Waves

What makes waves?• Ship wakes• Animal movements• Tsunami• Most commonly: Wind

Wave Diagram (yes, you need to draw this)

Wave vocabulary• Crest: Highest point of a wave• Trough: Lowest point of a wave• Wavelength: horizontal distance between either

two crests or two troughs• Wave height: vertical distance between one crest

and the next trough (or vice versa)

Wave Vocabulary cont.

• Wave period: the time it takes two crests (or two troughs) to pass a particular point

• Wave frequency: how often a number of waves pass a given point in a particular amount of time

What determines the size of a wave?

• The strength of the wind• The duration the wind has been blowing• The distance over which the wind travels (Fetch)

Deep Water Waves

• Do not “Feel” bottom• Individual water molecules travel in an orbital

motion• These waves are in water greater than ½ their

wavelength

Shallow Water Waves

• Feel bottom• Move toward land• These waves are in water shallower than

1/20th their wavelength• As they reach the shore, friction slows them

down, but they do become bigger

Deep Water vs. Shallow Water Waves

Deep Water Waves vs. Shallow Water Waves

The Wave Breaks

Three Types of Shallow Water Waves

• Surging breakers are considered destructive to beaches

• Plunging breakers frequently form tunnels (surfers love these)

• Spilling breakers are gentle and break far from shore

Summer Beach vs. Winter Beach

• Summer waves more gentle, constructive

• Winter waves more harsh, destructive

Longshore Currents and Drift• Caused by waves hitting the beach at an angle• Carries sand along the shoreline• http://www.youtube.com/watch?v=U9EhVa4MmEs

How humans deal with Longshore DriftGroins or jetties are

sometimes used to prevent the loss of sand to beach homes.

Can you see a problem for the houses immediately on the down current side of the groin?

Rip Currents –a potentially dangerous

result of Longshore Currents racing back out to sea

http://www.onr.navy.mil/focus/ocean/motion/currents2.htm

Tsunami• Shallow water waves that grow tall as they approach

the shore• Caused by seismic activity: earthquakes, landslides,

volcanoes• Largest one recorded was in Lituya Bay, AK (1,720’)

Rogue Waves• Also known as “Freak” Waves• When two wave crests combine, their height and

power is extremely huge• Most famous rogue wave occurred to the USS

Ramapo (112’)

Storm Surge• Rise in the ocean that is caused by strong winds

associated with a storm• Above and beyond the normal high tide water line• Typically causes flooding in coastal areas