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Littoral Zone Area of shoreline where land is subject to wave action Littoral Zone Subdivisions - Offshore - Nearshore - Foreshore - Backshore - Beach Offshore Where waves begin to break in the deeper water. Friction between the waves and the sea bed may cause some distortion of the wave shape. Nearshore Friction between the seabed and waves distorts the wave sufficiently to cause it to break. Possible breakpoint bar formation. Foreshore The area between the high tide and the low tide mark. Backshore The area above the high tide mark, affected by wave action only during major storm events. Why are Littoral zones dynamic zones of rapid change? Short term - Changing inputs, through flows and outputs of energy and material. High and low tide variation, wave energy due to weather. Long term - Sea level variation due to climate change Classifying Coasts - Long Term Criteria (2) - Geology - Sea Level Change Classifying Coasts - Geology - Characteristics of land, including lithology (rock type) and structure (arrangement of rock units). - Used to classify coasts as cliffed, sandy, estuarine, concordant and discordant Cliffed Coastline (4) - High energy environment - Rate of Erosion exceeds Deposition. - High relief varying from a few meters to hundreds of meters - Resistant Geology Sandy Coastline (5) - Low Relief with Sand Dunes and Beaches - Less Resistant Geology - Low energy environment - Rate of Deposition exceeds Erosion - Constructive waves Estuarine Coastline (5) - Low Relief with Salt Marshes and Mudflats - Form in River Mouths - Low energy environment - Rate of Deposition exceeds Erosion - Less Resistant Geolagy Classifying Coasts - Sea Level Change - Used to Classify Coasts as Emergent or Submergent - Caused by eustatic/isostatic changes - Caused by climate change Climate Change caused by Cycles - Sea Levels rise and fall in 100,000 year cycles - Due to Earths Orbit - Falls for 90,000 years as ice sheets expand - Rises for 10,000 years during interglacial periods - Rises when all surface ice melts Emergent Coastline As Sea Levels fall, coastline land is exposed which was previously covered by the sea Submergent Coastline As Sea Levels rise, the land is covered Concordant Coastline - Alternating bands of rock that run parallel to the coastline - Also called Dalmatian Coasts Discordant Coastline Erosion Wearing away of land due to wave action Mass movement Downslope movement of material due to the force of gravity. Formation of Coastal Plains - Formed by Coastal Accretion (Continuous net deposition causes coastline to extend seawards) - Can extend biologically if plants colonise shallow water, trapping sediment Where does Coastal Accretion come from? (2) - Offshore sources (transported by waves, currents and tides) - Terrestrial sources (transported by rivers, glaciers, wind or mass movement) Dynamic Equalibrium - When Erosion = Deposition - Continuous flows of energy and material through the coast but size of stores remains unchanged Concordant coastline - Lulworth Cove - Resistant Portland Limestone forms a protective stratum layer parallel to sea. - Less Resistant Purbeck Limestone and Wealden Clay lie behind the Portland Limestone. - Portland limestone erodes very slowly, retreating landwards by marine undercutting. - At points where Portland Limestone is weaker, erosion managed to break through leading to the erosion of the less resistant Purback Limestone and Wealden Clay. This is done by lateral erosion. - Destructive waves have a stronger backwash so material is dragged out the cove. This can cause small beaches. - Waves continue to erode Portland Limestone. Attrition and abrasion are responsible for the erosion and the cove is widened more and more. Concordant Coastline - Croatia - Dalmatian coastline on the Adriatic Sea (Croatia in particular) - Formed where the geological structure consists of folds parallel to the coastline - Folded Ridges (Anticlines) and Down Folded Valleys (Synclines) are aligned parallel to the coast - Sea Level rise at the end of the Devensian glacial period caused flooding of Synclines - This produced narrow islands parallel to the coast that are seperated by narrow sea channels Concordant Coastline - Haff Coastline - Formed when deposition produced unconsolidated geological structures parallel to the coastline - During Devesian Ice age, sea levels were 100m lower than today - Thick layers of sand and gravel