Transcript OMAHA Coastal Environment

A/S outline + Where is the natural environment, what is it like, what
natural features (landforms) are there and where are they located
(distribution)?
LESSON ONE
Demonstrate understanding of how interacting
processes shape a NZ Geographic environment
External exam
• Where is the natural environment, what is it like, what natural
features (landforms) are there and where are they located
(distribution)?
• What natural processes are interacting to form the landforms
(outcomes) and what are the interactions involved? What is the
scale of these processes (individual event, seasonal, short
term, long term or over geological timescale)?
• How and why do these processes show temporal variations?
• How and why do these processes show spatial variations?
• How and why is the environment being modified at the present
and is it likely to be changed in the future?
Omaha natural environment
• Where is Omaha?
Where is the natural
environment?
Location and Extent:
• 60km N of Auckland, on the East coast
• 36*20’ 26” S 174* 46’ 30” E
• Sand Spit 4kms long, orientated N-S,
between 2 rocky headlands, Ti Point to the N
and Karamuroa Point/Te Kie point to the S.
• The Whangateau Harbour entrance
separates the spit from Ti Point.
• The northenmost end of the spit is called Te
Taumutu Point.
Mapping activity
Location
Oblique aerial photograph
Origins of the sand spit
• The sand spit was formed 6,500 yrs ago after
the last ice-age ( sea levels 100m lower and
freeze-thaw weathering broke up rocks). Sands
were transported shoreward from the Hauraki
Gulf by rising sea levels.
• Sand spit formed by ocean currents depositing
sand in slack water in a Northerly direction from
Te Kie point.
• Over the last 100yrs sea levels have continued
to rise by approx 13-14cm.
What are the natural features?
Where are they located?
Ocean beach:
Dunes, fore dunes and back dunes
Sand ripples/beach cusps
Berm marking at high water mark
Ocean Beach: dunes
Back dunes
Fore dunes
Ocean Beach
Ocean Beach: sand
ripples/beach cusps
Ocean Beach: berm marking at
high water mark
What are the natural features?
Where are they located?
Ti Kie Point/Ti Point:
Cliffs/headland
Shore platform
Ti Kie Point/Ti Point:
Cliffs/headland
Ti Kie Point/Ti Point:
shore platform
Cliff with shore Platform
Cliff
Waitemata sandstone
Greywacke
Shore Platform
Features of Mangatawhiri Sand
Spit
(1) beach of sand composed of quartz and feldspar between 20 and
100m wide
(2) longitudinal sand dunes 1-4m high with spinifex, pingao, and
marram grasses on the fore dunes, and lupins, pohuehue and shrubs
on the back dunes. Dune ridges run parallel to the beach and have
steep windward slopes-(20*) and gentler leeward slopes (5*).
Sand ripples and beach cusps can be seen on the northern beach.
The Northern part is a bird reserve of 8 hectares.
Features of Mangatawhiri Sand
Spit
(3) At the southern end of the beach, Te Kie Point is a cliff, 20-50m
high of Waitemata sandstones and mudstones with
(4) a horizontal shore platform at the base of the cliff, up to 100m wide
of darker, harder greywacke.
(5) North of the Whanateau harbour, Ti Point is a headland of olivine
basalt.
Drawing a precis sketch
• A precis sketch is a simplified drawing of an area showing only
“points of interest” to you and your reader – in our case a precis
sketch of natural features at Muriwai.
• Use definite lines and do not use shading.
• Divide your picture into 3 parts: background, middle ground and
foreground. Draw one part in entirety at a time.
• Features in the background are smaller and darker (to show
darkness draw diagonal lines really close together).
• Features in the foreground look larger and are lighter (to show
lightness draw a few diagonal lines).
• Do not include moving objects like cars, people or gannets.
• Include a title, frame and labels (use a ruler and write the name of
the feature neatly).
