Coasts Flashcards
What is the littoral zone?
The wider coastal zone including adjacent land areas and shallow parts of the sea.
Split into subzones:
- coast
- backshore
- foreshore
- nearshore
- offshore
How can coasts be classified through formation processes
primary coasts - dominated by land-based processes such as deposition from rivers or new coastal land caused by lava flows.
secondary coasts - dominated by marine erosion or deposition processes
How can coasts be classified through relative sea level change
Emergent coasts are rising relative to sea level, for example due to tectonic uplift.
Submergent coasts are being flooded by the sea, either due to rising sea levels and/or subsiding land
How can coasts be classified through tidal range
Microtidal coasts (0-2m tidal range)
Mesotidal coasts (2-4m tidal range)
Macrotidal coasts (>4m tidal range)
How can coasts be classified through wave energy
Low energy coastlines are sheltered with limited fetch and low wind speeds resulting in small waves. They are often sandy and the rate of deposition exceeds the amount of erosion
High energy coastlines are exposed, facing prevailing winds with long fetches resulting in powerful waves. They are often rocky and the rate of erosion exceeds the rate of deposition
Cliff profile
The height and angle of a cliff face as well as its features such as wave-cut notches or changes in slope angle
Coastal morphology
The shape and form of coastal landscapes and their features
Lithology
The physical characteristics of particular rocks
What are the 2 main types of coast
Rocky/cliffed coasts:
- have cliffs varying in height, angle and hardness of rock
-the transition from land to sea is abrupt
Coastal plains/alluvial coasts:
- the land gradually slopes towards the sea across an area of deposited sediment
- sand dunes and mud flats common
- if there are sand dunes, at high tide the beach is inundated, but the dunes are not
- Coast may be estuarine, with mudflats and salt marshes at the mouth of a river
weathering
The chemical, biological and mechanical breakdown of rock into smaller fragments and new minerals in situ
mass movement
The detachment and movement of weathered and eroded material downslope under the influence of gravity
surface runoff
water that hasn’t permeated the rock flowing down a cliff face and causing erosion of it
What is erosion resistance/ ‘hardness’ of the rock influenced by
- how reactive minerals in the rock are when exposed to chemical weathering
e.g. calcite in limestone can be weathered by solution, quartz in sandstone cannot - whether rocks are clastic (sedimentary, cemented particles) or crystalline.
Igneous and metamorphic rock are crystalline, as they are made out of interlocking particles, so more resistant - cracks, fissures and fractures. These are weaknesses exploited by weathering and erosion
Coastal accretion
The deposition and buildup of sediment at the coast and the seaward growth of the coastline, creating new land. Often involved deposited sediment being stabilised by vegetation
Dynamic equilibrium
The balanced state of a coastal system where inputs and outputs balance over times and positive and negative feedback loops maintain the internal equilibrium
Fetch
The distance a wave travels. A long fetch creates a high energy wave
swash
The flow of water up the beach
backwash
The wave running back down the beach to meet the next incoming wave
What creates a destructive wave
A weak swash and strong backwash creates high, plunging waves with a short wavelength. Increased erosion of the coast, with a steep beach profile.
What creates a constructive wave
A strong swash and weak backwash creates low, surging waves with a long wavelength. Increased deposition on the coast, often creating a ridge of sediment.
Strata
The different layers of rock within an area and how they relate to each other
Bedding planes
horizontal cracks. Natural breaks in the strata caused by gaps in time during periods of rock formation
Joints
Vertical cracks. Fractures caused by contraction as sediments dry out or by earth movements during uplift. Divides rock strata up into blocks with a regular shape
Folds
Formed by pressure during tectonic activity which makes rocks buckle and crumple
Faults
formed by when stress or pressure to which a rock is subjected to (often by tectonic forces) exceeds its internal strength, causing it to fracture. Faults then slip or move along fault planes, moving rocks from their original positions on either sides of the fault line
Dip
The angle at which rock strata lie
What is a concordant coastline
When rock strata run parallel to the coastline. Bands of alternating resistant and non resistant rock leads to formations to bays and coves when marine erosion breaks through resistant rocks and then rapidly erode the soft rock behind.
e.g. the coast around Lulworth in Dorset
What is a discordant coastline
Formed when different rock strata intersect the coast at an angle, so geology varies across a coastline. Alternating bands of more and less resistant rock that run at right angles to the coast lead to alternating bays and headlands.
Why do waves break?
As a wave nears the shore it rears up into a crest as the bottom moves slower than the top as there is friction with the sea bed. This means wave energy increases as it reaches the shore.
Why are waves more destructive at headlands?
Waves are more destructive at headlands as it is deeper, so the waves break closer to the headland. Waves are less destructive at beaches because it is shallower, so the waves lose energy before they reach the floor.
Wave refraction; in bays, wave crests curve to fill the bay and wave height decreases. The straight wave crests refract, becoming curved. This means the waves spread out in bays and concentrate on headlands
How does a horizontal dip influence the cliff profile
A near vertical profile with notches reflecting strata that are more easily eroded
Fissures
Small cracks in the rock, but represent weaknesses erosion can exploit
How does a seaward dip affect the cliff profile
Low angle - rocks gently dip towards the sea, vertical joints opened by weathering and pressure release. Overhanging rock, vulnerable to rock falls
High angle - Sloping profile with one rock layer facing the sea, vulnerable to rock slide along bedding planes.
How does a landward dip affect the cliff profile?
Stable, steep cliffs. reduced rock falls
Traction
sediment (pebbles, cobbles, boulders) rolls along sea floor, pushed by waves
Saltation
sediment (sand sized particles) bounce along because of the force of the water or wind
Solution
dissolved material (chemical compounds in solution) is carried in water
What conditions will produce the most erosion?
- when waves are at their largest (influenced by wind speed and fetch), waves have a lot of energy so can hurl sediment at a cliff face
- waves are 90 degrees to the cliff face
- tide is high
- heavy rainfall (surface runoff and percolation weakens the cliff)
- debris from previous erosion has been removed from the cliff foot
hydraulic action
air trapped in cracks and fissures is compressed by the force of waves crashing against the cliff face. The pressure forces cracks open. More air is trapped so greater force is experienced in the next cycle of compression. Blocks of rock are dislodged off the cliff face. Heavily jointed/fissured sedimentary rocks are vulnerable
Abrasion
sediment picked up by breaking waves is thrown against the cliff face. This gradually wears the cliff down by removing rock particles, chiseling away at the surface. Loose sediment needs to be available, softer sedimentary rocks are more vulnerable