The Basics of Coastal Erosion

Erosion is the wearing away of earth surface materials.

Erosional processes loosen, dissolve, and redistribute rocks, sediments, and soils.

Source: http://www.geography.learnontheinternet.co.uk/images/coast/destructivewaves.gif

Wave action is a primary cause of coastal erosion.

The force of waves, particularly against weak rock units, breaks apart coastal landform.

Source: http://en.wikipedia.org/wiki/Image:Erodedcliffpacifica.jpg

An example of coastal erosion in California.

Longshore Drift

Source: http://www.geography.learnontheinternet.co.uk/images/holderness/longshoredrift.gif

The net transport of material along a coastline is called longshore drift. It is caused by waves meeting the shoreline at an oblique angle. As waves move, they pick up sediment and pull it out to sea perpendicular to the shore. When the next wave arrives, it pushes the sediment back onto the shoreline to a slightly different position; the path of sediment is diagramed by the “V” shapes in the figure above.

Barrier Islands

Source: http://www.geosci.unc.edu/faculty/glazner/Images/Coastlines/BarrierIslands/BogueBanks.jpg

Off the shoreline of much of the world are islands that detract from the impact of incoming weather. They absorb energy from waves and storms that otherwise would hit the mainland with full force. These barrier islands are also commonly residential areas. Currently, many are being deformed by processes such as longshore drift, creating an ecological source of damage for these communities.

Source: http://www.gfdl.noaa.gov/~tk/climate_dynamics/fig5.gif

As the world’s mean temperature rises, the global sea-level rises. This rise has begun to push coastlines back. The advancing coastlines move back, eroding the current landmass (Congxian et. al.) and destroying structures. The red portions of the graphic show areas that will be covered with seawater by progressively higher sea level rise. Without defensive measures, many portions of Bayport will be overcome by the moving shoreline.

Storm Action

--------------------Before---------------------------------After-----------------------

Many of the processes that erode the coasts of the world are enhanced greatly by storm activity. The picture on the left illustrates erosion before a storm and the picture on the right, after a storm. The yellow arrows show common points. Note how much closer the shore is to the buildings after the storm.