Shorelines Flashcards
what are shorelines
dynamic environments
Erosional + depositional processes combine along coasts to create landscapes that undergo rapid change
Ancient shoreline deposits occur as rock bodies that are important oil + gas reservoirs
Wind-generated waves provide most of the energy that shapes + modifies shorelines
what is the processes of waves?
Energy in normal water waves (I.e. except tsunamis), is derived from the wind
Tops of waves (crests) are separated by wave troughs
Wavelength: horizontal distance btwn wave crests
Wave height: vertical distance btwn trough + crest
Wave period: the time it takes for 2 successive crests to pass a given point
how do waves move in deep water
In deep, open waters, water molecules move in a circular path during the passage of a wave
The circular motion rapidly diminishes w/ increasing water depth
At a depth equal to abt half the wavelength, the movement of water particles becomes negligible (this depth is called wave base)
how do waves move in shallow water
As waves approach a shoreline, their characteristics will change
Waves will “feel bottom” at a water depth equal to abt half their wavelength (wave base)
Friction w/ the seafloor slows down advancing waves at their bases (at the sea surface, crests are still moving quickly)
Wavelength decreases, wave heigh increases
Eventually, the waves collapse (“break”) in the surf zone
what happens after a wave breaks
After a wave breaks, water moves up the slope of a beach as a sheet (this is called “swash”)
The sheet of water slows, stops, then returns to the sea as “backwash”)
Backwash > swash = erosion (destructive)
Swash > backwash = deposition (constructive)
waves are powerful agents of what?
erosion
most sediment deposited along most shorelines are deliver to the sea by what?
streams
sediment can travel alongshore by ____
beach drift
Along most shorelines, waves approach the shore at an oblique angle
Swash carries suspended particles up the beach at an oblique angle
Water always refunds to the sea under the influence of gravity (as backwash) in a direction perpendicular to the shoreline
As a result, each sand particle on the beach moves in a zig-zag pattern down the length of the beach
what is a offshore drift
Seaward of a beach, oblique waves can also produce turbulent longshore currents
Longshore currents easily move fine suspended sand + roll larger + gravel along the bottom
If it were not for beach drift + longshore currents, redistributing sediment from river mouths, many beaches would be nearly sandless
what is a tide
Repetitive daily changes in elevation of ocean surface due to gravitational attraction btwn Earth + the Moon (to lesser extent, the Sun)
The Moon’s gravitational force produces a bulge in the ocean. Due to inertia, a matching bulge also develops on the opposite side
what are tidal cycles
Bc position of Moon changes very little in a single day, we can imagine the tidal bulges remaining in place while Earth rotates through them
The pattern is little more complicated bc of Earth’s tilt (tides tend to be unequal due to this)
Bulges migrate very slightly as the Moon orbits around the Earth
as tide rises, landward- moving water generates what?
flood currents
as tide falls, seaward-moving water generates waht?
ebb currents
where do wave-cut cliffs originate from
originate by the undercutting action of the waves against the base of coastal land
what are shorelines where deposition dominates over erosion
“Fair-weather wave base” (FWWB) is the maximum water depth affected by normal, day-to-day
“Storm wave base” (SWB) is the water depth affected by storm waves (deeper than FWWB)
