MOTION IN THE OCEAN
Post on 03-Jan-2016
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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
Height = vertical distance from crest to trough
Wavelength = Horizontal distance between crest to crest or trough to trough
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
Importance of Waves
Shaping Coastlines
Erode cliffs Grind rock into sand
Ecology Returns O
2 to water
Stir up food for filter feeders
Types of WavesCHOP – Short period (back bays)
SWELL – Long period (boat rolls; seasickness)
SWASH – water up beach BACKWASH – back down
Links/Videos
Wave activity http://www.montere
yinstitute.org/noaa/lesson09/l9la1.html
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
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
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
Tides are very long, slow waves
They have a wave period of 12 hours 25 min
Tidal day is 24 hours 50 min
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
2. Centrifugal Forces
• Produced by motions of Earth, sun, & moon
• Bulge on opposite side because centr.
force > pull of moon
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
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
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
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?
Importance of Tides• Expose & submerge orgs
• Circulate water in bays & estuaries
• Trigger spawning (grunion, horseshoe crab)
• Circulates food, wastes, etc
Currents• What are currents?
- “Rivers” of circulating water
• Causes- Wind
- Rotating Earth
- Density Changes
• 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
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
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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