formation of coastal landforms Flashcards
Longshore drift
When the prevailing wind is at 45 degress to the coastline, the swash is parallel, and the backwash is at 90 degrees due to gravity. The swash deposits sediment and the backwash picks it up. This moves the sediment in a zigzag pattern across the beach. This will cause a build up of sediment on one end of the beach
Headland and Bays
Headland and bays form where there is a discordant coastline, alternating layers of hard and soft rock. Over time, the softer rock will retreat, leaving headlands of hard rock sticking out on either side
Cliffs and Wave cut platforms
Waves erode the base of the cliff through hydraulic action and abrasion, forming a wave-cut notch.
Continued erosion deepens the notch, undercutting the cliff.
Sub-aerial weathering weakens the cliff from above until it collapses due to gravity.
The process repeats, causing the cliff to retreat and leaving behind a wave-cut platform.
Cave, arch, stack, stump
A crack forms in a headland where there is a weakness, due to hydraulic action and abrasion.
Wave refraction concentrates energy on the sides of the headland, enlarging the crack into a cave.
Continued erosion deepens the cave until it breaks through the headland, forming an arch.
The arch is widened by erosion from hydraulic action and abrasion.
Sub-aerial weathering weakens the arch roof from above.
Eventually, the arch collapses due to gravity, leaving a stack, which is later eroded into a stump.
Beach
Beaches form in sheltered areas like bays where wave energy is lower.
Wave refraction disperses energy in the bay, causing waves to deposit sediment.
Constructive waves with strong swash and weak backwash build up the beach.
Sediment accumulates over time, forming a gently sloping beach.
Spit
Longshore drift moves sediment along the coast in a zigzag pattern due to angled swash and straight backwash.
Sediment is deposited where the coastline changes direction, forming a spit.
The spit continues to grow out to sea as more sediment is deposited.
A hooked end may form if the wind direction changes.
Bar
(Repeated spit explanation) Continued longshore drift can cause a spit to grow across a bay to join two headlands. This forms a bar, behind which is a bay wherein the sea is trapped, forming a lagoon.
