Coastal systems 2 Flashcards
What determines the nature of the kinds of beach features that develop?
The angle at which waves generally approach a coastline will determine the nature of the kinds of beach features that develope
Swash-aligned beaches
Swash-aligned beaches:
-Generally oriented parallel to the incoming wave crests
-Experience minimal longshore drift
-Can be found on irregular coastlines where longshore drift is impeded, and waves hit sections of the coast head-on
Drift-aligned beaches
Drift-aligned beaches:
-Generally oriented parallel to the dominant longshore drift
-Can have considerable amounts of sediment transported long distances along them
-Initially develop where a section of coastline if fairly regular, or where the predominant wave direction is at an angle to the beach
-Can extent out from the coastline if there is sudden change in the direction of the coastline, for example, upon reaching an estuary
Spit
A spit is an elongated, narrow ridge of land that has one end jointed to the mainland and projects out into the sea or across an estuary, usually on a drift-aligned coast
Formation of a spit
Formation of a spit:
1). Prevailing winds and fetch are from the southwest, so material will be carried form west to east along the coast by the process of longshore drift
2). Coastline changes to a more north-south orientation, there is a build up of sand and shingle in the more sheltered lee of the headland, as this material begins to project eastwards, storm builds up more material above the high water mark
3). Finer material carried eastwards into the deeper water of the estuary, and as the water loses its capacity to transport it further, is deposited, extending the ridge (spit) into the estuary
4). End of spit curves round due to second most dominant wind
Simple spits
Simple spits:
-Either straight or recurved
-Do not have minor spits, or recurved ridges, along their landward edge
Compound spits
Compound spits:
-Similar features to simple spits
-Have a number of recurved ridges, or minor spits, along their landward side, possibly marking the position where they terminated in the past
Sand dunes
Sand dunes develop as deposited sand dries out and is blown to the landward side of the spit, where it can accumulate and become stabilised by vegetation as species like marram grass get established.
Salt marshes
Salt marshes:
Low energy waves enter sheltered area between the land and the spit, and deposits finer material such as silt and clay
-These deposits build-up and are colonised by vegetation to become salt marshes
Tombolo
A spit that joins an island to the mainland is known as a tombolo
Bar
If a spit developes across a bay where there is no strong flow of water from the alndward side, it is possible for the sediment to reach across to the other side, this is known as a bar
-Some bars may of formed also as a result of sea levels rising from the last ice age
Offshore bar
When a ridge of beach material that remains semi-submerged accumulates seaward of the breaker zone, this is known as an offshore bar
A barrier beach
Barrier beach is an elongated bank of deposited sand or shingle lying parallel to the coastline and not submerged by incoming tides
-The sheltered area between the barrier beach and the island is known as a lagoon/coastal marsh, or in tropical locations mangrove swamps may develop
Barrier islands
Barrier islands develop where the bank is high enough to allow sand dunes to develop
Characteristic coastal landscapes
Characteristic coastal landscapes:
-Bays
-Estuaries
-Beaches
-Deltas
-Dunes
-Mud flats and salt marshes
Factors important in producing the present coastal landscape features
Factors important in producing the present coastal landscape features:
-Local tectonic processes
-Sea level change - global and local
-Climatic change - natural and that enhanced by human activity
-Changing ocean currents and wave regimes
-Natural disasters or events - including storms or tsunamis
-Changing sources, types and amounts of sediment
-The changing nature of human activity
Coastal sand dunes
Coastal sand dunes - accumulations of sand shaped into mounds by the wind - represents a dynamic landform - act as systems
Important inputs into coastal sand dunes
Important inputs into coastal sand dunes:
-An obstacle to trap the sand
-Vegetation growth to encourage further growth of the dune
Where do sand dunes develop?
Sand dunes develop:
-In sheltered areas where deposition occurs
-Where salt and fresh water meets
-Where there are no strong tides or currents to prevent deposition or accumulation
Formation of sand dunes
Formation of sand dunes:
-Sand trapped by obstacles
-Formation of embry o dunes
-Foredunes/yellow dunes
-Grey fixed dunes and dune ridges
-Wasting dunes with blowouts
-Dune slacks
Embryo dunes
-First dunes developed are embryo dunes, suitable for colonisation by grasses, able to grow upwards through accumulating wind-blown sand, prescne of plants adds organic matter to these dunes which aids water retention
Foredunes/mobile dunes
-Upward growth of embryo dunes raises height to create tall tunes, called foredunes/mobile dunes, these are initially yellow but dunes end up looking more grey due to increased vegetation cover
-Dunes gradually become more fixed , and an organic layer develops as other types of vegetaion colonises alongside the marram grass
Dune slacks
-In places dune slacks develop - these are depressions wihtin the dunes where the water table is on or near the surface and conditions are often damp
Wasting dunes/areas of dune heath
-Behind the yellow and grey dunes, the supply of sand is gradually cut off, giving smaller dune features. These areas may be referred to as wasting dunes, or are areas of dune heath
Blowouts in sand dunes
-Within the sand dune system , it is possible to find blowouts where wind has been funnelled through areas and has removed the sand. Wildlife or human activity can often be a catalyst for the formation of blowouts
Mudflats
Mudflats are found at the edges of estuaries, and are zones of net deposition of fine sediment - they only develop on sheltered shorelines that are no exposed to powerful waves
-Low-lying areas of shore that are submerged at high tide and are composed of silt and clay
Where are mudflats located
Mudflats are located in estuaries or on the landward side of a spit
How mudflats develop?
