Geo-Dictionary - coasts
This form of erosion is caused by material from the beach/river bed scraping or banging against the wetted perimeter of rivers or the cliffs at beaches. This causes the surfaces to be eroded. Abrasion forms potholes in river beds as the pebbles and stones swirl around in a circular motion into the bed of the river.
Advance the Line
This is a form of coastal defences. The defences are built seaward. Breakwaters are built offshore and they stop waves from eroding the coastline as they cause waves to break out at sea
This is caused/influences by humans for example anthropogenic damage is damage caused by humans.
Geo-Dictionary - coasts
This is another form of erosion it is different to all the others because it is the erosion of the material of the beach or in the river it’s self rather than the surrounding river bed or shore. For example if a river is carrying a lot of stones or pebbles and they are banging together they are not going to be eroding the bed they are going to be eroding each other, attrition causes pebbles and rocks to become smooth and rounded.
This is the area of a beach between the high tide mark and vegetation. This area of the beach is only affected by wave action if there is a severe storm.
This is an area of sea that is mainly surrounded by land. They form on discordant coastlines where a band of soft rock erodes faster than bands of hard rock either side of the band of soft rock. The wave refraction causes the bay shape to form.
A nearly horizontal plateau on the beach face or backshore, formed by the deposition of beach material by wave action.
Living organisms, such as plants and animals, cause rock to decompose. Plant and tree roots can work their way into the crevices of a rock, forcing it apart and ultimately causing it to fracture. Some plants give off organic acids that can chemically break down rock minerals. Worms can be responsible for biologically weathering rocks and rock particles. They physically break rocks apart during physical activities such as boring. Some lichens will anchor themselves to the surface of a rock and weather it either chemically or physically. They can either release various organic acids that will break down rock minerals or they can grow into the pores and cracks of the rock, making it vulnerable to fracture. When plants and animals decay, they release carbon dioxide into the air. When the carbon dioxide mixes with water, it forms carbonic acid, which can break down the minerals in rocks.
Rain water and carbon dioxide create carbonic acid. This mild acid interacts with minerals in soft rocks: lime, potash and soda. Calcium, magnesium and potassium convert into carbonate when mixed with carbonic acid and wash away with rain water. This type of chemical weathering often creates sinkholes and caverns.
A coastline where bands of different rock types run parallel to the shore. These rock types are usually of alternating resistance so the coastline forms distinctive landforms, such as coves.
Constructive waves -
A small type of bay or coastal inlet, usually narrow or restricted entrances, oftern circular or oval.
Cusps - Arc patterns of sediment found on the beach. Cusps are found all over the world, but are the most noticeable on pebble beaches and beaches where the sediment is courser.
They almost always occur in a regular pattern with equal size and spacing of the cusps along the shoreline.
Destructive wave - A plunging wave, with a short wavelength, a high frequency (13-15 per minute) and a high crest, which breaks so that the water crashes downwards from the wave crest and erodes the beach; backwash thus greatly exceeds swash. Plunging waves generally occur on steeply sloping beaches.
Discordant -A discordant coastline occurs where bands of differing rock type run perpendicular to the coast. The differing resistance to erosion leads to the formation of headlands and bays. A hard rock type such as granite is resistant to erosion and creates a promontory whilst a softer rock type such as the clays of Bagshot Beds is easily eroded creating a bay.
Part of the Dorset coastline running north from the Portland limestone of Durlston Head is a clear example of a discordant coastline. The Portland limestone is resistant to erosion; then to the north there is a bay at Swanage where the rock type is a softer greensand. North of Swanage, the chalk outcrop creates the headland which includes Old Harry Rocks.
Embryo Dunes - At the front of the dunes is the youngest dune called an embryo dune. This is a hostile environment for plants because of the salinity, lack of humus and pH of 8-9. The alkaline pH is a consequence of the presence of shell fragments in the sand. This is also a very dry environment and the rapid drainage and exposed nature of the site make it difficult for plant growth. (The term xerosere is sometimes used for plant succession in very dry environments) The plant which can colonise here is sand couch grass. This is a smaller version of sea couch grass which in Ireland is not found north of Dublin, on the east coast, and Galway, on the west. Couch is able to survive in the hostile environment by being resistant to salt, and is able to withstand drought, storing water in its succulent leaves. It also thrives on burial by the accumulating sand. The couch grass slows the blown sand from the beach and it gathers among the plants. Vegetation cover is sparse with perhaps 80% of the dune being exposed sand. Winter storms can sometimes wash away this dune but it builds up again in the summer.
