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Q: Are tsunamis considered as destructive or constructive waves?

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Q: Are tsunamis considered as destructive or constructive waves?

Destructive: - high wave height/ plunging

breakers - erosion process more

prominent- transports eroded sediments

away

Issues:wave frequency? no

backwash? gentle slope or sheltered coast?

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• Rising and falling of the sea level

• Cause : pull of the moon & sun, rotation of the earth

• Each coastal area receive two high tides and two low tides daily

Tides Text pg 91

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Tides

Areas between high and low tides have more erosion

Which area on the beach is the most prone to

erosion?

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LESSON OBJECTIVE•To describe and explain the 4 coastal erosion processes

•Describe what a longshore drift is ( time?)

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Erosion CorrasionAbrasionSolutionHydraulic action

TransportLongshore drift

Deposition Factors:-Supply of sediment-Gradient of slope-Coast position

3 C

OA

STA

L PR

OC

ESSES

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COASTAL EROSIONText pg 92 More

erosionLess erosion

Types of waves

-Destructive waves(more energy)

-Constructive waves(less energy)

Structure and composition of coastal rocks

- Numerous lines of weakness - Soft rocks

- No cracks- Hard rocks

Position of the coast

- Open coast - Protected and sheltered by structures

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GROUPWORK•Each group to receive one vanguard sheet and 4 markers

•While waiting, to hand up homework in front

•Those that has not completed, to stay back during recess to do.

GROUPWORK1. Determine which erosion process has created this coast :

Corrasion/ Attrition/ Solution/ Hydraulic action

2. Write down the characteristics and traits of the coastal features

3. Explain how the erosion process occur

4. Textbook time

5. Teacher time

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CORRASION/ABRASION•Impact of the materials carried by the waves scraping against the coast (pg 93)

•Turbulence of the currents produce a scouring effect

•Chiselling effect / grinding action on the coast

•Cutting and breaking the rocks on the coasts

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ATTRITION• Rocks rub or hit against

each other, breaks down into small round smooth pieces(pg 93)

• Materials from the waves collide with materials on the coast

• Impact causes materials to break into smaller pieces which becomes sand

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SUMMARY•Answered student question about destructive and constructive waves

•Definition of Tides

•Describe the characteristics of 4 coastal erosional process: CASH

•Explained how the processes occurs

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SOLUTION/CORROSION• Waves react chemically

with soluble minerals in the rocks and dissolve them (pg 93)

• Corrosion of rocks by seawater

• Wave action increases the rate of reaction by removing the reacted chemical solution

• Eg limestone

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HOMEWORK ANSWERS ON BLOG

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HYDRAULIC ACTION•Direct impact of the waves against the coast. Compress air and exert pressure in the cracks of rocks (pg 92)

•Enlarges lines of weaknesses after repeated crashes of waves

•Cavitation: water surges into cracks, joints, faults. Results in compressed air and builds pressure. Water retreat releases pressure and trapped air which breaks the rock up.

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LONGSHORE DRIFT

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• Large scale movement of water in the ocean driven by wind

• Longshore current: flow parallel to a coast ( form by waves approaching at an oblique angle)

Coasts are shaped by ...Text pg

189Currents

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QUIZUsing a labelled

diagram, describe the process of longshore

drift [4]

OL Geog N2004 P2 Q4

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COASTAL TRANSPORTATION• Longshore drift: waves transport sediment along

the coast

• Longshore drift: beach drift + longshore current

• Wave approach coast at an angle: Swash carries materials in oblique angle

• Backwash carries materials perpendicularly down because of gravity

• Zigzag movement: beach drift( sediments moving along beach)

PG 93

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LONGSHORE DRIFT

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DIAGRAM OF LONGSHORE DRIFT

Longshore current

(beach drift)

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Using a labelled diagram, describe the process of longshore drift [4]

1.Waves reach the coast at an oblique angle creates a longshore current

2.The materials move in a zigzag pattern in a down drift direction ( beach drift)

3.The swash carries materials up the beach at the same angle as when the war approaches the shore

4.As the swash dies away, the backwash and any materials carries by it return straight down the beach at right angles to the water line due to gravity.

5.Longshore drift = beach drift + longshore current24

COASTAL DEPOSITION

Pg 94More

depositionLess

deposition

Supply of sediment

Weak wave energy

Eg constructive waves

Strong wave energy eg destructive

waves

Gradient of slope

Gentler gradient reduces wave

energy because of friction

Steep gradient

Position of the coast

Calm costal conditions/

protected baysOpen coasts

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