Coastal Processes Flashcards
Wave Refraction
1) Waves bending with land as approach shore
2) Caused when waves are not parallel to shore OR if coastline uneven
3) Portion of wave reaching shallow water first slows down + causes wave line to bend (refract)
Effect of wave refraction
1) Smooths out coastline by wearing back headlands + increasing sediment accumulation
Headland
1) part that juts out in coast –> more erosion since waves have more energy
2) salt wedging + pneumatic weathering
Wave Erosion
1) Continually pounds shore
2) Storms bring huge strong waves, moving ~70 mph
3) Loosens rocks in coastline by forcing air into them, creating pneumatic action
4) saltwater = saltwater wedging in onshore rocks/cliffs
Tsunami
major oceanic wave system caused by sudden disruption
How are tsunamis formed
1) Abrupt movement on ocean floor, especially from reverse/thrust faults
2) Faults –> cause entire column of water to be disrupted –> shifts enormous volume of water
3) tsunamis in open water are small BUT have long wavelengths (125 miles) BUT this changes when it approaches coast + slows down
Tsunami effects
1) Arrive as very rapidly advancing surge of water up to 130 feet high
2) immediately behind wave crest is enormous volume of water that goes deep inland
Longshore Currents
1) causes water + sediment moves parallel to shoreline
2) caused by waves striking coast at slight angle
3) longshore currents = reflect local wind direction
Beach drifting
1) zigzag movement - short distance shifting of sand
2) sand is moved forward by waves BUT some is brought back when wave recedes + cycle keeps repeating
Beach
1) exposed deposit of loose sediment adjacent to water
2) relatively homogenous sediment
Beach profile
1) Backshore = upper part of beach + usually dry except when severe storms
2) foreshore = regularly covered + uncovered by tides
3) nearshore = place where waves break + surf action greatest; never exposed to atmosphere
4) offshore = always underwater AND deep enough that wave action doesn’t influence bottom
Sediment budget
Amount of sediment deposited by waves = amount of sediment removed
can change significantly during storms
Spits
1) Linear deposit of sediment attached to land at one end + extending into open water (in direction of longshore current)
2) can go connect land on other side OR move inward toward mainland
Baymouth Bar
1) spit that connects two separate pieces of land
2) “trapped” water is called a lagoon
Tombolo
1) Spit that connects mainland to a tiny island close by
2) acts like bridge of sorts
Barrier Island
1) Long, narrow island built up in shallow offshore waters
2) created by deposition of sediment when large waves “break” in shallow waters of continental shelves (reduced CC bc of slowed velocity)
Barrier Island Lagoon
1) Forms when barrier islands isolate water between itself + mainland
2) Results in more deposition of sediment from coastal streams + tidal deposits + wind –> creates mudflats –> coastal marshes
Barrier Island “migration”
1) After barrier island reaches certain size –> migrates shoreward bc more sediment deposited
2) Eventually merges with mainland
Problem with barrier islands
1) Very susceptible to large storms BC it’s just few meters above sea level
Groin
1) short wall/dam designed to impede longshore current + force sand deposition on up-current side of structure (reduced CC)
2) problem = does not stop erosion on the back side (down-current side) SO you could build a series of groins (groin field)
3) side where sand piles up IS where the longshore current comes from
Jetties
1) Built in pairs on either side of river
2) Confines flow of water to narrow zone + inhibits deposition in navigation channel
3) goal = maintain clear navigation channel by controlling sediment deposition
4) Whichever one has more sediment, that’s where longshore current comes from
Breakwaters
1) designed to provide shelter to small craft at anchor
2) horizontal bar behind which small boats can dock –> area inside breakwater has reduced energy + CC –> deposition
3) Must have angular face presented to wave approach + creates tombolos
Sea Wall
1) Massive structure originally designed to prevent storm-induced flooding BUT now used as beach-protection structure
2) High enough to block storm surge + parallel to shoreline –> traps sediment in trapped water bc of reduced CC
3) BEHIND the beach
Anatomy of a Wave
1) Crest = top
2) Trough = bottom
3) crest - crest = wavelength
4) wave height = amplitude
Why do waves increase in height as they approach shore
1) as approach beach, water is not as deep SO there is more friction –> energy needs to go somewhere, increasing height
Swash vs backwash
1) swash - wave hits + goes upward on coast
2) backwash - wave going backwards
SMOOTHING + SHAPING COAST
