Ch 2.5 How do waves shape our land?

Question 1

What is the interpretation of coast?

Answer 1

1. A coast is the zone between the land and the sea.
2. It can be divided into several zones. The division is mainly the result of different tidal ranges.
3. Tides are variations in sea level caused by the gravitational pull of the moon and the sun.

Question 2

How are waves generated?

Answer 2

When wind blows over the sea, waves are generated. Waves move in the same direction as the wind. Water particles in the waves rotate in a vertical circular orbit. Wavelength is an indicator of water energy. An decrease in wave length generates a large increase in energy.

Question 3

How waves break when they approach the shore? Explain more on the terms.

Answer 3

Swash: After the wave breaks, the water continues to run up to the beach.
Backwash: The water running back down the beach.

Question 4

What are the types of waves? Please state the definition on them.

Answer 4

Constructive waves: When swash is greater than backwash, and so build up materials on the beach.
Destructive waves: When backwash is larger than swaa\sh, so removes materials on the beach.

Question 5

What is the formation of constructive waves and destructive waves?

Answer 5

Constructive waves: Weak wind
Destructive waves: Strong wind

Question 6

What is the wave energy, wave height and wave length of constructive waves and destructive waves?

Answer 6

Wave energy: Little & Great.
Wave height: Low & High.
Wave length: Long & Short.

Question 7

What is the slope along the coast of constructive waves and destructive waves?

Answer 7

Constructive waves: gentle.
Destructive waves: steep.

Question 8

What is the coastal process of constructive waves and destructive waves?

Answer 8

Deposition & Erosion.

Question 9

What is the gain or loss of shore materials?

Answer 9

Gain & Loss.

Question 10

What is the resultant beach shape?

Answer 10

Wide and flat & Steep and narrow.

Question 11

What is the resultant landforms or features of constructive waves and destructive waves?

Answer 11

Constructive waves: Beach, spit, bar, tombolo.
Destructive waves: Sea caves, geo, sea arch, stack, cliff, wave-cut platform.

Question 12

What are the types of wave erosion?

Answer 12

1. Hydraulic action
2. Abrasion.
3. Attrition.
4. Solution/Corrosion.

Question 13

What is hydraulic action?

Answer 13

Wave splashes the coast and enlarges the joints or cracks in the rock between the high tide and low tide levels.

Question 14

What is abrasion?

Answer 14

Waves pick up rocks and hurl them at the shore, wearing away the coast line.

Question 15

What is solution?

Answer 15

Soluble minerals in rocks dissolve in seawater.

Question 16

What is attrition?

Answer 16

Rocks are hurled against one another. The rocks are worn down and become smaller and rounder.

Question 17

What are the conditions favourable to wave erosion?

Answer 17

Energy of waves and resistance of the coasts.

Question 18

What are the factors affecting the energy of waves?

Answer 18

1. Wind.
2. Offshore gradient.
3. Shape of coastline.
4. Roughness of seabed along the shore.

Question 19

What affects the strength of winds?

Answer 19

Wind speed, fetch, duration of wind.

Question 20

Explain on wind.

Answer 20

Higher wind speed -> Longer fetch -> Longer duration of wind -> erosion (due to the greater energy)
Lower wind speed -> shorter fetch -> shorter duration of wind -> deposition

Question 21

Explain on offshore gradient.

Answer 21

1. Steep offshore gradient, little energy is consumed to overcome friction with the seabed because of the deep water. Little energy is lost. When the waves reach the shore, they still have a lot of energy. Backwash is strong and results in erosion.
2. Gentle offshore gradient, much energy is lost to overcome friction with the seabed some distance from the shore because the water is shallow. When waves reach the shore, they spill over and create wash results in deposition.

Question 22

Explain on the shape of coastline.

Answer 22

1. Wave refraction towards headlands so energy is concentrated there -> erosion.
2. Wave spread out in bays, reducing the wave energy -> deposition

Question 23

Explain on the roughness of seabed along the shore.

Answer 23

A rough seabed needs much energy to overcome friction. This leads to loss of energy. Less energy is bought to the shore.

Question 24

What is the formation of sea cliffs and wave-cut platforms?

Answer 24

When swash is smaller than backwash, destructive waves occur. Wave erosion concentrates at the zones between the high tide and low tide level. Hydraulic action and abrasion erode the coast. A low sea cliff which is a notch is formed by erosion which is called undercutting. The overlying part collapses and forms a sea cliff. As a sea cliff retreats, a wave cut platform is formed. It is exposed during the low tide only. It is flat and extensive in front of the sea cliffs, Deposition is rare as destructive waves bring away the materials.

Question 25

What is the formation of sea caves and geo?

Answer 25

When swash is smaller than backwash, destructive waves occur. Erosion concentrates at the zone between high tide and low tide levels. It can widen the cracks/joints by hydraulic action and abrasion to form sea caves. When waves continue to splash against the roof of a narrow sea cave, the top part may collapse and form a narrow, linear crack, it is a geo.

Question 26

What is the formation of sea arches and stacks?

Answer 26

At the headland, swash is smaller than backwash, destructive waves occur and wave erosion occurs. Erosion concentrates at the zone between high tide and low tide levels. If sea caves continue to be eroded, it might cut through a headland and form a sea arch. The collapse of the roof of sea arch leaves and an isolated island with steep sides standing offshore, is called stack.

Question 27

What are the four types of transportation in the sea?

Answer 27

1. Traction: Large load slides and rolls on the seabed.
2. Saltation: small particles are moved in a series of hops and bounces.
3. Suspension: small, lighter particles are carried in water without touching the seabed.
4. Solution: Minerals are dissolved and carried by seawater.

Question 28

How do waves move sediment along the shore?

Answer 28

Most waves approach the shore at an oblique angle, the swash runs up the shore in a direction parallel to the prevailing wind. However, the backwash runs down the shore at right angles due to gravity. This process is repeated, leading to the gradual movement of sediment along the shore. This zigzag movement of sediment along the shore driven by waves is called longshore drift.

Question 29

What are the conditions favourable to wave deposition?

Answer 29

1. Shallow water along the coast.
2. Sheltered area like a bay.
3. The wind is weak.
4. There is abundant supply of material for deposition.

Question 30

What is the sorting process?

Answer 30

The smallest sediment is found at the nearshore while the largest sediment is found at the backshore. As backwash is weak, there is not enough energy to move large sediments back to the sea. Thus, they stay at the backshore.

Question 31

What is the formation of beaches?

Answer 31

When swash is greater than the backwash, constructive waves occur. Wave deposition occur. Eroded materials carried by swash will deposit in sheltered areas, between the highest and lowest water level. Three types of beaches can be identified according to the materials: sandy beaches, pebble beaches and boulder beaches.

Question 32

What is the formation of spits?

Answer 32

A spit is a long, narrow deposit of sediments formed with one and attached to the land and the other extending out to the sea. It is formed when materials are transported along the coasts by longshore drift. Swash is greater than backwash, constructive waves occur. Waves deposition occurs. Eroded materials carried by swash will deposit in sheltered areas, between the highest and lowest water level.

Question 33

What is the formation of bars?

Answer 33

A bar is a long, narrow deposit of sediments across a river mouth. It can be parallel to a beach and extend from headland to headland. A bar is an extension of split and a lagoon may form behind the bar.

Question 34

What is the formation of tombolos?

Answer 34

When swash is greater than a backwash, constructive wave occurs. Wave deposition occurs. If spit builds up and joins an island to the mainland or two islands together, a tombolo is formed. Spits were developed on both ends os islands. They are north and south Cheung Chau. Two spits finally joined to form a tombolo.