BEACH 



PLUNGING CLIFF 



CLIFF WITH 

 SHORE PLATFORM 



CLIFF BASE BEACH 



Figure 17. A variety of cliff morphologies in cross section. Plunging cliff is steeply sloping 

 and possibly shows a notch. Cliff with shore platform may develop from 

 increased notch development and mass movement of overlying material. Cliff 

 base beach may develop from cliff with shore platform if sediment supply 

 exceeds transport of materials 



Coasts of consolidated materials resist wave attack because of compressive, 

 tensile, and cohesive properties. Thus, because they are primarily erosional 

 rather than depositional in nature, they show distinctive morphologic features 

 in comparison with unconsolidated coastal sediments. Sustained wave attack 

 may etch notches in rock, the deepest notches occurring where dynamic 

 pressures are greatest. Multiple notches may form if there are various 

 dynamic wave horizons, most likely associated with changing water levels. 

 Notches may become sea caves along zones of structural weakness. Varia- 

 tions in resistance may also lead to the development of sea stacks and sea 

 arches seaward of the cliffs. 



Coastal slope recession typically leaves behind a shore platform, a surface 

 that is quasi-horizontal or of low slope angle, marking the lowest level to 

 which the erosion reached. Maximum width of such platforms is about 1 km 

 (Flemming 1965), and their profiles may be linear, concave, or convex. A 

 variety of processes act on platform surfaces, including abrasion, mechanical 

 wave erosion, weathering, and solution, which vary depending upon the 

 nature of the processes, rocks, structure, tides, age, and history. 



Abrasion from sand and shingle is concentrated on the upper shoreward 

 section of the platform since these abrasive materials are generally absent on 

 the lower levels (Robinson 1977; Trenhaile 1980). Considered by some to be 

 the most important, mechanical wave erosion may assist in breakup and plat- 

 form surface lowering by wave shock, wave hammer, air compression, and 

 other forms of dynamic pressure release (Trenhaile 1980). Several weathering 

 processes may also be involved, particularly those associated with alternate 



Chapter 3 Variable Coastal Features 



45 



