Edexcel IGCSE Geography 复习笔记 2.1.2 Coastal Landforms

Headland and Bay

• Found in areas of alternating bands of resistant (hard) and less resistant (soft) rocks running perpendicular to oncoming waves (discordant coastline)
• Initially, less resistant rock (e.g. clay) is eroded back, forming a bay
• A bay is an inlet of the sea where the land curves inwards, usually with a beach.
• The more resistant rock (e.g. limestone) is left protruding out to sea as a headland

Cove

• A cove forms where the coastline has bands of resistant and less resistant rock running parallel to the oncoming waves (concordant coastline)
• There is usually a band of resistant rock facing the oncoming waves, with a band of softer rock behind
• Wave processes of abrasion, corrosion and hydraulic action will exploit faults in the resistant rock and erode through to the softer rock
• Further wave action will erode the softer rock quickly, which will leave behind a circular cove with a narrow entrance to the sea
• Wave refraction within the cove spreads out the erosion in all directions, creating the typical horseshoe shape
• Lulworth Cove in Dorset, UK, is a good example of a cove

Cliff and Wave-cut Platform

• Cliffs are shaped through erosion and weathering processes
• Less resistant rock erodes quickly and will form sloping cliff faces
• Steep cliffs are formed where there is harder rock facing the sea
• A wave-cut platform is a wide gently sloped surface found at the foot of a cliff:
  • As the sea attacks the base of a cliff between the high and low water mark, a wave-cut notch is formed
  • Abrasion, corrosion and hydraulic action further extend the notch back into the cliff
  • The undercutting of the cliff leads to instability and collapse of the cliff
  • The backwash of the waves, carries away the eroded material, leaving behind a wave-cut platform
  • The process repeats and the cliff continues to retreat, leading to a coastal retreat

Cave, Arch, Stack and Stump

• Found on a headland due to wave action and sub-aerial weathering
• Any weaknesses in the headland are exploited by erosional processes of hydraulic action and corrosion
• As the crack begins to widen, abrasion will begin to wear away at the forming cave
• The cave will become larger and eventually breaks through the headland to form an arch
• The base of the arch continually becomes wider and thinner through erosion below and weathering from above
• Eventually, the roof of the arch collapses, leaving behind an isolated column of rock called a stack
• The stack is undercut at the base by wave action and sub-aerial weathering above, until it collapses to form a stump

Beach

• Form in sheltered areas such as bays
• Deposition occurs through constructive wave movement, where the swash is stronger than the backwash
• Beach formation usually occurs in the summer months when the weather is calmer
• Sometimes sand from offshore bars can blow onto the shore by strong winds
• Blown sand can create sand dunes at the backshore of a beach

Spit

• An extended stretch of sand or shingle that extends out to sea from the shore
• Spits occur when there is a change in the shape of the coastline
• Or the mouth of a river, which prevents a spit forming across the estuary
• A spit may or may not have a 'hooked' end, depending on opposing winds and currents
• A good example is Spurn Point, which stretches for three and half miles across the Humber Estuary in the northeast of England

Stages of Formation:

• Sediment is transported by longshore drift
• Where the coastline changes direction, a shallow, sheltered area allows for deposition of sediment
• Due to increased friction, more deposition occurs
• Eventually, a spit slowly builds up to sea level and extends in length
• If the wind changes direction, then the wave pattern alters and results in a hooked end
• The area behind the spit becomes sheltered
• Silts are deposited here to form salt marshes or mud flats

Bar

• When a spit grows across a bay, and joins two headlands together
• A bar of sand is formed (sandbar)
• Sandbars can also form offshore due to the action of breaking waves from a beach

Lagoon

• A lagoon is where a small body of water is cut off from the sea
• A lagoon may form behind a bar or tombolo
• Lagoons do not last forever and may fill with sediment and form new land

Tombolo

• A tombolo is formed when a spit joins the mainland to an island
• Chesil Beach in Dorset is a tombolo, as the mainland is joined to the Isle of Portland 

Barrier Island

• Barrier islands form parallel to the coast
• The main difference between a bar and barrier island is that a bar joins two headlands, whereas a barrier island is open at one or both ends