation of a sandbar, which can also develop offshore due to wave action.

Lagoon

• A lagoon is a small body of water separated from the sea.
• It may form behind a bar or tombolo but is not permanent and can fill with sediment, creating new land.

Tombolo

• A tombolo forms when a spit connects the mainland to an island.
• An example is Chesil Beach in Dorset, which links the mainland to the Isle of Portland.

Barrier Island

• Barrier islands develop alongside the coast in a parallel formation.
• The primary distinction between a bar and a barrier island lies in their connectivity to the mainland and water bodies. A bar connects two headlands, while a barrier island is open at one or both ends.

Sand dunes

• Sand dunes are characterized by their dynamic nature, undergoing rapid changes.
• Typically, sandy beaches are accompanied by sand dunes, resulting from strong onshore winds carrying dried-out, exposed sand.
• Dunes are formed when sand grains are caught and deposited against obstacles like debris, rocks, or driftwood.
• Onshore winds push the seaward side of dune ridges towards the leeward side, causing them to move inland.
• The formation of sand dunes is facilitated by the interplay between winds and vegetation.

Formation of a sand dune

• Windblown sand accumulates against barriers such as pebbles or driftwood.
• With the capture of more sand particles, dunes expand, organizing into rows perpendicular to the prevailing wind direction.
• Over time, vegetation colonizes and stabilizes the ridges of the dunes through a process known as succession.
• Pioneer plant species, the first to establish, encounter challenges such as:
  a. Salinity.
  b. Scarce moisture due to rapid drainage of sand (high permeability).
  c. Wind exposure.
  d. Temporary burial by wind-blown sand.
  e. Rising sea levels.

Embryo Dunes

• Wind-blown dry sand is trapped by debris, initiating deposition.
• Pioneer species like Lyme Grass and Sea Couch Grass start to establish.
• Soil content is minimal, and pH levels are high (alkaline).
• Embryo dunes are delicate and typically reach a maximum height of 1 meter.

Fore Dunes

• Embryo dunes provide some shelter from the prevailing wind.
• This allows for the growth of other plant species like Marram Grass.
• Marram grass begins to stabilize the dune with its root system.
• These plants contribute organic matter to the dunes, enhancing their suitability for subsequent plant growth.
• A microclimate forms in the dune slack.
• Fore dunes can reach a maximum height of 5 meters.

Yellow Dunes

• Initially, these dunes have a yellow hue which darkens over time as organic material enriches the soil.
• Marram grass remains dominant, but more delicate flowering plants and insects inhabit the dune slacks.
• Exposed sand decreases to 20% from an initial 80%.
• Maximum height does not exceed 8 meters.

Grey Dunes

• Grey dunes are more stable, with less than 10% of sand exposed, and exhibit greater biodiversity.
• Soil acidity and water content increase with the accumulation of humus.
• Shrubs and bushes start to appear.
• Height ranges from 8 to 10 meters.

Mature Dunes

• These are the oldest and most stable dunes, located several hundred meters or more from the shoreline.
• The soil can support diverse flora and fauna, including oak trees and alders, representing the climax vegetation.
• Mature dunes mark the final stage in succession, known as the climax community stage.