2 Relevant Processes and 

 Factors 



From both a temporal and spatial perspective, the geomorphic variability of 

 a coast reflects a balance between forces that promote change and materials 

 that resist change. Forces promoting change include atmospheric, 

 oceanographic, biologic, and terrestrial processes that act individually and in 

 combination. Some of these are important locally and others are important 

 regionally, over short- and long-term periods. The processes and products of 

 the interaction of the various factors in coastal environments are complex, and 

 it is often advantageous for a researcher to adopt a holistic approach. 



Because the coast lies at the boundary between the atmosphere, ocean, and 

 land, processes within each of these environments are important in promoting 

 coastal change. In the atmosphere, factors operating on varying spatial and 

 temporal scales include climate, wind, and cyclonic disturbances. Oceanic 

 processes that influence coasts include waves, tides, currents, storm surges, 

 tsunamis, and sea level (eustatic) changes. Terrestrial processes may be inter- 

 nally driven, such as by tectonic factors, or externally driven, by climatic and 

 meteorologic agents such as running water, groundwater, and ice. Biologic 

 processes may also come into play, influencing both the shape and material of 

 coastal environments. Interactions between many of the major processes are 

 described briefly in subsequent pages. 



Materials in coastal environments have varying properties, which charac- 

 terize their ability to resist deformation by stresses, their ability to resist 

 weathering and abrasion, and their ability to resist transportation by a fluid 

 agent. The strengths of materials depend on the nature of the solids that 

 comprise them, the nature of the voids (whether filled, or partly filled, with 

 water or with air), and the forces holding the aggregates together. Some 

 factors that characterize resistance to shear include rock strength, state of 

 weathering, and the spacing, width, and continuity of joints and voids. 

 Frictional and cohesive strength, mineral hardness, and fabric also cause mate- 

 rials to vary in their resistance to erosion by abrasion, fluid stresses, 

 corrosion, and plucking. Materials vary in their resistance to entrainment and 

 transportation by fluids according to their volume, density, and friction with 

 the bed. Because coastal sediments display a range of characteristics from 

 consolidated to unconsolidated, gravel to clay, terrigenous to biogenic, they 

 show great variety in their resistance to natural forces. The nature and 



Chapter 2 Relevant Processes and Factors 



