COASTS Flashcards
(32 cards)
Spit
Sand or shingle beach ridge extending beyond a turn in the coastline. usually greater than 30 degrees. At turn, the longshore drift current spreads out and loses energy leading to deposition. The length of a spit is determined by the existence of secondary currents causing erosion, either the flow of a river or wave action which limits its length
Bayhead Beach
- A awash aligned feature, where waves break at 90 degrees to the shoreline and move sediment into the bay, where a beach forms. Due to wave refraction, erosion is concentrated at headlands and the bay is an area of deposition
Tombolo
A sand or shingle bar that attaches the coastline to an offshore island. Tombolos form due to wave refraction around an offshore island which creates an area of calm water and deposition between the island and the coast. Opposing longshore currents may play a role, in which case the depositional feature is similar to a spit.
Barrier beach/bar
A sand or shingle beach connecting two areas of land with a shallow water lagoon behind. These features occur when a spit grows so long that it extends across a bay, closing it off.
Hooked/Recurved Spit
A spit whose end is curved landward, into a bay or inlet. The seaward end of the spit naturally curves landward into shallower water. The ‘hook’ may be made more pronounced by waves from a secondary direction to the prevailing wind
Offshore bar
A ridge of sand found offshore - can be submerged during high initially formed by riptide currents following destructive waves
mass movement processes
Landslide, Rotational slumping, slide, rock fall, topple, mudslides, slumping
weathering
mechanical, chemical, biological
Perculation
the movement of water through soil
Flocculation
when sediment is dropped, such as clays and polymers, they clump together
Sub Aerial Process
land-based processes which alter the shape of the coastline. These are a combination of weathering and mass movement.
Mechanical (physical) weathering
Mechanical or physical weathering is the fracture and breakdown of rocks into fragments. Freeze-thaw and Salt crystallisation
salt crystallisation
This is when salt crystals are deposited in cracks and over time the salt accumulates and applies pressure to the crack (similar to freeze-thaw weathering).
Chemical weathering
decomposition of rocks (literally, changing the minerals)
Soil Creep
Soil creep is a slow but continuous process. It typically occurs on most slopes over 5 degrees. Soil creep rarely exceeds speeds of 1cm per year. Creep occurs as the result of repeated expansion and contraction of material. Cycles of freeze-thaw heave particles upon freezing and allow them to fall further downslope when the ice melts. Alternating hydration and dehydration have the same effect.
Slump
Rainwater infiltrates the cliff through unconsolidated, porous material (e.g. boulder clay). This then creates a slip plane. The weight of the saturated clay causes the material to slump along the slip plane.
rock fall
They are most commonly triggered by undercutting in the inter-tidal zone or freeze-thaw weathering.
Mudflows
A mudflow is an earthflow consisting of material that is wet enough to flow rapidly and that contains at least 50 percent sand, silt, and clay-sized particles.
Soil creep
Soil creep is a slow but continuous process. It typically occurs on most slopes over 5 degrees. Soil creep rarely exceeds speeds of 1cm per year. Creep occurs as the result of repeated expansion and contraction of material.
Land slide
This is the downslope movement of a large block of material that moves as a coherent mass. This means it retains its internal structure until hitting the base of the slope and fracturing into smaller pieces. It is more common over wet periods, on steep slopes and often occurs on coastlines.
Marine Processes
Marine processes are those associated with the action of waves. This includes erosion, transportation and deposition.
Erosion
Erosion refers to the wearing away of the land surface and removal of materials by river and seawater, ice and wind. There are four main processes of erosion along the coast. These are hydraulic action, abrasion and corrasion, attrition and solution.
Hydraulic Action
Waves breaking at the foot of a cliff force air in cracks to be compressed. Loose rocks are dislodged and removed. When the wave retreats the compressed air rushes out of the crack and can further weaken faults in the cliff face.
Abrasion
Abrasion is the sandpaper effect of loose rocks being scraped along bare rock. It often smooths and polishes the rock.
