Page 352 - Fundamentals of Geomorphology

COASTAL LANDSCAPES 335

Coastal
dunes

Figure 13.14 World distribution of coastal dunes.
Source: Adapted from Carter et al. (1990)

Box 13.2
COASTAL DUNES: NATURE AND OCCURRENCE

Coastal dunes are fashioned by the interplay of wind, cover (Figure 13.15c). Single foredune ridges, which
waves, vegetation, and sediment supply (Pye 1990). grow upwards with no change of shore position, occur
Figure 13.15 depicts six basic cases. Rapidly prograd- when sand supplied to the beach is delivered to the
ing beach ridge plains with little dune development dunes and trapped by vegetation (Figure 13.15d).
form where the beach sand budget is positive and Slowly migrating parabolic dunes, blowouts, and
wind energy is low (Figure 13.15a). Parallel fore- salt-scalded vegetation occur behind beaches that
dune ridges occur under similar circumstances save slowly retreat landwards when the sand supplied
that wind energy is higher and sand-trapping vegeta- to the beach is slightly less than that supplied
tion is present, leading to slower beach progradation to the dunes (Figure 13.15e). Transgressive sand
(Figure 13.15b). Irregular ‘hummock’ dunes with sheets of low relief form when little or no sand
incipient blowouts and parabolic dunes form on is supplied to the beach and wind energy is high.
moderately prograding coasts where the beach-sand Under these conditions, the beach is rapidly low-
sediment budget is positive, wind energy is moder- ered and dune vegetation destroyed, which increases
ate, and there is an ineffectual or patchy vegetation exposure to storms and initiates coastal retreat.