how are coastal landforms developed - landforms Flashcards
1
Q
how are wave cut notches formed
A
- destructive waves repeatedly break on steep sloping coastline
- creates an undercut between high and low tide levels which forms a wave cut notch
2
Q
how are cliffs formed
A
- after a wave cut notch has formed…
- continued undercutting weakens support for the rock strata above
- this then eventually collapses -> steep profile cliff
- the regular removal of debris at bottom of cliff by waves keeps the cliff steep
3
Q
hows are shore platform formed
A
- when rock debris at bottom of cliff becomes boudler size its too big to be removed by the waves
- therefore it stays there, creating a platform
- this platform gets wider and wider creating shallow water and smaller waves
- friction then slows down waves and makes them break on the platform rather than base of cliff –> undercutting stops
- this creates the shoreplatform
4
Q
how are headlands and bays formed
A
- when there are different bands of different rock with different resistances to erosion
- weaker rock erodes faster - bay
- harder rock is left - headland
5
Q
whats wave refraction
A
- this takes place when waves approach an irregularly shaped coastline and therefore develop a formation parallel to the coastline
6
Q
how are geos formed
A
- narrow steep-sided inlets
- form by lines of weaknesses - JOINTS, FAULTS
- these get eroded more rapidly than resistant rock around them by HYDRAULIC ACTION which forces air and water into the joint cracks weakening the rock strata
7
Q
how are blowholes formed
A
- a pot hole on top of a cliff, created by chemical weathering, and a cave, formed by marine erosion.
- As the cave erodes deeper into the cliff face and the pothole deepens,
- a channel is created for incoming waves to travel into and up the cliff face (occasionally water splashes out of the top of the blowhole when energetic waves hit the cliff face).
8
Q
the formation process of a cave, arch, stack and stump
A
- joints and faults in resistant rock are attacked by waves
- hydraulic action and abrasion wide the weaknesses and undercuts the base of cliff - CAVE
- more erosion on the headland and hole is opened - ARCH
- cliff face recedes and forms a wave cut platform. the arch collapses and creates a STACK
- sea attacks base of stack and eventually wave cut notch undercut the stack and the STRUMP is left
9
Q
what are the erosional landforms
A
shore platform
wave cut notch
cliff
headlands
bays
blowhole
geo
cave
arch
stack
stump
10
Q
what are the depositional landforms
A
Beaches
spits
onshore bars
tombolos
salt marshes
deltas
11
Q
how are beaches formed - general
A
- beaches r the accumulation of material deposited between the lowest tides and highest storm wave
- 3 main sources of beach material (sand, pebbles, cobbles):
1. cliff erosion (5%)
2. offshore (5%)
3. rivers (90%)
12
Q
sand beaches
A
- gentle gradient - less than 5 degrees
- this is because small particles size means they are compact when wet which allows little percolation during backwash
- not much energy lost due to friction therefore material gets carried down in backwash rather than being left at the top
- this creates a gentle gradient
13
Q
shingle beaches
A
- mix of pebbles and S/M cobbles
- steeper beaches bc swash stronger than backwash
- shingle make up upper part of beach bc rapid percolation bc large air spaces means little backwash so sediment is left at top
14
Q
what are cusps
A
- small semi-circular depressions
- temporary features formed by collection of waves raching same point - when swash and backwash have similar strengths
- swash comes into the sides of a cusp and goes into the cnetre of the depression
- this creates a strong backwash dragging material down the beach from the cusp - enlarging the depression
15
Q
how are spits formed
A
- they are long narrow beaches of sand or shingle attached to the land at one end and extend across a bay or estuary.
- formed by LSD being dominant in one direction which carries material to the very end of the beach and off the end etc..
- the end of the spit becomes recurved bc of wave refraction
- in the sheltered area behind the spit - deposition will occur bc wave energy is reduced –> salt marsh
16
Q
how are onshore bars formed
A
- these develop when a spit grows across an indentation in the coastline, eg cove or bay, and joins onto the land on the other end
- this creates a lagoon
17
Q
how are tombolo’s formed
A
- these are beaches that connect the mainland to an offshore island
- formed from spits that have grown seaward until they reach another island
18
Q
salt marshes
A
- low energy environments
- vegetated areas of deposited clay and silts
- salt tolerant plants: eelgrass, spartina trap sediment to increase marsh height
- the higher the marsh - the shorter the time of full submergence and the less saline conditions
- low marshes are very saline, where few plants can survive
19
Q
how are deltas formed - what, how, where
A
- large areas of sediment found at mouths of rivers
- they form when rivers and tidal currents deposit sediment at a faster rate than waves and tides can remove it
- they form where: rivers entering sea are carrying large sediment loads, low energy environments, low tidal ranges
20
Q
what is the structure of deltas
A
- upper delta plain - further inland, beyond the reach of tides, entirely made of river deposits
- lower delta plain - inter-tidal zone, regularly submerged and made of both river and marine deposits
- submerged delta plain - below mean water mark, made of mainly marine sediments. represents seaward growth of delta
21
Q
3 types of deltas
A
- cuspate - pointed extension to the coastline, occurs when sediment is shaped by gentle currents from opposite directions
- arcuate - high sediment supply for delta to grow seawards but wave action strong enough to smooth and shorten its leading edge
- birds food - distributaries build out from the coast in a branching pattern, with river sediment supply exceeding rates of removal by waves and currents
