OVERVIEW

This chapter examines the processes and landforms that result when wind energy moves surface materials, either directly as wind or indirectly as waves. Both waves and wind are driven by the rotation and unequal surface heating of the earth.

• Shoreline refers to the line of contact between water and land, while coastline refers to the zone of influence of wave processes.
• Waves approaching a shoreline are slowed by the drag of the bottom, become steeper and eventually collapse to form breakers.
• The energy of breakers expended along a coastline causes erosion and transportation of shoreline materials.
• Weak or soft shoreline materials are eroded rapidly by wave action to form marine scarps, while more resistant materials are eroded slowly to form marine cliffs.
• Beaches are thick wedge-shaped accumulations of sand shaped by the swash and backwash of water along the shoreline.
• Waves striking a shoreline at an oblique angle cause littoral drift: the movement of sediment along the shore by the processes of beach drift and longshore drift.
• The sands transported by littoral drift can form spits, bars and pocket beaches along a coast.
• Variations in sediment transport along a coast can lead to progradation (building out) and retrogradation (cutting back) of the shoreline.
• Tides are regular fluctuations in sea level caused by the gravitational forces of the sun and moon.
• Tides drive ebb and flood currents which redistribute fine sediments within bays and estuaries.
• Coastlines of submergence result from partial drowning of the coast by a rise in sea level or sinking of the land. They tend to be deeply embayed with bold relief.
• Coastlines of emergence, where submarine deposits become exposed, usually have gentle relief and slope gently toward the ocean. Rapid emergence can produce raised shorelines and marine terraces.
• Global sea level has fluctuated substantially in the past and is presently rising slowly. The present rise may be due to the melting of glacier ice and thermal expansion of the oceans caused by global warming.
• Wind action is capable of moving dry, fine sediments that are not protected by a vegetation cover and is an effective landforming agent in deserts, semiarid regions and along coasts.
• The removal of loose particles from the ground surface by wind is called deflation. It can produce blowouts, desert pavements and dust storms.
• Sand dunes form where there is an abundant source of sand available for movement by wind.
  • Variations in wind conditions, vegetation cover and sand abundance produce a wide variety of dune types. Some of the more important are:
    • Barchan dunes - individual, cresent-shaped dunes with arms pointing downwind.
    • Transverse dunes - wave-like dunes with a crest aligned perpendicular to the wind direction.
    • Parabolic dunes - cresent-shaped dunes with arms pointing downwind.
• Loess is a sheet-like deposit of wind-transported silt. Extensive loess deposits in North America were derived from fresh glacial deposits exposed at the end of the last ice age.
• Human disturbance of the vegetation cover in semiarid regions can expose the soil to wind erosion.

KEY TERMS

shoreline          longshore drift    deflation          
coastline          ocean tide         barchan dune       
coast              progradation       transverse dune    
bay                retrogradation     parabolic dune     
estuary            submergence        blowout            
marine cliff       emergence          desert pavement    
beach              delta              dust storm         
littoral drift     coral reef         sand dune          
beach drift        atoll              loess              

STUDY QUESTIONS

1. What is the most important energy source driving wind and wave action?
2. Sea caves, sea arches and stacks are landforms often associated with marine cliffs. How do these features develop?
3. How do the processess of swash and backwash move sediment particles along a beach?
4. What is a pocket beach and how is it formed?
5. Why can the construction of a dam upstream of the mouth of a river induce retrogradation of the shoreline near the mouth?
6. What role do tidal currents play in the formation of a salt marsh?
7. Ria coasts and fjord coasts are both coastlines of submergence. How are they similar and how do they differ?
8. How do deltas form and how do they affect shoreline shape?
9. Distinguish between fringing reefs, barrier reefs and atolls.
10. What landforms you would expect to find along a bedrock coast that had been subjected to a several episodes of rapid emergence or uplift?
11. How might global warming affect global sea level and what implications might this have for human societies?
12. What is deflation and under what conditions is it effective?
13. Parabolic dunes are often found adjacent to beaches. Why do parabolic dunes develop at these sites?
14. What is the angle of repose? Which part of a sand dune would have a slope inclined at the angle of repose? Why?
15. What is loess and what are the primary sources of material for loess deposits?