Ocean WavesOcean Waves

CapillaryCapillary

GravityGravityWind Wind

generatedgenerated

TidesTides

TsunamisTsunamisSeichesSeiches

Tides

New Moon

Full Moon

First Quarter

Third Quarter

Lunar Phases

http://www.oceanservice.noaa.gov/education/kits/tides/media/supp_tide06a.html

Moon’s faster orbits about the Earth, compared to Earth’s orbit about the Sun, means that “Spring” and “Neap” tides aredefined by theLunar orbit.

New Moon

Full Moon

Spring Tides occur when the lunar and solar gravitational pulls add up

First Quarter

Third Quarter

Neap Tides occur when lunar and solar gravitational pulls are mutually perpendicular

Tides can beTides can be

SPRING and NEAP, SPRING and NEAP, depending on the relative depending on the relative positions of Sun and Moonpositions of Sun and Moon

DIURNAL, SEMIDIURNAL or DIURNAL, SEMIDIURNAL or MIXED, depending on their MIXED, depending on their daily cyclesdaily cycles

-1

0

1

0 360

Wave interference can be Wave interference can be constructive or destructiveconstructive or destructive

Constructive Constructive interferenceinterference

Constructive Constructive interferenceinterference

Constructive Constructive interferenceinterference

Destructive Destructive interferenceinterference

Destructive Destructive interferenceinterference-1

0

1

-1

-0.5

0

0.5

1

0 90 180 270 360

AABB

CC

Tides can be

1. Diurnal: or once daily

2. Semidiurnal or twice daily

and

3. Mixed

Semidiurnal tides are more common than diurnal and mixed tides

http://en.wikipedia.org/wiki/Amphidromic_point

An amphidromic point is a point within a tidal system where the tidal range is almost zero, i.e., there is almost no vertical move-ment. Such points occur because of the coriolis effect and interference within oceanic basins and bays creating a wave pattern which rotates around the amphidromic point. These points are located at Tahiti, off the coast of Newfoundland, near the South Shetlands, midway between Rio de Janeiro and Angola, at three points in the North Sea and at several other locations in the Pacific, Atlantic and Indian oceans. The island of Madagascar is an amphidromic point, as is New Zealand.

Tsunamis

The travel-path of the tsunami of April 1, 1946

Active ocean-

continent margins

should expect

tsunamis more

frequently than the passive

ones

The map below shows the position of the leading wave of a tsunami generated by a 1979 earthquake offshore Colombia, South America*. These contours are for the tsunami arrival times in hours.

*K. Ida & T. Iwasaki (Ed.): Tsunamis: Their Science and Engineering (D. Reidel, Boston MA, 1983)

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6

42

Consider an earthquake with its epicenter at Honolulu, Hawaii. The corresponding tsunami travel times (in hours) from Hawaii are given in this map of the Pacific Ocean.

No matter where an earthquake

occurs in the Pacific, Hawaii is barely 15 hours

away, at the most!

The Dec 2004 Asian Tsunami: The Dec 2004 Indian Ocean tsunami was

produced by perhaps the strongest earthquake of the past 100 years. It occurred in the Java trench,

off Bandar Aceh in north-western Sumatra. This animation was produced by the

National Oceanic and Atmospheric Administration