Coasts Key Concepts

Landform

Specific morphological feature as a result of processes in the area - shaping of the land

Landscape

The overall layout of the land as a result of many landforms

Sediment cell

a largely self-contained stretch of coastline where the movement of sediment is almost entirely contained

Sediment cells often located

Between two headlands or estuaries

How many sediment cells in the UK?

11

Sediment cells managed by?

Sediment management plan

pros and cons of sediment management plan

Pros: managed in their own cells so effects monitored correctly as cells span over many councils
Cons: Councils do not often agree on sediment management plans leading to conflict

Inputs into sediment cells

Where sediment is brought into the system

Examples of sediment cell input

Fluvial Processes, Offshore deposits, erosion of landofrms, weathering, Sea level rise

Sea level rise as an input

Pick up sediment during flooding

Outputs

Rare - often sediment cell is a closed system - but some sediment does get past each end or washed out to sea

Flows / Transfers - huge!

Sediment is moved around the cell / system

Flows / Transfers examples

Attrition, Saltation, Solution, Traction, Abrasion, Hydraulic Action, Suspension, Freeze thaw, Onion skin, carbonation, oxidation, hydraulysis, rockfall, rotational slump, mudflow,

Sinks - stores within the sediment cell

Any large storage of sediment - depostional

Sinks examples

Beach, spit, tombolo, dunes

What maintains the cell?

Dynamic Equilibrium

Negative feedback - Maintain DE - Example?

Erosion of cliff → Material in front of it → Protect the cliff from erosion as energy removed

Positive feedback example

Cliff eroded → Drop material → Material can be used in the long term as ammunition → Abrasion → More erosion

Why are these examples good?

Example of the differences in a positive / negative feedback over time-scale - dynamic environment

Energy in a sediment cell - high to low

Waves, tide, wind

Wave formation

Wind friction leads to capillary wave, turn into train of many waves, gain energy, meet shoreline

Wave power determined by

Fetch, strength of wind, direction of wind (Prevailing perpendicular = more)

Fetch

the distance of open water over which the wind blows the wave, in a single, uninterrupted direction.

Waves crash over the top due to

Frictional forces turn circular motion into elliptical - crest lifted too high and collapse

Destructive waves

High energy, Weak SW, Strong BW, High and steep, more frequent, erosional landforms

Constructive waves

Low energy, Strong SW, weak BW, Shallow and slow, less frequent, depositional

Tide

Rise and fall of sea level due to gravitational effect of moon and sun, and centrifugal force of their orbit and the rotation of the earth.

2 types of tide

Spring, Neap

Strongest tide?

Spring - highest variation in tidal range, when moon and sun are opposite to earth, 2 x a month

Weakest tide?

Neap, when moon and sun are at a relative 90 degrees to each other, happens 7 days after - effects relatively cancel out, lowest tidal variation

Why this way?

Gravity leads to bulge on close side - centrifugal leads to bulge on far side.

Spring = Amplified, Neap = Nullified

Wind - Aeolian

Pressure gradient - as a result of uneven heating leads to imbalance = movement of air

Wind

Can be strong - but typically low energy, does lead to waves - typically depositional landforms

Current

Flow of water due to changes in temperature and salinity - leads to transport of material

Where are currents most likely to be observed?

Through breaks or gaps in depositional landforms

High energy coastlines

Typically wave dominated with lots of erosional landforms, Steep shores, long fetch, exposed rock where erosion > deposition

Examples of high energy coastline erosional landforms

Wave cut platform, Cliff, Headlands and bays, Caves, arch, stack, stump

Low energy coastlines

Constructive waves, wind and tide dominated, Short fetch with gentle shores, Depositional landforms, Deposition > Erosion

Depositional landform examples

Reef, island, beach, spit, Slat marsh, mudflat

Sediment budget

Balance of sediment in / out of the cell

Positive budget

In > out, leads to accretion of sediment and then Shore Extension

Negative budget

Out > in, leads to removal of sediment and then Shore Retreat

Headland

Sticks out into the sea, eroded slower, leads to wave refraction

Wave refraction

Wave bend around headland to attack headland perpendicular to the coastline, leads to a reduction in energy of the wave too

