Coasts Exam Practice Flashcards
Explain how coasts are classified (8)
Coasts can be classified by long term processes such their relative sea level change, characterising them as either emergent or submergent coasts. Emergent coasts such as the Croatian dalmatian coastline, are where coasts are rising relative to sea level, this can be due to tectonic uplift from isostatic processes. Alternatively, submergent coasts are where coasts are being flooded by the sea, due to either rising sea levels or subsiding land.
Another long term classification of coasts are the formation processes. Primary coasts are dominated by land based processes such as deposition at the coasts from rivers or new coastal land formed from lava flows. Whereas secondary coasts are dominated by marine erosion or deposition processes.
Shorter term classifications of coasts include wave energy, either as high energy or low energy coastlines. Low energy coasts are sheltered with limited fetch and low wind speeds resulting in small waves. These coasts usually have gentle sloping beaches and do not display many features of erosion by hydraulic action. Whereas high energy exposed coasts, face prevailing winds with long wave fetches resulting in powerful waves. These coasts will have many features of erosion including wave-cut platforms, caves and steep cliffs.
Coasts can also be classified by their geological structure, a longer term classification. On a concordant coastline bands of different type of rock, some more resistant and some less resistant, are parallel to the sea. On a discordant coastline the different bands of rock are perpendicular to the sea, leading to more varying coastline due to the different resistances of rock being exposed to erosion; lots of bays and headlands form at discordant coastlines.
Explain how geological structure influences coastal morphology (8) (concordant and discordant, joints, faults, dips don’t influence to same extent)
Coastal morphology is the shape of the rocks along a coastline. The resistance of a rock can influence coastal morphology, this is shown by concordant and discordant coastlines. Along concordant coastlines band of different rock are parallel to the sea, with varying resistances. This can cause Haff coastlines such as lulworth cove where erosion has broken down the first more resistant layer and then caused much faster erosion onto the less resistant rock behind it. Alternatively, on a discordant coastline they are perpendicular, meaning varying types of rock can be found along the coastline. As less resistant rock is exposed to the same weathering and erosional processes as more resistant rock along discordant coastlines, bays and headlands are formed as less resistant cliff faces are eroded much faster than those with a high resistance.
The lithology, physical characteristics of particular rocks, can also influence coastal morphology. The strata, layers of rock which compose the cliff face, face seaward then the cliff will be more susceptible to mass movement such as landslides and slumping because of this seaward dip. Whereas if the strata have a landward dip this will give a more stable coastline which is less likely to collapse. In addition to this, the faults in a rock, formed when a rock is subjected to pressure and stress, can slip and move along fault lines if the stress exceeds its internal strength. These can be exploited by hydraulic action causing coastal recession. However, joints and strata are not as impactful influences on coastal morphology as concordant and discordant coasts are.
Explain the formation of erosional landforms (6)
Waves attack a weakness in a headland via hydraulic action and abrasion, opening up a joint or fault in the rock. The continued erosion of the headland produces a cave in the side of the headland which may then form a blow-hole. If waves break through to the other side of the cliff, an arch is formed. If this arch continues to erode it may collapse, leaving a stack cut off from the mainland. Sometimes a stack can become eroded down to form a stump and there may be a line of stacks/ stumps out to sea such as the Elegug Stacks along the Castlemartin coastline in Pembrokeshire.
Wave cut platforms are formed by a combination of marine erosion, weathering, and mass movement processes. Waves begin to undercut cliff faces through hydraulic action and abrasion, creating a wave cut notch. The rocks overhanging the notch will eventually collapse, aided by gravity, as the notch increases in size, presenting a steeper “new” cliff face. The process repeats and the position of the cliff retreats and as the overlying material is eroded, underoded rock at low tide level is left as flat rock surface; the wave cut platform.
A gloup or blowhole occurs when the roof of the cave collapses. Incoming waves may force air to rush upward or water to spout intermittently.
Geo is a narrow inlet in the face of a cliff, formed when fault line run perpendicular to the coast. The action of waves eroding the lower portion of a cliff forms a depression or sea cave/ The cliff face above can erode and collapse over time, creating a geo. Geos are common on the coastline of the Shetland and Orkney islands.
How do waves effect beach morphology and sediment profiles (8)
Constructive waves and destructive waves are the two main wave types which typically occur at different times of the years , impacting the shape and form of coasts and their features. Constructive waves are more common during the summer and are associated with less stormy conditions. These waves are characterised by long fetches and so lower wave heights. When they reach the beach, their low wave heights mean that they have spilling breakers which have stronger swash and a weaker back wash.
