1.2 How are coastal landscapes developed? Flashcards
1.2 How are coastal landforms developed?
Key idea ⮕ Coastal landforms develop due to a variety of interconnected climatic and geomorphic processes.
Discordant coastline
In this type of coastline, the layers of rock are perpendicular to the direction of the coastline. Bays and headlands begin to form.
Concordant coastline
In this type of coastline, the layers of rock are parallel to the direction of the coastline.
The outer hard rock provides a protective barrier to erosion of the softer rocks further inland. Sometimes the outer hard rock is punctured, allowing the sea to erode the softer rocks behind. This creates a cove, a circular area of water with a relatively narrow entrance from the sea.
Geomorphic processes
-Weathering (Physical or mechanical, Chemical, Biological)
-Mass movement (Rock fall, Slides)
-Erosion (Wave processes)
-Transportation (Wave processes)
-Deposition (Wave processes)
Weathering
-Physical or mechanical
-Chemical
-Biological
Weathering definition
Energy used to produce physically or chemically altered materials from the surface or near surface rock. In coastal environments some types of weathering are particularly significant and influence the formation of coastal landforms.
Physical or mechanical weathering
The breakdown of rock is largely achieved by physical weathering processes that produce smaller fragments of the same rock. No chemical alteration takes place during physical weathering. By increasing the exposed surface area of the rock, physical weathering allows further weathering to take place.
In many coastal landscapes, such as western Europe, the presence of the sea results in the moderation of temperatures and so air temperatures may seldom drop below 0ºC, reducing the extent of fluctuations and rendering some of the processes ineffective
Freeze-thaw (physical or mechanical weathering)
Water enters cracks/joints and expands by nearly 10 per cent when it freezes. In confined spaces this exerts pressure on the rock causing it to split or pieces to break off, even in very resistant rocks.
Pressure release (physical or mechanical weathering)
When overlying rocks are removed by weathering and erosion, the underlying rock expands and fractures parallel to the surface. This is significant in the exposure of sub-surface rocks such as granite and is also known as dilatation. The parallel fractures are sometimes called pseudo-bedding planes.
Thermal expansion (physical or mechanical weathering)
Rocks expand when heated and contract when cooled. If they are subjected to frequent cycles of temperature change then the outer layers may crack and flake off. This is also known as insolation weathering, although experiments have cast doubts on its effectiveness unless water is present.
Salt crystallisation (physical or mechanical weathering)
Solutions of salt can seep into the pore spaces in porous rocks. Here the salts precipitate, forming crystals. The growth of these crystals creates stress in the rock causing it to disintegrate. Sodium sulphate and sodium carbonate are particularly effective, expanding by about 300 per cent in areas of temperatures fluctuating around 26-28ºC.
Chemical weathering
The decay of rock is the result of chemical weathering, which involves chemical reactions between moisture and some minerals within the rock. Chemical weathering may reduce the rock to its chemical constituents or alter its chemical and mineral composition. Chemical weathering processes produce weak residues of different material that may then be easily removed by erosion or transportation processes.
Van’t Hoff’s Law and chemical weathering
States that a 10ºC increase in temperature leads to a 2.5 times increase in the rate of chemical reaction (up to 600ºC), so most chemical weathering processes occur at higher rates in tropical rather than temperate or polar regions. Thus moist tropical environments experience the fastest rates of chemical weathering and cold, locations the slowest. However, it is worth noting that carbonation can be more effective in low temperatures as carbon dioxide (CO2) is more soluble in cold water than in warm water.
Oxidation (chemical weathering)
Some minerals in rocks react with oxygen (O2), either in the air or in water. Iron is especially susceptible to this process. It becomes soluble under extremely acidic conditions and the original structure is destroyed. It often attacks the iron-rich cements that bind sand grains together in sandstone.
