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72 Cards in this Set
- Front
- Back
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what is the most important factor governing coastal morphology?
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plate tectonic setting
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5 influences of plate tectonic setting on coastal morphology
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- size of coasts
- relief of coasts - orientation of coasts - sediment supply - direction of transport |
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four continental factors influencing coasts
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- geologic structure (tectonic setting, shelf width/relief
- local geology (structure & rock type) - geomorphic processes (sediment supply/transport) - isostacy (tectonic, glacio-, hydroisostacy) |
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six oceanic factors influencing coasts
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- eustacy (glacial, circulation changes)
- wave climate (water body size, coast orient., storms) - tides (tidal range/type, currents) - ice effects (ice cover & movement) - coastal processes (sed. supply/transport & rates) - biology (mangrove/salt marsh/reef, etc) |
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local relative sea level
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tide gauges fixed to land, so record changes due to both sea level rise (thermal expansion, melting) and land subsidence - causes exaggeration of SLR
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4 trailing coast features (opp for collision)
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- wide shelf
- low gradient - thick sedimentation - coastal plain |
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wave dominated coasts occur in...
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high energy regions where spring tide <1.5m and avg. wave range 0.5 to 3m in height
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tide dominated coasts occur where...
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spring tide range is >3x average wave height in surf zone
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fluvially dominated coasts shaped by...
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large river outflows and sediment loads - form deltaic landforms
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7 factors influencing sediment load of rivers
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- size of drainage basin
- large scale relief - local relief - geology of drainage basin - climate - runoff - vegetation |
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6 processes that lead to transforms in wave height, speed, wavelength, shape, direction
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- wave shoaling
- wave refraction - dissipation due to bottom friction - interactions w/other waves & currents - breaking - beach run up |
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wave height determined by (5)
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- wind speed
- fetch (distance over which wind acts on waves) - bottom topography - depth - wind duration |
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what affects speed of deepwater vs. shallow water wave?
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- deep water = wavelength or period
- shallow water = water depth |
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significance of stokes drift
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can lead to net transport of water and suspended matter in direction of wave propagation
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what is wave setup and why does it cause wave-generated currents?
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- a rise in the mean water level above still water level caused by breaking waves
- gives rise to longshore/rip currents due to the return flow |
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four components of equilibrium tides
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- semi-diurnal
- diurnal inequality (orbit relative equator at angle) - spring-neap cycle - perigee-apogee |
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four reasons for different tidal ranges around coasts
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- irregular landmass distribution
- interaction w/ocean bed and margins - effects of intertia - coriolis force |
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diurnal inequality causes what
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- two uneven high and low tides
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perogee/apogee
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- perigee when moon is closest to earth - 20% higher tide at perigee
- cycle every 27.5 days |
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what produces the largest tidal range and currents?
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when perigee aligns with spring tide
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spring tide (syzygy)
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- position of earth/moon/sun
- in conjunction, sun-moon-earth = stronger gravity |
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four F number ranges
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0-0.25 = semidiurnal
0.25-1.5 = mixed semidiurnal 1.5-3.0 = mixed diurnal >3.0 = diurnal |
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three factors influencing tidal propagation in estuaries
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- bottom friction (slows tide @ low tide b/c water is shallower (more friction in shallow water)
- tidal variation in water depth - funneling (water piles up where shorelines converge) *friction vs. convergence counter/interact |
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bedload is
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grain movement by bouncing, rolling, sliding thru grain-grain contacts (slow form)
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suspended load is
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grains kept aloft by fluid turbulence (settle when turbulence drops below critical shear stress of deposition)
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free-stream layer
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layer near surface not affected by bottom friction
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can there be a bottom boundary layer under oscillatory (wave) flow?
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no - breaks down during each wave period from forward/back stroke
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viscous sublayer
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small layer above bed w/laminar flow that is shielded from turbulence above - present in hydraulically smooth beds
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reynolds equation and factors
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Re = u*D/v
u* = shear velocity D = sediment grain diameter v = kinematic viscosity |
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what does Re # tell us?
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whether flow-induced turbulence is sufficient to overcome the viscous force of molecular viscosity (whether turbulence above will penetrate viscous sublayer)
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why is the Re# important?
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tells us about erodability of the bottom
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transgressive/regressive coast migrate...
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landward and upward/seaward downward
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trans or regressive coast depends on...
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rate of sediment supply relative to sea level change
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regressive forms a ? and transgressive forms a ?
