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