13 - Cliffed and rocky coasts
from Part III - Coastal Systems
Summary
Synopsis
The focus of this chapter is on coasts where the shoreline is largely developed in rocks, or in sediments that possess some strength due to cohesion and thus are able to offer resistance to wave action. Beach material is generally scarce and is found primarily as a thin layer fronting the cliff toe, or in isolated pocket beaches. The term cliff is used where the slope angle >40º and thus cliffed shorelines are those characterised by steep slopes rising abruptly from the water or from the back of a platform that is narrow enough for the toe of the slope to be affected by wave action during storms. Cliffed shorelines develop in sedimentary rocks ranging from recent deposits with some cohesion due to the presence of clays or to overconsolidation due to glacial loading, through weakly cemented shale and sandstone. The most resistant cliffs are found in rocks such as limestone, where chemical bonding is important, and in massive igneous and metamorphic rocks such as basalt or granite that possess strength due to crystallisation from melt and high pressures. Unlike sandy coasts where erosion may be reversed by deposition and progradation, erosion of bedrock coasts destroys the bonding that provided strength and thus there is no reversal of the erosion process – cliffs remain stationary or they recede.
On hard, strong bedrock coasts rock strength greatly exceeds the erosional forces of individual waves and erosion takes place very slowly – perhaps millimetres to a few centimetres per century.
- Type
- Chapter
- Information
- Introduction to Coastal Processes and Geomorphology , pp. 396 - 438Publisher: Cambridge University PressPrint publication year: 2009