Alternatively, destructive waves are more common in stormy conditions normally found in the winter. These have higher wave heights and so their wave length are shorter. As they break on the beach, taller waves tend to produce plunging breakers which break more vertically, giving them less forward momentum and so they have a weaker swash and a stronger backwash.
The variation in wave types causes beach morphology to vary too. The plunging breakers and strong backwash of the destructive waves remove sediment from the top of the beach and carry it offshore. This lowers the level of the beach overall as well as making the beach profile less steep. However, during spring and summer constructive waves with their spilling breakers and stronger swash tend to move sediment back onto and up the beach. Sometimes building berm ridges from the larger shingle particles left towards the back of the beach at high tide mark. This increases beach height slowly and increases its gradient too.
These wave types also influence the beach sediment profiles. The most severe destructive waves during the winter throw the coarsest sediment up to the top of the beach, forming a storm RIDGE made up of shingle. Only the destructive waves have enough energy to move the largest beach material. The finer material including sand is found further down the beach, including the offshore bar which is a deposit of sand carried off the beach by the strong backwash of the destructive waves.
Explain how depositional landforms are created (8)
Beaches are an example of depositional landforms – formed from unconsolidated sands and shingle. Swash-aligned beaches are where wave crests approach parallel to the coast so there is no movement of sediment. This leads to large, wide beaches. Swash beaches are more associated with large beach profiles, with dunes and a variety of berms. In contrasts to this, drift-aligned beaches are where wave crests break at angles to the coasts, so there consistent longshore drift and the generation of elongated features. These beaches remain narrow and are mainly associated with spits bars and tombolos.
A spit is an extended stretch of sand or shingle that go beyond the coastlines. They form where longshore drift is continuing but energy is running low at a turn in the coastline, causing material to be deposited. The end of a spit begins to curve round when there is a change in wind direction and wave refraction carries material round into the more sheltered water behind the spit. This is known as a recurved spit. A double spit can also form when deposition occurs at both the northern and southern ends of a bay.
Offshore bars are submerged ridges of sand or coarse sediment deposited beyond the shoreline by currents and waves, only exposed at low tide. They form from sediment eroded by destructive waves and carried seawards by backwash. The sediment is deposite4d at the boundary of the offshore and nearshore zone, where the orbit of water particles ceases to reach the seabed. E.g Scroby Sabds in Norfolk is an example of where an offshore bar has been used to construct wind farms on.
Bars are linear ridges of sand/shingle extending across a bay and are connected to land on both sides. It traps a body of seawater behind it, forming a lagoon. They can form on drift-aligned coastlines, where longshore drift extends a spirt across the entire width of a bay. Alternatively, they can form when rising sea levels cause constructive waves to drive a ridge of sediment onshore to coastlines with a gently sloping shallow sea bed (barrier beach) e.g Start Bay in Devon theres a 9km barrier beach with Slapton Ley lagoon behind it.
Tombolos are linear ridges (or bar) of sand and shingle connecting an offshore island to the coastline of the mainland. They can form on drift aligned coastlines, when LSD builds a spit out from land until it contacts with an offshore island. They can also form on swash aligned coasts when theres a wave refraction around both sides of the island. E.g St Ninian’s tombolo on the Shetland Islands
Cuspate forelands are low lying triangular shaped headlands, extending out from a shoreline, formed from deposited sediment. They are formed when LSD currents from opposing directions converge at the boundary of two sediment cells. They can extent from a few meres to several kilometres. For example, Dungeness in Kent it extends for 11km.
What are the causes of short and long term sea level change? (8)
Isostatic readjustment – isostatic realignment following the land subsidence as a result of the weight of ice during an ice age. During the inter glacial periods the ice melts causing some areas to rebound and others to sink as the land rebalances. E.G SE UK is sinking at 1.5 mm a year while N is still rising
Eustatic – increase in volume of ocean water caused by thermal expansion and melting of land ice melt – 31 mm per years (1993-2993) Sea level rise of 120 m since the last ice age if Antarctic melted sea levels would rise by 50m.
Tectonic causes - fault line - push land upwards or create land depressions. 2004 Indian Ocean Earthquake involved fault line slipping and seabed rose several metres, reducing capacity of indian ocean and producing permanent rise in sea level.
