Waves and Tides

Question 1

What causes tides

Answer 1

Gravitational pull from the earths moon and the sun pull the ocean surface closer

Question 2

Neap Tide

Answer 2

Twice a month
Sun and Moon are at right angles to the earth
A tide where the difference between high and low tide is the least

Question 3

Strong spring tide

Answer 3

Occur few times a year - Full moon
Gravitational pull of the sun and moon upon the earth is strongest when moon is closest to the earth in its monthly orbit producing extreme high tides and erosion on beaches.

Question 4

Weak spring tide

Answer 4

Moon is furtherest from the earth in its monthly orbit making a lower spring tide.

Question 5

High and low tides

Answer 5

Two high tides and two low tides occur each day as part of the normal gravitational pull on the earth.

Question 6

What makes waves?

Answer 6

Winds blow over fetch zones at sea and form small ripples which join together to form waves in a rising sea which then move out of the fetch zone and become ocean swells

Question 7

What factors determine size of waves?

Answer 7

Size of fetch
Wind speed
Wind duration
Depth of water

Question 8

What happens to water particles during a wave?

Answer 8

Waves transport energy not water.

As a wave crest passes, the water particles move in circular paths (orbital motion)

Question 9

Fetch

Answer 9

Fetch, area of ocean or lake surface over which the wind blows in an essentially constant direction, thus generating waves.

Question 10

Wavelength and Waveheight

Answer 10

Wave length (distance from crest to crest)
Wave height (vertical distance between the top of the crest and the bottom of the trough)

Question 11

Wave Period

Answer 11

The wave period is the time for two consecutive crests to pass a fixed point. The wave speed, C, can be calculated by dividing the wavelength by the wave period (C=L/T) since a wave travels one wave length each wave period

Question 12

Orbit field

Answer 12

As the energy of a wave passes through water, the energy sets water particles into orbital motion

Question 13

Tsunami

Answer 13

Produced by large, sudden movements in the Earths crust (earthquakes, volcanoes). Produce high speed waves that travel in all directions from the source.

Question 14

Swell

Answer 14

Formed in fetch zones and transported through the worlds oceans without breaking. Rolling series of crests and troughs and can reach large heights and long wavelengths.

Question 15

Breakers

Answer 15

Occur in a huge number of different sizes and shapes depending on the size of the swell, the position of the tide, the slope and structure of the seabed and wind direction.

Question 16

Backwash

Answer 16

The motion after a wave breaks causing receding waves. The water runs back down the beach

Question 17

Plunging wave

Answer 17

Throw from the top where the bottom rises sharply.
A plunging wave occurs when the ocean floor is steep or has sudden depth changes, such as from a reef or sandbar. The crest of the wave becomes much steeper than a spilling wave, becomes vertical, then curls over and drops onto the trough of the wave, releasing most of its energy at once in a relatively violent impact.

Question 18

Surging wave

Answer 18

Break from the full face as deep water meets a cliff or rock.
Surging waves are produced when long period swells arrive at coastlines with steep beach profiles. The base of the wave moves fast and does not allow the crest to develop. As a result, the wave almost doesn’t break, and there is little whitewater.

Question 19

Spilling wave

Answer 19

Crumble from the top where the bottom slopes up gently to the shore.
Spilling waves are waves that are produced when the ocean floor has a gentle slope. As the wave approaches the shore, it slowly releases energy, and the crest gradually spills forward down its face until it is all whitewater. These waves take more time to break than any other wave.

Question 20

Swash

Answer 20

Turbulent water that washes up on beach after a wave has broken. Swash action can move beach materials up and down the beach.

Question 21

Construction waves

Answer 21

Low energy, gentle slope, high water absorption
High energy in swash - accretes sand onto the beach
Accreting beach - Swash is stronger than the backwash

Question 22

Destruction waves

Answer 22

Storm conditions create waves where energy is high and waves cause backwash that erodes sand off the beach.
Eroding beach - The backwash is stronger than the swash.

