waves and coasts waves agents of erosion as get closer to shore: –wavelength decreases –velocity...
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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
• 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