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 coastlines1. Ria Coast:

– coast that was formerly dissected by stream valleys; then sea level rose and inundated the valleys

Types of coastlines2. Fiord coast:

– coast that was formerly dissected by glacial troughs; then sea level rose and they became inundated

Types of coastlines3. Barrier Island Coast:

– sand bars (barrier islands) created by littoral drift, parallel shore, enclose lagoons

Types of coastlines4. Delta coast:

– where a stream enters the ocean; deposits a delta

Types of coastlines5. 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 coastlines6. Fault coast:

– land surface is uplifted (isostatic rebound) or sea level drops; marine cliffs and abrasion platforms are raised