Carbonation (chemical weathering)
Rainwater combines with dissolved carbon dioxide from the atmosphere to produce a weak carbonic acid. This reacts with calcium carbonate in rocks such as limestone to produce calcium bicarbonate, which is soluble. This process is reversible and precipitation of calcite happens during evaporation of calcium rich water in caves to form stalactites and stalagmites.
Solution (chemical weathering)
Some salts are soluble in water. Other minerals, such as iron, are only soluble in very acidic water, with a pH of about 3. Any process by which a mineral dissolves in water is known as solution, although mineral specific processes, such as carbonation, can be identified.
Hydrolysis (chemical weathering)
This is a chemical reaction between rock minerals and water. Silicates combine with water, producing secondary minerals such as clays. Feldspar in granite reacts with hydrogen in water to produce kaolin (china clay).
Hydration (chemical weathering)
Water molecules added to rock minerals create new minerals of a larger volume. This happens when anhydrite takes up water to form gypsum. Hydration causes surface flaking in many rocks, partly because some minerals also expand by about 0.5 per cent during the chemical change because they absorb water.
Biological weathering
Biological weathering may consist of physical actions such as the growth of plant roots or chemical processes such as chelation by organic acids. Although this, arguably, does not fit with the precise definition of weathering, biological processes are usually classed as a separate type of weathering.
Tree roots (biological weathering)
Tree roots grow into cracks or joints in rocks and exert outward pressure. This operates in a similar way and with similar effects to freeze-thaw. When trees topple, their roots can also exert leverage on rock and soil, bringing them to the surface and exposing them to further weathering. Burrowing animals may have a similar effect. This may be particularly significant on cliff tops and cliff faces.
Organic acids (biological weathering)
Organic acids produced during decomposition of plant and animal little cause soil water to become acidic and react with some minerals in a process called chelation. Blue-green algae can have a weathering effect, producing a shiny film of iron and manganese oxides on rocks. On shore platforms, molluscs may secrete acids which produce small surface hollows in the rock.
Organic acids diagram (biological weathering)
Chelation
Mass movement
-Rock fall
-Slides
Mass movement definition
Mass movement occurs when the forces acting on slope material, mainly the resultant force of gravity, exceed the forces trying to keep the material on the slope, predominantly friction.
In coastal landscape systems, the most significant mass movement processes are those acting on cliffs, which lead to the addition of material to the sediment budget by transferring rocks and regolith down onto the shore below. The main processes involved are rock fall and slides.
Rock fall (mass movement)
On cliffs of 40º or more, especially if the cliff face is bare, rocks may become detached from the slope by physical weathering processes. These then fall to the foot of the cliff under gravity. Wave processes usually remove this material, or it may accumulate as a relatively straight, lower angled scree slope.
Slides (mass movement)
These may be linear, with movement along a straight line slip plane, such as a fault or a bedding plane between layers of rock, or rotational, with movement taking place along a curved slip plane. Rotational slides are also known as slumps. In coastal landscape systems, slides often occur due to undercutting by wave erosion at the base of the cliff which removes support for the materials above.
Slumps are common in weak rocks, such as clay, which also become heavier when wet, adding to the downslope force. A layer of sand above a layer of clay may particularly encourage this, as rainwater passes through the sand but cannot penetrate the impermeable clay below, thus increasing pore pressure in the sands.
Waves processes
-Erosion (Abrasion (or corrasion), Attrition, Hydraulic action, Pounding, Solution (or corrosion))
-Transportation (Solution, Suspension, Saltation, Traction)
-Deposition
Waves processes definition
Waves are a source of energy in coastal landscape systems, and when they break onshore, the energy can be expended through geomorphic processes to shape landforms. They can also supply material to the system in the form of sediment, which is either deposited in, or transported within, the coastal system.
Erosion (waves processes)
-Abrasion (or corrasion)
-Attrition
-Hydraulic action
-Pounding
-Solution (or corrosion)
Erosion (waves processes) definition
Breaking waves are able to erode the coastline with a range of processes.
Abrasion (or corrasion) (Erosion (waves processes))
When waves armed with rock particles scour the coastline; rock rubbing against rock.
