8.2 Coastal landforms Flashcards
depositional landforms - powerpoint & brisk (39 cards)
What are the two different aspects of geology influencing coastal morphology and cliff profiles
- The dip angle of the rock strata (layers of the rock). Dip angle of the rock strata in relation to the horizontal and/or in relation to the coastline
- The resistance of the rock to erosion (lithology)
What causes the dip of the rock and the tilt of the strata
This is determined by tectonic forces. When Tectonic activity causes crustal compression - plates collide and compress the crust, causing it to buckle and fold. this forms a series of anticline and synclines.
what does the term clastic mean
a sedimentary rock made of cemented sediments
what does the term crystaline mean
igneous rocks made of interlocked crystals
what is the difference between fissures and joints
Joints are cracks that divide most rocks up into blocks. FIssures are small cracks, a few centimetres or millimeters long. They both represent weaknesses that enable erosion or sub-aerial processes
what rock type experiences very slow erosion rates
- Igneous rocks: they are crystaline, the interlocking crystals make for strong, hard erosion resistant rocks.
- eg granite, basalt
what rock type experiences moderate to fast erosion rates
- sedimentary rocks with many bedding planes and fractures, such as shale are often most vulnerable to erosion
why do headlands experience more intense erosion than bays
Headlands protude into the sea, making them more exposed to powerful waves. Wave refraction also occurs with water slowing down in more shallow areas as the friction with the sea bed increases, but this remains faster near the headlands, causing waves to refract towards headlands which concentrates energy and erosion
explain why bays often have sandy beaches, while headlands are rocky
Due to wave refraction, waves lose energy as they enter bays and deposit sediment, while they gain energy at headlands and erode them. The decrease in energy in bays would allow finer sediments like sand to accumulate, forming beaches. Headlands which are more exposed, experience intense erosion through hydraulic action, abrasion and solution. This makes the headlands more rocky.
what type of erosion is most responsible for the formation of caves?
The formation of caves is mainly caused by hydraulic action, where waves force air and water into cracks, gradually widening them. Abrasion also plays a role as rocks and sediment wear away the surface. In limestone areas, chemical erosion (solution) occurs when acidic rainwater dissolves minerals, further enlarging the cave.
how can a cave develop into a stack
As a result of wave refraction which distorts the wave direction, destructive waves concentrate their energy on the sides which deepens the cave. Then overtime the arch becomes unstable and collapses under its own weight to form a pillar called a stack for example Old Harry’s rock
what is the difference between a stack and stump
A stack is a tall, isolated column of rock that remains after an arch collapses due to erosion. It stands above the water, separated from the headland. A stump is the eroded remnant of a stack, which has been further worn down by waves, eventually reducing it to a low-lying rock formation visible at low tide.
How does wave energy vary between a steep and gently sloping cliff?
Steep cliffs experience high energy waves that hit directly at their case. The waves are less likely to break before impact, leading to strong hydraulic action and abrasion which cause rapid undercutting and cliff retreat. Gently sloping cliffs experience lower energy waves because the gradual slope causes waves to break further out at sea, reducing down cliff retreat
explain why cliff profiles vary
Cliff profiles vary due to differences in rock type, wave energy, erosion, weathering, and geological structure. Hard rocks like granite form steep cliffs, while soft rocks like clay erode more quickly, creating gentler slopes. High-energy coastlines with strong waves cause steep, undercut cliffs, while low-energy areas experience more deposition, leading to gradual slopes. Weathering and mass movement, such as landslides and slumping, also shape cliff profiles by weakening rock and causing collapses. Additionally, geological structure influences cliff shape, with horizontal layers forming steep cliffs and tilted or faulted layers creating irregular profiles.
Explain the formation of coastal saltmarshes
Flocculation occurs in low energy areas which form mudbanks over sand.
A thin mud layer is flooded regularly by tides and algae colonize the muddy surface. Creeks form as water recedes, creating small channels. More mud is deposited, stabilising the surface and pioneer species like glasswork trap silt which promotes mud accretion. This causes the channels to deepen and enhances tidal flow.