Draw a precis sketch of this
view
Elements and natural processes (1)
LESSON 2
Do now
• Name 2 features at Ocean Beach
• Name 2 features at Te Kie Point
Do now
• Name 2 features at Ocean Beach
Ocean beach:
Dunes, fore dunes and back dunes
Sand ripples/beach cusps
Berm marking at high water mark
• Name 2 features at Te Kie Point
Cliffs/headland
Shore platform
Do now
Describe the location, size and extent of the Omaha
coastal environment
Do now
Describe the location, size and extent of the Omaha
coastal environment
• Location:
60km N of Auckland, on the East coast 36*20’ 26” S
174* 46’ 30”
• Extent:
The limit of Little Omaha Bay (Ocean Beach) is Ti Point in
the North and Karauroa Point in the South. The
Whangateau Harbour entrance separates the spit from Ti
Point. The northenmost end of the spit is called Te
Taumutu Point.
• Size:
Sand Spit 4kms long, orientated N-S, between 2 rocky
headlands
Definitions
- how many do you know?
•
•
•
•
•
Cliff
Bay
Esturary
Spit
Beach
Definitions
- how many do you know?
• Cliff
A steep rock face along the coastline
• Bay
Indents in the coastline between two headlands
• Estuary
The part of the wide lower course of a river where its
current is met by the tides
Definitions
- how many do you know?
• Spit
A ridge of sand deposited parallel to the coast by long
shore drift
• Beach
The area of deposited sediment between the lowest spring
tide level and the point reached by the storm waves in the
highest tides
• To know what the natural processes are,
we need to know what the individual
elements are that work to form processes.
• What could be some examples of
elements?
Elements/Inputs
Processes
Features/Phenomena
Sand____________
Past Processes
1______________________________
2____________________________________
Weathering
1___________________________
2____________________________________
3____________________________________
Mass Wasting
_____________________________________
_____________________________________
Wave erosion(destructive waves)
1____________________________________
2____________________________________
3____________________________________
Wave
transportation(LSD)_____________________
_____________________________________
Wave deposition(constructive
waves)________________________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
Wind____________
Waves___________
Tides____________
Sunshine hrs______
Vegetation________
________________
Rock____________
Wind transportation
1____________________________________
2____________________________________
3____________________________________
Wind
deposition_____________________________
_____________________________________
Fluvial transportation and deposition
_____________________________________
_________________________________
Tidal
flow__________________________________
____________________________________
Feedback
Rock eroded from cliff
deposited on beach as
sand_______________
1. Inputs/Elements
Write these on handout
• Inputs: winds NE to SE
: waves NE to SE
: tides 0.2-2.7m. Into the harbour (flood) and out (ebb)
of harbour
: sand fine (0.17mm)- (0.3mm) to medium-coarser at
harbour entrance-high feldspar content=volcanic origin from
central N Island via Waikato R. through Hauraki Plains.
: base rock- greywacke with Waitemata Sandstone on
top Ti Point-olivine basalt intrusion-hard rock but jointed,
Karamuroa-sandstone
: vegetation: marram, spinifex, pingao
: sunshine
: rain
How to measure wind?
Wind Erosion, Transportation and Deposition.
Beaufort Wind ScaleDeveloped in 1805 by Sir Francis Beaufort
of England
Wind
WMO
Force (Knots) Classification
0
Less
than 1
1
Appearance of Wind Effects
On the Water
On Land
Calm
Sea surface smooth and
mirror-like
Calm, smoke rises
vertically
1-3
Light Air
Scaly ripples, no foam
crests
Smoke drift indicates
wind direction, still
wind vanes
2
4-6
Light Breeze
Small wavelets, crests
glassy, no breaking
Wind felt on face,
leaves rustle, vanes
begin to move
3
7-10
Large wavelets, crests begin Leaves and small twigs
Gentle Breeze to break, scattered
constantly moving,
whitecaps
light flags extended
4
11-16
Moderate
Breeze
Small waves 1-4 ft.
