INTRODUCTION TO BEACHES & COASTS GEOL 1033 (Lesson 32) Ppt file

Coastal Classifications There are many old coastal classifications Plate tectonic classification is newest: –Collision coast (like southern BC) –Trailing-edge coast (Atlantic Canada) –Translational (= transform-fault) coast (San Andreas Fault Zone) –Marginal sea coast (Sea of Japan) Secondary influences involve: –Sediment supply –Glaciers –Climate –Hydrodynamics (waves & tides)

What is a Beach? Loose, unconsolidated sediment: –Usually sand (1/16 mm to 2 mm) –Silts & clays are washed (winnowed) away –Can be pebbles, cobbles, etc. –Water-borne –Well-sorted (narrow size range) Beachface slopes seaward –Coarser sediments = steeper slopes –Finer sediments = gentler slopes Located between –Mean low tide level & –Landward change in Physiography Vegetation Effective (reach of) waves and tides

Beach Subdivisions Foreshore: – Beachface – Low-tide terrace Backshore: –Where berms are located Offshore (beyond beach): –Offshore bars

Beach Equilibrium Profiles Generalized profiles below are equilibrium profiles. Profiles adjust to disruptions/changes over periods of weeks. Storm beach profiles: –Typical of winter & after storms –Erosional –Coarser grained sediment –Steeper slopes –Large, high berms –Narrow backshore Swell beach profiles: –Typical of fair-weather conditions –Depositional –Finer grained sediment –Gentler slopes –Small, lower berms –Broad backshore

Sand Spits Linear extension downdrift from: –Mainland beaches –Island beaches Extend into mouth of a bay bay

Barrier Islands Found along –Microtidal coasts –Mesotidal coasts Composed basically of –Beach sands oceanward, –Salt marshes landward, & –Windblown dune sands in the middle

Tidal Flats & Salt Marshes Tidal flats –Either sandy or muddy –Somewhat protected areas –Low and mid-tide range –No vegetation Salt marshes –Fine-grained sediments –Protected coastal areas –High intertidal range –Salt-tolerant vegetation Southerly = mangrove trees Northerly = grasses dominate

World Distribution of Marshes

mangrove coasts New England/Maritime saltmarsh

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BEACH PROFILE OF EQUILIBRIUM The generalized profile below is a typical response of shoreline sediments to coastal processes, etc. It will change or adjust over periods of only weeks if conditions change, e. g., storm versus fair weather conditions or "storm profile" versus. "swell profile" Nearshore Beach face

Sand Spits Develop downdrift from beaches Linear extension from –Mainland beaches –Islands Over a platform Into the mouth of a bay Protected bay/lagoonal area behind develops: –Tidal flats –Salt marshes –Fills in with sediments eventually bay

Barrier Islands Found along microtidal & mesotidal coasts 3 origins: –Coastal ridge embayment associated with sea-level rise –Breached spits –Wave-built offshore shoals emerge Complex environmental settings –Beach –Dune field –Salt marshes –Tidal flats –Tidal channels –Spits –Lagoons