2.3 Coastal Recession

Question 1

What is lithology?

Answer 1

• it refers to the physical characteristics of the rock

- this can be igneous, metamorphic, sedimentary or unconsolidated sediment as each have different characteristics

Question 2

What is the structure of igneous rock, and what effect does this have on coastal recession?

Answer 2

• crystalline structure (interlocking crystals) menas they are well connected, impermeable and have few joints
• they created rocky coastlines with steep profile cliffs and erode very slowly
• recession rate is 0.1 - 0.3 cm/yr
• e.g. Lands End in Cornwall is Granite

Question 3

What is the structure of metamorphic rock, and what effects does this have on coastal recession?

Answer 3

• well connected and impermeable due to crystalline structure
• often folded and faulted due to extreme pressure and heat leading to weaknesses
• create rocky coastlines with steep cliff profiles and erode slowly
• recession rate 0.5-1 cm/yr
• e.g St. Ives in north Cornwall is made of slate

Question 4

What structure do sedimentary rocks have, and what effects does this have on coastal recession?

Answer 4

• limestone and chalk are relatively resistant but they are more vulnerable to erosion as they are CLASTIC ( meaning they are made up of cemented sediment rather than interlocking crystals)
• formed in strata (layers) with joints provide weaknesses meaning many of these rocks are permeable
• chalk is porous (there are air spaces between the particles) and is also permeable but can still form steep cliffs and headlands as well as wave cut platforms
• limestone recession rate 1-2 cm/year
• chalk recession rate 1-100 cm/yr
• e.g. white cliffs of Dover is chalk

Question 5

What is marram grass? where does it grow? what does it do?

Answer 5

• marram grass is a xerophyte
• it grows on sand dunes
• it protects sand dunes from erosion by having extremely long roots, of up to 3m, meaning it can hold sediment together allowing the dunes to become more stable and develop denser vegetation
• as it binds sediment together it protects the dunes from wind erosion
• xerophytes are drought resistant and wind erosion resistant

Question 6

What is glasswort? Where does glasswort grow? What does glasswort do?

Answer 6

• glasswort is a halophyte
• it grows in salt marshes
• when submerged in high tide its succulent stem and leaves provide a protective layer so that the sediment is not directly exposed to erosion by the tide, it also contributes dead organic matter to the sediment leading to the development of soil which is less vulnerable to erosion
• halophytes and salt resistant and water erosion resistant

Question 7

What is the psammosere?

Answer 7

• it refers to the changing structure of the plant community over time on a sand dune
• it begins with the colonisation of pioneer species and leads all the way to the climax community with trees
• this type of coastal succession occurs at coastlines where deposition is taking place in typically low energy environments that are sheltered from high energy waves

Question 8

Explain sand dune succession (psammosere)

Answer 8

1. Sand accumulates to form an embryo dune in a coastal area with low energy waves
2. Pioneer species, like marram grass, colonise the dune, stabilising it and help to trap more sand
3. A fore dune develops when enough sand has been trapped and the dune starts to become more stable
4. Now an established dune will become more vegetated by marram grass. It provides dead organic matter to the sand and aids the development of soil, improving the living conditions for other species
5. With soil now developed the dune goes from a yellow dune to a grey dune. This is now a permanent dune and the conditions are suited to a greater biodiversity of plant species, including grasses and heather
6. Between dunes, dune slacks can form. Wind erosion can deepen these craters and they can become waterlogged in high tide condition as they sit below the water table
7. Furthest inland it the climax community or mature dunes. Here the soil is fully developed and stabilised. Species diversity is at its highest and trees can grow here

Question 9

What is the halosere?

Answer 9

• this refers to the changing structures of plant communities over time in salt marshes
• they occur at low energy coastlines in the slack water of an estuary, or behind a spit
• they initially being with pioneer species like glasswort and eventually reach the climax community with trees

Question 10

Explain salt marsh succession (halosere)

Answer 10

1. In the low energy environments of estuaries, sheltered bays and behind spits, rivers bring fine mud sand silts whilst tidal conditions bring other conditions like salts, all of which are deposited
2. Tiny sediment particles combine in a process called FLOCCULATION. This increases deposition meaning the area can more easily be colonised by algae
3. This vegetation helps to trap more sediment and builds the height of the dune marsh making it more suitable for other species to grow. Halophytic species like glasswort and cordgrass can now grow
4. These pioneer species stabilise the sediment and add dead organic matter, leading to the development of soil. Now that the height of the marsh has increased more species can grow as the area is less salty due to the infrequent submergence of the salt marsh
5. At the most inland end of the marsh, soil has developed and the climax community is established facilitating the growth of trees