2.1.3 Sediment sources, cells and budgets

Question 1

What does coastal sediment include?

Answer 1

• Clay
• Sand
• Pebbles
• Boulders
• Biogenic sediment

Question 2

Clastic rocks

Answer 2

Rocks created from fragments of older rocks

Question 3

Biogenic rocks

Answer 3

Rocks created from organisms.

Question 4

Sources of sediment in the coast

Answer 4

• 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)

Question 5

Sediment budget

Answer 5

The difference between the amount of sediment that enters the system and the amount that leaves.

Question 6

What is a positive sediment budget?

Answer 6

Where more sediment enters than leaves - overall the coastline builds outwards.

Question 7

What is a negative sediment budget?

Answer 7

Where more sediment leaves than enters - overall the coastline retreats.

Question 8

Sediment cell

Answer 8

A stretch of coastline, usually bordered by two prominent headlands, where the movement of sediment is more or less contained.

Question 9

How many sediment cells are there in England and Wales?

Answer 9

11

Question 10

How are sediment cells closed systems?

Answer 10

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.

Question 11

Inputs in sediment cells

Answer 11

Primarily derived from rivers, coastal erosion and offshore sources such as bars or banks.

Question 12

Transfers in sediment cells

Answer 12

These involve longshore drift together with onshore and offshore processes such as rip currents.

Question 13

Stores in sediment cells

Answer 13

These include the beach, sand dunes and offshore deposits.

Question 14

What are sub cells?

Answer 14

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.

Question 15

What are concordant coastlines?

Answer 15

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.

Question 16

What are discordant coastlines?

Answer 16

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.

Question 17

Rates of erosion differ for different types of rock.

Answer 17

Question 18

Examples of how geology affects the coastline

Answer 18

• 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.

Question 19

The Tees-Exe Line

Answer 19

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.

Question 20

Joints

Answer 20

Fractures, caused either by contraction as sediments dry out, or by earth movements during uplift.

Question 21

Strata

Answer 21

Layers of rock.

Question 22

Dip

Answer 22

The angle at which rock strata lie (horizontally, vertically, dipping towards the sea or dipping inland).

Question 23

Lithology

Answer 23

The physical characteristics of particular rocks.

Question 24

Coastal morphology

Answer 24

The shape and form of coastal landscapes and their features.

Question 25

Bedding planes

Answer 25

These are natural breaks in the strata, caused by gaps in time during periods of rock formation.

Question 26

Folds

Answer 26

Formed by pressure during tectonic activity which makes rocks buckle and crumple.

Question 27

Faults

Answer 27

Formed when the stress or pressure to which a rock is subjected, exceeds its internal strength (causing it to fracture). The faults then slip or move along fault planes.