Waves, tides, and currents revised

1. Waves, Tides, and CurrentsWaves, Tides, and Currents
Chapter 16.2Chapter 16.2
MOTIONMOTION IN THE IN THE
OCEANOCEAN

2. WavesWaves
A disturbance which A disturbance which
moves through or moves through or
over the surface of a over the surface of a
fluidfluid
Mostly caused by Mostly caused by
windswinds
(Also earthquakes, (Also earthquakes,
volcanoes, grav. volcanoes, grav.
pull)pull)
Form of great energyForm of great energy

3. Wave CharacteristicsWave Characteristics
Parts of a WaveParts of a Wave

CrestCrest = high point = high point

TroughTrough = low point = low point

HeightHeight = vertical = vertical
distance from crest to distance from crest to
troughtrough

WavelengthWavelength = =
Horizontal distance Horizontal distance
between crest to crest between crest to crest
or trough to troughor trough to trough

4. Wave period : time for 2 crests to pass fixed point (T) sec
Wave speed (C) : C = wavelength / T (m/s)
Wave steepness : H / wavelength
When H / wavelength = 1/7 or angle at crest 120 or less =
Breaker

5. Size of Wind Generated Size of Wind Generated
WavesWaves

Depends on 3 thingsDepends on 3 things::

Wind SpeedWind Speed

Wind Duration (length of Wind Duration (length of
time wind blows)time wind blows)

““Fetch” Extent of open Fetch” Extent of open
water across which the water across which the
wind can blowwind can blow

6. Water Motion in WavesWater Motion in Waves
Water travels in vertical Water travels in vertical
circular orbitscircular orbits
Wave moves, particles don’t!Wave moves, particles don’t!

7. Importance of WavesImportance of Waves
Shaping Shaping
CoastlinesCoastlines

Erode cliffsErode cliffs

Grind rock into sandGrind rock into sand
EcologyEcology
Returns OReturns O
2 2
to waterto water

Stir up food for filter Stir up food for filter
feedersfeeders

8. Types of WavesTypes of Waves
CHOP – Short period (back bays)
SWELL – Long period (boat rolls; seasickness)
SWASH – water up beach BACKWASH – back down

9. Caused by undersea quake or volcano
• Wavelength = ~150 mi. Wave height = 6” – 1’
Can NOT perceive in boat Speed > 500 mph
Slows down to ~25 mph at shore; water builds up to ~65+ ft
TSUNAMI “TIDAL WAVE”

10. Tsunami Waves

11. Creation of a TsunamiCreation of a Tsunami

12. TidesTides
The rhythmic rise and The rhythmic rise and
fall of the ocean’s waterfall of the ocean’s water
High tide = rising, incoming
tide, flow
Low tide = receding, outgoing
tide, ebb
Slack tide = vertical movement
stops

13. Tides are very long, Tides are very long,
slow wavesslow waves

They have a wave They have a wave
period of 12 hours 25 period of 12 hours 25
minmin

Tidal day is 24 hours Tidal day is 24 hours
50 min50 min

NJ has 2 high and 2 NJ has 2 high and 2
low tides dailylow tides daily

14. 1. Gravitational pull of 1. Gravitational pull of
sun & moon on Earthsun & moon on Earth
What Causes Tides?What Causes Tides?
• Moon closer, therefore
> effect
• Like magnet, pulls water
away from surface
= TIDAL BULGE

15. 2. Centrifugal Forces
• Produced by motions of
Earth, sun, & moon
• Bulge on opposite side
because centr. force >
pull of moon

16. Types of TidesTypes of Tides

2x’s/month2x’s/month
•Spring Tide
- Moon and sun are in direct
line with one another
- Results in unusually
high tidal range

-Tidal Range = vertical
distance between high &
low tides

17. Neap TideNeap Tide

sun and moon are at sun and moon are at
right angles right angles

Pulls cancel each Pulls cancel each
other out – causes a other out – causes a
weak pullweak pull

unusually low tidal unusually low tidal
rangerange

2 x’s / month2 x’s / month

18. Spring vs. Neap TidesSpring vs. Neap Tides

19. Distance bet. Moon & EarthDistance bet. Moon & Earth
Perigee TidesPerigee Tides
•Moon closest to earth, very high tides (causes Moon closest to earth, very high tides (causes
flooding)flooding)
Apogee TidesApogee Tides
•Moon farthest away from earth, very low tidesMoon farthest away from earth, very low tides

21. Types of Tides ContinuedTypes of Tides Continued
Diurnal TidesDiurnal Tides

1 high & 1 low / day1 high & 1 low / day

Parts of Gulf of Mexico and AsiaParts of Gulf of Mexico and Asia
Semi-Diurnal TidesSemi-Diurnal Tides

2 high & 2 low / day2 high & 2 low / day

Atlantic coasts of North America and EuropeAtlantic coasts of North America and Europe
MixedMixed

2 high & 2 low / day (height varies)2 high & 2 low / day (height varies)

Pacific coastPacific coast

22. Importance of TidesImportance of Tides
• Expose & submerge orgs
• Circulate water in bays &
estuaries
• Trigger spawning (grunion,
horseshoe crab)
• Circulates food, wastes, etc

23. CurrentsCurrents
• What are currents?
- “Rivers” of circulating water
• Causes
- Wind
- Rotating Earth
- Density Changes

25. Surface Ocean CurrentsSurface Ocean Currents
• Broad, slow drifts; never
cross equator
• Wind generated; circular
gyres

26. • Coriolis Effect
- N. Hemis – clockwise; Right
- S. Hemis – counterclockwise; Left

27. • Gulf Stream
- Brings warm water
from equator north along
east coast of N. A.
- N. Atlantic
-Sometimes form eddies –
circulating water that pinches
off from the current

28. MIGRATION
NAVIGATION
WEATHER

29. Localized Surface CurrentsLocalized Surface Currents
Longshore CurrentLongshore Current..

Flows parallel to shore; move sedimentFlows parallel to shore; move sediment

30. RIP CURRENT
- Caused by converging longshore currents
- Very dangerous ; Red Flag
- DO NOT fight rip current; swim parallel to shore to
get out of channel

32. Deep Ocean CurrentsDeep Ocean Currents
Separated from surface Separated from surface
currents by boundary currents by boundary
called a “called a “ThermohalineThermohaline” ”
(diff in densities)(diff in densities)
Flow beneath surface; cross Flow beneath surface; cross
equatorequator
Move North to SouthMove North to South

33. Importance Of Deep Importance Of Deep
CurrentsCurrents
UpwellingUpwelling
•Brings deep water to surf.Brings deep water to surf.
•Circulates nutrients upCirculates nutrients up
•Moves plankton & larvaeMoves plankton & larvae