Chapter 10: Shores

barrier island features

ocean beach, dune, barrier flat, salt marshes, lagoon

popular building sites, ppl love to live near oceans

ocean beach

closest part of the island to the ocean

dune

stabilized by grasses, protect lagoon from strong storms

barrier flat

grassy area that forms behind dunes

salt marshes

inland of barrier flat, high salt marsh extends to highest spring tide line, low salt marsh extends from mean sea level to high neap tide line

lagoon

btwn. mainland and barrier island. peat bed underneath lagoon and barrier island

barrier island migration

migrate landward over time due to rising sea levels, older peat levels found on ocean beach

deltas

triangular deposits of sediment where rivers empty into oceans or seas

high productivity, high O2 [ ]

distributaries

branching channels carrying sediment to ocean

delta shoreline components

shoreline smoothed when erosion exceeds deposition.

large fisheries, high productivity,

nile river delta currently eroding

nile river delta

currently eroding, if longshore drift carries sediment deposits, curved delta front similar to nile river delta will form.

beach compartments

rivers that supply beach sediment

beach itself

offshore submarine canyons

beach starvation

human activities block supply of sand to beach compartments.

Dams across rivers block sediment

longshore transport process continues to operate in absence of river sediment input. if all streams supplying sediment are dammed, beaches will disappear

emerging shorelines

shorelines rising above current sea level.

marine terraces (flat platforms backed by cliffs),

stranded beach deposits (indication that former shoreline has risen above sea level)

US Pacific coast

submerging shorelines

shorelines sinking below current sea level

drowned beaches

submerged dune topography, drowned river valleys,

US Atlantic coast is one

marine terraces

stranded beach deposits at diff levels

two major processes for sea level change

local tectonic processes raise or lower crust

worldwide changes in sea level

movement of earth’s crust

tectonic movements

isostatic adjustment

changes in relative sea level, land changes, not sea

tectonic movements

crustal uplift, localized folding, tilting

pacific coast

isostatic adjustments

earth’s crust sinks under heavy loads of ice, piles of sediment.

rebound of crust after removal

eustatic sea level changes

worldwide, due to changes in seawater volume or ocean basin capacity.

caused by formation of inland lakes, decrease in sea level, sea floor spreading rate changes

formation of glaciers

sea floor spreading rate

changes: shape of ocean basins change due to tectonic movement

basin = larger, volume =larger, sea level falls, bc same amount in bigger container.

pleistocene epoch

2 million-10k years ago, 4 ice ages affected earth

it was 120 m (400 ft) sea level lower

if all ice melts today, sea level rises another 70 m (230 ft)

hard stabilization

structures built to decrease coastal erosion and interfere with sand movement.

“armoring of shore” sand traps,

4 major types of hard stabilization structures

groins and groin fields

jetties,

breakwaters

seawalls

groins and groin fields

perpendicular to beach: built of rip rap, large blocky material

traps sand upcoast, causing erosion downcoast of longshore current

another groin downcoast, causes groin field. sand distributed differently, no additional sand on beach

Jettie

similar to groin, built perpendicular to shore in pairs.

protects harbor entrances and only secondarily traps sand.

cause more upcoast deposition and downcoast erosion

breakwaters

parallel to shore, protect harbor from waves, cause excessive erosion, requires dredging to keep area stable

seawalls

most destructive

parallel to shore, armor coast and protect developments

one large storm removes beach, wave activity eventually destroys structure, needs maintanence

alternatives to hard stabilization

construction restrictions

beach replenishment

relocation

construction restrictions

simplest alternative, limit building near shore

national flood insurance program encourages construction

beach replenishment

Sand added to beach/longshore current

costs between $5 and $10 per cubic yard

Sand must be dredged from elsewhere

relocation

move structures rather than protect them in areas of erosion

allow humans to live in natural balance with beach processes

coastal waters characteristics

salinity, temp, coastal geostrophic currents

halocline

represents salinity variations with depth in water column

isohaline

uniform salinity from surface to deeper layers

freshwater runoff causes lower surface salinities at coast

combo of these two causes vertical mixing, moderate salinity, and water column that is isohaline

isothermal

water temp is uniform throughout water column

thermocline

temp variation with depth.

