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