deposited by meltwater rivers - Holocene interglacial constructive waves moved the deposited sediment landwards as sea levels rose - Bars formed across bays and river mouthes, causing lagoons to be formed behind the bar (East of Gdansk) Discordant coastline - Swanage Bay - Isle of Purbeck in East Dorset - The waves erode the less resistant Wealden Clay which eventually forms a bay, where wave energy is low. - More resistant rock is resistant to erosion, so sticks out and forms a headland, where the wave energy is high. - Jurassic Portland Limestone forms a headland extending 1km out into sea - Resistant Cretaceous chalk forms another headland extending 2.5km out into the sea - As the waves approach the headland, it absorbs wave power and refracts - meaning they change motion and direction around the headland. - After the wave hits the headland, it is likely to become a constructive wave. These waves carry material and deposit it as swash is more powerful than backwash. - The bay will eventually come forwards and become a beach, whilst the headlands are slowly eroded by hydraulic action. - The coastline eventually becomes smooth until the process repeats. Geological Structure Characteristics and arrangement of rock units. Strata Different layers (or beds) of rock. Bedding Plane Surface separating layers of strata. Deformation Degree of tilting of folding of rock. Dip Angle of inclination of titled strata. Fold Tectonic forced that distort rock strata Folding increases erasion rates - Folded rock are heavily fissured and jointed, meaning they are more easily eroded. - Rock is stretched along anticline crests and compressed in syncline troughs. Fault - Mineral Composition - Rock Class - Structure Mineral Composition - Resistance - Some rocks contain reactive minerals easily broken down by chemical weathering, e.g. calcite in limestone. - Other minerals are more inert that chemically weather more slowly Rock Class - Resistance - Clastic Sedimentary rocks = limestone - Cements that are reactive and easily chemically weathered = iron oxide - Sedimentary rocks with weak cementation = boulder clay - Crystalline and strong chemically bonded igneous rack = Granite Structure - Resistance - Rocks with fissures (faults and joints) or air spaces (porous) rocks, weather and erode rapidly. Igneous Rock - Formed from solidified lava or magma - Composed of interlocking crystals, forming hard, resistant rock - Tend to have fewer joints and weaknesses, therefore being more resistant - Erode at 0.1cm p.a. Metamorphic Rock - Formed by the recrystallisation of sedimentary and igneous rocks through heat and pressure - Has a crystalline structure - Less resistant than igneous rock due to crystals not being interlocked and the rock often containing folds and faults - Erode at 0.1-0.3cm p.a. Sedimentary Rock - Formed by compaction and cementation of deposited sediment - Contain weak bedding planes - They are clastic - Often heavily joined due to compaction - Erode at 0.5em-10cm p.a. Unconsolidated Sediment - Sediment that has not yet been cemented to form solid rock - Example of this includes boulder clay - Erode easily at 2-10m p.a. Complex Cliff Profile - Composed of strata of differing lithology - Less resistant strata erode and weather quickly, being cut back rapidly. This can form wave cut notches - Resistant strata erode and weather slowly, retreating less rapidly. - Overhang eventually collapses due to gravitational forces Permeable Rock Allow water to flow through them. Impermeable Rock Do not allow water to flow through them. Complex Cliff Profile (Permeable/Impermeable Strata) Permeable rocks tend to be less resistant to weathering because water percolating comes into contact with a large surface area that can be chemically weathered. Vegetation and Stabilisation - Vegetation can stabilise unconsolidated sediment and protect it from erosion - Plant roots bind sediment together, making it harder to erode - Leaves covering the surface protect sediment from wave erosion and longshore drift - Also protect sediment from wind erosion Vegetation and sediment accumulation - Vegetation can increase the rate of sediment accumulation - Plant leaves interrupt flows of water and wind. This encourages deposition - As vegetation dies, hummus is added to the soil Why are coasts harsh environments for plants? (5) - Exposed to high wind speeds during low tide - Lack of shade produces high temperature range - Vegetation submerged in salty