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Waves and Tides MOTION IN THE OCEAN
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MOTION IN THE OCEAN

Jan 03, 2016

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MOTION IN THE OCEAN. Waves and Tides. 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. Wave Characteristics. Parts of a Wave Crest = high point Trough = low point - PowerPoint PPT Presentation
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Page 1: MOTION IN THE OCEAN

Waves and Tides

MOTION IN THE OCEAN

Page 2: MOTION IN THE OCEAN

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

Page 3: MOTION IN THE OCEAN

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

Page 4: MOTION IN THE OCEAN

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

Page 5: MOTION IN THE OCEAN

Water Motion in Waves

Water travels in vertical circular orbits

Wave moves, particles don’t!

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Importance of Waves

Shaping Coastlines

Erode cliffs Grind rock into sand

Ecology Returns O

2 to water

Stir up food for filter feeders

Page 7: MOTION IN THE OCEAN

Types of WavesCHOP – Short period (back bays)

SWELL – Long period (boat rolls; seasickness)

SWASH – water up beach BACKWASH – back down

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Page 10: MOTION IN THE OCEAN

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 = “harbor wave” in Japanese

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Tsunami Waves

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Indian Ocean Tsunami 2004

http://www.montereyinstitute.org/noaa/lesson09/l9ex1.htm

Indian Ocean 2004

http://www.montereyinstitute.org/noaa/lesson09.html

Global Impact

December 26, 2004 9+ magnitude

earthquake Indian plate slid under

Burma Plate, off coast of Sumatra

250.000 dead 15,000 missing 2 million displaced

Page 13: MOTION IN THE OCEAN

Tsunamis

Page 14: MOTION IN THE OCEAN

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

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Tides are very long, slow waves

They have a wave period of 12 hours 25 min

Tidal day is 24 hours 50 min

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1. Gravitational pull of sun & moon on Earth

What Causes Tides?

• Although Sun is HUGE, Moon closer, therefore > effect

• Like magnet, pulls water away from surface = TIDAL BULGE

Page 17: MOTION IN THE OCEAN

2. Centrifugal Forces

• Produced by motions of Earth, sun, & moon

• Bulge on opposite side because centr.

force > pull of moon

Page 18: MOTION IN THE OCEAN

Types of Tides

2x’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

Page 19: MOTION IN THE OCEAN

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

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Spring vs. Neap Tides

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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

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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

Why different types of tides?

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Types of Tides

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Importance of Tides• Expose & submerge orgs

• Circulate water in bays & estuaries

• Trigger spawning (grunion, horseshoe crab)

• Circulates food, wastes, etc

Page 26: MOTION IN THE OCEAN

Currents• What are currents?

- “Rivers” of circulating water

• Causes- Wind

- Rotating Earth

- Density Changes

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Page 28: MOTION IN THE OCEAN

Surface Ocean Currents

• Broad, slow drifts; never cross equator

• Wind generated; circular gyres

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• Coriolis Effect

- N. Hemis – clockwise; Right

- S. Hemis – counterclockwise; Left

Page 30: MOTION IN THE OCEAN

• 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

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MIGRATION NAVIGATION

WEATHER

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Localized Surface Currents

Longshore Current.

Flows parallel to shore; move sediment

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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

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Deep Ocean Currents

Separated from surface currents by boundary called a “Thermohaline” (diff in densities)

Flow beneath surface; cross equator

Move North to South

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Importance Of Deep Currents Upwelling

• Brings deep water to surf.• Circulates nutrients up• Moves plankton & larvae