Question 23

Erosion

Answer 23

Removal of sediment (sand/rock) from the beach caused by destruction waves.

Question 24

Accretion

Answer 24

Accumulation of sediment (sand) on the beach caused by construction waves. Causes the beach to become wider.

Question 25

Microridge

Answer 25

Waves leave ripple marks of sand deposits on the beach known as microridges. Visible on accreting beaches

Question 26

3 types of waves

Answer 26

Swell
Breakers
Tsunami

Question 27

Wave Calculations

Answer 27

Wave period (Time it takes a wave crest to travel one wavelength = secs )
Wave speed (Distance between crests = distance per second)
Wave steepness (Wave height / wavelength)

Question 28

Speed of a wave depends on

Answer 28

Gravity, wavelength, water depth
Waves with longer wavelength move faster than waves with shorter wavelength in deep water.
Waves travel slower in shallower water regardless of wave length.
As a wave moves from deep water to shallow water the speed decrease as the orbital field interacts with the sea floor

Question 29

Ocean Currents

Answer 29

Ocean currents circle the globe, transferring heat, nutrients, and life within the water column and across ocean basins.

Question 30

How are ocean currents driven

Answer 30

Temperature
Wind
Gravity

Question 31

Wave formation processes

Answer 31

Consider:
Fetch
Wave height and type
Water depth
Wave celerity (speed at which a wave advances or propagates)

Question 32

What happens to waves as they enter shallow water?

Answer 32

Speed decreases, wavelength decreases, height increases. The orbits of water molecules flatten because of the interference of the ocean bottom
The swell becomes higher and steeper and forms a crest wave shape that then breaks

Question 33

What causes a wave to break?

Answer 33

Usually shallow-water waves begin to break when the ratio of wave height to wavelength is 1 to 7 (H/L = 1/7), when the wave’s crest peak is steep (less than 120˚), or when the wave height is three-fourths of the water depth (H = > 3/4 D).

Question 34

Bar

Answer 34

Elongated sand body created by tidal currents or by waves. Can often be seen above water level at low tide.

Question 35

Rip

Answer 35

Current that moves away from the shore bringing surplus water carried over breaker bars back into deeper water. Result of interaction between breaking waves and the nearshore bathymetry

Question 36

How does water depth affect wave height

Answer 36

As waves enter shallow water, the orbit field causes interaction with the bottom and alters the waves and they decrease speed, wavelength shortens and wave height increases causing them to break.

Question 37

How does wind speed affect waves

Answer 37

If wind speed is slow only small waves result, regardless of wind duration or fetch.

Question 38

What affects wave height

Answer 38

Wind speed (stronger = bigger waves)
Wind duration (longer = bigger waves)
Size of fetch (larger = bigger waves)
Depth of water/roughness of sea bed
Direction and speed of tide

Question 39

Shoaling

Answer 39

As waves travel from deep to shallow water, their shape alters (wave height increases, speed decreases, and length decreases as wave orbits become asymmetrical).

Question 40

Wave Celerity

Speed of propagation of the wave crest or trough

Answer 40

In deep water the wave celerity may be calculated by the equation: c = (gλ/2π) 2 = 1.25√λ, where λ is the wavelength in metres and g is the acceleration due to gravity (9.81 m/s). The speed of shallow-water waves may be calculated by the equation: c = (gd) 1/2 = 3.13√d, where d is the depth of water in metres.

Question 41

Visible signs of a rip

Answer 41

Waves not breaking

Swash reaching further up the beach

Question 42

FORMULA Wave Period

Answer 42

= wavelength/speed(velocity) OR
= 1/frequency OR
= time/no. of waves during time

unit of measure = seconds

Question 43

FORMULA Wave Speed

Answer 43

= wavelength x frequency
= wavelength / wave period

unit of measure = m/s (metres per second)

Question 44

FORMULA Wave Steepness

Answer 44

= wave height / wave length

unit of measure = no units just a fraction