Cliff+erosion+factors

Geologists who have studied erosion in Calvert Cliffs inform us that there are one of two processes at work at any one time (35):


 * 1) **Slope failure and bluff (cliff) retreat** - this process occurs naturally as a result of forces like wind and rain breaking down the sand and clay components that make up the cliffs. Scientists who study **global climate change** believe that melting ice caps are contributing to rising water levels in the Chesapeake Bay, and also causing more coastal storms, both of which speed up this process. Later in the course, a special study group will look into the effect that global change is having on the Chesapeake Bay. **Figure 1A summarizes slope failure and bluff retreat**. If this process is halted by building a **revetment** or retaininig wall at the base of the cliff (toe), the second process is initiated;
 * 2) **Top retreat** - this form of erosion continues until a stable angle of repose is achieved. In Calvert County, the tops of bluffs along the bay will continue to tumble down (referred to as slumps and rotational slides) until the slope of the cliff below is reduced to a 35 degree angle. In other words, the material from the top of the cliff falls down to the toe, to build up the lower part of the cliff. The material that reforms the cliff base is called **colluvium**. As the cliff reforms into a stable 35 degree angle, the top of the cliff, and whatever was built there will slide to the bottom. **Figure 1B summarizes top retreat erosion**.




 * What does this mean?**

If rapid slope failure is underway at a bluff in Calvert county then building revetments will only hasten the collapse of the cliff top. The new erosion pattern shown in Figure 1B, will restore the bluff toe, but at the expense of the top of cliff. The only cliffs where revetments will slow erosion, is where the process is naturally occuring slowly to begin with.

In Calvert county, **less than half of the potential sites for Puritan tiger beetle habitat are eroding quickly**, and are confronted with an inescapable and inevitable sequence of slope failures and top retreat over time (35), even if revetments are built to control erosion.