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Waves, Tides, and Currents

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Presentation on theme: "Waves, Tides, and Currents"— Presentation transcript:

1 Waves, Tides, and Currents
MOTION IN THE OCEAN Waves, Tides, and Currents

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 Ecology 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

10 Tsunami Waves

11 Creation of a Tsunami

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 because centr. force > pull of moon Produced by motions of Earth, sun, & 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

18 Spring vs. Neap Tides

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


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? Causes - “Rivers” of circulating water
- Wind - Rotating Earth - Density Changes


25 Surface 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 - 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


29 Localized Surface Currents
Longshore Current. Flows 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 Currents Flow beneath surface; cross equator
Separated from surface currents by boundary called a “Thermohaline” (diff in densities) Move North to South

33 Importance Of Deep Currents
Upwelling Brings deep water to surf. Circulates nutrients up Moves plankton & larvae

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