They develop in estuaries where the flow of fresh water out of the river is slow and the seawater flows into the river mouth with each high tide and out with each low tide:
1).Saltwater brings in lots of fine sediment which meets the river that is carrying its own sediment
2). The two flows meet and the fine particles settle out of suspension by flocculation, where the individual clay particles come together to form large heavy particle that sink to the bed.
What are mudflats susceptible to?
Mudflats are not permanent, as they are susceptible to changes in sea level, wave action, changes in discharge levels in the river and changes to tidal flows
What do mudflats develop into?
Mudflats can develop into salt marshes
-A vegetation sucession also develops, and is known as a halosere (tolerant of salty conditions)
How do mudflats act as systems?
-Apositive feedback loopoperates, amplifying the initial deposition as submerged and semi-submerged plants trap more sediment and reduce water velocity leading to increased deposition.
-Plant life-cycles deposit decaying material on top of which new plants grow, gradually raising the height of the saltmarsh. This means salt marshes work as a system, as sediment is being moved in as inputs.
What is a halosere?
A halosere is a succession in a saline environment. An example of a halosere is a salt marsh.
Halosere sucession
Primary succession can happen when bare mud on depositional coasts, bays, and estuaries is colonised by plants. Over time the mud builds up into a saltmarsh, raising the ground level above the height of the land above sea level. Succession in a saltmarsh is sometimes called a halosere.
How does salt marshes act as systems?
Salt marshes as sytems:
-Inputs and processes: mud and silt deposited along sheltered part of the coastline
-Outputs: vegetation sucession forms as plants develop (known as a halosere), salt marshes have formed from mudflats
Stages of vegetation sucession/halosere in salt marshes
Stages of vegetation sucession/halosere in salt marshes:
-Low-lying vegetation grows on mudflats, this slows the current and leads to increased, uneven deposition
-Pioneer plants colonise
-Pioneers gradually develop close vegetation over the mud allowing colonisation by other plants such as marsh grass and sea lavender
-These form a dense mat of vegation, which slows the tidal currents, leads to more mud and silt accumulation, including dead organic matter
-As mud levels rise, complex creek systems develop that channel the tides which deepens as marsh gets higher
-Trees such as oak and hollows eventually forms to complete sucession
Pioneer plants
Pioneer plants - tolerates salt and periodic submergence by the sea - known as halophytes (grows in areas of high salinity)
Spartina
Spartina -> two root systems -> a fine mat of surface roots to bind the mud and long, thick deep rots that can secure up to two metres of deposited material
-This enables the plant to trap more mud than other pioneers and so it has become the dominant vegetation on tidal flats in the british isles
Rias
A ria is a drowned river valley - a section of river valley flooded by the sea, whilst leaving the higher land dry and exposed
Emergent coastlines
Emergent coastlines = produced by post-glacial adjustment -> where a fall in sea level exposed land once part of the seabed -> eg raised beaches, fossil beaches (eg Isle of Arran)
Salt marsh sucession feedback system type
Salt marsh sucession is a positive feed back loop, because submerged and semi-submerged plants trap sediment -> decreases velocity -> traps more sediment + saline levels then decrease
Hydrosere
Hydrosere is a plant sucession, which eventually becomes a climax community
Lithology and geology difference
Lithology refers to rock type wheras geology refers to rock characteristics
Submergent coastlines
Submergent coastlines is where sea level rise has flooded land, eg rias (drowned river valley) and fjords (drowned glacial valleys)
Sediment sources
Sediment sources include:
-Rivers (transported by waves, tides, currents) and into places such as estuaries
-Cliff erosion (due to retreating)
-Wind
-Glaciers (from being stored in the ice)
-Offshore
-Longshore drift
What is the littoral zone?
The littoral zone is the area of land between the cliffs or dunes on the coast and the offshore area that is beyond the influence of waves
Why is the littoral zone constantly changing?
The littoral zone is constantly changing due to:
-Short-term factors like tides and storm surges
-Long-term factors like changes in sea level and human intervention
What is onshore?
Onshore is the area of land not covered by the sea, but close to it
What is offshore?
Offshore is the area beyond the influence of waves
Sources of energy at the coast
Sources of energy at the coast include:
-Sun
-Waves which are formed offshore and generated by wind
-Tectonic activity or underwater landslides (causing tsunami waves)
Wave formation
Wave formation:
-Winds move across water surface, causing frictional drag which creates small ripples and waves, leads to circular orbital motion of water particles in the ocean
-As seabed becomes shallower towards the coastline, orbit of water particles becomes elliptical, leading to horizontal movement of water
-Wave height increases, wavelength and velocity decrease
-Causes water to back up from behind wave until wave breaks and surges up the beach
What is frictional drag?
