waves basics

What is a wave?

A marine process; it is a disturbance of the surface of the sea that is formed as wind blows over the surface of the sea as a moving ridge/swell

How does wind create a wave?

Caused by the energy transfer from the wind to the sea - the wind blowing over the surface of the sea creates friction, which then forms the waves.

What affects the height and strength of a wave?

1. The fetch (how far the wind blows over the sea)

2. The amount of time the wind is blowing

3. The strength of the wind

What things create a larger wave?

A greater strength, time blowing and fetch of the wind

What causes a wave to break?

1. The wave enters shallower water along the coast

2. There is more frictional drag

3. The friction causes the base of the wave to slow, causing the velocity of the wave at the top of the wave to be greater than at the bottom

4. The wave tilts forward, breaks, and moves towards the shore in the surf zone

What are the two types of waves?

Constructive or destructive

What is swash?

The movement of a wave up a beach

What is backwash?

The movement of a wave down a beach, back to the sea

What are constructive waves?

The waves that ‘build’ beaches.

What are the features of a constructive wave?

• Long wavelength

• Low frequency (8-10 a minute)

• Low height, under a metre in height typically

• Wavefront gently slopes, and doesn’t gain much height

• Water spreads a long way up the beach

Where are constructive waves found?

Sheltered bays and spits, creating sandy beaches

Predominate in calm weather, due to less energy transfer to water

How does the orbit change in a wave? Why?

From circular, to elliptical as the shallow water builds friction at the base of the wave

How does the swash and backwash of a constructive wave compare?

• Strong swash

• Weak backwash

How does a constructive wave deposit material on the beach?

1. Carries material up the beach

2. Material is the deposited in backwash as the backwash soaks into the sand or slowly drains away

3. The following breaking wave is able to deposit more material without being affected ‘captured’ by the preceding wave’s backwash

What do destructive waves do?

Destroy beaches

What are the characteristics of a destructive wave?

1. tall in height

2. Short wavelength

3. High frequency

4. Steep wave front, usually over a metre tall

5. Do not travel far up a beach

How does the swash and backwash in a destructive wave compare?

Weak swash, strong backwash

How does the swash of a destructive wave compare to a constructive wave?

• Destructive swash is much stronger

• Destructive backwash is stronger than the swash unlike constructive

How do destructive waves cause a net loss in material?

• Destructive backwash is much stronger than its swash

• This causes beach material to be transported back in to the sea

How does the beach profile where there are destructive and constructive waves differ?

Destructive: steep beach profile

Constructive: gentle beach profile

Where are destructive waves common?

Exposed areas with destructive weather