Coasts - Waves & Tides

Question 1

What causes tides?

Answer 1

Tides = The periodic rise and fall in the level of the sea.
Caused by the gravitational pull of the sun and the moon.
The moon is nearer so has the greatest influence.
The moon pulls water towards it, creating high tide, with a compensatory bulge on the opposite side of the earth.

Question 2

Spring and neap tides

Answer 2

Twice in a lunar month, when the moon, sun and Earth are aligned, the tidal force is at its strongest. This produces the highest monthly tidal range, known as the spring tide.

When the moon and sun are at 90° to each other (also twice per lunar month) the alignments produces the lowest monthly tidal range, known as the neap tide.

Question 3

What is a wave?

Answer 3

Crest = peak of wave (highest point)
Trough = base of wave
Wave height = difference between crest and trough
Wave length = distance between consecutive crests
Amplitude = ½ wave height
‘Set’ = A group of waves (usually 7) before spell (break or gap).
Swell = Waves that have enough energy to travel well beyond the place of their origin. Itmarches in broader lines and with bigger gaps between each crest.

Question 4

How are waves formed?

Answer 4

Wind blows over surface of water & creates friction.

Frictional drag causes water particles to begin to rotate and energy is transferred forward in the form of a wave.

As a wave reaches shallow water, friction ↑ b/w the sea bed and base of the wave, causes the wave to slow down.

Top of wave = unaffected by the friction  becomes steeper  breaks.

When it breaks, water moving up the beach is the swash and the water moving back down the beach in backwash.

Question 5

How do waves break?

Answer 5

A wave slows down in shallow water due to more friction with seafloor (bottom).

The energy of the wave is altered as the waves breaks because the energy is transferred from the wave to water  moving mass of water.

Steep shorelines impact the type of wave break due to it dumping violent waves that form very quickly causing erosion.

Gentle shorelines impact the type of wave break due to spilling waves which form gradually causing deposition.

Question 6

Swash and backwash

Answer 6

Swash = water as it slides up the beach.

Backwash = water as it slides back down the beach to the ocean.

Rip = A current flowing back out to sea in a channel created by backwash. (A focused/intense stream of backwash).

Question 7

constructive waves

Answer 7

With a constructive wave, the swash is stronger than the backwash.
Low energy
Deposits sand onshore (deposition)
Low height (<1m)
Low frequency (<10/min)
Typically in summer

Question 8

destructive waves

Answer 8

With a destructive wave, the backwash is stronger than the swash.
High energy
Deposits sand offshore (erosion)
High height (>1m)
High frequency (>10/min)
Typically in winter

Question 9

What determines wave strength?

Answer 9

Strength and speed of wind = Faster the wind, the more energy transferred = the bigger waves produced.

Duration of the wind = Length of time for which the wind has blown  longer the wind blows for = the more energy is transferred to the wave.

Fetch = The distance over which the wind has blown (i.e. how far the wave has travelled), the longer the fetch = the stronger the wave.

Seasonal weather (wind) explains why we get bigger or rougher seas during winter or cold wet days etc.