Dust, leaves, and loose
becoming longer, numerous paper lifted, small tree
whitecaps
branches move
5
17-21
Fresh Breeze
Moderate waves 4-8 ft
taking longer form, many
whitecaps, some spray
6
22-27
Larger waves 8-13 ft,
Strong Breeze whitecaps common, more
spray
7
28-33
Near Gale
Sea heaps up, waves 13-20
ft, white foam streaks off
breakers
Whole trees moving,
resistance felt walking
against wind
Gale
Moderately high (13-20 ft)
waves of greater length,
edges of crests begin to
break into spindrift, foam
blown in streaks
Whole trees in motion,
resistance felt walking
against wind
Strong Gale
High waves (20 ft), sea
begins to roll, dense streaks
of foam, spray may reduce
visibility
Slight structural
damage occurs, slate
blows off roofs
10
48-55
Storm
Very high waves (20-30 ft)
with overhanging crests, sea
white with densely blown
foam, heavy rolling,
lowered visibility
Seldom experienced on
land, trees broken or
uprooted, "considerable
structural damage"
11
56-63
Violent Storm Exceptionally high (30-45
8
9
34-40
41-47
Small trees in leaf
begin to sway
Larger tree branches
moving, whistling in
wires
WAVES
wave length
crest
wave
height
trough
particles in
waves follow a
circular pattern
Waves are measured as wave length from wave crest to crest
Wave height is measured from trough to crest
Copy and draw a diagram
Waves transfer energy from one place to
another as the water particles move forward
in a circular motion. The water itself will rise
and fall with the movement of the wave.
Waves at sea are created by the transfer of
energy from wind to the sea surface.
Copy and draw a diagram
As the waves approach Te Kie Point, the
sea becomes shallow and the base of the
wave is slowed down by frictional drag. In
turn, the wave crest becomes higher and the
wave length shorter. When the wave height
is greater than the wave depth, the crest
breaks. As Te Kie Point, a headland, juts out
into the sea, the wave breaks directly on the
headland at high tide.
Wave Types
TIDES
Are daily changes in sea levels
• Tides rise (FLOOD) to produce
a HIGH TIDE
• And fall (EBB) (LOW TIDE)
• Produced by the gravitational
pull that the Sun and Moon exert
on the Earth’s surface and the
oceans on 1 side and the other
side bulges out because of inertia
•there are two high tides on Earth
at any one time
Moon/
Sun
• Can you think of any examples of natural
processes?
Elements/Inputs
Processes
Features/Phenomena
Sand____________
Past Processes
1______________________________
2____________________________________
Weathering
1___________________________
2____________________________________
3____________________________________
Mass Wasting
_____________________________________
_____________________________________
Wave erosion(destructive waves)
1____________________________________
2____________________________________
3____________________________________
Wave
transportation(LSD)_____________________
_____________________________________
Wave deposition(constructive
waves)________________________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
Wind____________
Waves___________
Tides____________
Sunshine hrs______
Vegetation________
________________
Rock____________
Wind transportation
1____________________________________
2____________________________________
3____________________________________
Wind
deposition_____________________________
_____________________________________
Fluvial transportation and deposition
_____________________________________
_________________________________
Tidal
flow__________________________________
____________________________________
Feedback
Rock eroded from cliff
deposited on beach as
sand_______________
2. Natural processes
Write these on handout
1 Past volcanic processes and past weathering (frostshattering during peri-glacial times) to produce the sand.
2 Processes that erode or wear away the rocks.
• Weathering (salt crystal growth and exfoliation) and
• Mass Wasting (rock falls, landslides)
• Wave erosion (by destructive waves), wave quarrying,
hydraulic action (30 tonnes per m2), abrasion, attrition.
• Wave Refraction around Te Kie Point
3 Processes that deposit or build up the beach.
• Wave transportation ( longshore drift ) and wave deposition
by constructive waves pushing sand up the beach in the
swash.
• Wind (Aeolian) transportation by saltation, surface creep
and suspension and wind deposition when the wind drops
or sand hits vegetation, fence etc.
Processes that erode rocks
- weathering
exfoliation
Exfoliation occurs where there is alternative
heating of the rock during the day and
cooling during the night. This results in the
expansion and contraction of the rock which
weakens the sandstone. The outer layers
brake off as concentric layers.
Exfoliation or Onion Weathering
Processes that erode rocks
- weathering
Salt crystalisation
• Salt crystals attack porous, coarsely
granular rock.
• Saline water enters pores and as it
evaporates salt crystals form.
• As they grow pressure is put on the rock,
or the rock is dissolved and/or split by
incoming water.
Processes that erode rocks
- weathering
Mass wasting (rock falls, landslides)
Is the removal of material downslope and
occurs due to gravity. This allows soil and
rock to fall down the steep slopes and form
a scree slope at the bottom where it
accumulates
Elements and natural processes (2)
LESSON 3
Processes that erode rocks
Wave erosion (by destructive waves), wave pounding,
hydraulic action, abrasion, attrition.