water for half the day - Evaporated sea spray makes sediment saline - Sand lacks nutrients Plant Succession The changing structure of a plant community over time as an area of initially bare sediment is colonised Pioneer plants The first plants to colonise freshly deposited sediment. How do Pioneer Plants modify the environment? (3) - Soil has improved nutrients and moisture retention. - Non-xerophytic plants colonise the dunes until a climax plant community is reached, in equilibrium with the climate and soil conditions Halophytes Plants specifically adapted to saline conditions. They are able to colonise in mud and salt water. Halosere Plant Succession in salty water Why are Estuarine areas ideal for salt marshes? (2) - Sheltered from strong waves (enables deposition) - Rivers transport sediment to the river mouth which can add to deposition Salt Marsh Succession 1) Flocculation = Mixing of sea water and fresh water causing clay particles to stick together and sink 2) Blue-green algae colonise mud, exposed at low tide for only a few hours. 3) Algae binds mud, adds organic matter, and traps sediment. 4) Sediment thickens, water depth reduces so mud is covered by tide far less time 5) Halaphytic cord grass calonises. The marsh is still low and covered by high tide each day 6) Accumulation of organic matter rises the height of the marsh 7) Salt marsh becomes colonised by plants such as scurvy grass 8) Rainwater washes salt out of the high marsh soil 9) Land plants continue to colonise until a climax community is reached What does wave size depend on? (4) - Strength of wind - Duration for which the wind blows - Water depth - Wave fetch Constructive Waves - Low energy waves - Low, flat wave height (<1m) - Long wavelength (up to 100 m) - Low wave frequency (about 6-9 per minute) - Strong swash that pushes sediment up the beach. Weak backwash means that a lot of material is deposited Destructive Waves - High energy waves - Large wave height (>1 m) - Short wavelength (about 20 m) - High wave frequency (13-15 per minute) - Weak Swash and strong backwash. Causes sediment to get eroded from the beach Beach Morphology Shape of the Beach Beach sediment profile Pattern of distribution of different sized or shaped deposited material. How do constructive waves alter beach morphology and beach sediment profiles? - Net movement of sediment up the beach causing a steeper beach profile - Berms (Ridge of Material) can be created at the point where the swash reaches at high tide - Sorting of material due to swash/backwash energy. Sand closer to water and heavy sediment towards back of beach - Coarse sand deposited in the middle of the beach whereas only fine sand makes it dawn to the water How do destructive waves alter beach morphology and beach sediment profiles? - Reduced beach gradient due to net transport of sediment down the beach (weak swash and strong backwash) - Sediment thrown from waves can accumulate as a storm ridge - Large sediment particles dragged to the water and deposited below low tide mark Decadal Variation of Beach Morphology and Beach Sediment Profiles - Climate change is expected to bring more extreme weather events to the UK - Winter profiles may be present for longer time over course of year - More frequent and powerful destructive waves could decrease beach size and increase rates of erosion Seasonal Variation (Winter - UK) of Beach Morphology and Beach Sediment Profiles - Destructive, high-energy waves dominate - Lowers angle of beach profile - Shingle spread over the whole beach - Offshore bars formed causing deposition of sediment offshore Seasonal Variation (Summer - UK) of Beach Morphology and Beach Sediment Profiles - Constructive, low-energy waves dominate - Beach angle steepens - Particles sorted by size along the beach (larger shingle towards back of beach) - Berm ridges constructed at high tide mark Monthly Variation of Beach Morphology and Beach Sediment Profiles Wave Cut Platform - Flat rock surface exposed at low tide, extending out to sea from the base of a cliff. - Starts with a wave cut notch - Eventually, overhang of the wave cut notch collapses by mass movement due to gravity - Process is repeated and cliff moves landwards leaving a flat rock surface at the low tide level. Cliffs - Steep slopes that are usually don't contain vegetation - Wave cut notch forms - Notch deepens until overhand collapses by mass movement due to gravity - Exposed rock face forms a cliff Cave - Arch - Stack - Stump - Rock eroded by hydraulic erosion due to joints and faults. Widening of these weak points forms a cave. - Eventually, marine erosion will cause the cave to break through to the other side of the headland forming an arch - Hydraulic action and abrasion attack the sides of the arch between low tide and high tide, forming wave cut notches. - Overhang eventually collapses by mass movement due to gravity. This widens the arch. - Weathering and other sub-aerial processes attack the arch roof. Eventually the roof collapses due to block fall leaving a stack. - Marine erosion attacks the stack forming a notch until the stack collapses due to block fall. - Causes a stump to form (small projection of rock exposed at low tide) Transportation Processes (4) - Traction - Saltation - Suspension - Solution Traction Where large, heavy load items are rolled along the sea bed. Saltation Where lighter sediment bounces along the sea bed. Suspension Where very light sediment is carried aloft within a body of water or air Solution Where sediment is carried dissolved within the water Angle of Wave Attack (Sediment Transportation) - Main determinant of sediment transportation - Sediment transported in the direction of the wind blowing towards the beach - Backwash transports sediment perpendicular down the beach Longshore Drift (LSD) (Sediment Transportation) - Net lateral movement of material along the coastline - Swash transports the material up the beach at an angle - Gravitational backwash causes material to move down the beach perpendicular to the coastline - Process repeats - Wave angle of 30' produces strongest LSD movement - Prevailing wind is usually the dominant direction of LSD Tides (Sediment Transportation) - Tides are changes in sea level produced by the gravitational pull of the moon and the Sun. - Incoming and ebbing tide can create tidal currents in the nearshore and offshore zones that transport sediment. Currents (Sediment Transportation) - Flow of water in a particular direction that transport sediment in the nearshore and offshore zones - Can be driven by winds - Can be initiated by water density, temperature or salinity Swash-Aligned Coastline Waves break parallel with the coast. Drift-Aligned Coastline Waves break at an angle to the coast. Beaches - Accumulations of sand and shingle found in the foreshore and backshore zones. - Produced by material being deposited by constructive waves - Swash has energy to carry material up the beach - Weak backwash only has energy to carry finest sediment down the beach, leaving the remaining material up the beach Spits - Ridges of sand or shingle beach stretching into the sea beyond a turn in the coastline (usually 30' or more e.g. bay or river mouth) - At the turn, LSD continues in original direction however energy is dispersed leading to deposition - Over time, sufficient sediment is deposited forming a spit that extents into the sea - 11 Primary sediment cells Example: - Flamborough head = source region - Holderness coast = transfer zone - Spurn point head = sink region Sediment Cell Inputs Sources are places where sediment is generated. - Cliff Erosion - River Transport - Land Sediment blown by wind Sediment Cell Transfer Zone Sediment moved along a coast. - Longshore Drift - Swash - Backwash - Tidal Currents - Sea/Ocean Currents - Wind Sediment Cell Outputs Sinks are locations where the dominant process is deposition and depositional landforms are created. - Spits - Sand Dunes - Beaches - Bars Why are Sediment Cells Dynamic Systems? Sediment is constantly generated in the source region, transported through the transfer region and deposited in the sink region. How can dynamic equilibrium be dynamic itself? - Changes of energy and sediment inputs are constantly altered - Climate change creates more frequent storms - System equilibrium may be disrupted but will return to normal due to negative feedback Negative Feedback When the change produced creates effects that operate to reduce or work against the original change. Positive Feedback When a change produces an effect that operates to increase the original change. Physical Weathering Breaks down rocks by the exertion of a physical force, and does not involve any chemical change. Types of Physical Weathering (3) - Freeze-Thaw Weathering - Salt Crystal Growth - Wetting and Drying Freeze-Thaw Weathering - Water seeps into cracks in rocks - Water freezes, it expands in volume by 9%, exerting a tensional