Geology Reference
In-Depth Information
Macrotidal
(>4m)
Mesotidal
(2-4m)
Microtidal
(<2m)
Figure 13.4
Global pattern of tidal range. The ranges indicated are for spring tides.
Source:
Adapted from Davies (1980, 51)
environments under the 'depositional landform' rubric,
and to isolate rocky coasts as the quintessential landforms
of destructive wave action.
terraces, wave-cut benches, and wave-cut platforms.
Some of these terms indicate causal agents, e.g. 'wave-cut'
and 'abrasion'. Because the processes involved in platform
evolution are not fully known, the purely descriptive
term 'shore platform' is preferable to any others from
the wide choice available.
Sloping platforms
are eye-
catching features of rocky coasts (Plate 13.2). As their
name intimates, they slope gently between about 1
◦
and 5
◦
. They are variously styled abrasion platforms,
beach platforms, benches, coastal platforms, shore plat-
forms, submarine platforms, wave-cut benches, wave-cut
platforms, wave-cut terraces, and wave ramps.
Shore platforms can form only if cliffs recede through
cliff erosion, which involves weathering and the removal
of material by mass movement. Two basic factors deter-
mine the degree of cliff erosion: the force of the assailing
waves and the resisting force of the rocks. Rock resistance
to wave attack depends on weathering and fatigue effects
Shore platforms and plunging cliffs
Rocky coasts fall into three chief types - two varieties
of
shore platform
(sloping shore platform and horizon-
tal shore platform) and
plunging cliff
(Figure 13.5).
Variants of these basic types reflect rock types and geo-
logical structures, weathering properties of rocks, tides,
exposure to wave attack, and the inheritance of minor
changes in relative sea level (Sunamura 1992, 139).
Horizontal platforms
are flat or almost so
(Plate 13.1). They go by a host of names: abrasion
or denuded benches, coastal platforms, low-rock ter-
races or platforms, marine benches, rock platforms, shore
benches, shore platforms, storm-wave platforms, storm
