week 8-elle Flashcards
how many people live within 100km of the coast
2.75 billion & increasing
two zones of costal areas
- Coast
- Shore
What is a Coast
-large zone affected by ocean driven processes
-extends inland as far as costal processes reach and/or ocean-related features occur
What is the shore
-the zone where ocean meets the land
-between low tide and highest point storm waves reach
**can be further subdivided
what is a coastline
-point where highestwavepoints reach
5 parts of the shore
- Shoreline
- Backshore
- Foreshore
- Nearshore
- Offshore
Shoreline
position changes, at waters edge
(very point where water hits oceans hits land)
Backshore
above high tide level, covered by water only during storms
Foreshore
exposed at low tide, covered at high tide
Nearshore
from low tide shoreline to breaking waves (low tide)
Offshore
waves unaffected by the bottom
can shoreline be the same as coastline
yes, but rarely and only during very big storms
Beach face
gentle decline of the shore
what is created from the rolling of waves
longshore trough & bars in nearshore zone
wide gentle sloped beaches reduce the
vertical transfer of wave energy
(less energetic breakers, less potential for longshore bars)
what is needed for deposition
low energy (high energy=no deposition)
main driver of beach shapes is
energy
Do all beaches have cliffs/bluffs
no some have rolling dunes
what is a berm
a nearly horizontal, shore-parallel ridge of sand or gravel formed by wave action, typically located above the high tide line and acting as a natural sand barrier
when would high dunes occur
low wave activity and high winds
Dune features in the west facing parts of ontario
- sediment builds up
- winds push sediment back from water
4 variable compostitions of a beach
- volcanic
- Anthropogenic
- Biological
- Mixture
volcanic beaches
basalt, andesite olivine
example: Pa’iloa beach, Maui
Anthropogenic beach
glass fragments
ex. fort bragg, california
Biological beach
shells, teeth
ex. Shell Beach, west austrailia
example of mixture beach
belinho beach, portugal
what determines composition of beaches
what you get is reminiscent of minerals in that area
Swash
-water moving onto beach
-wave energy
-carries sediment onshore
-increases slope of beach
Backwash
-water returning to ocean
- can also transport sediment back into ocean
-gravity energy
-
which energy is stronger swash or backwash?
swash, therefore more sediment pulled onshore than what is taken away
why are beaches mostly sand and pebbles not silt/clay
b/c pebbles are the biggest particles and clay is the smallest so it takes more energy to transport pebbles and clay
**also water cannot go through clay
which moves bigger and more sediment backwash or swash?
swash
when is backwash energy greater?
on a steeper beach
seasonal beach appearance
-changes between summer and winter
-more storms in winter increase wave energy moving material onshore and carrying material offshore
(can be reverse in regions with greater summer storms)
generally, when are beaches bigger
in the summer
Winter (stormy weather) beach
-sand stored offshore (longshore bar)
-narrow berm
Summer (calm weather) beach
wide berm, sand stored on beach
Longshore current
a current that runs parallel to the shoreline caused by waves breaking at an oblique angle to the coast (even with wave refraction)
energy in a longshore current
part of the waves energy is directed perpendicular to the shore and part is directed parallel
what type of wave energy generates a longshore current
parallel energy which runs along the shoreline
where is the maximum parallel energy in a longshore current
just off the shoreline
wha tis a longshore drift
movement of sediment along the shore by zig zag movement
what do longshore currents and longshore drifts create
depositional coasts
net transfer of sediment ends up being
parallel to shore
Erosional Coast
-coast on which the dominant processes are those that remove costal material
***usually associated with rocky coasts
Depositional Coasts
material (sediment or biologically derrived material) is accumulated
***usually associated with beaches
depositional coasts are shaped by
longshore currents and drifts
what leads to deposition
loss of energy of physical obstruction
example of depositional coast
perth australia
features of depositional coasts
- beach
-spit
-tombolo
-delta
-bay barrier
-barrier island
where in canada are there many depositional coasts
on east coast
example of spit
Farewell spit New Zealand
Spits
accumulation of sediment that is attached to land at one end
Tombolos
-strip of sediment accumulating between an offshore island or sea stack and the main shoreline
-connects mainland to sea island
Wave Shadow
-low energy environment
-longshore current gets disrupted and split by nearby island
Baymouth bar (bar barrier)
-spit growing across a bay, river mouth
-narrow inlet may be present
Example of baymouth bar
Hungry Head Beach, NSW, Austrailia
Deltas
-depotisiton of sediment at rivers mouth
-fertile, shallow areas
-type/form depends on dominant process
3 types of deltas
- River-dominated
- Tide-dominated
- wave-dominated
River Dominated Deltas
- low tidal range (River Input, low wave energy)
- River extends into the sea
- formation of individual lobes
Examples of RIver-dominated deltas
-Mississippi River
-Ural river delta
Tide-dominated Deltas
-strong tidal influence
-long narrow sand bodies separated by tidal channels
-tidal channels parallel tide direction
examples of tide-dominated deltas
-Mekong river delta
- Ganges-Brahmaputra delta in india (largest in the world)
Wave-dominated deltas
-wave erosion controls shape
-straight shorelines & beaches parallel to the coast
-hit by waves frequently, washing sediment away
Examples of Wave-dominated deltas
Sao Francisco River, Brazil
Barrier Islands
-distinctive zones
-afftected by longshore currents, waves and tidal activity
Barrier islands are
MOBILE & BIG
-landward migration of island; storm activity and/or sea level rise
Largest sea (sand barrier) island in the world
Kgari (fraser)
what is Kgari (Fraser) caused by
longshore drigt and change in direction of continent
Barrier Islands protect
true coast against storms and sea level rise
Overwash
process where water and sediment flow over the crest of a barrier island, dune or spit by waves and in most cases, storm surge
Erosional Coast
-most are rocky
-75-80% of worlds coasts
-limited beach development
-erosional rates > sediment rates
-low sediment supply to beach
-areas of high energy
what causes weathering and erosion?