Attrition (Erosion (waves processes))
Occurs when rock particles, transported by wave action, collide with each other and with coastal rocks and progressively become worn away. They become smoother and more rounded as well as well as smaller, eventually producing sand.
Hydraulic action (Erosion (waves processes))
Occurs when waves break against a cliff face, and air and water trapped in cracks and crevices becomes compressed. As the wave recedes the pressure is released, the air and water suddenly expands and the crack is widened. The average pressure exerted by breaking Atlantic waves is 11,000 kg per m³.
Pounding (Erosion (waves processes))
Occurs when the mass of a breaking wave exerts pressure on the rock causing it to weaken. Forces of as much as 30 tonnes per m² can be exerted by high-energy waves.
Solution (or corrosion) (Erosion (waves processes))
Involves dissolving minerals like magnesium carbonate minerals in coastal rock. However, as the pH of sea water is invariably around 7 or 8 this process is usually of limited significance unless the water is locally polluted and acidic. Even then, only coastal rocks containing significant amounts of soluble minerals are likely to be affected by this.
Transportation (waves processes)
-Solution
-Suspension
-Saltation
-Traction
Transportation (waves processes) definition
Waves, as well as tides and currents, can move material shorewards in a variety of ways.
Solution (Transportation (waves processes))
Minerals that have been dissolved into the mass of moving water. This type of load is invisible and the minerals will remain in solution until water is evaporated and they precipitate out of solution.
Suspension (Transportation (waves processes))
Small particles of sand, silt and clay can be carried by currents; this accounts for the brown or muddy appearance of some sea water. Lager particles can also be carried in this way, perhaps during storm events.
Saltation (Transportation (waves processes))
This is a sense of irregular movements of material which is too heavy to be carried continuously in suspension. Turbulent flow may enable sand-sized particles to be picked up (entrained) and carried for a short distance only to drop back down again. Similarly, other particles may be dislodged by the impact, allowing water to get beneath them and cause entrainment.
Deposition (waves processes)
Material is deposited when there is a loss of energy caused by a decrease in velocity and / or volume of water. Depositional tends to take place in coastal landscape systems that follow a number of traits:
-Where the rate of sediment accumulation exceeds the rate of removal
-When waves slow down immediately after breaking
-At the top of the swash, where for a brief moment the water is no longer moving
-During the backwash, when water percolates into the beach material
-In low-energy environments, such as those sheltered from winds and waves, e.g. estuaries.
Traction (Transportation (waves processes))
The largest particles in the load may be pushed along the sea floor by the force of the flow. Although this can be called rolling, again the movement is seldom continuous. Large boulders may undertake a partial rotation before coming to rest again.
Settling velocity
The velocity at which sediment particles are deposited. The larger and heavier particles require more energy to transport them. As flow velocity decreases, the largest particles being carried are deposited first and so on, sequentially until the finest particles are deposited (see image).
Fluvial processes
-Erosion
-Transportation
-Deposition
Fluvial processes definition
In coastal environments such as river mouths, fluvial processes often play an important part in the development of landforms. Low-energy, estuarine environments have distinctive characteristics.
Erosion (fluvial processes)
Fluvial erosion in the upper catchment is the main source of a river’s sediment load. Rivers use similar erosional processes to waves, with most channel erosion occurring during high-flow, high-energy events. Sediment is also derived from weathering and mass movement processes that result in material moving into river channels from the valley sides.
Transportation (fluvial processes)
Rivers also transport sediment by traction, suspension, saltation and solution - similar processes to those of waves.
Deposition (fluvial processes)
As rivers enter the sea, there is a noticeable reduction in their velocity as the flowing water moving through the channel enters the relatively static body of sea water. Indeed, tides and currents may be moving in the opposite direction to the river flow, providing a major resistance to its forward movement. Available energy is reduced and so some, or all, of the river’s sediment load is deposited. As the reduction in energy is progressive, deposition is sequential, with the largest particles being deposited first and the finest being carried further out to sea. In addition, the meeting of fresh water and salt water causes flocculation of clay particles. These fine, light materials clump together due to electrical charges between them in saline conditions. As a result they become heavier and sink to the sea bed.
