Waves

Question 1

What forms wind waves?

Answer 1

Wind waves are initiated by the transfer of energy from the wind to the water due to friction between the surface tension of water and air (fluids). (Tension=ripples). As wind continues to blow over the water surface the transfer of energy continues causing the initial ripple to build up into a wave. As a result the longer the fetch (distance travelled) the greater the strength (energy) of a wave as more energy has transferred from the air to the water.

Question 2

What are the 2 types of wind waves?

Answer 2

Swell waves (wind waves that have organised over time in deep water) and storm waves (waves generated by stormy conditions and are typically more irregular and contain more energy)

Question 3

What is wave length?

Answer 3

The distance between wave crests

Question 4

What is wave frequency?

Answer 4

The number of wave crests passing a point per second

Question 5

What is the wave period?

Answer 5

The time it takes for a wave crest to travel between 2 points.

Question 6

What is wave height?

Answer 6

Height of wave crest- height of wave trough

Question 7

What is wave velocity?

Answer 7

Wavelength/waveperiod

Question 8

What is celerity?

Answer 8

The phase velocity if a wave (the speed of the shape of the water)

Question 9

What is the relationship between wave period, velocity and length?

Answer 9

A small increase in wave period = large increase in wave length. Longer wave length = greater wave velocity

Fastest waves in deep water have longest wave length

Question 10

Can wave lengths,periods and height combine?

Answer 10

Yes in deep water these factors can combine

Question 11

What types of waves create greatest coastal change

Answer 11

24/7 wind waves due to how many and how consistent they are (storm waves can cause dramatic change but not most of the coastal change)

Question 12

Why do west coast beaches have different waves to east coast beaches?

Answer 12

West coast beaches normally have a predominant wind direction of SW/W driving waves towards beach (opposes waves on east coast) and have long fetch. (Each coast waves face many obstacles ie;islands and so have shorter fetches =less energy and waves are more choppy as they are long and short fetch waves)

Question 13

What is the key to the formation of wind waves?

Answer 13

Air and water have different densities

Question 14

When is wave height amplified?

Answer 14

When wave crests and troughs are in phase with eachmother

Question 15

Why do different sets have different heights?

Answer 15

These periods if different wave heights are caused by the arrival of different wave trains some in phase and some not

Question 16

What is the surface beat?

Answer 16

The alternating arrival of higher and lower (height) wave sets

Question 17

What is orbital motion?

Answer 17

The movement of water particles in closed rotational orbits below a wave

Question 18

How far does below the water surface is water motion occurring in a wave?

Answer 18

Surface wave motion affects water particles to a depth of 1/2 wave length (1/4 L)

Question 19

What is the wave base?

Answer 19

1/2 wave length or where water particles are no longer affected by surface wave motion.

Question 20

What is shallow water?

Answer 20

Shallow water is water where the wave base is in contact with the sea floor

Question 21

What is deep water?

Answer 21

Deep water is where the wave base is mot in contact with the sea fooor

Question 22

What are the 2 important properties of orbital motion?

Answer 22

Velocity is proportional to wave height

Velocity decreases with depth

Question 23

What is stokes drift?

Answer 23

During orbital motion watermparticles move very slightly (do not return to the exact same position after rotation).

As velocity decreases (decreased depth) there is a net drift of water in the direction of the wave. A.k.a. Stokes drift

Question 24

What happens to wave velocity in the transfer from deep to shallow water?

Answer 24

Wave velocity decreases

Question 25

What happens to wavelength in the transfer from deep to shallow water?

Answer 25

Wavelength decreases.

Question 26

What happens to wave. During the transfer of deep to shallow water?

Answer 26

The wave period stays the same as the waves decrease in velocity at the same rate

Question 27

Why does wave period stay the same?

Answer 27

Waves decelerate at the same rate

Question 28

What happens to wave height during the transfer from deep to shallow water?

Answer 28

Wave height increases

Question 29

What is Shoaling?

Answer 29

Wave Shing occurs when the wave face encounters the sea flow causing wave height and steepness to increase.

Question 30

When do waves break?

Answer 30

Waves break when the wave height is greater than the base stability

or when the heigh/ length is greater than 1/7 (120°).

Question 31

What happens to orbital motion as waves move into shallow water?

Answer 31

The orbital motion is compressed becoming elliptical in very shallow water these orbits become flattened.

This can be visualised by wave buildup and eventual break .

Question 32

How is sediment affected by shallow water orbital motion?

Answer 32

Elliptical or flattened orbital motion causes sediment to be kicked up (see wave induced current for more)

Question 33

Young and Ribal (2019) imagery and data from wave boys to estimate ocean windspeeds and ocean wave heights overtime. What conclusion was reached?

Answer 33

It was discovered since 1985 Ocean wind speeds have been increasing leading to a corresponding increase in wave heights.

Question 34

What is suggested to be causing increased wave power?

Answer 34

A study by Reguero et al. (2019) suggest this is being caused by oceanic warming.

Question 35

What are the four types of breaking waves?

Answer 35

Spilling, plunging, collapsing, surging

Question 36

What determines spilling or surging waves?

Answer 36

Spilling or surging waves are determined by the slope of the wave.

Question 37

What type of beach do spilling waves occur at?

Answer 37

Spilling waves occur at beaches which is seafloor are very long and shallow is this forces the wave to slowly disperse its energy on the long run up to the beach itself. These beaches are a natural occurrence and are a natural defence against very high energy waves in order to stop enormous erosion of the immediate beach and coastal environment.

Question 38

What type of beaches do surging waves occur?

Answer 38

Searching waves occur at beaches that are very steep.

Question 39

What are infragravity waves?

Answer 39

Infra gravity waves are waves with a very long period and a low frequency. They are standing waves that move in the same position as they are trapped within the surf zone. (between first breaking wave and swash zone)

Question 40

How can you identify infragravity waves?

Answer 40

Infra gravity waves are waves that can be observed at the beach as squash that comes far higher up the beach than most other waves.

Question 41

What causes tsunami waves?

Answer 41

Tsunami waves are caused by massive water displacement. Typically this is caused by under sea earthquakes under volcanic eruptions or under sea landslides.

Question 42

What is a tsunami wavelength?

Answer 42

Tsunami wavelength that 100s of kilometres long.

Question 43

Why is tsunamis difficult to identify when in deepwater?

Answer 43

Tsunamis can be difficult to identify as they can be waves in the border no more than one meter high and there are hundreds of kilometres between different waves.

Question 44

What is the most dangerous part of a tsunami?

Answer 44

The backwash of the tsunami is the most dangerous part

Question 45

What do tsunamis look like when they arrive at shore?

Answer 45

Tsunamis can look like large waves however they can also look like large tides or even just wind waves

Question 46

What is the key difference between a wind wave and a tsunami?

Answer 46

Wind waves are formed by friction between the surface tension of air and water where is tsunamis are caused by water displacement, most commonly under the earthquakes.