Beach

A beach is the zone of unconsolidated material that extends from the low water line to where there is an abrupt change in physiographic form or vegetation (e.g. dune scarp, seawall, etc). Beaches occur wherever there is mobile sediment along the shore, in the region between extreme low and extreme high water.

Important concepts

• A beach adopts the form that is most effective in dissipating the energy supplied to it.
• As long as sediment is available and mobile, a beach can maintain dynamic equilibrium with its environment.

 

Beach sediment

Composition:

Beaches are composed of whatever sediment is available.

• siliciclastic sand -Common where sediment source is fluvial
• volcanic debris (black and green olivine-bearing sands) Iceland and Hawaii
• gravel (shingle) - New England, England and glaciated coasts where till and rocky headlands are the principle sediment source
• Shelly carbonate debris - Florida beaches and sandy beach on Mt. Desert in Maine.
• Minerals precipitated directly for seawater (hydrogenous)- oolitic and glaconitic sands
• Wood (Dri Kai)
• beer cans, trash and sewage outfall

 

• Rivers
• erosion of glacial sediment and submerged fluvial sediments
• offshore sources
• biogenic sources (shell debris)
• Cliff erosion of rock, glacial sediment, etc.
• hydrogenous sources
• Man

Composition of beaches in New England

• Gravel - derived from the erosion of glacial till and bedrock highlands
• Sand - derived from erosion of glacial-fluvial sediments, modern fluvial sources, and the granular disintegration of certain granitic rocks (e.g. Cape Ann Granite)
• Shells - shelly material (periwinkle, muscle, oyster, echinoderm) is most abundant in sheltered beaches.

Types of beaches

The is no single, all-incompassing classification of beaches. The list given below is a simple descriptive classification.

• Mainland beach: beach not backed by lagoons or marsh
  • linear
  • pocket beach - beach lying between two headlands
• Barrier beach: Beach that are separated from the mainland by a lagoon, or marsh and tidal creek system
  • Barrier beaches (sensu stricto) beaches fronting barrier islands and barrier spits
  • Baymouth barriers: barrier attached to headlands and backed by a bay
• Spit:
  • simple spit
  • recurved spit
  • flying spit
  • detached spit
•  Tombolo
  • single
  • double
• Beach ridge: any beach or relict beach that forms a prominent ridge
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  Lindley Hanson/email /Gls214
  Department of Geological Sciences, Salem State College, Salem, MA