Aeolian processes
-Erosion
-Transportation
-Deposition
Aeolian processes definition
Due to their exposure to open sea surfaces, coastal landscapes can be significantly influenced by winds, especially those blowing onshore.
Erosion (aeolian processes)
Wind is able to pick up sand particles and move them by deflation. At speeds of 40 km/hour, sand grains are moved by surface rolling (surface creep) and saltation. As grains of this size are relatively heavy, compared with silt and clay particles, they are seldom carried in suspension. This restricts erosion by abrasion to a height of about 1 m and has a limited effect in the erosion of rocky coastlines and cliffs. Erosive force increases exponentially with increases in wind velocity. For example a velocity increase from 2 to 4 metres per second causes an eight-fold increase in erosive capacity.
Dry sand is much easier for wind to pick up than wet sand, as the moisture increases cohesion between particles, helping them to stick together. Attrition on land is particularly effective in wind as particles tend to be carried for much greater distances than in water, and the particles are not protected from collisions by the film of water around them.
Transportation (aeolian processes)
With the exception of solution, moving air is able to transport material using the same mechanisms as water moving in rivers and waves. Once particles have been entrained, they can be carried at velocities as low as 20 km/hour. Saltating grains are typically 0.15-0.25 mm in diameter, while those 0.26-2.00 mm, which are too heavy to be saltated, move by surface creep. Only the smallest grains (0.05-0.14 mm) can be carried in suspension.
Deposition (aeolian processes)
Material carried by wind will be deposited when the wind speed falls, usually as a result of surface friction. In coastal areas this will occur inland, where friction from vegetation and surface irregularities is much greater than on the open sea.
Coastal landforms
Although coastal landforms develop due to a variety of interconnected processes, each one will tend to be predominantly influenced either by erosion or deposition.
Erosional landforms (coastal landforms)
-Cliff and shore platforms
-Bays and headlands
-Geos and blowholes
-Caves, arches, stacks and stumps
Cliffs and shore platforms (Erosional landforms (coastal landforms))
Cliffs are shaped through erosion and weathering. Less resistant rock erodes quickly and forms gentle sloping cliffs, whereas more resistant rock forms steep cliffs. A wave cut platform is a wide gently-sloping surface found at the foot of a cliff.
Cliffs and shore platforms (Erosional landforms (coastal landforms)) (Processes)
- Destructive waves target the wave attack zone (undercutting weakens strata)
- Wave cut notch is formed by erosional processes such as abrasion and hydraulic action
- The notch size increases in size, the cliff becomes unstable and collapses, leading to cliff retreat
- Backwash carries away the eroded material, leaving a wave-cut platform.
- The process repeats. The cliff continues to retreat.
Horizontally bedded strata
Undercutting by wave action leads to rockfall; the cliffs retreat inland, parallel to the coast.
Seaward-dipping strata
Undercutting by wave action remove basal support; rock layers loosened by weathering slide into the sea along the bedding planes.
Landward-dipping strata
Rocks loosened by weathering and wave action are difficult to dislodge; the slope profile is gradually lowered by weathering and mass movement.
Bays and headlands (Erosional landforms (coastal landforms))
Cliffs along the coastline do not erode at the same pace. When a stretch of coastline is formed from different types of rock, headlands and bays can form.
Bands of soft rock such as clay and sand are weaker therefore they can be eroded quickly. This process forms bays. A bay is an inlet of the sea where the land curves inwards, usually with a beach. Hard rock such as chalk is more resistant to the processes of erosion. When the softer rock is eroded inwards, the hard rock sticks out into the sea, forming a headland.
Erosional features such as wave-cut platforms and cliffs can be found on headlands, since they are more open to the waves. Bays are more sheltered with constructive waves which deposit sediment to form a beach.
