Geomorphic Processes In Coastal Landscapes Flashcards
(34 cards)
How are coastal landscapes developed
Key idea ⮕ Coastal landforms develop due to a variety of interconnected climatic and geomorphic processes.
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
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 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 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 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 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.
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.
Wave processes
-Erosion (Abrasion (or corrasion), Attrition, Hydraulic action, Pounding, Solution (or corrosion))
-Transportation (Solution, Suspension, Saltation, Traction)
-Deposition
Wave 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) 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.
