Shores and coastal processes

Goal To understand how coastal processes shape shores and coastlines and how these processes affect people.

Coast and shore defined Coast: 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 tides Waves: 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 tides Tides: 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 coasts Bay of Fundy tidal range up to 75 ft. Hawaii tidal range ~1.5 ft. High tideLow tide

Coastal erosion Waves are dominant mechanism in coastal erosion— Water forced into cracks in rock at high pressures

Coastal erosion Wave 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 deposition Occurs 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 deposition Spit 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 deposition Barrier islands: Long narrow Islands made of sand that flank main shoreline and separate bays from open ocean

Coastal deposition Tombolo: Narrow strip of sediment deposited behind a sea stack by refracted waves

Coastal deposition Humans 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 coasts Primary coast: Shaped by non-marine processes (glaciations, streams, ect.)—Usually a landscape drowned by rising sea level

Types of coasts Secondary 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 coasts Rifted continental margins tend to be dominated by depositional features Active continental margins tend to be dominated by erosional features