Bays and headlands (Erosional landforms (coastal landforms)) (Processes)
- Different bands of rock, perpendicular to the coastline, differing resistance of rock
- Less resistant bands of rock are eroded more rapidly to form bays
- More resistant bands of rock remain between bays as headlands
- Leads to the formation of a discordant coastline
Geos and blowholes (Erosional landforms (coastal landforms))
A geo is formed by the action of waves eroding the lower portion of a cliff. A depression or sea cave may form. The cliff face above the cave can erode and collapse over a period of time, creating a geo or extending the cave deeper in to the cliff.
If the back of the cave is eroded and a shaft is created that opens out onto the top of the headland we then call it a blow hole. In Cornwall we find some huge blowholes but they are also a result of a collapsed tin mining shaft.
Located example: Huntsman’s Leap in Pembrokeshire, 35m deep and eroded along a large joint in the carboniferous limestone.
Geo (Erosional landforms (coastal landforms)) (Explaination)
A long, narrow, steep-sided slit formed by erosion in coastal cliffs.
Blowhole (Erosional landforms (coastal landforms)) (Explaination)
A crack or fissure in coastal rock through which air and spray is expelled when waves break on the shore.
Geos and blowholes (Erosional landforms (coastal landforms)) (Processes)
Geos
1. Lines of weakness (e.g. joints and faults) are eroded rapidly by wave action
2. Hydraulic action is particularly important in forcing air and water into the joints and weakens the rock strata.
3. Geos sometimes initially form as tunnel-like caves running at right angles to the cliff line
4. As these geos continue to be eroded, roof collapse may occur.
Blowholes
1. When part of the tunnel-like cave collapses along a master joint it may form a vertical shaft that reaches the cliff top.
2. In storm conditions large waves may force spray out of the blowhole as plumes of white, aerated water.
Wave refraction
The bending of waves in shallow water so that they move nearly parallel to the shoreline.
Caves, arches, stacks and stumps (Erosional landforms (coastal landforms))
Weathering and erosion can create caves, arches, stacks and stumps along a headland.
-Caves occur when waves force their way into cracks in the cliff face. The water contains sand and other materials that grind away at the rock until the cracks become a cave. Hydraulic action is the predominant process.
-If the cave is formed in a headland, it may eventually break through to the other side forming an arch.
-The arch will gradually become bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
-The stack will be attacked at the base in the same way that a wave-cut notch is formed. This weakens the structure and it will eventually collapse to form a stump.
One of the best examples in Britain is Old Harry Rocks, a stack found off a headland in the Isle of Purbeck.
Caves (Erosional landforms (coastal landforms)) (Processes)
- Due to refraction, energy is concentrated on the sides of headlands
- Points of weakness, such as faults or joints, are exploited by erosion processes
- A cave may emerge on one side, or even both sides
- Wave attack is concentrated between high and low tide levels (wave attack zone) this is where caves form
Arches (Erosional landforms (coastal landforms)) (Processes)
- When caves enlarge it will extend through through to the other side if the headland, possibly meeting another cave.
- Continued erosion widens the arch and weakens its support.
Stacks (Erosional landforms (coastal landforms)) (Processes)
- Aided by weathering processes, the arch may collapse, leaving an isolated stack separated from the headland.
Stumps (Erosional landforms (coastal landforms)) (Processes)
- Further erosion at the base of the stack may eventually cause further collapse leaving a small, flat portion of the original stack as a stump.
- This may only be visible at low tide.
Depositional landforms (coastal landforms)
-Beaches
-Spits
-Onshore bars
-Tombolos
-Salt marshes
-Deltas
Beaches (Depositional landforms (coastal landforms))
Beaches are a common feature of a coastline. Beaches are made up of eroded material that has been transported from elsewhere and deposited by the sea.
Constructive waves help to build up beaches. The material found on a beach (ie sand or shingle) depends on the geology of the area and wave energy.
