Oceanography
Last Modified 2002-October-23
Beaches
Steep beach
Monastery Beach (just south of Carmel, California)
The energy is used in one huge plunging breaker right on
shore
(this is very powerful and deceptive surf).
The sand granularity is course (like rock salt from a water
softener).
Illustration:
Steep Beach
Shallow beach
Del Monte Beach (just north of Monterey, California)
The energy is spread over two or three sets of breakers over
a wide area.
The sand granularity is fine (a little finer than table
sugar).
Illustration:
Shallow Beach
Rocky beach
The outside north wall at Salt Point State Park or
Stewart's Point (just south of Carmel, Ca.)
Illustration:
Rocky Beach
Be very careful of the slippery rocks.
Breakers
Swells slow down when they "feel" the bottom, causing
them to build in height until the topple becoming breakers.
If you look at the surf line and see an 8 foot
[2.4m] breaker, the water is about 6 feet
[1.9m] deep where the breaker is breaking.
(approximate ratio = 1.3 breaker height to depth)
Spilling breaker
Illustration:
Spilling Breaker
Slow breaker, feels the bottom early (shallow angle
beach). Breaks over a long distance, dispelling energy as it
goes along. The water from the crest does not have enough
speed and spills down the face. (creating white water on the
face.)
Plunging breaker
Illustration:
Plunging Breaker
Fast breaker, feels the bottom late (steep beach or step
up to a reef). Builds and breaks in a very short distance,
dispelling all it energy in one place. The water from the
crest has enough speed and shoots out over the face of wave
plunging into the bottom of the trough forming a tube.
Offshore breaker
Illustration:
Offshore Breaker
Waves
Energy travelling through the water. (The water itself
doesn't move much, see Surge)
Illustration:
Wave Nominclature
Swells
Long rolling waves; generated a long way away. (more than
200 miles [322km]) Caused by wind blowing steadily
in one direction over a long distance (fetch). Most of our
swells come from the Gulf of Alaska and Northwest Pacific.
(A long fetch = Big Swells; A strong wind = Swell that are
close together)
Illustration:
Swells vs Surge
Surge
The back and forth motion of the water caused by swells.
The affects of surge gets smaller and smaller the deeper you
go. A general rule: the longer the swell the deeper the
surge will be felt.
When swimming, use the surge to your advantage. (i.e., if
the surge is going the way you want to go, swim with it; if
the surge is against you, put your hand down and hold on to
the bottom. [this uses very little energy])
Wind Chop (Seas)
Short choppy waves; generated locally (within 200 miles
[322km]). Seas are chop on top of the swells and
usually come up in the afternoon (when the wind blows on
shore).
Currents
Longshore Current
The surf pushes water (and sand, etc.) in the direction
it's going causing a longshore current.
Illustration:
Longshore Current
Tidal Current
Caused by the relative difference of water levels between
two bodies of water separated by a narrow channel. (For
example, the Ocean and the Bay below.) When diving in
locations with strong tidal currents (the Puget Sound), plan
your dives around the slack tides.
Illustration:
Tidal Current
Rip Current
Caused by water flowing out a low spot on the beach.
- Surf knocked down where the rip goes through.
- Use the rip as an easy route thru the surf line.
- If you're caught in a rip, swim perpendicular (90
degrees) to the rip.
- Don't try to swim agains the rip, the ocean doesn't
get tired.
Illustration:
Rip Current
The California Current
This is the major oceanic current that flows from about
the US/Canada border down the the west coast of North
America to the tip of Baja California.
Tides
The biggest influences on the tides are the moon and the
sun.
- 27 days, 7 hrs, 43 min, and 11.47 sec for one lunar
orbit around the earth.
- 29 days, 12 hrs, 44 min, and 2.78 sec for the moon to
go from full moon to full moon (a lunar month), the
difference is because of the earth orbiting the sun.
- Approximately 24 hrs, 50min per tide cycle.
Spring tide
The sun and moon pull together. (Full Moon/New
Moon)
Neap tide
The sun and moon pull at 90° to the earth.
(Waxing Quarter/Waning Quarter)
Illustration:
Tides
Ripples in the Sand
Ripples from a current
These ripples are generally small, usually less than a
hand's width in height and about two hand widths in
length.
Illustration:
Ripples from a current
Ripples from the surge
These ripples are symetrical, run parallel to the beach,
and can get quite large depending on the strength of the
surge. (Monastry Beach has 12 to 15 inch [30 to
35cm] high ripples, spaced about three feet [1m]
crest to crest.)
Illustration:
Ripples from the surge
© 1997, 2002 Chris Simmons. All rights reserved.
Last Modified 2002-October-23
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