Coasts and Changing Coastlines Study Guide

The Dynamic Nature of Coastlines

Coastlines are perpetually in a state of flux, undergoing constant transformation over many years. The energetic action of sea waves modifies the physical shape of countries by simultaneously building new land in certain locations and wearing it away in others. This dynamic process ensures that even features like beaches are never static; they are continuously reshaped by the combined forces of waves, winds, and tides.

The Process of Longshore Drift

Longshore drift is the geomorphological process by which waves move sand and pebbles along a shoreline. This phenomenon occurs in areas where the prevailing wind directs waves toward the shore at an oblique angle rather than head-on. The movement follows a specific repetitive pattern:

  1. Waves approach the beach at an angle, carrying materials (swash).
  2. Instead of returning to the sea at that same angle, the water flows straight back down the beach due to gravity (backwash).
  3. Any sand or pebbles transported by the waves are moved in a zig-zag pattern along the coast.

This sequence of movement—from the first position of a pebble to a second, third, and subsequent positions—effectively transports sediment long distances from its point of origin.

Problems Resulting from Longshore Drift

While longshore drift is a natural process, it creates significant challenges for human infrastructure and coastal management. Over time, the process can carry away an entire beach, sometimes in as short a duration as one year. This loss of sediment is particularly detrimental to holiday resorts, which may be forced to invest in expensive operations to pour or pump fresh sand onto their beaches to replace what was lost. Additionally, the movement of sand and shingle can lead to the total blockage of harbours, as the material accumulates and impedes maritime access.

Deposition and the Formation of Coastal Features

Deposition occurs when waves encounter obstacles or geographical features, such as a bay or a river mouth, that cause them to lose velocity and energy. When waves slow down, they can no longer support the weight of the sand and shingle they are transporting. Consequently, the waves drop or deposit these materials. Over time, these deposits can accumulate to form significant landforms:

  • Spit: A ridge of sand and shingle that piles up across part of a bay or a river mouth.
  • Bar: This is formed when a spit grows continuously until it reaches all the way across a bay.
  • Lagoon: When a bar is formed, the shallow pool of water that becomes trapped behind it is classified as a lagoon.
  • Barrier Island: If a bar develops to the point that it remains consistently above sea level, it may form a barrier island.

Named Geographic Examples and Statistics

The following specific geographic features serve as examples of the scales at which longshore drift and deposition operate:

  • Arabat Spit (Sea of Azov, Ukraine): Known as the longest spit in the world, it measures approximately $110\,km$ in length.
  • Lagoa dos Patos (Brazil): A lagoon that is approximately $280\,km$ long and reaches a maximum width of about $70\,km$.
  • Farewell Spit (South Island, New Zealand): This feature has a visible length of $26\,km$, with an additional $6\,km$ extending underwater.
  • Chesil Beach (Dorset, England): Recognized as the longest bar in Europe, it is approximately $16\,km$ long and encloses a lagoon known as the Fleet.
  • Hatteras Island (North Carolina, USA): A notable example of a barrier island located off the coast of the United States of America.

Activities and Vocabulary

To master the concepts of coastal geography, students are encouraged to define the following key terms:

  • Erosion: The wearing away of land by natural forces.
  • Lagoon: A shallow body of water separated from the sea by a bar.
  • Longshore Drift: The zig-zag movement of sediment along a coast.
  • Deposition: The process of dropping sediment when wave energy decreases.
  • Spit: A coastal landform consisting of a ridge of sand or shingle extending from the land.
  • Beach: A landform alongside a body of water which consists of loose particles.
  • Bar: A ridge of sand or shingle that extends across the mouth of a bay.
  • Cliff: A steep rock face, frequently at the edge of the sea.

Further practical activities include studying large-scale maps to sketch predicted coastline shapes and designing illustrated leaflets for walkers or holidaymakers to explain the formation of visible coastal features.