in low and high latitude regions, water is isothermal year round

in midlatitude areas, surface temps are coolest in winter and warmest in summer

coastal geostrophic currents

move circular path

generated in coastal areas by wind and runoff

wedge of freshwater runoff on coast generates surface flow towards open ocean

davidson current

coast of Washington and Oregon

estuaries

partially enclosed coastal body of water in which freshwater runoffs from a river dilutes the input of salty ocean water

4 types of estuaries

coastal plain estuary

fjord

bar built estuary

tectonic estuary

coastal plain estuary

forms  as  sea  level  rises  and  floods  existing  river  valleys.  Also  called  drowned  river  valleys – Chesapeake Bay

fjord

forms when sea level rises and floods an existing glaciated valley. These valleys typically are U shaped and have steep walls with glacier debris near ocean entrances

bar built estuary

includes  lagoons  that  separate  barrier  islands  from  the  mainland.  They  are  generated  from sand bars that are deposited parallel to the coast by  ocean wave processes – U.S. Gulf coast and East Coast

tectonic estuary

forms with faulting or folding of rocks that generate a geologically dropped location that the sea floods

San Fran Bay

vertically mixed estuary

shallow, low-volume. Net flow from head to mouth of estuary, salinity increases from the head to the mouth of the estuary

slightly stratified estuary

salinity increases from head to mouth at all depths. Two distinct layers, less-saline(less dense) upper layer and more saline(more dense) lower layer

highly stratified estuary

deep with upper layer salinity increasing from head to mouth

salt wedge estuary

wedge of salty water from ocean moves in under river water

estuaries and human activities

threatened by human populations

breeding grounds and nurseries

human activities can damage estuarine environments

columbia river estuary

salt wedge estuary

principal conduit for logging industry

increased sediment load

dredging of sediment carries increased pollution risk

chesapeake bay

slightly stratified

large seasonal changes in temp, salinity, dissolved o2

max freshwater river flow in spring

issues with chesapeake bay

waters become anoxic from May-August.

major kills of commercially important blue crabs, oysters, and other bottom dwelling species

increased nutrients from sewage and agricultural causing algal blooms and environmental issues

lagoons

protected shallow water bodies landward of barrier islands.

bar built estuary

restricted circulation with ocean, therefore 3 distinct zones.

freshwater zone

near head of lagoon

transitional zone

middle of lagoon

saltwater zone

near mouth of lagoon

laguna madre

along Texas coast, btwn. Corpus Christi and Rio Grande.

protected by Padre Island, barrier island 160 km long

hypersaline

large seasonal variations

ocean water flows as a surface wedge over denser lagoon water

marginal seas

large semi isolated bodies of water

result from tectonic events that isolated ocean crust btwn. continents or created behind volcanic island arcs

Mediterranean and Caribbean sea

mediterranean sea

remnant of tethys sea

Shallow and narrow connection to Atlantic Ocean and Black Sea

Irregular coastline, divides it into subseas, like the Aegean and Adriatic Sea

underwater sill or ridge separates mediterranean into two major basins

mediterranean circulation

unique pattern due to middle east heat

large surface in flow from Atlantic to replace evaporated surface h2o

opposite of most estuaries

wetlands

ecosystems with water table close to surface

generally saturated, fresh or coastal

efficient at cleaning polluted water. remove agricultural runoff

salt marshes

btwn. 30 and 65 degrees latitude

support salt tolerant grasses and other halophytic low lying plants: cordgrass, salt meadow cordgrass

mangroves

tropics below 30 degrees latitude

salt tolerant trees, shrubs, palms

tall tripod like root systems

caribbean, florida, southeast Asia

characteristics of coastal wetlands

diverse plants and animals

most productive

enormous economic benefit

nurseries for more than half of commercially important fish species in SE US

what do coastal wetlands do

soak up farmland runoff

remove inorganic nitrogen compounds

“nature’s kidneys”

protect shoreline

1 acre of wetland can filter 2.76 million liters of water each year

loss of wetlands

more than half of US wetlands have vanished

filled in and developed

originally 87 million hectares, now 43 million.

49.7 % remain

EPA established office of wetland protection.

tasked with enforcing regs against pollution and identifying important ones