Topic 6B:
6B – Slide 1
Shorelines
Online Lecture:
Shoreline Features
○ Estuaries
○ Headlands & Coves
○ Wetlands
○ Sea Arches & Sea Stacks
○ Deltas
○ Wave-Cut & Marine Terraces
○ Barrier Islands
○ Coastal Cliffs
Where do they come from?
How do we use them?
6B – Slide 2
Estuaries
Estuary
Land
ua r
y
Ocean
○ bodies
of water
partially
surrounded by land
Est
○ many names:
bay, harbor,
sound, mouth
of a river,
lagoon, etc.
Estuary
○ where fresh
& salty water
meet
○ major cause
of currents:
tides
Ocean
Harbor
Land
Estuaries & Humans
6B – Slide 3
○ contain more life than the nearby ocean. Why?
more nutrients:
“Nurseries”
● washed off the land from 2+ sides
● “trapped” in the estuary by the surrounding land
Nutrients are used by…
Used for
shipping,
industry,
recreation,
waste
disposal,
etc…
Also: salinity,
water depth
Wetlands
What do they look like?
○ covered by water
part of the time,
primarily due to tides
(also: freshwater
runoff from the land)
○ 2 kinds of
coastal wetlands:
salt marshes &
mangrove forests
Where are each found?
common along
the shorelines
of estuaries
6B – Slide 4
Benefits of Wetlands
6B – Slide 5
○ flood control: rain & storm surge
○ protect shoreline from erosion by waves
○ filter pollutants out of runoff: keep them
Pollutants are less
out of the ocean (= cleaner ocean)
biologically dangerous
○ “nurseries” for marine life. How? Why?
in the sediments.
like estuaries, plants absorb nutrients in runoff and…
Also: salinity, hiding places
Major Food
Source:
“Detritus”
Deltas
6B – Slide 6
○ A delta forms when a river brings down sand & mud
more quickly than waves carry it away
– sand piles up at the mouth of the river,
eventually blocking it and causing it to shift
(change course, to find a new way to the ocean).
– shifting & seasonal flooding allow rivers to spread
sediments and nutrients over the land
Excellent
Farmland
Nutrients ≠
Sediments
Examples:
Nile,
Mississippi,
SacramentoSan Joaquin
Humans and Deltas
6B – Slide 7
○ Build levees & dikes (piles of dirt) to protect buildings
○ Dredge (remove) sand from bottom of rivers
so that ships can go up and down them
Result: land in deltas tends to sink. Why?
– water in the sediments is squeezed out
by the weight of the stuff above
– no new land from sediments piling up
New Orleans
is ≈ 8 ft below
sea level.
“like squeezing
a sponge”
Barrier Islands
6B – Slide 8
Living on
Barrier Islands
Estu
ary
Ocean
MainLand
Barrier
Islands
Barrie
r Islan
r
Ba
nd
a
sl
I
r
e
i
r
d
○ long, thin islands made of sand,
typically oriented parallel to the coast.
– separated from the land by an
estuary bordered by wetlands
○ common along the eastern and
southern coasts of the United States
er
i
r
r
Ba
d
n
a
Isl
a nd
Headl
Cove
Cove
Cove
Cove
d
dlan
nd
dla
Hea
H ea
Cove
6B – Slide 9
Photographs
of Headlands
and Coves
Cove
Cove
Headland
Cove
6B – Slide 10
Headlands and Coves
○ waves erode the “softer” rock
in-between the “harder” rock
more quickly, pushing back
the land and creating coves
○ the places with “harder” rock
are left sticking out into
the ocean: in other words,
they become headlands
Examples of “harder”
and “softer” rocks?
Note: wave refraction
At First
Wave Crests
#3
Sea Arches & Sea Stacks
○ Sea arches & sea stacks
can form if the rock behind
the headland is “softer” &
therefore erodes
more quickly.
○ When too much of the
material is eroded away,
the arch collapses, & the
“hard rock” is left standing
on its own (is a sea stack)
At First
#2
#3
6B – Slide 11
Arch
Sea
Stack
Sea
Stack
Headland
#4
#5
Land
Wave Crests
Ocean
Note: wave refraction
Wave-Cut
Terraces
○ Waves erode
the shoreline,
pushing back
the cliffs and
leaving behind
a broad, flat
area called a
wave-cut terrace.
6B – Slide 12
What is a
terrace?
Wave-Cut
Terrace
Before Erosion
Cliff
Marine Terrace
After Erosion
Pushed Back
Wave-Cut
Terrace
Wave-Cut Terrace
Marine Terraces I
6B – Slide 13
○ If sea level sinks dramatically, the flat area
What could
cause a change
is out of the water at the top of a cliff.
in sea level?
It is now called a marine terrace.
Before Uplift
Marine Terrace
Wave-Cut Terrace
Marine
Terrace
Marine Terrace
After Uplift
Marine Terraces II
○ Waves will begin eroding
a new wave-cut terrace,
producing a new cliff.
6B – Slide 14
After Uplift & More Erosion
Marine Terrace
Wave-Cut Terrace
Marine Terrace #3
Marine Terrace #2
Why no longer flat?
Marine T
errace #2
Marine Terrace #1
Palos
Verdes
from
Point
Vincente
Marine Terrac
e #1
Coastal Cliffs formed on the Bottom of the Ocean 6B – Slide 15
Note the Layers
Evidence?
Sediments vs. Sedimentary Rocks: What’s the difference?
Formation of Coastal Cliffs
6B – Slide 16
#2
#1
Rivers
and Runoff
Bodies of Organisms
Layer
of Sediments
Layers
#3
#4
Rivers
and Runoff
Coastal
Cliffs
Layers
Uplift
Layers
Fault