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