Waves and Coasts
Feb 09, 2016
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