Waves and Coasts

waves Agents of erosion as get closer to shore: –wavelength decreases –velocity decreases –amplitude increases –in shallow water, waves BREAK

Breaking waves scoop out a TROUGH and deposit a BAR

Turbulent water from breaker rushes up beach (SWASH) and then flows back (BACKWASH) waves come in to the shore at an angle (REFRACTION)

Consequence of wave refraction Littoral Drift –Beach drift: movement of sand particles down the beach by swash and backwash –Longshore drift: movement of particle just offshore by the longshore current (parallel to beach)

Landforms resulting from littoral drift: 1. Spit (e.g., Park Point)

Landforms resulting from littoral drift: 2. baymouth bar and lagoon

Landforms resulting from littoral drift: 3. tombolo

Stockton Island, Apostle Islands

On an embayed coast, Wave energy converges on HEADLANDS, and therefore erosion is concentrated there: CLIFFS BAYS receive less energy, less erosion,and therefore deposition of sand occurs there: BEACHES

landforms on the headlands: 1. Wave-cut abrasion platforms: –sloping rock surfaces abraded by waves beneath breakers

landforms on the headlands: 2. Wave-cut notches

landforms on the headlands: 3. Sea stacks and sea arches

Where does beach sand come from? Erosion of headlands offshore material brought to shore fluvial sediment

Types of coastlines 1. Ria Coast: –coast that was formerly dissected by stream valleys; then sea level rose and inundated the valleys

Types of coastlines 2. Fiord coast: –coast that was formerly dissected by glacial troughs; then sea level rose and they became inundated

Types of coastlines 3. Barrier Island Coast: –sand bars (barrier islands) created by littoral drift, parallel shore, enclose lagoons

Types of coastlines 4. Delta coast: –where a stream enters the ocean; deposits a delta

Types of coastlines 5. Volcano and Coral reef coast: –coral reef builds around volcanic island; begins as a fringing reef; as volcano erodes, becomes a barrier reef; eventually volcano is eroded below surface of water; coral reef remains as an atoll

Types of coastlines 6. Fault coast: –land surface is uplifted (isostatic rebound) or sea level drops; marine cliffs and abrasion platforms are raised