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Depositional Coasts

Depositional Coasts. Deposition of sediments outpaces erosion and forms sandy beaches. Beach: zone of loose particles that covers part or all of a shore. U.S. has about 11,000 miles of beaches (30% of shoreline).

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Depositional Coasts

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  1. Depositional Coasts Deposition of sediments outpaces erosion and forms sandy beaches. Beach: zone of loose particles that covers part or all of a shore. U.S. has about 11,000 miles of beaches (30% of shoreline). Beaches form at calm spots between headlands, shores sheltered by barrier islands (Outer Banks/Sandbridge), or places with moderate surf.

  2. Depositional Coast

  3. Composition and Slope of Beaches • Boulders • Cobbles • Pebbles • Gravel • Sand • Silt • Shells • Corals • Glass/Trash • Flatter the beach, the finer the grains. • Due to porosity. • Sandy beaches have low porosity so water easily washes in and out bringing equal amounts of sand in and backwashed back to sea. • Cobble beaches have high porosity and water sinks as it comes in. This deposits material but makes it difficult to bring material back out.

  4. Beach and Slope Cobble Beach: High slope of 9 to 24 degrees Sandy Beach: Low Slope of 1 to 9 degrees

  5. Beach Shape

  6. Beach Features • Berm: Accumulation of sediment that runs parallel to shore and marks the normal limit of sand deposition by waves. (Usually have a steeper berm in summer and smaller or no berm in winter) • Berm Crest: highest point on beach. • Backshore: Furthest part where beach is deposited. • Foreshore: Seaward of berm crest to the shoreline. • Beach Scarp: Vertical wall of variable height carved by waves at high tide. • Longshore trough: Carved by waves and turbulent backwash. • Longshore bars: Submerged or exposed accumulations of sand.

  7. Longshore Transport • Longshore Current: Form when waves approach the beach at an angle. • Sand is moved by these currents forming sandbars and spits. • Often called longshore drift. • Along U.S. coast, this drift is from North to South because of storm systems in the north.

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