Factors affecting coastal recession and stability

Edexcel A level geography

Coastal recession

• the retreat of the coastline inland

• could be due to:

  • erosion

  • seal level rise

  • submergance

• where coastal recession is the result of erosion, this is dependent on the lithology of the coast

  • mineral composition

  • rock classification

  • structure

Mineral composition

• some minerals are more reactive than others

  • this affects rate of chemical weathering, e.g.

    • Calcite is reactive so easily chemically weathered

    • quartz is inert so chemical weathering is much slower

sedimentary rocks

• form as a result of compaction and cementation of material called lithification

• sedimentary rocks:

  • erode and weather faster than other rock types

  • form in layers

  • have weak bedding planes

  • they are clastic (made of sediment particles called clasts)

  • are heavily jointed

  • often have many bedding planes and fractures

• e.g. shales, sandstone, limestone

metamorphic rocks

• form when sedimentary and igneous rocks are altered through heat and pressure, but do not melt in the process

• metamorphic rocks:

  • have a crystalline structure

  • are often folded and faulted

  • are more resistant than sedimentary rock but less resistant than igneous rocks

  • the crystals have a parallel arrangement (foliation) which means they are weaker than igneous rocks

• e.g. slate, marble

igneous rocks

• form when molten rock from the Earth’s mantle cools and hardens

• igneous rocks:

  • erode and weather very slowly

  • has interlocking crystals

  • fewer joints and weaknesses than in other rocks

  • can be categorised into two types

  • intrusive igneous rock - forms within the ground, cools slowly, and has large, course crystals

  • extrusive igneous rock - forms on the Earth’s surface, and cools quickly, forming smaller crystals

differential erosion

• changing rates of erosion of different rock types

• more resistant rocks erode more slowly than less resistant rocks

• differential erosion:

  • leads to complex cliff profiles

  • influences rates of recession

• the differences in geology contribute to landforms generated by processes on the coast

• on a discordant coastline differential erosion leads to headlands and bays

• where there are layers of alternating rock types (strata) this creates a cliff profile where the more resistant rock layers jut out due to faster erosion of less resistant rock

• permeability also impacts rate of erosion

Granite lithology

• Rock type: igneous

• rate of coastal recession: 0.1-0.3cm/yr

Limestone lithology

• Rock type: sedimentary

• rate of coastal recession: 1-2cm/year

Chalk lithology

• Rock type: sedimentary

• rate of coastal recession: 1-100

sandstone lithology

• Rock type: sedimentary

• rate of coastal recession: 10-100

shale

• Rock type: sedimentary

clay lithology

• Rock type: unconsolidated

• rate of coastal recession: 100-1000

unconsolidated meaning

• materials e.g. sand, gravel, clay and silt that is loosely arranged or unstratified, or whose particles are not cemented together

• very easily eroded