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delta, estuary
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5 types of currents that influence beaches and barriers
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- tidal currents
- nearshore currents - wind-driven currents - wave-orbital currents - swash zone flow |
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3 zones of beaches
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- breaker
- surf - swash |
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wave setup
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- rise in mean water level due to "piling up" of water
- pressure gradient = current |
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3 types of nearshore currents
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- bed return flow (perp) (undertow)
- longshore (parallel) - rip (nearly perp) |
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velocity of longshore increases with...(2)
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- angle of wave approach, wave height in breaker
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longshore drift
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- net alongshore transport of sediment due to longshore current - gives rise to barrier spits and beaches, causes sediment buildup at jetties
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main effect of tides on waves
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moderate the height of breaking waves on the beach
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what wave and sediment properties control beach slope?
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- strength and volume of backwash/swash (fxn of steepness)
- grain size |
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how does slope change with steepness and grain size?
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increase steepness, flatten slope
- increase grain size decrease backwash transport = steeper slope |
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estuary definition
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semi-enclosed body of water that contains seawater diluted from river/land runoff and is a "drowned coastal embayment"
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delta definition
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low, alluvial tract of land at mouth of a river extending into the sea that is the result of accumulation of sediment that isn't removed by waves, currents or tides
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interplay between what three factors dictates a delta or estuary?
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- rates of relative sea level change, sediment supply, coastal topography
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4 types of geologic estuaries and examples
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- coastal plain - drowned river valley (DE, Ches Bay)
- fjord-type - drowned fjord - (Puget Sound WA) - bar-built - shallow lagoon behind barrier island (Sandy Hook Bay NJ) - tectonic - land-drowning by tectonic mvmt (San Fran) |
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3 types of salinity estuaries
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- salt wedge (strong strat) - weak tidal/landward flow
- partially mixed - dominant upstream flow - well mixed |
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gravitational circulation and clays
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- because of bottom flow landward, clays that settle from top tend to get brought back and not out to sea
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null zone
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place in estuary where sediment deposition/accumulation highest - floccs accumulate - end of SW intrusion
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why are deltas of economic importance?
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large burial of OM to produce oil
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examples of deltas
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- amazon
- congo - nile - yangtze - yellow |
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hydroperiod
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amount of time marsh is flooded with tide water
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salt marsh plant zonation reflects (2)
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tolerance to salt stress and soil saturation, plant competition
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general theory of isotopes
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- differences in atomic mass have slightly diff. chem/phys properties but *behavior* similar
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differences between lighter and heavier isotopes
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lighter has
- increased vibrational frequency - weaker bonds (broken easier) - more reactive |
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fractionation is (2)
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- partitioning of isotopes between two substances or two phases of same substance
- preferential uptake of one isotope over another |
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4 reasons delta 18O becomes more negative poleward
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- isotopic fractionation due to differences in vapor pressure at given temperature
- decreasing temperature increases fractionation factor - re-evap of surface water enriches 16O - evapotranspiration favors 16O |
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molecules with lighter of two isotopes (3)
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- form weaker bonds
- higher vibrational frequency - more reactive |
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kinetic fractionation examples (3)
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- psynth
- diffusion - evaporation |
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what happens to delta18O of vapor as temperature decreases?
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decreases, so does it's precip
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surface water d13C and PO4
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enriched in d13C, depleted PO4
- deep water opposite |
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d18O values of mississippi, global ocean, polar ice, subtropical gyre
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-4 - -1
0 -40 1.2 |
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high ice (colder t) and foram d18O
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- ice caps enriched in 16O
- ocean enriched in 18O - forams enriched in 18O - lower T - lower sea level |
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limitations of d18O in forams for paleo
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- biology has strong differences in amount of fractionation
- dissolution/diagenesis after burial - changes to salinity - can't get d18O of paleo-water so temp change is RELATIVE not absolute |
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why does psynth deplete surface 12C/enrich 13C
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12C diffuses readily
large preference for light isotope during psynth (kinetic effects) |
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change in fractionation factor with decreased temp
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increases
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why does tidal amplitude increase over shelves?
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- wave feels bottom - reduction in speed translated to increase in height -
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when do waves interact with the bottom?
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when h/L >0.5 water depth/wavelength
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what causes wave refraction on the coast?
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uneven bathymetry - changes wave speeds differently
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why semidiurnal vs. diurnal
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- changes in moon position relative to equator ( equator = semidiurnal)
- *earth not perfect sphere, position of continents blocks/interferes with tide wave as it moves - different sizes of ocean basins |
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which moves sediment, oscillatory currents produced by wind waves or tidal currents?
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tidal currents
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