Page 79 - (DK) Ocean - The Definitive Visual Guide

77

PLUNGING BREAKER
“Barrel” or “tube-forming” breakers like
this occur when the waves reaching shore
have large amounts of energy. The seabed
must be firm and quite steep.

water motion occurs wave shortens in length wave finally
direction of offshore to depth of and decreases in speed breaks
wave motion half the wavelength but increases in height

water carried
wave reaches critical up shore in
ratio of height to length swash zone
and begins to break

water motion Arrival on Shore
caused by the
wave begins
to interact As waves approach a shore, the motion they generate at depth begins
with the sea to interact with the sea floor. This slows the waves down and causes
bed and
slow down the crests in a series of waves to bunch up—an effect called shoaling.
The period of the waves does not change, but they gain height as the
SHOALING AND BREAKING energy each contains is compressed into a shorter horizontal distance,
Shoaling occurs as waves enter and eventually break.
shallow water. The wave length and
speed both decrease, but the wave There are two main types of breaker. Spilling breakers occur on flatter
gains height. When the crest gets shores: their crests break and cascade down the front as they draw near
too steep, it curls and breaks. the shore, dissipating energy gradually. In a plunging breaker, which
occurs on steeper shores,
the crest curls and falls over
HUMAN IMPACT
the front of the advancing
RIDING THE WAVES wave, and the whole wave
then collapses at once.
When a swell reaches a suitably Waves can also refract as
shaped beach, it can produce
excellent surfing conditions. they reach a coastline. This
Small spilling breakers are ideal concentrates wave energy
for novice surfers, while experts onto headlands (see p.93)
seek out large plunging breakers and shapes some types of
that form a “tube” they can beach (see p.106).
ride along. For tube-riding, the
break of the wave must progress
smoothly either to the right or INTRODUCTION
left. Here, a surfer rides a right- WAVE REFRACTION
When waves enter a bay enclosed
breaking wave in Hawaii— by headlands, they are refracted
it is breaking from left to right (bent) as different parts of the
behind the surfer. wave-front encounter shallow
water and slow down.