Abrasion
• This is caused by boulders, pebbles and sand being
hurled against the base of the cliff by breaking waves.
This results in rock breakup.
• When a cliff consists of differing layers of rock of differing
resistance, the less resistant rocks are eroded away
rapidly, while the more resistant rock remains.
Draw a diagram
Waves carrying
sand, shingle is
hurled at the cliff
Processes that erode rocks
Wave erosion (by destructive waves), wave pounding,
hydraulic action, abrasion, attrition.
Hydraulic action
When water is thrown against a cliff by breaking waves it
often compresses the air in cracks and crevices in the
rocks. When the waves retreat the air expands, sometimes
explosively. This causes rocks to shatter as the cracks are
enlarged and extended.
Draw a diagram
Air can become
compressed and
will expand when
the wave retreats
Processes that erode rocks
Wave erosion (by destructive waves), wave pounding,
hydraulic action, abrasion, attrition.
Attrition
• As boulders and rocks, already eroded from cliffs, are
hurled against the shore, and against each other by
breaking waves, they gradually break down into smaller
and more rounded pieces.
• Takes place along side other erosional processes
• Accounts for the varying sediment sizes
Draw a diagram
Break down
of sediment
on the shore
Processes that erode rocks
Wave erosion (by destructive waves), wave pounding,
hydraulic action, abrasion, attrition.
Wave pounding
Steep waves have considerable energy. When they break
as they hit the foot of cliffs or sea walls, they may generate
shock-waves, which may produce pressures of up to 30
tonnes per square metre.
Draw a diagram
Sheer
force
Processes that erode rocks
Wave refraction
• Process by which waves undergo a
change of direction as they approach
headlands and beaches.
• Generally most beaches are concave
towards the sea. This is due to wave
refraction.
Wave refraction
• Close to the coast, water gets more shallow and
waves are slowed down. This causes the waves
to bend around Te Kie Point, concentrating the
wave energy and making it possible for the
waves to attack all sides of a headland.
• On Ocean Beach, because the beach is
concave, the waves spread out as they slow
down and the energy is dissipated.
• As a wave approaches
a headland

• Water depth
decreases, causing
that section of the wave
to slow down due to
friction from the sea
floor

• The change in speed
causes the remaining
deep water wave
section to refract
(bend) towards the
headland.
Coastal Kung Fu
1
2
3
Rockfalls
Wave action
Relief: Omaha climate graph/ wind rose?
LESSON 4
Elements and natural processes (3)
LESSON 5
Beaches
Beaches are the most unlikely of
landforms to be found facing the open
sea.
They are, after all, merely piles of
loose sand and shingle and yet they
manage to remain intact on coastlines
where waves can reduce concrete sea
walls to rubble in a very short time.
The secret of their geomorphic
success lies, of course, in this very
fact-that they are only loose sand.
Beaches can both adapt their shape
very quickly to changes in wave energy
and also dissipate this energy in minor
adjustments of the position of sand or
shingle.
The beach is therefore able to
maintain itself in a dynamic equilibrium
with its environment due to the
inherent mobility of its sediments.
Pethick, 1984
Processes that deposit or build
up at the beach
Wave transportation ( longshore drift ) and
wave deposition by constructive waves
pushing sand up the beach in the swash.
Write/guess definitions for
• Wave transportation
• Longshore drift
• Wave deposition
Wave Types
Longshore Drift- Wave
Transportation
• Swash - water sliding up
beach at the same angle as
the wave approaches the
shore
• Backwash - water flowing
back down beach to sea at
90’ to the beach.
• This transports sand along
the beach. Omaha, sand
deposition to S of Southern
Groyne suggests S to N
movement.
Processes that deposit or build
up at the beach
Wind transportation and deposition by saltation,
surface creep and suspension
• The movement of sand in air is a highly complex
process.
• Airflow (wind) experiences frictional drag over a sand
surface (beach), therefore the airflow slows down i.e.
there is a decrease in wind velocity.
• The beach surface should be visualised as a continous
layer of sand grains with a superfacial scattering of
individual grains lying on it. This upper layer consists of
grains with a range of diameters which project (poke up)
through the air flow.
