Page 338 - Fundamentals of Geomorphology

COASTAL LANDSCAPES 321

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, terraces, wave-cut benches, and wave-cut platforms.
and to isolate rocky coasts as the quintessential landforms Some of these terms indicate causal agents, e.g. ‘wave-cut’
of destructive wave action. 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
Shore platforms and plunging cliffs
the wide choice available. Sloping platforms are eye-
Rocky coasts fall into three chief types – two varieties catching features of rocky coasts (Plate 13.2). As their
of shore platform (sloping shore platform and horizon- name intimates, they slope gently between about 1 ◦
tal shore platform) and plunging cliff (Figure 13.5). and 5 . They are variously styled abrasion platforms,
◦
Variants of these basic types reflect rock types and geo- beach platforms, benches, coastal platforms, shore plat-
logical structures, weathering properties of rocks, tides, forms, submarine platforms, wave-cut benches, wave-cut
exposure to wave attack, and the inheritance of minor platforms, wave-cut terraces, and wave ramps.
changes in relative sea level (Sunamura 1992, 139). Shore platforms can form only if cliffs recede through
Horizontal platforms are flat or almost so cliff erosion, which involves weathering and the removal
(Plate 13.1). They go by a host of names: abrasion of material by mass movement. Two basic factors deter-
or denuded benches, coastal platforms, low-rock ter- mine the degree of cliff erosion: the force of the assailing
races or platforms, marine benches, rock platforms, shore waves and the resisting force of the rocks. Rock resistance
benches, shore platforms, storm-wave platforms, storm to wave attack depends on weathering and fatigue effects