Coastal Processes
Chapter 14—Planet Earth
(291-298)
http://highered.mcgrawhill.com/sites/0072402466/student_view0/chapter14/flashcards.html#
Some Background information
Coastal landscapes are quite unique when compared
with other distinctive landscapes:
• All climates and bedrocksInteraction between
lithosphere and hydrosphere.
• It extends a short distance inland and out into the
ocean/sea/lake. (meaning that the interaction
between the two spheres occurs over a short
distanceCoastline interact with wave forces)
How do waves and currents form?
• Differences in heating and thus pressure
from one location to another (wind).
• The resulting winds transfer some of their
energy on the surface of the water to form
waves and currents.
http://www.classzone.com/books/earth_scie
nce/terc/content/visualizations/es1604/es1
604page01.cfm?chapter_no=visualization
A breaker.
•
As waves approach a shoreline, changes begin to occur when
the water depth is approximately half of the wave length.
•
The bottom of the wave is slowed by the frictional drag of the
shallowing bottom, while the top of the wave continues on at its
former pace.
•
Once the wave “leans over” it breaks, spending its energy
against the shore line.
•
an oversteepened wave that falls on itself, spending its energy
against the shoreline
http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21400
http://www.classzone.com/books/earth_science/terc/content/visual
izations/es1605/es1605page01.cfm?chapter_no=visualization
2) Define headland.
A point of land that extends outwards into a body of water
from a coastline; often having a steep cliff face
b) Wave refraction: Bending action of waves-read Sovio-pp.
55
Animations:http://www.wiley.com/college/strahler/0471480533/animations/ch19_animations/ani
mation2.html
http://almandine.geol.wwu.edu/~dave/courses/101resources/coasts/38_WaveMotion.swf
Major Processes of Erosion by
Waves
6a) Abrasion, also known as
corrasion, occurs as waves hurl
bits of rock and sand against
cliffs and headlands.
b) Describe hydraulic pressure.
As water enters cracks…
I couldn’t find a better image!
c) Attrition occurs when rock
fragments broken away from the
rock surfaces hit against each other
and erode into smaller fragments.
d) Describe corrosion (aka solution).
Soluble minerals dissolved by water.
(limestone headlands)
5)Write an explanation of the sequence of
events associated with the erosion of the
headland shown in figure 14.16.
A) Wave energy is concentrated on a headland
as a result of wave refraction. Zones of
weakness, such as joints, faults, and
nonresistent beds, erode faster, so sea caves
develop in those areas.
B)Sea caves enlarge to form a sea arch
C)Eventually, the arch collapses, leaving a sea
stack. A new arch can develop from the
remaining headland.
http://www.uky.edu/AS/Geology/howell/goodie
s/elearning/module14swf.swf
http://faculty.palomar.edu/lyon/Animations/
WaveMotion.swf
http://highered.mcgrawhill.com/sites/0072402466/student_view0/c
hapter14/animations_and_movies.html#
Here we have some of the typical features of coastal erosion. Take a
moment and locate them on your sheet.
We will
examine
features in this
area first.
Sea cliffs: retreat
mostly as a
consequence of
hydraulic action
and abrasion at
their bases.
As a sea cliff is undercut by erosion,
the upper part is left unsupported
and susceptible to mass wasting
processes. Thus, they retreat little
by little.
Headlands: Sea cliffs
do not erode uniformly,
and therefore, large
sea-ward projecting
parts of the shoreline
called headlands are
formed by wave
refraction.
Sea Caves: when
wave refraction
causes erosion on a
headland, a sea cave
may form.
When two sea caves meet
through a headland, and the
roof collapses, a Sea stack is
formed.
Blow holes are caused when the roof of a sea-ward facing
sea cave cracks or collapses. Waves entering the sea
cave are then forced through the hole and spray out like a
fountain.
As the sea cliff is
eroded, remnants of
the cliff material will
form a sea-ward
facing beach.
Wave Cut Platform:The gently sloping
surface that is left underwater, as sea
cliffs retreat.
Sea Arches: are
formed when two sea
caves meet. This is
the transitional phase
between cave and
stack.
6) Describe the formation of a
wave-cut platform.