Processes that deposit or build
up at the beach
Wind transportation and deposition by saltation,
surface creep and suspension
• Surface creep
Wind rises to a minimum of 4.5m/s in speed
Sand is rolled along the surface
• Saltation
Wind speed increases to 5m/s
Sand is picked up into the air briefly and then falls
back due to gravity, striking the next grain which in
turn is lifted into the air
Processes that deposit or build
up at the beach
Wind transportation and deposition by saltation,
surface creep and suspension
• Suspension
Is found in very strong winds or if the sand grains
are very small in dimension.
Sand grains are suspended in the air
WIND TRANSPORTATION
Movement of sand over dunes with no vegetation to trap sand.
wind direction
BACKSLOPE
SLIPFACE
crest
angle of
repose
Beach Profile
Recap processes
What natural processes are interacting to form the landforms
(outcomes) and what are the interactions involved?
LESSON 6
Elements/Inputs
Processes
Features/Phenomena
Sand____________
Past Processes
1______________________________
2____________________________________
Weathering
1___________________________
2____________________________________
3____________________________________
Mass Wasting
_____________________________________
_____________________________________
Wave erosion(destructive waves)
1____________________________________
2____________________________________
3____________________________________
Wave
transportation(LSD)_____________________
_____________________________________
Wave deposition(constructive
waves)________________________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
________________
Wind____________
Waves___________
Tides____________
Sunshine hrs______
Vegetation________
________________
Rock____________
Wind transportation
1____________________________________
2____________________________________
3____________________________________
Wind
deposition_____________________________
_____________________________________
Fluvial transportation and deposition
_____________________________________
_________________________________
Tidal
flow__________________________________
____________________________________
Feedback
Rock eroded from cliff
deposited on beach as
sand_______________
Looking at natural processes, which ones do
you think interact?
The formation of ONE natural feature within a Coastal
Geographic Environment: Sand Dunes
Interaction between hydrological and aeolian processes
2 SE wind direction /waves approach
Ocean beach from SE, transporting
sand, less than 1mm diam. feldspar
and quartz, constructive waves(
)
push sand up beach.= hydrological
deposition
3 SE wind picks up sand as it
dries(saltation moves 80%) and
blows it inland up the leeward slope
of the dune and over the crest
(? m high)and down
the steeper slipface. = aeolian
transportation and deposition
1 Longshore drift moves
sand along the beach
from s-n at 1m in 1 min.
=hydrological
transportaion
The formation of ONE natural feature within a
Coastal Geographic Environment: Sand Dunes
Interaction between hydrological and aeolian
processes
• From the diagram you have drawn, write a
series of paragraphs to explain how two
interacting processes have created a
named landform feature
1.Sub-aerial
weathering
affects cliff
shape so not
90*. Waitemata
sst. ( ?m )
2.Undercutting of cliff
Causes collapse and
mass wasting
3.Wave erosion (hydraulic action etc
at H.tide erodes cliff, leaving shore
Platform ( ) of harder Greywacke
the cliff
retreats
The formation of ONE natural feature within a
Coastal Geographic Environment:
Cliffs and Shore Platform
First of all… Notches
• The most important
erosional process is
wave pounding.
• As waves attack cliffs
they undercut the cliff
and form a notch.
• When a cliff face can no longer be supported by its base,
the cliff face collapses.
• Material eroded from the cliff will be caught up in the
wave action and will act abrasively- add a cutting
compound of gravel and sands.
• As the cliff face continues to be eroded away, as its less
resistant rock is exposed, a shore platform will develop..
• The shore platform will develop to a depth determined
by the power of the wave.
• Beyond the platform eroded material will be deposited.
• The platform will become wide enough that waves will
break well before the cliff, and the erosion on the cliff will
decrease.
• The shore platform, an area of resistant rock, will remain
until erosional wave processes, or weathering, break it
down.
