Coral reefs are best developed in subtropical and tropical climates but 

 certain species of coral can tolerate colder water temperatures. The actual 

 amount of coral in a reef varies. It can be relatively small, providing a 

 framework that fills out with the hard parts of plants and animals that flourish 

 in the typical coral reef environment. Coralline algae are important in reef 

 construction because they form calcium carbonate crusts that help hold the dif- 

 ferent reef materials together. 



Mass Wasting and Mass Transf 



Once clastic and biogenic materials are broken apart by mechanical and 

 chemical weathering, they are more susceptible to downslope movement under 

 the influence of gravitational processes. These processes, collectively termed 

 mass wasting, may vary in scale, occurring either slowly or quickly in a 

 number of parent materials. Causes and mechanics of mass wasting are 

 variable, but depend in part on slope, soil moisture, and physical properties. 

 While most attention is given to subaerial mass wasting, submarine failures 

 occur on deltas and on the Continental Shelf (Prior and Coleman 1978). 



The shape of failures and distribution of debris may take on a variety of 

 forms. Thus, in coastal settings, mass wasting may directly influence 

 geomorphic variability (Figure 7). Along cliff coasts, especially in unconsoli- 

 dated material, gravity movement is important and is often aided by wave 

 undercutting of the base. Waves and currents are important in removing mass 

 wasting debris, thus reexposing the cliff face to wave attack (Figure 8). 



Mass wasting of hillslopes, whether at the coast or inland, may also fa- 

 cilitate sediment supply. Mass wasting directly by gravity is distinguished 

 from other gravity-induced movements in which the material is carried by 

 transporting agents such as running water, groundwater, ice, snow, and air. 

 Direct movement by these agents is termed mass transport, although, in 

 nature, mass wasting and mass transport merge into each other so that in some 

 cases the distinction becomes arbitrary. Abrasion or mechanical wear of 

 materials by solid particles transported in fluids, and corrosion or chemical 

 wear from the reaction of rocks with substances in water are additional 

 processes involved in the erosion of materials. 



Materials may be transported in one of three major modes within a fluid 

 (dissolved load, suspended load, or bed load). The dissolved load consists of 

 material transported in solution. The suspended load consists primarily of fine 

 particles, which are entrained and maintained into the flow primarily by 

 turbulent mixing processes. In bed load transport, particles move by rolling, 

 sliding, or saltating at velocities less than those of the surrounding flow. 



The great majority of material is transported from inland areas to coasts by 

 running water. The magnitude of sediment yield by running water is con- 



Chapter 2 Relevant Processes and Factors 



27 