• b) Insert an image of a wave-cut
platform from the internet.
http://emvc.geol.ucsb.edu/anima
tions/quicktime/TerCut5.mov
Destructive waves at an exposed coast erode a steep
coastal slope through processes like hydraulic action and
abrasion.
The waves erode along lines of weakness in the rock face to form a
notch.
Continued erosion enlarges the notch and causes its roof to
collapse, and a cliff is formed.
Further undercutting at the base of the cliff results in an
overhanging cliff which eventually collapses.
As the steep cliff retreats landwards,
a flat terrace at the foot of the cliff is
exposed --- wave-cut platform
.
The eroded materials which are transported away
may be deposited in the sea to form an offshore
terrace.
4a) Explain why waves, in most cases, do not approach the coastline straight on but rather at an angle other
than 90 degrees.
When shallow water is reached, the end of the wave closest to the shore begins to drag along the ocean floor.
This slows the wave at that end, but at the other end the wave is still in deep water and continues to move
faster and begins to catch up to the slower end.
Waves bend to become a reflection of the shape of the coastline and wind direction.
b) While the waves may approach the coastline at an oblique angle, they return straight back to the sea
under the force of gravity. Hence, if one was to release a beach ball a short distance from the coastline, it
would follow a zigzag pattern of movement as illustrated in the diagram below. Similarly, sand and pebbles
would be carried along in such a fashion. This current that moves down a coastline within the shallow
breaker zone next to the shoreline is known as longshore driftTHIS HAS TO DO WITH DEPOSITION - WE’LL
LEARN MORE ABOUT FEATURE LATER!
http://www.youtube.com/watch?v=U9Eh
Va4MmEs
c) A concern regarding this net
transport of materials down
the coastline is the loss of sand
from a beach. To combat this,
structures are built
perpendicular to the coastline
to try to keep sand in place.
These structures, shown in the
pictures below, are known as
groynes or groins.
Courtesy: P. Mleziva
9) To prevent erosion of the coastline or to shelter boats from
strong waves, breakwaters are built. These can be large
piles of rocks or other objects placed parallel to the
coastline to help break the force of the incoming waves.
http://www.uky.edu/AS/Geology/howell/goodies/elearning/
module14swf.swf
http://faculty.palomar.edu/lyon/Animations/BreakWater.s
wf
10) Define the following terms and look at figures 14.18 and
14.19 carefully.
Insert an image for three of the following items from the
internet. ALL DEPOSITIONAL FEATURES!
a) bayhead beach: An extensive deposit of sand and/or
gravel in the form of a beach at the back of a bay.
b) spit: A long and narrow accumulation of sand and/or
gravel that projects into a body of ocean water. These
features form as the result of the deposition of sediments
by longshore drift.
c) baymouth sand bar: A narrow deposit of sand and/or
gravel found across the mouth of a bay.
http://www.school-portal.co.uk/GroupRenderCustomPage.asp?GroupID=12426&ResourceId=61278
d) tombolo:
A coastal feature that forms when a belt sand
and/or gravel is deposited between an island and the
mainland. This feature is above sea-level for most of the
time.
e) barrier island or offshore bar Long, narrow islands of sand
and/or gravel that are usually aligned parallel to the
shore of some coasts.
Bayhead beach:An extensive deposit of sand and/or gravel in the form of a beach at the back of
a bay.
http://www.uky.edu/AS/Geology/howell/goodies/elearning/module14swf.swf
spit: A long and narrow accumulation of sand and/or gravel that projects into a body of
ocean water. These features form as the result of the deposition of sediments by longshore
drift.
http://www.school-portal.co.uk/GroupDownloadFile.asp?file=21605
c) baymouth sand bar: A narrow deposit of sand
and/or gravel found across the mouth of a bay.
http://highered.mcgraw-hill.com/sites/0072402466/student_view0/chapter14/animations_and_movies.html
e)
barrier island or offshore bar Long, narrow islands of sand and/or gravel that are
usually aligned parallel to the shore of some coasts
http://geography.cst.cmich.edu/Franc1M/Animations/animation_list_posted.htm
tombolo: A coastal feature that forms when a belt sand and/or gravel is deposited between an island and the
mainland. This feature is above sea-level for most of the time.
f) lagoon: the coastal water body separating a barrier island or offshore bar from the mainland or the water
trapped behind a baymouth sand bar.