-precipitation
-heat (sun)
-freezing temperatures
-wind
-waves
why is temperature a contributor of erosion
causes expansion & contraction
Hydraulic pressure
pressure of water smashing against rock
Abrasion
waves pick up sediment, ‘throw it’ against the cliffs, wear down the cliffs
Attrition
sediment hits each other, become smaller and smoother
Corrosion
breaking down of rock naturally by a chemical reaction
Features of erosional rocky coasts
-wave-cut platforms
-sea caves & arches
- sea stacks
Wave-cut platforms
-irregular shoreline (headbands and bays/coves)
-rocks of differing hardness and resistance
- wave refraction concentrates energy
Pocket Beach
-lower energy zone
-feature of wave cut platform
Stages of wave cut platform
- Original position or cliff
- Wave-cut notch
- Notch increases and cliff collapses
- Cliff retreats
- Wave-cut platform
waves cut into the cliff overtime to create a
notch
Example of wave cut platform
Delimara, Malta
Sea Caves (future arch)
-essentially extended notches
-hydraulic action causes deep cracking that gets larger and larger
-arches form when caves on either side of a headland join
Process of evolution of features of rocky coasts
- crack open by hydraulic pressure
- crack grows by hydraulic action & abrasion
- cave becomes larger
- cave breaks through the headland forming a natural arch
- arch eroded and collapses
- leaves tall rock stack
- stackerodes forming stump
famous sea stacks
12-> 8 apostles in australia
Estuaries
-body of water and associated costal habitats found where rivers meet the ocean
-saline water mixes with fresh water to create brackish water
-contains unique plant and animal communities
-area of transition
most productive ecosysmtems on earth
Estuaries
lots of fish nursaries because high productivity
primary productivity
rate at which plants convert solar energy into food that animals can use
what is needed for primary producivity
sunlight and nutrients; shallow water has lots of this
benefits of esuaries for the ecosystem
- large cleaning properties
- critical habitat for species that are values commercially, recreationally, and culturally
-water filtration, habitat and shoreline protection
-buffer zones
-fish habitat & nursaries
-natural barriers against storms
Autotrophs
use sunlight to make energy
Chemoheterotrophs
eat autotrophs & consume oxygen & other primary producers
Salinity of estuaries
variable
Well mixed estuaries
- river flow low & tidal currents are moderate to strong
-salinity same from surface to bottom
-salinity is highest near ocean and decreases as it moves upriver
-brackish waters
Partially Mixed estuaries
- saltwater and freshwater mix at all depths
- lower layers of water remain saltier than upper layers
- salinity greatest at estuary mouth and decreases upstream
Salt wedge, high stratified (vertically) estuaries
- least mixed (most stratified)
- sharp boundary between water masses, freshwater floats on top, and wedge of saltwater on bottom
-occurs when rapidly flowing river enters ocean where tidal currents are weak
Estuary species distribution
changes rapidly based on salinity
how do we know sea level is changing
-coastline (shoreline) positions have fluctuated
-geological, archaeological and paleontological evidence
-mastodon and mammoth remains on continental shelf
coastlines and sea level changes in vertical water level
minor shifts on steep coasts but significant shift on gently sloping coasts
shoreline/coastline positions change in response to
sea level changes and vertical land movements
EUstatic change
global change
Isostatic change
regional/local change
reasons for Eustatic sea level change
- Variation in amnt of water in ocean
- Variations in water temperature
- Changes in volume of oceans container
why does Variation in amnt of water in ocean contribute to global sea level change?
glacial periods vs. interglacial periods
- weight of ice depresses land
-reason for present-day sea level rise
last glacial period
-last glacial periods was 110000-12000 yrs ago
-ice sheets covered almost all of canada
-sea level was 120m lower
why does variation in water temperature affect global sea level change
as water warms = less dense = less expansion
cold seawater expands and occupies more volume, rising the sea level
highest temperature density of water
4 degrees celcius
why does changes in volume of oceans container contribute to sea level rise?
- seafloor spreading
- rapid erosion into the ocean
- geological timescale changes
Changes to the oceans container at high sea level
smaller basin, fat profile, fast spreading, wide ridge crest
Changes to the oceans container at low sea level
larger basin, thin profile, slow spreading, narrow ridge crest
Isostatic sea level change
-land adjustments; movement of land relative to sea
- tectonic changes on a regional scale are isostatic
Emergent coasts
wave erosion produces a wave cut bench along an emergent coast. as the land rises, the bench becomes a terrace, and a new wave cut bench forms
Submergent coasts
costal land is sinking (subsidence, eustatic sea level rise)
**costal land is falling relative to sea level
Emergent Coasts
costal land is rising (uplift, eustatic sea level fall)
**wave-cut terraces and platforms are exposed
marine terraces
exposed as the sea level becomes lower