Reduction of wave energy leads to

Depositional landforms forming in the bay behind the headland

Landforms as a result of wave refraction

Crack, Cave, Arch, Stack, Stump

Erosion

The degredation and subsequent removal of material

Agent of erosion

Waves, winds, tides

Coastal erosion examples

Abrasion, Solution, Hydraulic action, wave quarrying, cavitation, attrition

Abrasion

Material is dragged and scoured along the rock - leads to removal and smoothing

Hydraulic action

Air and water is compressed into rocks, leading to widening and weakening

Cavitation

As wave recedes out of the gap, it pulls back on the air creating low pressure, air rapidly expand and weaken crack

Wave quarrying

Energy of the wave removes material

Solution

Material is dissolved into the seawater

Attrition

Erosional material e.g. pebbles collides with other erosional material - leads to small smooth material

Transportation

The movement of sediment

Agents of transportation

Gravity, waves, current, wind

Transportation examples

Traction, Saltation, Suspension, Solution

Traction

Larga particles and boulders get pushed and rolled along the sea floor

Saltation

Smaller stones or pebbles getting bounced along the sea floor - too heavy to be suspended

Suspension

Turbulent water picks up finer sediment - water appears murky and cloudy

Solution

Material is dissolved and carried in the water

Deposition

Decreasing energty levels leads to the dropping of sediment

Deposition can be

Marine or Aeolian

Deposiotion happens when

Sediment load exceeds waters ability to carry it

Energy decrease due to

Increase in friction - Shallow water etc

Turbulent flow - obstacles slow the flow down

Weathering

The breakdown of material in situ

3 types of weathering

Physical, Chemical, Biological

Chemical weathering examples

Carbonation, Oxidation, Solution

Carbonation

Linked heavily to the carbon cycle, especially prominent in limestone - high calcium carbonate

Chemical reaction in carbonation

Calcium Carbonate + carbonic acid → Calcium bicarbonate which then dissolves into the water

Oxidation

Dissolved oxygen in the water reacts and oxidises - disintegrate - leaves brown / yellow stain

Solution

Chemicals and acidity of the water directly dissolves other products into it

Biological

Plant roots, animal burrowing, marine processes

Plant roots

Plant roots dig through and weaken the ground / remove material - prompting collapse

Animal burrowing

Animals dig holes and weaken the land - typically at the top of cliffs - prompting collpase

Marine processes

Piddock shellfish drill into rock and weaken it - digest it directly

Seawees atttaches to and tuggs at rocks until they are pulled away

Physical / Mechanical

Freeze Thaw, Salt, Wet and dry

Freeze thaw

Water fills up cracks - freezes - expands - applies pressure and force crack open

Salt

Crystallizes in gaps in the rock - crystals grow and expand applying pressure - can also be corrosive

Wet and dry

Especially in porous rock - expansion and contraction leads to weaknesses

Mass Movement defnition

The movement of a large volume consolidated or unconsolidated material due to gravity

5 types of mass movement

Slides, slumps, rockfalls, mudflows, soil creep

Slide

Movement of material down the slope - no internal derangement - fall as one block - Resistant cliff material e.g. rock

Slump

Landslide with rotation derangement - Unconsolidated - soil etc - Slumps down the cliff - Heavy and undercut

Rockfall

Spontaneous - Only on over 40 degree slopes - Fragments break off during rapid free fall of material - vulnerable bare jointed rock

Mudlfow

Heavily saturated - typically over unconsolidated material - flows down the slope - steep ish - no vegetation to support

Soil creep

Slowest movement - less than 1cm per year - continuous on slopes due to expand / contract of soil

Categories of coast

Emergent, Submergent, erosional, depositional, cliffed, flat, gradiented, concordant, discordant

These categories depend on

Geology, energy supply, lithology, erosion, deposition

Wave refraction

Waves come into shallower water around a headland first

Get bent around the headland and attack at angles

Dissipates wave energy

Factors affect erosion rate

Energy, sea depth, gelogy, lithology: bedding plane dip, human activity, wave angle,