Depositional Landforms
Common Depositional Landforms
Longshore Processes and Depositional Coastlines
Hooked Spit due
to northward current
and flow into bay
Classifications of Coastlines
13a) Recall from the Glacier Unit that U shaped valleys leading down to the sea that have been drowned as a result of a rise in sea level are
known as fjords.
British Columbia has this type of coastline.
http://www.geocities.com/Yosemite/Rapids/4233/klikfjord.htm
b) V shaped valleys leading to the sea that have been drowned as a result of a rise in sea level are known as rias.
c) A longitudinal coastline involves folded mountains and valleys that are parallel to the coastline.
A fjord coastline consists of U shaped, formerly glaciated valleys, leading down to the coastline that have become flooded due to sea level rise
since the end of the last ice age. They are generally quite broad and deep and act as natural harbours. The illustration that best shows this is A.
B shows a longitudinal coastline where the flooded valleys parallel the coastline.
C shows an estuarine delta.
D shows a ria coastline with drowned V shaped, non-glaciated valleys.
Coral Reefs
14)
Coral reefs occur in warm tropical waters where soft-bodied creatures, known as corals, produce a skeleton of calcium carbonate; when these
creatures die, their skeletons form a foundation upon which new corals can grow resulting in the continual growth of the coral reef.
An atoll is a Pacific circular reef enclosing a lagoon.
http://www.classzone.com/books/earth_science/terc/content/visualizations/es2303/es2303page01.cfm?chapter_no=visualization
More about reefs: http://oceanworld.tamu.edu/students/coral/index.html
http://en.wikipedia.org/wiki/Coral_reef
Coral Reefs
• Coral polyps excrete external skeletons of
calcium carbonate (limestone) – Coral
Reefs
• New reefs form on top of old, dead reefs
• 30º N - 25º S latitude, water warmer than
20º C
• 3 settings:
– Fringing reef – on shallows around island
– Barrier reef – line of coral parallel to shore
– Atoll – semicircular reef around degraded
volcanic island
Development of Atoll
Global Distribution of Coral Reefs
Emerged versus Submerged Shorelines
15) Emerged Shorelines: the land has risen; the water has become shallower.
Significance to Humans
Pros: newly emerged coastal plain potentially offers an area of land for
agricultural settlement; beaches and / or lagoons develop into resort areas.
Cons: difficult for commercial shipping because of offshore bars and few deep
water ports
16) Submerged Shorelines: land has sunk and / or the water has risen.
Significance to Humans
Pros: Irregular coastlines offer sheltered, deepwater harbours which are
excellent for ports
Cons: Irregular coastlines hinder land transportation along the coast and rough
terrain hinders human settlement
Which one of the following features would not be associated with a submerged
coastline?
a) rias
b) fiords
c) spit
d) offshore bar
e) baymouth bar
Human Impacts on Coastlines
• 37% of world pop. live <60 mi. from shore
(2 billion) – 50% within 120 miles of shore
• In US, 53% of pop. live near coastline
• Coastal Engineering Purposes:
– Protecting shore & property from hazards
– Stabilizing & nourishing beaches
– Maintaining traffic & trade into ports
Mitigating Coastal Hazards
• Raise buildings on stilts so waves roll
underneath
• Sea wall – vertical, concrete wall to absorb
energy of waves
• Revetment – slope covered with large rocks
(rip-rap) to absorb energy of waves
• These work locally, but they aggravate
erosion up and down shore from wall due to
wave refraction
Beach Nourishment
• Bringing sand to beaches that have eroded
– over $336M spent in Florida since 1960s
• How?
– Trucking in sand from remote location
– Limit loss of sand through groins – low walls
built at right angles to beach – intercept
longshore drift
• Jetties – stone or concrete structures to
keep channel open, keep sand to side
Groins and Jetties
Groins
Jetties
Impact of Global Climate Change
on Coastlines
• Melting ice sheets will lead to sea level rise –
estimates of 5-35 inches – areas <5 ft elevation
at greatest risk
• Pacific Islands & low-lying coastal areas will
suffer greater erosion & flooding potential
• Coral bleaching by unusually warm water has also
become a problem – ultimately kills coral
Warming Threat on North Carolina Coast
Baymouth Bar
Headland
Offshore Bar
Sea Stacks
Spit
Tombolo
Water Cut Terrace