Feeder Bluff Information
A feeder bluff is a geomorphological term whose use is primarily restricted to the Puget Sound region. It is not a standard or widely-accepted geologic term. The concept of a feeder bluff was first developed at Western Washington University, and it has not been extensively researched. Specific criteria have not been developed that distinguish feeder bluffs from other types of bluffs. Quantities and rates of sediment supply to beaches and the littoral drift are unspecified and unknown. The overall contribution of "feeder bluffs" to beach processes, unlike the well-researched effects of sediment from rivers, is still undetermined.
A feeder bluff is a coastal cliff or headland that feeds the beaches down current. As the waves approach the bluff, they erode away sediment which then gets carried along the coastline and deposited across other beaches. The majority of the wave energy is concentrated at the base of the bluff, where it is most accessible for the wave action.
The bluff will be more susceptible to erosion if the sediment is unconsolidated, and is found to be more resistant in crystalline rocks, like granite. The difference between the two is quite drastic, a difference of thousands of cm/year to less than 1 cm/year of retreat respectively. Rocks that are heavily fractured are also very likely to suffer from excess erosion because the water can flow between the cracks to speed up the process. The bluff will retreat towards land as the erosion processes continue.
Types
Evidence of erosion causing mass movement at Jefferson Beach in Kingston, WashingtonThere are two main types of feeder bluff erosion, defined by the patterns of wave energy. These patterns are also highly variable, even within themselves. The first type consists of erratic erosion patterns, light waves with intermittent large storms, those tend to be rocky slopes. The majority of the erosion that occurs happens during storms. The high energy storm waves have more power to take sediment away and deposit it along the coast with the long shore drift. The high energy of a single storm has the ability to take up to 5 to 30 m of the bluff into the water with it.
The second type of bluff is adding sediment at a rate nearly equal to the rate of erosion. In this case, the sediment load is balanced and between storms. There will almost always be a talus, mass of eroded material, at the base of the bluff. This talus will help protect the base of the cliff from further erosion as long as it is present.
References
- Easterbrook, Don J. (1999). Surface Processes and Landforms (2nd Edition ed.). Upper Saddle River, N.J.: Prentice Hall. ISBN 978-0-13-860958-0.
External links
Categories: Geomorphology | Cliffs | Coastal geography
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