Emergent Coastline - Emergent coastlines are stretches along the coast that have been exposed by the sea due to a relative fall in sea levels. This occurs due to either isostacy or eustacy. Emergent coastline are the opposite of submergent coastlines which have experienced a relative rise in sea-levels.The specific landform of an emergent coastline may be:
Eustatic Change - Eustatic change results in an alteration to the global sea levels due to changes in either the volume of water in the world oceans or net changes in the volume of the ocean basins.
A halophyte is a plant that grows where it is affected by salinity in the root area or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs, and seashores. An example of a halophyte is the salt marsh grass Spartina alterniflora (smooth cordgrass). Relatively few plant species are halophytes - perhaps only 2% of all plant species. The large majority of plant species are "glycophytes", and are damaged fairly easily by salinity.
Is when in the day the rock expands due to the heat and in the evening it gets cooler causing the rock to contract. If this happens continuously and the rock keeps expanding and contracting, it will put pressure on it and cause the layers to peel off like an onion skin.
Fetch: Is a term for the length of water over which a given wind has blown. It plays a large part in longshore drift. Fetch length along with the wind speed (or strength) determines the size of waves produced. The longer the fetch length and the faster the wind speed, the larger and stronger the wave will be. The fetch length determines the power and energy of the wave.
Foreshore: The area of a shore that lies between the average high tide mark and the average low tide mark. Also it can be known as the part of a shore between the water and occupied or cultivated land.
Freeze thaw: Is a form of physical weathering. It is commonly found in mountains and glacial environments, caused by the expansion of water as it freezes. Water in a crack freezes and expands in volume by 9% as it turns to ice. This expansion exerts great pressure on the rock, causing the crack to enlarge. For freeze–thaw to operate effectively the temperature must fluctuate regularly above and below 0°C/32°F. It is therefore uncommon in areas of extreme and perpetual cold, such as the polar regions.
Geos: On any cliff line the sea will attack the weakest parts such as joints, crack and on bedding planes. Along a joint the sea will cut inland widening the crack to form a narrow steep sided inlet known as a geo.
Glacial till: Is material that is directly deposited from glacial ice. Till includes a mixture of undifferentiated material ranging from clay size to boulders, the usual composition of a moraine.
Halosere: Succession in a saline environment, an example of this would be a salt marsh. Anything waterlogged with salt water, or land that has recently been raised out of the ocean counts as halosere, plants that can grow here (are tolerant of salty conditions) are called halophytes.
Hold the Line: Using hard and soft sea defences to “fix” the coastline and thus hold the seat bay, usually to protect valuable infrastructure behind. There are two ways of doing this:
Hard Engineering: Permanent rock and concrete structures designed to last for around 20-30 years. Seawalls, groynes, detached breakwaters and revetments are the most common examples in Europe. A man made structures that directly influence coastal processes. They were often favoured in the past before proper knowledge of the environment allowed us to work with the natural processes of the area.
Soft Engineering: Sand nourishment/beach replenishment is an example; building using natural processes and relying upon beaches, sad dunes and salt marshes to hold back the erosion form the sea.
Hydraulic action: An erosional process where the sheer power of the water causes sediment to be loosened from the river bed and water being forced into cracks in the rock. This pushes the air further back down the crack, trapping it at the back. As the water withdraws the air is released and the sudden drop in pressure creates an explosive force that is capable of chipping away at the rock over time, eroding the river bank.
Hard Rock - A hard rock is just that – a rock that is hard. That are many different rock types and all have different properties. Hard rocks tend to be more resistant to weathering, due to being cemented and well consolidated. They are usually stable than softer rocks. Many features such as stacks, arches and caves are generally formed in harder rocks.
Headlands: A Headland is a piece of land that extends out into the sea. It is usually made of a hard rock that resists erosion. Often associated with bays, headlands are formed when rock banding is discordant to the direction of waves, creating different areas of high and low erosion.
Hydration: Hydration is a chemical weathering process involving the addition of water to a rock or mineral.
Hydrolysis: Hydrolysis is a chemical weathering process involving the ionisation of water. It affects carbonate and silicate minerals. One mineral which is susceptible to hydrolysis is feldspar.
Intertidal Zone: The area that is above water at low tide and under water at high tide (area between tide marks)
Isostatic change is where the land level changes relative to the sea. This means that with stable levels of water, isostatic change may still cause alterations in sea level, at least for that area. This can be due to melting ice sheets that release long term pressure on the area causing rebound, and effectively lowering sea level.
