Chapter 10Waves and Tides

Anatomy of a WaveWhat is a wave?-Transmission of energy through matter; matter moves back and forth or rotates, but then returns to its original positionThree types of progressive waves:1) Longitudinal: when matter moves back and forth

in same direction energy travels2) Transverse: motion of matter is perpendicular to

the direction in which the whole wave is moving3) Orbital: transmit through fluids only; main waves

that concern us with respect to the ocean; energy moves fluid in a circular motion

Wave TerminologyWavelength: measured as horizontal

distance between identical points on two waves; crest to crest

Crest: highest point above the avg water level

Trough: lowest pointHeight: vertical distance from the trough to

the crestPeriod: time it takes for the same spot on

two waves to pass a single pointFrequency: number of waves that pass a

fixed point in one second

Forces that Cause WavesDisturbing forces

(cause waves):1. Winds (most

common)2. Changes in gravity3. Seismic activity:

eartquakes and volcanic eruptions (tsunamis)

Restoring forces (resist waves):

1. Gravity (main force here for large waves)

2. Coriolis Effect: good for resisting tides

3. Surface tension: resists surface distrubances in tiny waves

Deep Water Waves vs. Shallow Water WavesDeepwater Waves:- Occur in water that

is deeper than half their wavelength

- No interaction with the bottom floor can change any wave characteristics

- The orbital motion progression is also unaffected

Shallow-water Waves:

- Occur in water that is shallower than one-fourth the wavelength

- Bottom creates a drag that affects the orbital motion

- Flattens the circular motionBoth can exist at the same

time!

What causes internal waves?Occur within different density layersCan be more than 30 m tall, but move very

slowlyScientists don’t really know what causes

these waves; likely that they get their energy from wind, gravity, or seismic forces (like surface waves)

Breaking WavesWhat makes a wave break?-waves break when the height exceeds the wavelength by a certain ratio; the wave breaks as white capsWhat are the three basic types of wave breaks?1) Plunging breakers: curl as the top of the wave

pitches through the air before splashing into the bottom; occur on steep beaches

2) Spilling breakers: occur on gentle slope beaches; top of the wave tumbles and slides down the front of the wave

3) Surging breakers: occur on very steep beaches; little to no bottom contact, waves don’t slow down, but surge forcefully unbroken; can be very destructive

Refraction, diffraction, deflectionRefraction: bending of light rays; bend the

ocean waves as well when waves begin to approach the ocean shore at an angle

Diffraction: occurs when waves pass an obstacle, like a jetty; energy shift within a wave, allowing a new wave pattern to form

Reflection: occurs when waves hit an abrupt obstacle that is nearly perpendicular in the water, like a sea wall; in this case, the wave retains much of its energy and bounces back towards open waters

What is a standing wave?Vertical oscillation in which water rocks

back and forth, rising and falling at the ends, but relatively motionless near the center

Like coffee sloshing back and forth after you bump the cup

Destructive Waves: storm surges, seiches, tsunamisWhat causes a storm surge?- This is a destructive wave that forms when high

winds push water against the shore, where it piles up

What causes seiches?- This is a form of standing wave that can be

destructive; result from a strong wind that pushes the water level up on one side of a lake or basin

What causes tsunamis? -results from sudden water displacement caused by a landslide, an iceberg falling into sea from a glacier, a volcanic eruption, or an earthquake (most common)

Tides

What causes the tides?Tides: variations in the ocean’s levelResult from the gravitational pull of the

moon and (to a lesser degree) the sunThey pull the ocean into a huge wave with a

wave length the size of an ocean basinSun and moon create two bulges on

opposite sides of the Earth; position of the sun and moon change slowly, causing the bulge to rotate around the Earth

As a coastline rotates into the bulge, the tide rises; as it rotates out, the tide falls

What influences besides lunar and solar gravity affect the tides?The imperfect sphere of the EarthThe seasonTime of the monthThe shape of the ocean basinCoriolis effect

**All influence the tides!**

Types of tides: vary with locationDiurnal: single high and low tide that occurs

daily in certain locations; Gulf of MexicoSemidiurnal: have two roughly equal high

and low tides daily; happens on east coast of US

Mixed: consists of two unequal high and low tides daily; happens in Pacific coast of the US

What are tidal currents and a tidal bore?Tidal Currents: the daily tides create a current that flows into and out of bays, rivers, harbors, and other restricted places-Inflow= flood current-Outflow= slack current

Tidal Bore: when the incoming tide produces a wave that flows into a river, bay, or other relatively narrow area; also known as a true tidal wave that can be several meters high

Sun, Moon, and Types of TidesThe influence of the moon on the tides is

about twice the influence of the sun1) Spring Tides: when the sun and the moon

are aligned on the same side of Earth (new moon) AND when the sun and moon are aligned on opposite sides of Earth (full moon)

2) Neap Tides: when the sun’s gravitation pulls to the side of the moon’s tidal bulge and tends to raise low tides and lower the high tide