Higher Coastal Landforms & Processes In this part of the course we will be looking at both: coastal erosion and deposition.
Coastal Erosion • We will be looking at the following: • Waves our agent of erosion • Different types of erosion • Landforms of erosion
Coastal Deposition • We will be looking at: • a. Beach profiles (X sections) & WaveTypes • b. Longshore Drift • c. Landforms of deposition
Coastal Erosion To start, we must recognise that waves are responsible for coastal erosion and that generally the bigger the wave, and the more frequent, the greater the erosion.This means that we will need to look at how waves form and differ in size. To do this we will look at Task 1 in your work book.
Fetch = Distance + Wind Fetch = Distance + Wind
Coastal Erosion Now for Task 2 all about waves actually breaking down rock, or erosion.
Wave Erosion There are 3 ways thatwaves erode the coast. It is very important to describe and explain these as that will get you easy marks in an exam. You’ll need to show how they contribute towards the development of coastally eroded landforms. Watch the slides to find out more.
Hydraulic Pressure Crack In Rock Breaking Wave Air Compressed By Water
Hydraulic Pressure Over time rock weakens and breaks off cliff Air explodes out of crack
Hydraulic Pressure Key words to describe hydraulic pressure. breaking waves ~ cliff ~ water ~ cracks compresses air ~ air explodes ~ rock ~ time ~ breaks ~ force of water pounding ~ erodes ~ time
Corrasion Waves carry rocks, shingle, sand Rocks hit each other Rocks erode over time
Corrasion (abrasive) Key words to describe corrasion. broken rock ~ picked ~ waves thrown ~ cliff faces ~ hard rock -erode ~ time
Attrition Waves carry rocks Small rocks rub against cliff
Attrition Key words to describe attrition. small rocks ~ H.P. ~ Corrasion waves ~ rub ~ cliff ~ erosion
Corrosion A Fourth Type Of Erosion This is when the rock is broken down by chemicals in the sea such as salt. Rocks can either dissolve or rot and so start to crumble away. This is similar to solution in Limestone areas or the corrosion of stone carried in rivers.
Landforms Of Coastal Erosion We shall look at three principal types of landforms: i. Cliffs/Wave Cut Platforms ii. Headlands/Bays iii.Headland Erosion (On Sides)
Sea Cliff Erosion Wave Cut Platforms (Task 3) wave cut platform sea cliff erosion
Sea Cliff Erosion Cracks In rock are weak points These are eroded by waves at high tides by the 4 processes we’ve looked
Sea Cliff Erosion collapse of overhang cracks get larger & form a cave undercutting of cliff by cave
Sea Cliff Erosion Repeated collapse over time flat terrace remnant of base of cliff
Sea Cliff Erosion Now do Task 3 Question 1 by filling in the key
Wave Cut Platform W.C.P. exposed at low tide, but created at high tide for later
Task 3 Question 2 • Waves ~ erosion ~ 4 types ~ name ~ general effect ~ high tide • Cracks ~ weak ~ widen ~ wave cut notch ~ cave ~ time ~ overhang ~ collapse of cliff (why) ~ repeats ~ retreats • Base of cliff ~ flat terrace ~ name it ~ exposed low tide
Headlands & Bays Task 4 large headland large bay small bay small headland
Headlands & Bays concordant parallel to sea two types discordant at 90º to sea
Concordant Headlands crack in rock eroded by waves soft rock hard rock hard rock resists waves so narrow crack
Concordant Headlands Bay Headland soft rock erodes easily so wide bay
Discordant Headlands soft rock hard rock softer rocks erode more easily than harder ones ~ differential erosion
Discordant Headlands bay headland indents or bays form on the coast where the soft rock has receded
Task Question 3 • Geology ~ 2 key factors ~ (1) different rock types ~ hard ~ soft ~ side by side ~ (2) Layers 90º ~ sea • Waves erode ~ hard rock ~ slow ~ resistant ~ soft rock ~ fast ~ soft indents ~ bays hard rock ~ sticks out ~ headlands
Headland Erosion (On Sides) These are a series of landforms developing one after the other on the side of a headland.
Caves/Blowholes/Arches/Stacks Label the sketch below in your work book using the word box for task 7.
Caves/Blowholes/Arches/Stacks stack blowhole needle wave cut platform cave arch
Caves/Blowholes/Arches/Stacks 1 erosion on side of headland waves erode cracks into caves
Caves/Blowholes/Arches/Stacks 1 Cont. Explain sedimentary rocks easily exploited many cracks name your 3 types of erosion in exam
Caves/Blowholes/Arches/Stacks 2 blowhole in top of headland waves crash into back of cave and erode upwards into headland
Caves/Blowholes/Arches/Stacks 2 Cont. blowholes are relatively rare vertical cracks in rock help them to form
Blowhole Roof collapses due to erosion from waves splashing upwards from back of cave
Caves/Blowholes/Arches/Stacks 3 eventual break through to other side forms an arch continued erosion of back of cave
Caves/Blowholes/Arches/Stacks 3 Cont. process can be sped up if cracks on other side being eroded
Caves/Blowholes/Arches/Stacks 4 little support so eventual collapse ofroof further erosion sees widening of arch
Caves/Blowholes/Arches/Stacks 4 Cont. process can be aided by blowhole weakening roof
Caves/Blowholes/Arches/Stacks Now try and piece together the explanations for all of these landforms Task 7 question 2
Caves/Blowholes/Arches/Stacks 1)Waves crash into headlands eroding weaker parts such as cracks. 2)The cracks are eroded by 3 different processes:- hydraulic pressure, corrasion & attrition. In an exam you should explain each of these! 3)The crack starts to widen and form a cave, it can be undercut causing the roof to collapse due to lack of support for the roof. This helps the cave get larger.
Caves/Blowholes/Arches/Stacks 4) As the cave gets larger, waves start to hit into its back wall and on impact are sent crashing into the roof of the cave where erosion occurs. 5)The erosion of the cave roof can lead to a blowhole, where waves continue to erode upwards and through the top of the headland. This is quite rare and needs a vertical crack line to be exploited (Sedimentary Rocks!).
Caves/Blowholes/Arches/Stacks 6) At the same time caves and blowholes develop, wave erosion can also lead to the development of an arch. This is when thecave erodes all the way through to the other side of the headland. 7) There may be similar cracks on the other side of the headland with erosion taking place, speeding up the development of the arch. Arches don’t necessary need blow holes to be present when they develop!
Caves/Blowholes/Arches/Stacks 8) Over time the waves continue to widen the walls of the arch leaving less support for the roof, leading to its collapse. This leaves a new headland on the landward side of the arch and the old wall still standing on the seaward side. 9) this old wall is called a stack or a pillar and is also subject to erosion by the sea. As it erodes it gets thinner at its base and parts of it collapse leaving a narrower pillar called a needle.