waves, beaches and coastal erosion
DESCRIPTION
Waves, Beaches and Coastal Erosion. 1. Tidal forces associated with Moon. Tidal forces associated with Sun and Moon. High tide stays aligned with moon but Earth rotates, yielding 2 high and 2 low tides each day. Tidal forces associated with Sun and Moon. - PowerPoint PPT PresentationTRANSCRIPT
Waves, Beaches and Coastal Erosion
Tidal forces associated with Moon1
Tidal forces associated with Sun and Moon
High tide staysaligned with moon but Earthrotates, yielding2 high and 2 lowtides each day.
Tides are cyclical floods
Tidal forces associated with Sun and Moon
Neap tides: Sun and Moon tides are out of phase
Spring tides: Two tides are in phase--High tide will be higher than usual
Tidal Ranges Are Highly Variable: Bay of Fundy--17 m!
Tidal Ranges influenced by local conditions and bathymetry
Bays tend to focus the water and create larger ranges
Organisms are stratified basedon tidal zone
2) Sea Level: What and When?Mean sea level is the average height of the sea…
Relative to what?
When? High or low tide?
Measured with tide gauges
Sea Level: Changes through time
Eustatic Sea Level Changes“Eustatic” refers to changes related to amount of water in the oceans
3) Tidal Flats: exposed mud at low tide
4) Waves and Sediment Transport
Wave Velocity-
Deep Water
Wave Energy
Doubling wave height quadruples energy:Ew = 0.125rgH2Lwhere:Ew = energy of waver = water density (g/cm3; close to 1)g = acceleration of gravity (9.8 m/sec2)H = wave height (m)L = wavelength (m)
Passive continental margin
Submarine canyons
Coastal plain
Continental shelf
Continental slope
Continental rise
ContinentalcrustOceanic c
rust
Mantle
Deep-sea fanAbyssal plain
Path ofwaterparticles
Longshorecurrent
Ripcurrent
Path ofsandparticles
5) Waves approaching the shore at an angle cause a longshore current.
Longshore drift results from movement of sand particles by swash and backwash.
Sand will move in this direction
The beach is a “river of sand”
6)Headlands receive
strong wave energy-leads toerosion
7) Rip Currents
7) Rip Currents
8) Sand Supply/Loss
8) Sand Supply/Loss
8) Sand Supply/Loss
Offshore sand bars migrate to beach during summer
Winter storms remove beach sand to deeper water
Hurricanes result in summer beach sand loss
8) Sand Supply/Loss
Engineered Beach Protection Structures
9) Erosion of Gently Sloping Coasts and Barrier Islands
Beach migrated 400 m in 60 years
Barrier Islands are Geologically Temporary
Chandeleur Islands
Before (above) and after (below)
Hurricane
Katrina
10) Sea Cliff Erosion
Headlands erode from wave actionCreates caves, arches, sea stacks
Sea Cave
Arches
Sea Stacks
Sea Stacks
Sea Stacks
Sea Cliff Erosion
Coastal Erosion