1.5 Understand how ocean waves
and currents change the face
of coastal areas.
1.5.1
Define the term spit. (P. 44-45)
Spit
Longshore drift consists of the
transportation of sediments (clay,
silt and sand) along a coast at an
angle to the shoreline, which is
dependent on the prevailing wind
direction.
•A ridge of sand running
away from the coast, usually
with a curved seaward end.
Spit grows in the prevailing
direction of longshore drift.
Ends are curved by the
action of waves in different
directions
Spit
Spit
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What can you tell about
the direction of long
shore drift?
Sea Cave
A sea cave is a large,
natural hollow in a
headland caused by wave
erosion
Sea Arch
A sea arch is a feature
which results when
two caves occurring
on either side of a
headland are cut.
Arches are usually
temporary, until the
roof collapses and
isolates the seaward
end
Sea Stack
A sea stack is a geological
landform consisting of a steep
and often vertical column or
columns of rock in the sea
near a coast, formed by
erosion. Stacks are formed
over time by wind and water.
1.5.3

•
Describe how sea caves, sea arches
and sea stacks are formed. (P. 48)
In order for these three
coastal structures occur on
“emerging” coast lines,
there must be steep cliffs &
a headland.
1st Sea caves form , 2nd sea arches form and 3rd sea stacks
form.
What is a Coastal Headland?

A headland is a coastal
landform, a point of land
usually high and often
with a sheer drop, that
extends out into a body of
water.
1.5.3
Describe how sea caves are
formed. (P. 48)
1. Waves strike the headland first
2. Waves refract around the
headland and put hydraulic
pressure on the sides of the
headland.
3. Erosion of the weak portions
create caves & blow holes in the
sides of the headland.
1.5.3
Describe how sea arches are
formed. (P. 48)
4. Eventually the sea caves get deeper
until they connect inside the headland
forming a complete passage way or
tunnel or “arch” through the head
land


It is difficult to see or imagine
from the top view.
However the side view
provides a better picture.
1.5.3
Describe how sea stacks are
formed. (P. 48)
5. Continuous erosion causes the
collapse of the ground over the arch
6. This leaves a pillar or column or
“STACK” of land standing alone
where the headland was.
•Sea stacks are common in eastern
Canada.
•Many have plant growth on top.
* 1.5.4


Analyze the processes that result in the
straightening out” of an irregular coastline.
(P. 48) [emerging]
Emerging coastlines straighten in much the same
fashion as submerging coastlines.
Erosion of headlands creates sea caves, sea arches
and sea stacks instead of bay beaches, spits & bay
bars. However the result is similar in that headlands
are reduced in size.
1.5.4 Describe the three process by which wave
action erodes coastal areas. (P.31 * same as
three for river erosion)


Hydraulic pressure =
The pounding force of water/waves
2. Corrosion =
•
Minerals such as calcium carbonate &
limestone dissolve in the water
3. Abrasion =
•
rock & sand particles suspended in
the water bump, grind, scrape &
gouge surfaces the water hits
* 1.5.4
Analyze the processes that result in the
straightening out” of an irregular
coastline.
(P. 42 questions # 11 & 12)
[submerged]
1. Weathering of
Headland
 What forces cause
the weathering &
erosion?
 Hydraulic
 Corrosive
 Abrasive
4.
Summary:
2. Transportation
of silt
 How is silt
transported?
 Longshore Drift
 Waves
 Currents
3. Deposition of silt
 Where does
deposition occur?
 Bay beaches;
filling inlets
 Bay bars; closing
off inlets
Submerged coasts straighten due to erosion.
Video

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Sea stacks of NL
http://vimeo.com/68174431