Steep bluffs rim most of the Sound shoreline, rising 50 to 500 vertical feet high. Many of these bluffs are made of glacial and interglacial deposits of sand, gravel, silt and clay.

Bluffs Nourish Beaches

Eroding bluffs provide building materials for beaches. Sediment or eroded "bluff stuff" drops to the base of the bluffs, where it is gradually carried along the shore by wind and waves. These bluff sediments help build shore forms such as spits, tombolos, and barrier beaches.


Eroding sandy bluffs provide plenty of building materials for Dungeness Spit in Clallam County...

Eroding bluffs in Discovery Park near Seattle reveal glacial legacies...

Bluff erosion occurs naturally on Puget Sound. Many bluffs are naturally unstable because of soil, slope, and water conditions...
Bluff Erosion: How fast?  

Bluff erosion is affected by geology, waves, and weather. All three factors vary widely within the Puget Sound region, so bluff erosion rates can range from a fraction of an inch to more than 2 feet per year. The erosion rate for a bluff can be regular over the years, or it can change from near zero for decades to tens of feet in a matter of seconds. Once steepened to an unstable angle, bluffs can continue to erode without wave action.

Bluffs and Bulkheads

High glacial bluffs are subject to continuing erosion. Usually this process is not considered significant until people move onto the bluff or the shorelines nearby. To keep land, people often build bulkheads and other structures. Such structures, however, may remove a major source of beach building materials. Erosion can increase just downdrift of the structures. Downdrift beaches often steepen and/or lower.

Related Topics

Erosion, Understanding land loss.
Landscaping, Keeping plants to prevent erosion.
Bulkheads, Bulkheads can increase beach erosion.
Drainage, Controlling excess runoff.

Related Links

Puget Sound Nearshore Environments, Eroding Bluffs and Development, King County Department of Natural Resources. Bluffs and the effects of development and bulkheads; two color illustrations.

Controlling Erosion Using Vegetation, Department of Ecology. An online guide to controlling erosion on slopes and bluffs using vegetation.

Managing Drainage On Coastal Bluffs, Department of Ecology. An online guide to drainage control for erosion prevention on coastal bluffs.

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