force that widens the rock - Later, more water can enter the cracks causing the process to repeat until cracks are large Salt Crystal Growth - Seawater penetrates cracks at high tide and evaporates at low tide, leaving precipitated salt crystals - This process repeats until the build up of salt crystals exerts pressure on the cracks - Eventually, the rock breaks off Wetting and Drying - At high tide minerals on the rock surface are soaked with sea water and expand in volume. - At low tide, minerals dry and shrink. - Repeated cycles of expansion and contraction eventually cause the rock to fragment and crumble. Chemical Weathering Chemical reactions attack individual minerals in the rock, breaking bonds and producing new chemical compounds. Types of Chemical Weathering (3) - Carbonation - Hydrolysis - Oxidation Carbonation - Rainwater mixed with carbon dioxide from the air to form weak carbonic acid (pH 5.6). - The acidic rain mixes with calcium carbonate to form soluble calcium bicarbonate solution. - 'Rock disappears’ as minerals dissolve into a solution. Hydrolysis - Breakdown of minerals to form new clay minerals, plus materials in solution, due to the effect of water and dissolved carbon dioxide. - Vulnerable Rocks = Igneous and Metamorphic rocks containing feldspar and other silicate minerals - Movement of material downhill along a curved rock plane. - Slumping material usually moves intact as a single mass, without any internal deformation of material. - May take minutes, hours, days or even years Conditions for Rotational Slumping - Weak Rocks - Unconsolidated Material - Water, which adds weight to the material and reduces friction by lubrication Example of Rotational Slumping - Christchurch Bay, Barton-on-Sea - Unconsolidated sand lies over clay - Water accumulates in sand and is unable to reach impermeable clay - Water adds weight intensifying gravitational downforces eventually causing slumping Landslides - The sudden and rapid movement of a large amount of material down a slope - Released by mechanical weathering, then pulled downhill due to gravity Conditions for Landslides - Consolidated rocks with joints or bedding planes sloping seawards. - Rainstorm events can encourage a landslide, lubricating the slip plane, reducing the resistance. Landforms produced by mass movement (3) - Rotational Scar - Talus Scree Slope - Terraced Cliff Profile Rotational Scar - Fresh, curved, unweathered and unvegetated rock surface on the cliff face - The detached slope section, often with vegetation intact on top of the slump, forms a beach or terraced cliff profile. Talus Scree Slope - Blockfall debris accumulates at the cliff foot forming a fan shaped mound of material. - Undercutting of cliffs by the creation of wave-cut notches can lead to large falls and talus scree slopes at their base. - A talus scree slope has a slope angle of 34-40' Example of Talus Scree Slope - St Oswald's Bay, South Dorset Coast - Alarge fan shaped talus scree slope (from blockfall) was created at the slope foot, extending 30 m into the sea that will protect the cliff from further erosion for a decade or more. Eustatic Change Change in sea level due to change in the volume of water in the oceans Eustatic Change - Milankovitch Cycles Climate change occurs cyclically due to changes in the Earth's orbit around the sun. Milankovitch Cycles - Glacial Period - 90,000 year colder phases, leading to the formation of ice sheets - Changes in global hydrological cycle - Evaporated ocean water falls on land as snow and compresses to form ice - Decrease in volume of ocean water produces a global fall in sea level - Devesian Ice Age - Global sea levels lower by 120m Marine Regression Sea levels fall and so the sea bed gets exposed as land Milankovitch Cycles - Interglacial Period - 10,000 year warmer phase. Ice sheets shrink - Water transferred from land back to acean stores. Volume of ocean water increases - Rising temperatures lead to thermal expansion, further increasing volume Marine Transgression Rising sea levels flood lowland areas Sea Level Change since 1750s - Anthropogenic Forcing = Humans accelerating natural interglacial warming through greenhouse gas emissions - 21cm rise (1870-2010) - Melting of Antarctic Ice sheets expected to increase sea levels by 50cm Isostatic Change A change in local land level Isostatic Rises in local land level (3) Causes a fall in local sea levels - Post-glacial adjustment - Accretion - Tectonics 
