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Tales of the Coast
Coastal Dynamics

Waves and Sea Cliffs

Cliffs are often found along shores where wave erosion rather than deposition is the dominant coastal process. As waves attack the shore, headlands are eroded, producing steep sea cliffs.

The waves vigorously attack the portion of the cliff near sea level where joints, fissures, and softer strata are especially vulnerable. The cliffs are undermined and caves are formed. Pocket beaches may accumulate between headlands from sediment carried by longshore currents. Especially durable pinnacles of rock may survive offshore as stacks or arches. Over time, the coast is straightened as the headlands are eroded back.

Beaches may also form at the base of cliffs if the rubble that has fallen from the cliff face (known as talus) is unconsolidated or breaks down rapidly under wave attack. If the rock debris is durable, it may serve to armor the shore, protecting it from further wave attack except during the most severe storms.

Along the Great Lakes, cobbles and boulders, known as lag deposits, have accumulated at the base of bluffs and created erosion-resistant nearshore shelves that protect the bluffs from wave energy.

At the base of cliffs that have been progressively cut back by waves, near-horizontal platforms may form just below sea level.

 

Waves and Sea Cliffs

Pacific Coast: An irregular shore may be formed when differing rock types outcrop at the coast. The Pacific coast of Washington off the Olympic Peninsula is irregular because of the complex geology and variety of exposed rock formations.