Short term causes of sea level change include daily tides. Neap tides are moderate tides, slightly slower than average, which will lead to lower sea levels. In contrast to this, spring tides are the highest tides formed when the earth, sun and moon are lined up in a row, occurring every two weeks during a new moon or full moon. Spring tides will cause a short term rise in sea level.
A storm surge during a storm where winds “push” water towards a coast cause an increase in wave height. In addition to this, stormy conditions can lead to destructive waves with tall wave heights, increasing sea level temporarily. Constructive waves, usually found in summer season, will have lower wave heights, thus creating a lower sea level.
Atmospheric air pressure has an influence on sea level – low air pressure causes a slight rise in sea level.
Explain the formation of submergent and emergent coastlines
A submergent coastline is where a rise in sea level floods the coast, this can create rias, fjords and dalmatian coasts. Rias are drowned river valleys, formed when valleys in a dissected upland area are flooded. They are common in south-west England, where sea levels rose after the last Ice Age - drowning the lower parts of many rivers and their estuaries. e.g The Kingsbridge Estuary in Devon is now a natural harbour. Dalmatian coasts are also submergent coastal landforms. Similar to rias but the rivers flow almost parallel to the coast rather than at right angles. The Dalmatian coast in croatia gives it is name. Fjords are drowned glacial valley. Formed As sea levels rise, U-shaped valleys left by glaciers are submerged. They are deeper inland than near the coast. Shallower entrance marks where the glacier left the valley. Scotland (Loch Torridon), Norway, New Zealand are good examples.
Emergent coastlines are where a fall in sea level due to isostatic activity rise exposes land previously covered by the sea. Emergent coastlines can be identified by raised beaches, where the remains of eroded cliff lines (relic cliffs) can be found behind the raised beach, with wave cut notches and caves as evidences of past marine erosion. For example, on the Isle of Arran, three distinct raised beaches represent separate changes in sea level
How do local factors increase flood risk? (8)
The building of dams on rivers can trap river sediment, this will starve the coast downstream of sediment source. By starving the coast of sediment, they will become more prone to floodrisk. Such is the case in the mega-deltas of Asia where dams constructed upstream have trapped sediment. This is seen in Bangladesh, a country which consists of 70% flood plains.
In addition to this, the destruction of mangroves for tourism and wood can reduce barriers to flooding, making communities more at risk of flooding.
The height of a place above sea level, if it is already low It will be more prone to flooding. By 2060, 12% of the population will live in low elevation coastal zones that are below 10m above sea level. This creates an increased flood risk.
Policy decisions such as river straightening for navigation increases flow of river and the sediment is not deposited at the shore.
How does vegetation stabilise sandy coastlines?
At sandy coastlines, sand dunes are fragile as they are made of unconsolidated material, so they require vegetation to ensure they are not destroyed by weathering or marine processes. On an embryo dune, pioneer species such as marram grass bind sediment together using their roots, which makes dunes harder to erode. This vegetation is made up of halophyte plants, so can tolerate salty conditions close to the sea and are sometimes submerged at high tide.
Seeds are blown further backward on the coastline and once again halophyte vegetation is able to grow. Further back there are bigger dunes and less wind, so more grass can decompose and regrow, meaning that the sand begins to become more soil and nutrient based. This is called a grey dune. Due to there being more organic material, this gives rise to other species that can survive in better conditions. Once again, seeds are blown backwards, and a mature dune will begin to have even more species, such as Xerophyte plants – those that can tolerate extremely dry conditions due to sand being very draining. This is now a climax community due to its high biodiversity. This process assists the dunes in the long term because it can act as a natural buffer to the sea if the area is prone to coastal erosion.
Another example of coastline stabilization is the formation of saltmarshes. As a river mouth opens up to the sea, fast flowing water collides with the sea and quickly slows down. This change in water velocity as wave energy is absorbed creates a shallow calm environment where algae can grow, allowing halophytes to eventually grow. These halophytes bind loose sediment together, allowing a salt marsh to cultivate. A salt marsh is a natural barrier between the land and the sea, helping to stabilise the area, and also creating many new habitats.
Mangroves are a type of tropical halophyte species that grow on beaches, mainly along the Atlantic coast in places like Florida and Argentina. They have thick roots that bind sand together. This means that they create a barrier and reduce impacts of erosion, storm surges and sometimes tsunamis. Also, they slow down wave energy and encourage deposition of sediment, which then also contributes to reducing erosion. Mangrove plantation projects were carried out in Eastern Asia in 2004 to decrease impacts from Tsunamis.
