Processes that Shape the Coastline

why is it precarious to build on a barrier island?

bc it has many changes within a lifetime

sea walls reflect wave energy, eventually, what happens to the beach?

it disappears

Where are the coastlines eroding in the US?

severely on the east coast and louisiana area

waves will refract around headlands and so the waves push the water?

towards the middle of the bay and will shoot out to be a part of the ocean

cliffs retreat (erode)

wave action erodes base of cliffs. This can cause cliffs to collapse causing landslides

longshore drift

waves strike the beach at an oblique angle, sediment moves along the shore

delta dynamics

when river hits standing water, flow fans out and loses its carrying capacity, sediment falls out

Long shore transport

when the waves are hitting the beach at an angle and moving the sand along with the beach

why do we have eroding coastlines?

- rising ocean levels - sand deprivation from man made structures

long shore bar

acts as a reservoir for sand, when the ocean is running low on sand it takes from the long shore bar. a beach that doesn't have sand dunes is missing a reservoir of sand

Wave-cut platform (terrace)

The smooth, level terrace sometimes found on erosional coasts that marks the submerged limit of rapid marine erosion

33% of N american shoreline is a ________

beach

why are barrier islands always moving towards land?

because its always being bombarded with waves and pushed towards mainland

typical beach structure

- beaches aren't flat, they have crests (aka berm crest) which is the highest point of the beach - many beaches have sand dunes behind the beach - many beaches have sand piled up underwater (long shore/ off shore bar)

why should we care about the coastline?

43% of US pop live in coastal counties, most us tourism revenues from coastal areas, most us disaster loses result from costal storms

delta

a low triangular area where a river divides before entering a larger body of water, pile of sediment delivered to the coast

rip current

a rush of water that flows rapidly back to deeper sea

lagoon

a stretch of salt water separated from the sea by a low sandbank or coral reef (not always trapped)

tidal flat zones

areas where the tides fluctuate up & down

lagoons can also exist in a?

atoll

very rarely does the wave train move directly onto the _______

beach, as the wave nears the beach it "feels the bottom" and starts to slow down so then the wave train starts to refract (bend)

all estuaries have sea water entering at depth, mixing with riverine freshwater, and _________ water leaving at the surface

brackish

remember coastlines are places of change, these barrier islands shift with the balance of?

erosion and deposition

storms and hurricanes cause storm surge (flooding) and high waves cause?

erosion, sea level rise causes inundation

fjord is a typ of?

estuary (flooded glacial valley)

Supratidal Marsh

ex: bolsa chica wetlands, wetlands are important for migrating birds, lot of important life in the wetlands

estuary type circulation

fresh water on top, seawater on bottom

this power play between erosion and deposition determines..?

how a coastline changes

submarine canyons _______ sediment, it goes down to the turbidity currents and we lose sand from the coastal system

intercept

How are barrier islands formed?

pushing sand out off of mainland beach and forming long sandbar

barrier islands

ribbons of sand between ocean and mainland

Spits

sand deposits that form when longshore currents that move sand along the shoreline encounter deeper water in a bay and drop their sediment loads

net erosion

sediment is taken away faster than it is added

under what conditions do deltas form?

sediment supply excess wave erosion, supplied by rivers w/ large drainage areas, on passive margins where material can accumulate (not too much wave energy)

shoreline is a dynamic balance between the _________ supply and the ocean's _________

sediment, energy

the waves approach the beach at an angle, they throw material up onto the beach at that angle as they break, but the beach is always sloping down towards the water. what does this mean?

that whatever gets thrown upon the beach will, by gravity, tend to move straight back down

supratidal zone

the area above the intertidal zone up to the sand dunes (high tide), is flooded by extreme tides/storms

intertidal zone

the area of shoreline between low and high tides, exposed on a daily basis

Estuary (drowned river)

the area where a freshwater & salt water or river stream merges with the ocean

the coastline is modified by what?

the balance/imbalance in sediment supply from the land (deposition) and the ocean's energy to carry it away (erosion)

subtidal zone

the coastal life zone that remains underwater (below low tide)

why is the coastline like a car bumper?

the coastline acts as a point of impact of ocean energy impacting the continent ex: Sri Lanka

whats pushing & pulling the waves?

the energy of the ocean, more energetic waves will pull the sandy more into the water

why are there tree trunks buried in the sand in the front of the barrier island?

the islands are moving backwards all the time so that the tree, originally in a grassy area, has now been moved to a different area and is covered up with sand

in california because there's a predominant orientation of waves coming from the northwest the sand moves primarily towards?

the south

whats happenin to waves in the winter? (bigger waves)

the waves grab the sand and pull it down off the beach & store it back in the ocean underwater. takes all the sand off the beach so that theres no more sandy beach

whats happenin to waves in the summer? (smaller waves)

the waves push the off shore bar up the beach so that the off shore bar becomes part of the beach & broadens the beach. This makes the beach flatter since the bumpy off shore bar was removed and pushed onto the beach

how do beaches have sand?

there's a supply of sand and it hasn't all been pulled away by the waves--the energy of the environment was stronger than the supply of sand

when we build a dam, what happens to the beaches?

they shrink since we're depriving the beach of sand

what happens when you build something in the middle of the long shore transport

you change the distribution of sand on the beach