Geoscience Reference
In-Depth Information
8
Temperate coastal environments
Andrew Cooper
8.1
spatial distribution, the forms that they take and
the controls on their development are outlined
in this chapter. Morphological change over time
is discussed in order to provide an appreciation
of the control of changing environmental condi-
tions on coastal morphology. The interaction of
humans with these dynamic coastal systems adds
an additional layer of complexity to the dynam-
ics and future evolution of temperate coasts,
and thus past human interventions and future
management options are assessed.
INTRODUCTION
This chapter addresses the sedimentology of
the clastic depositional environments of open
ocean temperate coasts. The environments that
will be considered are associated with beaches,
barriers and barrier islands composed largely of
reworked terrigenous material. These environ-
ments are commonly sandy, but reference will
also be made to coarser grained gravel-, cobble-
and boulder-dominated systems. These types
of environment are typical of the temperate
latitudes. In the tropics they are often replaced
by systems in which organic materials dominate
(Chapter 9). Estuarine and deltaic environments
are considered in Chapter 7.
The common characteristic of the environ-
ments considered is the non-cohesive nature of
the constituent clasts. The consequent ability for
clasts to readily be reorganized into different geo-
morphological forms in response to changes in
environmental conditions is a key characteristic.
It is commonly asserted that beaches, as loose
accumulations of small grains of sand or peb-
bles, are among the most unlikely landforms
to exist in the often-harsh conditions of open
coastal areas (Pethick 1984). The very ability of
these accumulations to change shape and absorb
excess energy in response to storms is central to
their ability to survive when more solid struc-
tures, such as seawalls, can be destroyed under
the same conditions.
Thus open coast sedimentary environments,
composed of a range of non-cohesive clast sizes,
under a variety of energy conditions, take many
geomorphological forms. The controls on their
8.2
NATURE AND SIGNIFICANCE OF TEMPERATE COASTS
Temperate coasts (Fig. 8.1) are widely distributed
in the Northern Hemisphere on Atlantic and
Pacific coasts of North America, Europe and
North Africa, and the Far East. In the Southern
Hemisphere they are limited to the Argentinean
and Chilean coasts of South America, Southern
Africa, and the southern coasts of Australia and
New Zealand. They are bounded toward the
poles by coasts with sea ice, and toward the
equator by tropical coasts. Temperate coasts can
be crudely categorized into open ocean coasts
(swell- or storm-wave dominated - see section
8.2.3), sheltered seas and areas subject to tropi-
cal storms (Fig. 8.1).
Sedimentary environments considered here
are beaches, barriers, barrier islands and coastal
sand dunes (Fig. 8.2). A beach is an accumula-
tion of wave-deposited, non-cohesive sediment
that typically spans the subtidal-supratidal inter-
face. Sustained beach sedimentation can give
rise to a barrier (Woodroffe 2002). Barriers are