A cross-section of a beach is called a beach profile. The shingle ridges often found towards the back of a beach are called berms.
The material found on a beach varies in size and type as you move further away from the shoreline. The smallest material is deposited near the water and larger material is found nearer to the cliffs at the back of the beach. Large material is deposited at the back of the beach in times of high energy, for example during a storm. Most waves break near the shoreline, so sediment near the water is more effectively broken down by attrition.
Sandy beaches have gently sloping profiles and shingle and pebble beaches are steeper.
Beach cusps
Semi-circular, scalloped depressions cut into the lower edge of the storm beach.
Beaches (Depositional landforms (coastal landforms)) (Angle)
-Sand produces beaches with a gentle gradient; usually less than 5º, because of its small particle size means that it becomes compact when wet, allowing little percolation during backwash
Cobbles (Min diameter: 32mm; Beach angle: 24º)
Pebbles (Min diameter: 4mm; Beach angle: 17º)
Coarse sand (Min diameter: 2mm; Beach angle: 7º)
Medium sand (Min diameter: 0.2mm; Beach angle: 5º)
Fine sand (Min diameter: 0.02mm; Beach angle: 3º)
Very fine sand (Min diameter: 0.002mm; Beach angle: 1º)
Beaches (Depositional landforms (coastal landforms)) (Sources of sediment)
-Cliff erosion: typically only about 5%
-Offshore: Combed from the sea bed, often during periods of rising sea levels; again about 5%
-Rivers: The remaining 90% carried into the coastal system as suspended and bed load through river mouths
Bed load ((Beaches (Depositional landforms (coastal landforms)) (Processes)))
Sand, pebbles, and boulders that are moved along the bed of a stream and that are too heavy to be carried in suspension.
Spits (Depositional landforms (coastal landforms))
Spits are created by deposition. A spit is an extended stretch of beach material that projects out to sea and is joined to the mainland at one end.
Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in longshore drift. An example of a spit is Spurn Head, found along the Holderness coast in Humberside.
Spits (Depositional landforms (coastal landforms)) (Processes)
- Longshore drift moves material along the coastline.
- A spit forms when the material is deposited.
- Over time, the spit grows and develops a hook if wind direction changes further out.
- Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshesform.
Long shore drift
Longshore (littoral) drift is the movement of material along the shore by wave action. It happens when waves approach the beach at an angle. The swash (waves moving up the beach) carries material up and along the beach. The backwash (waves moving back down the beach) carries material back down the beach at right angles. This is the result of gravity. This process slowly moves material along the beach and provides a link between erosionand deposition.
The material is transported through suspension, traction, solution and saltation. Longshore drift provides a link between erosion, transportation and deposition.
Longshore drift contributes towards the formation of a range of depositional landforms such as spits and onshore bars. Spurn Point is a coastal spit formed by the transportation of coastal sediment by longshore drift along the Holderness Coast. This material is then deposited at the mouth of the Humber Estuary.
Long shore drift (Processes)
Long shore drift occurs as a result of wave action.
1. It happens when waves approach the beach at an angle.
2. The swash carries material up and along the beach.
3. The backwash carries material back down the beach at right angles. This is the result of gravity.
4. This process slowly moves material along the beach and provides a link between erosion and deposition.
Onshore bars (Depositional landforms (coastal landforms))
A bar is created when there is a gap in the coastland with water in it. This could be a bay or a natural hollow in the coastland. The process of longshore drift occurs and this carries material across the front of the bay.
Material is pushed up onto beaches at an 45º angle when the swash brings it onto the coastline. The backwash takes it back out towards the sea at a right angle to the coast. Through this process material is constantly moved along the coastline.
The deposited material eventually joins up with the other side of the bay and a strip of deposited material blocks off the water in the bay. The area behind the newly formed bar is known as a lagoon.
Onshore bars (Depositional landforms (coastal landforms)) (Processes)
- Following the formation of a bay, there is a gap in the coastland with water in it.