Frictional drag is resistance to the wind by the water
Factors affecting wave energy
Factors affecting wave energy:
-Wind strength - the greater the pressure gradient, stronger the winds
-Duration of the wind - more active, energy incraeses
-Size of fetch - greater fetch, more powerful winds
What is meant by fetch?
Fetch is the distance over which the wind blows
What causes the difference in pressure of wind?
The different pressure areas are caused by variations in surface heating by the sun
Rip currents
Rip currents are powerful underwater currents occuring in areas close to shoreline, when plunging waves cause a buildup of water at the top of the beach - backwash is forced under surface and forms the current
Factors affecting erosion
Factors affecting erosion:
-Waves
-Beaches (absorbs wave energy and reduces erosion)
-Subaerial processes (weathering and mass movement)
-Rock type (eg sedimentary being more eoded and less for igneous and metamorphic)
-Rock faults (cracks, joints, more susceptible to erosion)
-Rock lithology (characteristics
Igneous rocks
Igneous rocks - granite, basalt - slow erosion - interlocking crystals which allow for high resistance to erosion
Metamorphosis rocks
Metamorphosis rock - slate, schist, marble - slow eorsion - crystal all orentated in the same direction, resisting reosion
Sedimentary rock
Sedimentary rock - limestone - fast erosion - lots of faults making them weak and vulnerable to erosion
Types of mechanical weathering
Types of mechanical weathering:
-Freeze-thaw (water enters rock, they freeze, water expands, pressure increases, and rock breaks off)
-Salt crystallisation (seawater evaporates, salt left behind, crystals grow, exerts pressure, cracks widen
-Wetting and drying (rocks expand when wet, contracts when dry, causing them to break apart
What is a dalmatian coast?
A Dalmatian coast is a submergent coastline where valleys have been flooded by a rise in sea level leaving a series of islands parallel to the coastline
Role of weathering in the development of coastal landforms
Role of weathering in the development of coastal landforms:
-Can weaken coastal landforms such as cliffs, making them more susceptible to processes of coastal erosion
-Weathering adds sediment to the shoreline which can then be used by other coastal processes (eventual development of beaches)
-Causes cliffs to retreat due to subaerial weathering and erosion -> creates notch at high water mark and forms wave-cut platform
-Landforms such as stacks and stumps may also form
What is subaerial weathering?
-Subaerial processes are land-based processes and occur above the waterline
-They include weathering and mass movement, which happen on the cliff rocks
Sustainable approaches available for coastal management
Sustainable approaches available for coastal management:
-Managing natural resources to ensure long-term longevity (fish, agriculture, water supply)
-Relocation to safer areas (providing alternate livelihoods)
-Education
-Monitoring areas
-Use of alternative building supplies
Why can sustainable coastal management lead to conflict?
Sustainable coastal management can lead to conflict because:
-Less natural resources used -> loss of income
-Relocation can be costly
-Erosion may always occur
-Future trends may change
What is the littoral zone?
The littoral zone is a series of subzones to represent the features of the wider coastlines from sea to land
Four key sub-zones in the littoral zones?
Four key sub-zones in the littoral zones:
-Offshore
-Nearshore
-Foreshore
-Backshore
What is cavitation as an erosional process?
Cavitation is a form of erosion where air bubbles trapped in water are compressed into small spaces.
Cavitation happens when waves hit cliffs and air bubbles are forced into cracks in the rock face. Pressure compresses the air bubbles, forcing them into solution.
What is the main process of solution?
The main process of solution is when calcium carbonate in rocks such as limestone is dissolved.
What are the subaerial processes?
Subaerial processes = mass movement, weathering
Formby Point - Sefton coast case study
Formby Point - Sefton coast case study:
-Sand dune system
-1920-1970 lost 700m - loss is due to periodic storms, high tides, dredging, hard engineering defences with groynes up north, offroad vehicles, trampling
-0.3metre sea level rise in 16yrs due to climate change
-Soft engineering strategies (nourishment, boardwalk, signpost, education)
Heysham and Morecombe coast case study
Heysham and Morecombe coast case study:
-Lancashire coast
-1989-2017 £30 million in defences
-Mixed hard eng with sustainability - hold the line, groynes, sea wall, rip rap
-11k homes and commercial buildings protected as a result
Sundabarns case study
Sundabarns case study:
-Background - bangladesh, bangel bay, vegetated low lying, 3 rivers inc meghna
-Threats = removal of mangroves (more vulnerable to tropical storms), retreating coasts, increased sea temp -> increased soil salinity
-Impacts = reduced agricultral land, oveexploitation of fish farming decrases hauil, job workers emmigrating
-Responses = wildlife refuge areas, temporary fishing camps
Difference between emergent and submergent coastlines?
Emergent coastlines = eustatic change -> sea levels decrease -> produced by glaciation
Submergent coastlines = isostatic change -> lands and sea leel sirse - rias (drowned river valley), Fjord (drowned glacial valleys), dalmation coasts
