2.1.3 Sediment sources, cells and budgets Flashcards
What does coastal sediment include?
- Clay
- Sand
- Pebbles
- Boulders
- Biogenic sediment
Clastic rocks
Rocks created from fragments of older rocks
Biogenic rocks
Rocks created from organisms.
Sources of sediment in the coast
- Weathering
- Mass movement
- Cliff erosion / longshore drift
- Waves / tides / currents / storm surges
- Onshore deposits (beaches)
- Offshore deposits (silt/clay and sand deposits on sea floor)
- Rivers
- Sea shells / marine skeletons (calcium carbonate)
- Human activity (beach nourishment)
Sediment budget
The difference between the amount of sediment that enters the system and the amount that leaves.
What is a positive sediment budget?
Where more sediment enters than leaves - overall the coastline builds outwards.
What is a negative sediment budget?
Where more sediment leaves than enters - overall the coastline retreats.
Sediment cell
A stretch of coastline, usually bordered by two prominent headlands, where the movement of sediment is more or less contained.
How many sediment cells are there in England and Wales?
11
How are sediment cells closed systems?
Each one is a distinct area of coastline separated by well defined boundaries – meaning that in theory, processes going on in one cell don’t affect the movement of sediment in another cell.
In theory, sediment cells can be classed as a closed system. In reality, sediment can find its way around headlands and into neighbouring cells.
Inputs in sediment cells
Primarily derived from rivers, coastal erosion and offshore sources such as bars or banks.
Transfers in sediment cells
These involve longshore drift together with onshore and offshore processes such as rip currents.
Stores in sediment cells
These include the beach, sand dunes and offshore deposits.
What are sub cells?
Sediment cells can vary in size. The larger ones are divided into smaller sub-cells to allow closer study and management.
For example, sub cell 2a and 2b in the Holderness region on the East Coast near the Humer Estuary.
What are concordant coastlines?
A concordant coastline is where the type of rock runs parallel to the coast. You can see that the limestone at A forms the concordant coastline on the South Dorset coastline.
What are discordant coastlines?
A discordant coastline is where the type of rock runs perpendicular (at a right angle) to the coastline. The layers at B show the discordant coastline on the east Dorset coastline.
Rates of erosion differ for different types of rock.
Examples of how geology affects the coastline
- Cornwall – The Cornish coastline (SW of England) is made mainly of Basalt. Basalt is a resistant igneous rock.
- Robin Hood’s Bay – Sedimentary rocks are easily erodible – creating the bay.
- Holderness – The Holderness coastline is the fastest eroding coastline in Europe. It is made of boulder clay, glacial till and chalk.
- St Bees – St Bees is a village on the Cumbrian coastline. It is made of sandstone and glacial till. The sedimentary stone and glacial till is quickly eroding.
The Tees-Exe Line
The complex geology of the UK can be simplified by this line running from Teesside to Exeter.
- The SE and E of the UK is generally made up of softer rock such as chalk and clay, whereas the SW and N is harder rock such as basalt.
- The SE of the line is dominated by lowland landscapes whereas the NW of the line is dominated by the highest landscape.
Joints
Fractures, caused either by contraction as sediments dry out, or by earth movements during uplift.
Strata
Layers of rock.
Dip
The angle at which rock strata lie (horizontally, vertically, dipping towards the sea or dipping inland).
Lithology
The physical characteristics of particular rocks.
Coastal morphology
The shape and form of coastal landscapes and their features.