The cordgrass and other plants replace pioneers, stabilizing mudbanks and high rides flood the marsh l low tides are confined to creeks. Creeks deepen further, shaping the marsh. When there is dense vegetation the marsh stabilizes. The creeks maintain water flow and sediment transport/ The ecosystem provides long term benefits like flood defense.
An example of this can be behind the spurn point spit not he holderness coastline which is a low energy environment sheltered from waves and prone to longshore drift and tidal flows causing sediment deposition
explain the difference between a concordant and discordant coastline
A concordant coastline has layers of rock that run parallel to the shore. As a result the same type of rock is exposed to the sea, creating a more uniform apperance. EG Lulworth corve, dorset with hard outer later of limestone
Discordant coastline has rock layers that run perpendicular to the coast. this causes alternating bands of hard and soft rock to be exposed to the sea. the hard rock forms headlands and soft rocks erodes into bays. EG holderness coast with resistant rock of chalk forming flamborough head
steep cliffs
most common where the rock is strong and failry resistant to erosion. sedimentary rocks that have vertical strata are also more reistant to erosion, creating steep cliffs. Long fetch and high energy waves and an absence of a beach is common to areas w steep cliffs. Mostly found inhigh energy environments eg flamborough head, holderness coast
gentle cliffs
most commonly found in areas with weaker rocks which are less resistant to erosion and are prone to slumping. low energy waves and a short fetch will lead to the formation of a scree mound at the base of the cliff, reducing the overall clidd angle. A large beach would also reduce wave energy and prevent the development of steep cliffs by reducing erosion rates. most commonly foun din low energy environments
what is the rate of cliff retreat dependent on
on the relative importance of marine factors (fetch, beach, wave energy) and terrestial factors (subaerial processes, geology, rock strength) the cliff’s most likely to retreat are those that are made of unconsolidated rock and sands
explain the formation of a wavecut notch and wave cut platform
- when the waves erode a cliff, the erosion is mostly concentrated around the high tide line. the main processes of hydrualic action and corrasion create a wave cut notch
- as the notch becomes depper (as subaerial weathering weakens the cliff from the top) the cliff face becomes unstable and collapses through mass movement
- this leaves behind a platform
- over time the same processes repeat leading to a wave-cut platform to be formed which is normally exposed at high-tide
explain the formation of headlands and bays
They form on discordant coaslines where a non resistant rock such as clay is found between twor esistant rocks. This results in differential erosion. The processes of hydraulic action and abraision cause most of the erosion. Once the headland and bay shape has been formed the headlands receive most of the erosional energy from the sea, protecting the softer rock of the bay. Bay becomes sheltered so constructive waves can allow for deposition in the bay. Wave refraction bends towards the headlands, making them subject to erosion.
Cave arch stack stump formation
- verticalc racks in the headland are widedned by hydrualic action and abraision
- as destructive waves continue to erode the crack, it begins to open up to form a cave. wave refraction bends the waves towards the crack in the headland, focusing wave energy and increasing erosion
- the cave becomes larger and eventually breaks through the headland to form an arch. wave refraction can cause waves to erode a crack on both sides of the headland. In these cases, the backs of the caves erode towards each other, meeting in the middle of the headland
- the base of the arch continually becomes wider through further erosion which creates a wave cut notch. Weathering such as freeze thaw weakens the span of the arch
- eventually the span of the arch becomes too heavy, it collapses into the sea. this leaves a stack
- the stack is undercut by hydraulic action and abrasion at the base, forming a notch until it collapses to form a stump - the base of the stack visible at low tide
how can dip angle of strata affect profile of cliff
the strata become exposed to elements on a cliffed coastline. the dip angle of strata affects which strata are expose to erosion and subaerial processes. this in turn affects the prifile of the cliff and overall shape of the coast.
What are factors affecting the level of resistance of a cliff
- Consolodiation of different rock types on each strata (less = easier to erode)
- Rock type: clastic or crystaline
- Susceptibility to chemical weathering (eg feldspare for hyrdolysis)
- size of faults in rock
- fissures and joints
