Coastlines:oceanic borders

G.Burgess

2009.

Dynamic environment

• Zone where, ocean waters meet continental margins and the atmosphere

• Marked by beaches, rocky shores, cliffs, etc.

• Constantly changing shape and form

Erosion• Erosion is destructive waves wearing away the coast.

There are four main processes which cause coastal erosion. These are corrasion/abrasion, hydraulic action, attrition and corrosion/solution.

• Corrasion/abrasion – When waves pick up beach material (e.g. pebbles)

and hurl them at the base of a cliff. (physical action)• hydraulic action

– When waves hit the base of a cliff air is compressed into cracks. When the wave retreats the air rushes out of the gap. Often this causes cliff material to break away.

• Attrition– when waves cause rocks and pebbles to bump into

each other and break up. • Corrosion/solution

– when certain types of cliff erode as a result of weak acids in the sea. (chemical action)

Transportation• Transportation is the movement of material in the sea

and along the coast by waves. • Longshore Drift

– movement of material along the shore by wave action.

• happens when waves moves towards the coast at an angle.

• The swash (waves moving up the beach) carries material up and along the beach. The backwash carries material back down the beach at right angles. This is the result of gravity. This process slowly moves material along the beach.

• longshore drift provides a link between erosion and deposition. Material in one place is eroded, transported then deposited elsewhere.

Transportation

• material moves in four different ways; – Traction

– large material is rolled along the sea floor. – Saltation

– beach material is bounced along the sea floor.

– Suspension – beach material is suspended and carried by

the waves. . – Solution

• material is dissolved and carried by the water.

Deposition

• Deposition– when eroded material is dropped by constructive

waves. – happens when the wave loses energy and is not

able to carry the suspended materials– Helps to sort materials by size

• Heavy materials (large rocks) drop first and lighter materials (sand/silt) drop last.

– Deposition creates a range of landforms.

Nova Scotia Be

aches Act, 198

9.

Beaches • The beach is the area between the lowest spring tide level and the

point reached by the storm waves in the highest tides. • Every beach is different but they are usually made up of material

deposited on a wave-cut platform.

Sand Dunes • created by strong winds (not by coastal erosion or deposition)• sand is blown up a beach forming small hills.• as depression and hills are formed, more sand gets trapped until there

is enough that plants may take root. • Dunes are held together by long-rooted grasses such as marram

grass. The root systems hold the grains of sand so that they cannot be blown away

• Root systems enable the collection of moisture that enables the growth of other plants and development of new food webs

Spit

• Longshore drift moves material along a coastline. • Where there is an obstruction or the power of the waves

is reduced the material is deposited. • Where rivers or estuaries meet the sea deposition often

occurs.• over the years materials build up forming a long ridge of

material, called a spit. Salt Marshes • A salt marsh is a coastal marsh that forms on mud flats. • They usually form in very sheltered inlets and estuaries,

or behind spits (places where fine sediment accumulates).

• form as vegetation builds up on mud flats .

Sand Bar

• Waves transport sand making a trough• This forms a division that separates how materials are

deposited• Material in backwash is deposited on sand bar and the

rest is deposited on the beach

Bays, inlets

• Usually formed by erosion and transportation of materials.

• Wave action will transport the soft rock or sediment to other locations

• Factors of transport; storm surges, glaciation (melt and movement of ice during ice age)

• Narrow bay = fjiord• Large bay = gulf• Small rounded inlet = cove• Headland (Cape Breton Island): raised area protruding

out into the ocean.

Atlantic Canada r

elieved as hurrica

ne Bill blows by

 

Human Influences

1. Breakwater• An artificial structure of a durable material that

interrupts the progress of waves to shore. • used to dissipate some of the oceans wave energy• can be made of a build up of rocks, cement,

timbers, boulders, etc. • usually found at the mouth of a harbour to protect

the area on the other side of the breakwater

What do Breakwaters do?

• interrupt the wave energy heading to the beach, weakening the longshore current and allowing sand to accumulate

• eventually causes the sand of the beach to approach the breakwater; filling in the area the breakwater is designed to protect the coastline properties.

• Also, it may cause erosion further down the coast because of the diverted energy

Human Influences (continued)2. Groin• A structure extending from the beach into the water. • help to trap sand from the current, accumulating sand

on the updrift side.• Usually make erosion worse on the downdrift side

where the beach is sand deprived

Souris

homes threat

ened by cliff e

rosion

Human Influences (continued)

3. Sea Wall• A wall constructed of a durable substance that protects

the beach or shoreline from eroding. • the protection is usually temporary because the sea

wall is only as good as the substrate it is made of. • they can increase beach erosion because they are

deflecting wave energy. • Also, high waves can crash over the wall and erode

both sides