Longshore Drift: Longshore drift is the movement of sediment across the coast as a result of prevailing winds causing waves to travel certain directions. Waves can hit the coast at slight angles, but retreat perpendicular to the coast. Over time sediment will travel the direction of the wind creating the waves. Features such as spits and bar are closely related to longshore drift.
Land use management: The way that land use is managed, for example for farming, housing, commercial or industry in relation to the natural environment.
In coastal management it allows an area that was not previously exposed to the sea to flood, by breaching or removing the current sea defences. Managed retreat is often used in low-lying estuaries and land that has at some point been claimed from the sea (Eg Somerset Levels). Usually a salt marsh is allowed to form to protect the coast by dissipating the wave’s energy as they strike the coast at high tides. The scheme’s advantages are that new habitats are created and there is no direct cost, and almost no maintenance costs. The disadvantages would be that as salt marshes take a while to form they are often unsightly, and the farmland has to be brought by the local council so it can be flooded.
Management- 5 different types:
Do nothing – carry out no defence except for safety measures.
Managed retreat – adopt a more landward position of defence
Hold the line – maintain, upgrade or build new defences to the level of protection provided by existing defences.
Advance the line - adopt a more seaward position
Observe and Monitor - exactly what it says on the tin.
Marram grass - A pioneer species for psammoseres, it can survive being partially submerged, it binds dunes
Mass movement - the downward movement of weathered material via the force of gravity.
Neap tide - lowest of the high tides due to the Earth, moon and sun being at a right angle.
Nearshore – The areas between the low water mark and the point where waves cease to have any influence on the land beneath them.
Offshore – the area beyond the point where waves cease to impact upon the seabed and in which activity is limited to deposition of sediment.
Oxidation - when iron reacts with oxygen in the air or water causing it to rust, red colour
Reduction - when iron reacts with water but no oxygen present, rocks go green
Pressure release cracks - when mass from top of rock is released, causes rock to expand and forms cracks in the rock, this increases surface area so more weathering processes can occur.
Psammosere – A form of ecological succession that began on coastal sands.
Refraction - Friction with a headland or the seabed as waves approach the shore causes the wave front to become distorted and refracted as velocity is reduced.
Ridges and runnels - Small ridges of sediment that accumulate parallel to the beach in between berms on shingle beaches. Runnels are the corresponding depressions
Salt Crystallisation - when saline water enter a rock and evaporate leaving small crystals that grow and force the rock apart.
Sediment cells - a self contained area or unit, usually between two major headlands where coarse sediment does not migrate.
Soft Engineering - Working with the environment to create a sustainable engineering method that works alongside natural processes, for example beach nourishment. Approaches are less expensive, are more long term, attractive and sustainable as they work with natural processes.
Soft Rock – Easily eroded rock such as limestone and chalk, more susceptible to weathering than other types of rock. When banded with hard rock, they form headlands and bays creating concordant and discordant coastlines.
Solution – Minerals from rocks such as limestone are dissolved in water.
Spring tide – Spring tides happen just after every full and new moon, when the sun, moon and earth are in line. This is when lunar and solar tides line up and reinforce each other, making a bigger total tide.
Storm Surges – Generated by tropical and extra tropical storms. The low pressure and wind setup combine to produce large temporary rises in sea level. They then have the capacity to cause extensive flooding over coastal lowlands.
Sub-Aerial Weathering – Weathering that takes place on the surface of exposed rocks as opposed to that caused by the sea. Examples include freeze thaw, chemical weathering, biological weathering and salt crystallisation.
Submergent coastlines – Coastlines sinking as a result of sea level rise, causing the flooding of valleys and drowning of old coastlines.
Succession – may be initiated either by the formation of new or unoccupied habitats caused by lava flows or land slides which strip the land bare, allowing for primary succession which will eventually become a climax community.
Terminal groyne syndrome- area of coastline that receives little or no sediment due to up the coastline perhaps a groyne has been put in place.
Terrestrial- animals or plants or processes that operating or live or grow on land
Tidal bore- Tidal Bore, a wall of water that travels upstream from the mouth of a tidal river as the tide rises. Bores occur only in a few rivers. The largest bore in the world occurs in the Tsientang Kiang
Tides - The variation in the surface level of the oceans caused by gravitational attraction of the moon and sun. Peak and neap tide.
Water layer weathering- physical type of weathering, other processes combine in the top layer of rock and break it off, replenishing the beach with sediment.