Transcript 103-29-CoastalClassif&Beaches

INTRODUCTION
TO
BEACHES
&
COASTS
GEOL 1033
(Lesson 32)
Ppt file 103-29
Coastal Classifications
• There are many old coastal classifications
• Plate tectonic classification is newest:
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Collision coast (like southern BC)
Trailing-edge coast (Atlantic Canada)
MAJOR
LITHOSPHERIC
PLATES,
R
Translational (= transform-fault) coast (San Andreas Fault Zone)
TRANSFORM
FAULTS, & TRENC
Marginal sea coast (Sea
of Japan)
• Secondary influences involve:
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Sediment supply
Glaciers
Climate
Hydrodynamics (waves & tides)
What is a Beach?
• Loose, unconsolidated sediment:
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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:
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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:
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Typical of winter & after storms
Erosional
Coarser grained sediment
Steeper slopes
Large, high berms
Narrow backshore
• Swell beach profiles:
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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
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Either sandy or muddy
Somewhat protected areas
Low and mid-tide range
No vegetation
• Salt marshes
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Fine-grained sediments
Protected coastal areas
High intertidal range
Salt-tolerant vegetation
• Southerly = mangrove trees
• Northerly = grasses
dominate
World Distribution of Marshes
New England/Maritime saltmarsh
mangrove coasts
END OF FILE
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
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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
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Beach
Dune field
Salt marshes
Tidal flats
Tidal channels
Spits
Lagoons