- The process of longshore drift occurs and this carries material across the front of the bay.
- Swash brings material onto beaches at a 45º angle.
- This material is moved along the coast by way of backwash (at a right angle to the coast).
- Deposited material eventually joins up with the other side of the bay.
- This strip of deposited material blocks off the water in the bay
The area behind the onshore bar is known as a lagoon.
Tombolos (Depositional landforms (coastal landforms))
A tombolo is a spit connecting an island to the mainland. An example of a tombolo is Chesil Beach, which connects the Isle of Portland to the mainland of the Dorset coast.
Chesil Beach stretches for 18 miles. Lagoons have formed behind the stretch of beach material.
Tombolos (Depositional landforms (coastal landforms)) (Processes)
- Longshore currents and longshore drift moves sediment until a change in the shape of the coastline causes a build up of shingle and other sediment / material.
- A spit is constructed by means of deposition of shingle and other sediment / material
- The spit extends out to an island, making a connection
Salt marshes (Depositional landforms (coastal landforms))
A coastal ecosystem between land and open saltwater or brackish water that is regularly flooded by the tides.
It is dominated by dense stands of salt-tolerant plants such as herbs, grasses, or low shrubs. These plants are terrestrial in origin and are essential to the stability of the salt marsh in trapping and binding sediments.
Salt marshes play a large role in the aquatic food web and the delivery of nutrients to coastal waters. They also support terrestrial animals and provide coastal protection.
Salt marshes (Depositional landforms (coastal landforms)) (Processes)
Features of low-energy environments such as estuaries and on the landward side of spits.
1. The zone behind a spit becomes a sheltered area.
2. Water movement slows down and so more material is deposited. (Mud is deposited in low-energy or sheltered environments)
3. Deposition may form a salt marsh.
4. The roots of salt-tolerant species such as eelgrass and spartina help trap sediment, gradually increasing the height of the marsh.
5. The stems and leaves of the plants act as baffles and trap sediment in by tidal currents while the roots stabilise the sediment.
Landward
Facing towards the land; away from the sea.
Deltas (Depositional landforms (coastal landforms))
Deltas are landforms formed at the mouth of a river, where the river meets a body of water with a lower velocity than the river (e.g. a lake or sea), resulting in the reduction in the river’s capacity to transport sediment.
Deltas are dynamic areas that change quickly due to the erosion of unstable land during storm and flood events and the creation of new land. Deltas are fertile areas which often support large populations due to their agricultural productivity. Examples include the Ganges delta in Bangladesh and the Nile delta in Egypt.
Deltas (Depositional landforms (coastal landforms)) (Processes)
- As the river channel flows over the ground and makes contact with soil, it carries with it sediment.
- When a river channel encounters another body of water, its velocity decreases and deposits sediments.
- The sediment deposited is called Alluvium.
- This sediment piles up into several layers called beds. 5. The delta becomes a main channel that divides substantial land masses into various streams called distributaries.
Distributaries appear like a maze of water channels.
Channel
A type of landform consisting of the outline of a path of relatively shallow and narrow body of fluid, most commonly the confine of a river, river delta or strait. The word is related to canal, and sometimes takes this form, e.g. the Hood Canal.
The River Nile case study facts
-6,650 km long (one of the longest)
-3 million km² catchment area
-600 mm of annual rainfall in this catchment
-Average discharge is less than 3,000 m³/s (among the lowest of the world’s greatest rivers)
m³/s
A cubic metre per second (m³/s) is a derived SI unit of volumetric flow rate equal to that of a stere or cube with sides of 1 metre in length exchanged or moving each second. It is popularly used for water flow, especially in rivers and streams, and fractions for HVAC values measuring air flow.
Catchment area
The area from which the streams and tributaries collect water from inside the drainage basin.
SI unit
A physical unit in the international SI system which is based on the metre, kilogram, second, ampere, kelvin, candela, and mole, together with a set of prefixes to indicate multiplication or division by a power of ten.
a.k.a. metric system
