Enduring understanding: systems and changes
The interactions between physical and human systems over space and time can influence the sustainability of the coastal habitat.
Coastlines are very active parts of continents with energy and sediments being continuously carried from and/or delivered to a narrow environment that produces a variety of erosional and depositional landforms.
Coasts can be prudently managed to ensure the sustainability of both physical and human environments.
Generalisation
Change can occur in different ways. The coastal environment is dynamic – change can occur at different rates and at different scales.
Changes in coastal areas are taking place all over the world, caused by natural processes and human activities.
Processes that shape the coast
Weathering
Mass movement
Wave action
Human activities
Erosion processes
abrasion/corrasion
attrition
hydraulic action
solution/corrosion
abrasion/corrasion
Rock fragments (such as cobbles, pebbles & gravel) carried by the waves are hurled against the coast and break up the rocks forming the coast
attrition
As the rock fragments carried by the waves are thrown against one another, they gradually break up into smaller, smoother and more rounded pieces
hydraulic action
The weight of the waves smashing against the coast repeatedly weaken and loosen rocks so that ultimately they break off. Water also surges into cracks, joints and faults of rocks and compresses the air inside tightly. The compressed air exerts pressure on these lines of weakness. When the water retreats, there is a release of pressure and the trapped air expands. This action, repeated many times, widens the and weakens these lines of weakness, ultimately breaking the rocks up
solution/corrosion
Soluble minerals in coastal rocks are dissolved in and removed by the seawater. When solution occurs, the rocks are weakened and will ultimately disintegrate
weathering
- disintegration/breaking down of rocks in-situ on or near earth’s surface
- caused by weather elements (rain, temperature change) and biotic factors
erosion
- wearing away of rocks by moving agents which then carry rock materials away from their original site
- caused by winds, water, waves, rivers, glaciers
note
- Weathering and erosion do the most damage at the weakest points
- Weathering helps to weaken rocks, making them more susceptible to erosion
mass movement
- downward movement of regolith (loose, weathered rock) and/or soil on the sloped top layers of the Earth’s surface by force of gravity
- Water still plays a key role, BUT movement is without the aid of transporting medium such as water, ice or wind
- Occurs when shear stress overcomes the shear strength (frictional resistance and cohesion among the particles that make up the rock)
slumping
- Coastal hills and cliffs are also subjected to weathering, erosion and mass movement, besides wave/ marine processes🡪 causing retreat of these hills and cliffs🡪 coastline retreating landwards.
- A slump is a form of mass wasting that occurs when a coherent mass of loosely consolidated materials or a rock layer moves a short distance down a slope.
- Movement is characterized by sliding along a concave-upward or planar surface.
- Distinct layers can clearly be seen (soil, vegetation, boulder clay and layers of sand and gravels) Norwich Crag
- Biological weathering - the influence of plants (roots gradually break up cliff material and nesting holes in cliffs made by birds provide weakness for further weathering and erosion to attack)
landslide
- A landslide is defined as the movement of a mass of rock, debris, or earth down a slope. Landslides are a type of “mass wasting,” which denotes any down-slope movement of soil and rock under the direct influence of gravity.
→ triggered by prolonged wave action and weathering
denudation
wearing down of earth’s surface/ landforms through processes of weathering, erosion and mass wasting
