Geography Reference
In-Depth Information
their crests aligned at oblique angles to the shoreline (Figure 4.3).
They are also affected by winds and longshore currents can be
particularly strong when winds are blowing in the same direction
as the longshore current. Longshore currents can transport large
quantities of sediment, often known as
longshore drift
. The cur-
rents can be fast flowing and this is assisted by sediment being
stirred up by wave breaking, making the sediment easier to pick up
and transport. Another type of nearshore current which all those
who go swimming or surfing in near shore coastal waters should be
aware of is the rip current. These are strong, narrow, seaward
flowing currents which flow back through gaps between sandbars.
The water piles up as a result of the waves approaching at an
oblique angle and this water rushes back through the surf zone at
key points.
A final important wave type is that of a tsunami. These can
result in an enormous wave which floods coastal areas and causes
massive loss of life such as in the event on 26 December 2004
around coastlines of the Indian Ocean which killed an estimated
quarter of a million people. That particular tsunami was caused by
an earthquake which displaced water deep within the ocean. Tsu-
namis can also be caused by a large landslide entering the sea such
as that which occurred after the eruption of the Krakatoa volcano
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Figure 4.3
Longshore current produced by the combination of waves arriving
at oblique angles to the sea perpendicular to the shore. The result is
an overall movement of water and sediment along the coastline.
