2.a. Coastal landforms develop due to a variety of interconnected climatic and geomorphic processes. Flashcards
shore platforms
Cliffs are common features of coastal environments.
Over time, cliffs retreat due to a combination of sub-aerial processes e.g. weathering and mass movement and coastal erosion.
During high tide, when the sea has more kinetic energy, erosion occurs at the base of the cliff via the processes of hydraulic action (water) and abrasion (the rubbing together of rocks), together with weathering processes, such as solution, freeze thaw and salt crystallisation.
A wave cut notch is then formed, between the high tide and low tide level.
Over time the wave-cut notch will develop into a cave.
Eventually, the weight of the unsupported cliff will cause it to collapse. As the cliff collapses an area of hard, flat rock is left behind called a wavecut platform.
The platform typically has a slope of less than 4 degrees, which is often only fully exposed at low tide and is composed of a more resistant rock.
It has grooves and ridges, which are formed through processes of erosion and can be found alongside small pond and rock pools where small marine species live.
Wave cut platforms have a significant impact on the ability of waves to erode the base of the cliff.
This is because the waves have further to travel in very shallow water as the platform grows.
Waves tend to break earlier before they can erode the base of the cliff.
An example of a wave cut platform can be seen at Robin Hood’s Bay in Yorkshire, which has been eroded into Lower Lias shales.
The platform slopes at a typical angle of 1˚, although ramped sections are as steep as 15˚. It has a maximum width of about 500m, but extends much further into the off-shore zone.
Based on current rates of erosion and retreat, it is possible that these platforms such as these could have been formed within the last 6000 years, during times of predominantly stable sea level
What is an Geo?
Geos are narrow steep sided inlets
Explain the formation of Geos and blowholes?
1.A geo is a narrow, steep sided inlet, which can be found within a cliff due to lines of weakness in the rock, such as joints and faults.
2.These weak points are eroded more rapidly by wave action (kinetic energy), than the more resistant rock surrounding it.
-Hydraulic action is particularly significant as it forces air and water into joints, and weakens the rock strata
- with abrasion (the scouring of the rock face by other particles carried in the approaching wave) and attrition (wearing down of rocks and pebbles as they rub against each other, making them smaller and rounder, eventually producing sand).
4.Glacier movements can also cut depressions in steep rock formations that may erode to form a geo.
An example of a geo is Huntsman’s Leap, which is located in Pembrokeshire.
It is 35m deep and has eroded along a large joint in the carboniferous limestone.
Sometimes Geos intially form as tunnel like caves running at right angles to the coastline and as they face continued erodion the roof collapses forming a geo.
If part of the roof of a tunnel-like cave collapses along a master joint, it may form a vertical shaft that reaches the cliff top.
This is known as a blowhole. During storm conditions, large waves can force spray out of the blowhole as plumes of white, aerated water.
Blowholes may also be associated with mining shafts or the collapse of a cave roof. The same applies to geos. A particularly good example of a blowhole can be found on Cornwall’s north coast.
It is called The Trevone Bay Round Hole. It is 25mdeep and was formed after thousands of years of erosion. As a result, the walls are extremely unstable.
What are Blowholes?
Vertical shaft that reaches a cliff top.
Explain the formation of caves, arches stacks and stumps
Caves, arches, stacks and stumps represent a sequence of erosional landforms which typically form around headlands, even though they may be seen independently of each other on upland coasts.
1.Owing to wave refraction, energy is concentrated on the sides of headlands.
2.Points of weakness, for example faults or joints, are then exploited by erosional processes and a small cave may develop on one side, or even both sides of the headland.
3.Wave action/attack is concentrated between high and low tide levels. This is the point where caves form. An arch is formed when a cave enlarges to such an extent that it extends through to the other side of the headland, possibly meeting another cave creating an arch.
4.Continual erosion widens the arch and therefore weakens its support. By several weathering processes (salt crystallisation and biological weathering), the arch may collapse, which forms a stack,isolated from the headland.
Further erosion at the base of the stack will eventually collapse, resultingin a small, flat portion of the original stack called a stump. However, this may only be visible at lowtide.
A particularly good example of these landscapes can be found at the seaward end of The Forelandnear Swanage on the Isle of Purbeck. It is known as Old Harry Rocks and is composed of chalk.
