Geology Reference
In-Depth Information
Figure 15-2:
Oscil-
latory wave mo-
tion.
This oscillatory motion is what causes boats to bob up and down in the
ocean, moving only slightly in the direction of the waves. The circular motion of
the water in oscillatory waves continues to circulate beneath the surface of the
water to a depth approximately equal to half the distance of the wave's length.
When oscillatory waves move into shallow water, such as near the shore, the below-sur-
face oscillatory wave motion is interrupted by hitting the bottom. In response to this
friction, the wave slows down. Other incoming waves catch up to it, and they get
bunched together in a traffic jam of waves approaching the shore. The combined water
of the multiple waves builds a higher wave that is eventually too tall to support itself
and collapses, or breaks, as it hits the shore; see Figure 15-3.
Figure 15-3:
Trans-
ition of waves from
oscillatory to
translatory motion
in shallow water.
These
breakers,
or waves that collapse and hit the shore, are waves of translation or
translatory waves.
Unlike the oscillatory waves of the open sea, translatory waves move
the water some distance up onto the beach. The water moving up onto the beach is
called
swash,
and the water that moves back toward the sea is called
backwash.
