Waves and Tsunami - University of Hawaii at Hilo

advertisement

Waves and Tsunami

Waves are generally generated from winds in the open ocean.

Size of the wave depends on the:

Wind speed

Duration of the wind

Area over which the wind blows (called the “fetch”)

Wave Anatomy

Wavelength

Amplitude

Height

Period

Steepness

Wave speed depends on the wavelength, longer waves travel faster

Consequently, they tend to sort themselves out into trains of similar wavelength waves: SWELL

Water molecules move in a circular pattern in the wave in smaller and smaller concentric circles with depth.

DEEP water waves have water motion down to about ½ the wavelength

SHALLOW water waves are those in which the wavelength is 1/20 the depth.

Steepness = height/length. Waves get steeper as they “feel” the bottom of the ocean, top continues to move forward, base is caught up in the frictional resistance of the bottom, and eventually they “break”

Spilling breakers (flatest bottom)

Surging breakers (steepest bottom)

Plunging breakers

Waves distribute their energy as they interact with the surroundings:

REFLECTION

REFRACTION

DIFFRACTION

Tsunami: seismic sea wave formed from underwater earthquake moving the seafloor and disrupting the water above

Very long wavelength (100s km) and small height in the open ocean

Travel fast (about 500 mi per hour)

Pacific Ocean is the most common place for them to originate

Huge sediment influx onto the land

Huge energy knocking things over

Hawaii: Local and “foreign” tsunami

1946, 1960 foreign, 1975 Kalapana local EQ.

Download