Flashcards in Coasts Deck (70)
How is the coastline protected?
-coastal sand dunes
-coastal salt marshes, found in many river estuaries
-coastal mangrove swamps, which are found on tropical coastlines
How does hydraulic action influence a beaches lithology.
Heavily joined fissured sedimentary rocks are vulnerable. In very hard igneous rocks basalt granite hydraulic action on cooling cracks my be the only erosive process of operating.
What two categories can coats be divided into?
What is a swash-aligned beach?
Wave crests approach parallel to the coast so there's limited long shore movement of sediment.
What is a drift-aligned beach?
Wave crests break at an angle to the coast so there is consistent long shore drift and elongated depositions features.
What 2 ways can deposition occur in?
• Gravity settling
What is gravity settling?
• Energy of transporting waves becomes too low to move sediment.
• Large sediment will be deposited first followed by smaller sediment
• Pebbles -> sand -> silt
• Depositional process very important for very small particles e.g. Clay, which are so small they remain suspended in water.
• Clay particles lump together because of electrical or chemical attraction and become large enough to sink.
What are spits?
• Definition: sand or shingle beach ridge extending beyond a turn in the coastline usually greater than 30 degrees.
• At the turn, the long shore drift current spreads out and loses energy leading to deposition.
• The length of the spit is determined by the existence of secondary currents causing erosion (flow of a river or a wave action which limits its length).
The geological epoch that began about 12,000 years ago at the end of the last Pleistocene ice age.
What is a rocky coastline?
It is a cliff varying in height
What is a coastal plain?
Land which gradually slopes towards the sea across an area of deposited sediment. They also have sand dunes and mud flats. These are sometimes referred to as alluvial coasts
What are primary coasts?
These are coasts dominated by land based processes as deposition at the coast from rivers or new coastal land formed from lava flows
What are secondary coasts?
These are coasts dominated by marine erosion or deposition processes.
What are emergent coasts?
These are coasts where they are rising due to sea level or tectonic uplift.
What are submergent coasts?
These are coasts flooded by the sea, either due to rising sea levels and/or subsiding land.
Explain the different types of wave energy
Low energy: limited fetch and low wind speeds resulting in smaller waves.
High energy: prevailing winds with long wave fetches resulting in powerful waves.
Define the term cliff profile?
The height and angle of a cliff face as well as its features, such as the wave-cut notches or changes in slope angle
What is the Littoral zone?
The wider coastal zone including adjacent land areas and shallow parts of the sea just offshore
What is unconsolidated sediment?
Material such as sand, gravel, clay and slit that has not been compacted and cemented to become sedimentary rock (it has not undergone the process of lithification) and so is loose and easily eroded.
When does most wave erosion occur?
Most waves occur when waves have a larger fetch and speed
Waves approach the coast at 90 degrees
The tide is high, propelling higher up the cliff face.
When old debris has been removed so the cliff face has no protection
What is a fault?
Faults represent major weaknesses within rock layer. Either side of a fault line, rocks are often heavily fractured and broken and these weaknesses are exploited by marine erosion.
Where do joints occur?
Joints occur in most rocks, often in regular patterns, dividing rock strata up into `blocks with a regular shape.
What are fissures?
Fissures are much smaller cracks in rocks, often only a few centimetres or millimetres long.
State two dominant cliff profile characteristics.
1. The resistance erosion of the rock
2. The dip of rock strata in relation to the coastline.
What is pore water pressure?
The pressure water experiences at a particular point below the water table due to the weight of water above it.
How does abrasion influence a beaches lithology.
Loose sediment such as shingles and pebbles are formed . softer rocks are more vulnerable than hard igneous rock.
How does attrition influence a beaches lithology.
Softer rocks are very rapidly reduced in size by attrition.
How does solution influence a beaches lithology.
Mainly affects limestone which is vulnerable to solution by weak acids.