Waves & Tides

Question 1

waves form by ____ with air

Answer 1

friction

(energy from wind is transferred to waves)

Question 2

What are the 4 principles of waves?

Answer 2

1. only energy moves (there’s very little net movement of water horizontally or vertically)
2. water particles move in circular orbits
3. orbit diameter decreases with distance from the seafloor
4. waves reflect from objects with no energy loss

Question 3

the size of a wave’s circular orbit depends on ___ ___ and they become ___ against shores

Answer 3

wind speed

compressed

Question 4

t/f
due to waves, the whole water column moves horizontally

Answer 4

false!
it moves in circular orbits

Question 5

What is the crest of a wave? A trough?

Answer 5

crest= the highest point of a wave

trough= the lowest point of the wave surface

Question 6

wave length (L) measures from ___ to ___ and it varies depending on amount of ____

Answer 6

crest to crest

energy

Question 7

What is the height/amplitude (H) of a wave? What’s the period (t, sec) of a wave?

Answer 7

H= measure from trough to crest

t= time of passage of successive crests

Question 8

What’s the depth of a wave?
How is the velocity of a wave measured?

Answer 8

D= half the length of a wave (L/2)

V= L/t for waves in deep water

Question 9

Water motion is negligible when:

a) D < L/2
b) D > L/2
c) D = L/2

Answer 9

b) D > L/2

Question 10

In deep water: waves action ____ the deeper you go

In shallow water: wave action doesn’t ____, the energy ___ off the bottom (orbits become ____)

Answer 10

diminishes

diminish
reflects
compressed

Question 11

In shallow water, when does a wave become unstable and breaks?

Answer 11

When the ratio of height to length (H/L) is greater than 1/7
ie when the wave gets too high it breaks

Question 12

when the water depth is less than half the length (D < L/2), the waves become ___ and particles are ____

Answer 12

elliptical

displaced

Question 13

wind generates friction over the water, which first causes ____ then ____ then ____

Answer 13

ripples –> swells –> waves

Question 14

final wave height is determined by 3 things:
1
2
3

Answer 14

1. average velocity of the wind
2. length of time the wind blows
3. fetch: the distance over which the wind blows (high velocity= high fetch)

Question 15

What are the 2 types of wind waves? How do they differ?

Answer 15

1. local seas: have short periods (less than 8 secs) and are irregular
   - wind driven
2. swell: long period (10-15sec) and are regular
   - driven by distant weather conditions (energy transferred into the water and travels very far)

Question 16

why don’t marginal seas experience swells?

Answer 16

swells are driven by distant weather conditions, so marginal seas don’t get them because they’re protected

Question 17

What are 3 types of waves that are not wind waves?

Answer 17

rogue waves

tsunamis

internal waves

Question 18

rogue waves=

Answer 18

summation of several wave trains (come from interaction of storms with currents)

unusually huge waves that come without warning

*not a wind wave

Question 19

tsunamis=

Answer 19

caused by undersea earthquakes that can move up to 800km/h

they have long wavelengths (huge orbits) and lose very little energy

*not a wind wave

Question 20

Internal waves are driven by ___, not ___

where do they occur?

Answer 20

density

wind

they occur where low density water lies over higher density water

Question 21

In shallow waters, internal waves are influenced by ____. How?

Answer 21

tides

in an esturary where fresh water is coming out and the saltier water coming in with the tide = there’s a wedge

Question 22

What are the 3 types of tides? Explain each

Answer 22

1. diurnal: once a day (1 high per day & 1 low per day)
2. semi-diurnal: twice a day
3. mixed semi-diurnal: different highs and lows during the day (twice)

Question 23

what causes the tides?

Answer 23

the gravitational pull of the sun and the moon

Question 24

What does the type/ number of tides depend on?

Answer 24

location!

eg
- geography
- ocean vs marginal sea
- ice cover

Question 25

The gravitational pull of the moon is ___ times stronger than the sun. Why?

Answer 25

6x!

because it’s closer

Question 26

The moon’s rotation around the earth gives a monthly cycle of ___ and ___ tides. What are each?

Answer 26

spring and neap

Spring tides= greatest vertical tidal range (highest high and lowest low)
Neap tides= smallest vertical tidal range

Question 27

Earth’s rotation gives a(n) ___ cycle of tides

Earth’s orbit around the sun gives a(n) ____ cycle of tides

Answer 27

daily

annual

Question 28

Spring tides are highest with a ___ moon, and spring tides occur when the moon ___ (is/ isn’t) in line with the sun

Answer 28

new

spring tide= moon IS in line with the sun (& earth)

Question 29

Neap tides occur when the moon __ (is/ isn’t) in line with the sun & earth

Answer 29

is not

Question 30

How often do daily tide cycles occur and what causes them?

Answer 30

one cycle a day (12h 25min & 24hr 50min)

gravitational pull of the moon and the rotation of earth about the axis (1x per day)
- motion of the moon in the same direction as the earth’s rotation

Question 31

Biweekly tide cycles (every 14 days) are caused by:

Answer 31

the rotation of the moon around the earth (~28 days)
- caused by combo of earth/ moon/ sun and their alignments

Question 32

Half-yearly tidal cycles (every 6 months) are caused by:

Answer 32

rotation of the earth around the sun (~365 days)

• Earth, moon, sun interactions (orbits) and the tilt of the earth (diff distances from the sun)

Question 33

Tide cycles in different locations are a function of ____, and basin ___/___

Answer 33

latitude

basin shape and size

Question 34

What is a tidal bore and what causes it?

Answer 34

Tidal bore= tide moving up a channel against the retreating water

caused by the narrowing of channels

Question 35

What is a Seiche and what causes it?

Answer 35

Seiche= a standing wave caused by the wave reflecting off shorelines (b/c of the channel narrowing)

Question 36

How can weather (specifically atmospheric pressure) affect tides?

Answer 36

low pressure can cause storm surges or storm tides
eg. hurricane irma