Shores and coastal processes. Goal To understand how coastal processes shape shores and coastlines...
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Transcript of Shores and coastal processes. Goal To understand how coastal processes shape shores and coastlines...
Shores and coastal processes
GoalTo understand how coastal processes shape
shores and coastlines and how these processes affect people.
Coast and shore definedCoast: Area of contact between land and sea—Extend
inland until meets a different geographical setting
Shoreline: Precise boundary where water meets adjacent dry land
Shoreline Coast in MD, DE, & NJ
Waves and tidesWaves: transport energy by motion—ultimate source
of wave energy is the sun
Longshore current: Current that parallels shoreline developed by waves coming in at an angle to shore—Maine sand found in NC
Beach Drift and Longshore Currents
Waves and tidesTides: Daily fluctuations in the height of the ocean—
Caused by gravitational attraction of water to sun and moon
Tidal range: varies depending on latitude and the shape of the coastsBay of Fundy tidal range up to 75 ft. Hawaii tidal range ~1.5 ft.
High tide Low tide
Coastal erosionWaves are dominant mechanism in coastal erosion—
Water forced into cracks in rock at high pressures
Coastal erosionWave energy is focused on headlands: prominent
cliffs that jut out into deep water• attack the sides of headlands and form sea caves,
sea arches, and sea stacks by undercutting them
Sea stack with sea arch in it
Preventing coastal erosion• Can establish sand dunes and stabilize existing
dunes• Can build seawalls: concrete or riprap structures
designed to protect shoreline from waves
Riprap sea wall
Sea wall in action
Coastal depositionOccurs when amount of sediment exceeds
wave/current ability to transport it
Beaches: relatively narrow strips of sand, pebbles, or cobbles deposited along a shoreline
• 90% of beach sediment comes from streams that drain to coast—transported by longshore currents
Coastal depositionSpit and/or hook: Narrow strip of sand that grows
across the mouth of bay due to longshore current (hooks are hook-shaped)
Cape Henlopen at mouth of Delaware Bay
Coastal depositionBarrier islands: Long narrow Islands made of sand
that flank main shoreline and separate bays from open ocean
Coastal depositionTombolo: Narrow strip of sediment deposited behind a
sea stack by refracted waves
Coastal depositionHumans often induce coastal deposition on purpose
or by accident• Use groins or breakwaters to disrupt longshore
currents or block waves and induce deposition
Groins
Breakwater
Coastal Stabilization Structures
Types of coastsPrimary coast: Shaped by non-marine processes
(glaciations, streams, ect.)—Usually a landscape drowned by rising sea level
Types of coastsSecondary coast: Shaped by coastal erosion and
deposition features outlined above• Primary coasts often have secondary coastal
features
Cape Henlopen at mouth of bay—Secondary
Delaware Bay—Primary
Plate tectonics and coastsRifted continental margins tend to be dominated by
depositional features
Active continental margins tend to be dominated by erosional features