Draw a series of diagrams to show how two
interacting processes have created a named
landform feature
- Interacting processes = hydrological
processes of wave refraction and wave
pounding
Remember to annotate
Remember to include specific information
Field trip to Omaha
LESSON 7
Go through field trip booklet. Diagram of features/processes (How
and why do these processes show spatial variations
LESSON 8
Map to show Spatial Pattern of Processes
Weathering, mass wasting and
wave erosion. Wave refraction
Wave transportation and deposition, aeolian
Transportation and deposition
Weathering, mass wasting and
wave erosion. Wave refraction
Map to show Spatial Pattern of Features or
Outputs
1 Cliff
3 Beach
4 Fore and Back Dunes
1 Cliff
2 Shore Platform
How and why do these processes show temporal variations?
LESSON 9
Can you think of how the processes can
change over time (temporal variation)
• Weathering
• Hydrological
• Aeolian
Temporal Variations
• Mangatawhiri spit was formed over the last
6,500yrs as the sea level rose 100-120m after
the last ice-age, due to wave transportation
and deposition.Aeolian processes have built
up the dunes on the spit.
• Summer storms, LP systems bring storm
surges and large waves erode the beach eg
TC Maranui 1968 removed 0.5ha from the tip
of the spit overnight.
• Season changes in the beach profile occur.
Temporal Variations in features
and processes at Omaha
• From the diagrams, describe and explain
the temporal variation in the operation of a
natural process in the Omaha coastal
environment
How and why is the environment being modified at the present and
is it likely to be changed in the future?
LESSON 10
From the field trip
• Can you think of any examples of human
modification?
Human and why the whole environment
is being modified, now and in the future
Omaha beach is a natural
system, modified by natural
processes and by the actions
of humans.
Human modification of Omaha
sandspit
• 1930’s began farming
• 1942-1963 sand mining of 380,000m3 from sandbank E of
Whangateau Harbour. Caused ebb tide to change direction
from S to SE so sand supply to beach ended. Used for Beach
Replenishment on Ocean Beach N of southern groyne.
• 1970 beginning of subdivision and golf course and causeway.
Developers bulldozed the fore dunes and built a timber
seawall.
• Jun/July 1978 storms destroyed seawall and eroded sections.
• 1979/80 beach protection following major erosion. Because
of fear of loss of property.3 Groynes built to trap sand. Quartz
dolerite blocks from Flat Top Hill quarry,Wainui,10km W of
Orewa and Greywacke from quarry at end of Omaha Valley
Rd.were used in the groynes.
Groynes 1970 $1.3 million
Groynes
Natural process modified
Extent of modification
Northern
groyne
Built to redirect the ebb tide
current to its original southerly
direction to increase wave
deposition on spit and to prevent
sea waves from entering
Whangateau Estuary
Successful as wave
deposition has increased.
Southern
groyne
Built to increase wave deposition
and interrupt longshore drift
Successful in increasing
wave deposition as shown
by high water mark being
34m further out to sea
Swash
groyne
Build to decrease wave erosion
on the base of the Southern
groyne
Successful as wave
deposition increased and
est accreation was 7000m3
What process did the groynes modify?
1 Longshore drift.
Draw 3 sketches of 1 before groynes
2 groynes
3 after groynes
Human action= building of groynes to modify the process of
wave transportation(LSD), resulting in growth of beach to s of
southern groyne to 100m
1. before groynes
2. 3 groynes built
3.Sand trapped to s
In 1979. southern,
of s groyne, widening
Swash and northern
beach to 100m wide.
2 Dredging of harbour 1953-1988
Resulted in Ebb Tide and sand being redirected out to sea and
out of the system. Prior to dredging, Ebb Tide and sand flowed
south along the spit replenishing the supply.
2 Dredging of harbour 19531988
Natural process
Extent of modification
modification
• Extreme as 300m of
• Removal of sand
tip of spit was lost by
caused the ebb current
wave erosion.
to be redirected from S • Occurred over an
direction to SE
extended period of
direction (depositing
time and did not end
sand in bay and
when dredging did
forming sandbank
outside harbour
entrance)
OTHER Processes modified.
Wind deposition.Dune fences: N end trap
sand and build dunes. Cloth has short lifespan and fences get buried.
Pedestrian accessways prevent Dune
erosion: elevated timber boardwalks and
fencing to protect dunes and plants. 20
provided
Harbourside erosion: 1.8km of seawall.
Southern 1km around golf course rip-rap
and fibrolite, northern section gabion
baskets. Need repair over next 5-15yrs.