Works Of The Sea And Development Of The Related Landforms For Presentation
Motion in the Ocean: Waves, Tides and Currents
1. MOTION IN THE
OCEAN
Waves, Tides, and Currents
Chapter 16.2
2. Waves
A disturbance which
moves through or
over the surface of a
fluid
Mostly caused by
winds
(Also earthquakes,
volcanoes, grav.
pull)
Form of great energy
3. Wave Characteristics
Parts of a Wave
Crest = high point
Trough = low point
Height = vertical
distance from crest to
trough
Wavelength =
Horizontal distance
between crest to crest
or 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
Waves
Depends on 3 things:
Wind Speed
Wind Duration (length of
time wind blows)
“Fetch” Extent of open
water across which the
wind can blow
6. Water Motion in Waves
Water travels in vertical
circular orbits
Wave moves, particles don’t!
7. Importance of Waves
Shaping
Coastlines
Erode cliffs
Grind rock into sand
Ecology
Returns O2 to water
Stir up food for filter
feeders
8. Types of Waves
CHOP – Short period (back bays)
SWELL – Long period (boat rolls; seasickness)
SWASH – water up beach BACKWASH – back down
9. TSUNAMI “TIDAL WAVE”
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
12. Tides
The rhythmic rise and
fall 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,
slow waves
They have a wave
period of 12 hours 25
min
Tidal day is 24 hours
50 min
NJ has 2 high and 2
low tides daily
14. What Causes Tides?
1. Gravitational pull of
sun & moon on Earth
• Moon closer, therefore
> effect
• Like magnet, pulls water
away from surface
= TIDAL BULGE
15. 2. Centrifugal Forces
• Bulge on opposite side
• Produced by motions of
because centr. force >
Earth, sun, & moon
pull of moon
16. Types of Tides
•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
2x’s/month
17. Neap Tide
sun and moon are at
right angles
Pulls cancel each
other out – causes a
weak pull
unusually low tidal
range
2 x’s / month
19. Distance bet. Moon & Earth
Perigee Tides
• Moon closest to earth, very high tides (causes
flooding)
Apogee Tides
• Moon farthest away from earth, very low tides
20.
21. Types of Tides Continued
Diurnal Tides
1 high & 1 low / day
Parts of Gulf of Mexico and Asia
Semi-Diurnal Tides
2 high & 2 low / day
Atlantic coasts of North America and Europe
Mixed
2 high & 2 low / day (height varies)
Pacific coast
22. Importance of Tides
• Expose & submerge orgs
• Circulate water in bays &
estuaries
• Circulates food, wastes, etc
• Trigger spawning (grunion,
horseshoe crab)
23. Currents
• What are currents?
- “Rivers” of circulating water
• Causes
- Wind
- Rotating Earth
- Density Changes
26. • Coriolis Effect
- N. Hemis – clockwise; Right
- S. Hemis – counterclockwise; Left
27. • Gulf Stream
- N. Atlantic
- Brings warm water
from equator north along
east coast of N. A.
-Sometimes form eddies –
circulating water that pinches
off from the current
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
31.
32. Deep Ocean Currents
Flow beneath surface; cross
equator
Move North to South
Separated from surface
currents by boundary
called a “Thermohaline”
(diff in densities)
33. Importance Of Deep
Upwelling Currents
• Brings deep water to surf.
• Circulates nutrients up
• Moves plankton & larvae