6B – Slide 1Topic 6B:Shorelines

Online Lecture:Shoreline Features

○ Estuaries

○ Wetlands

○ Deltas

○ Barrier Islands

○ Headlands & Coves

○ Sea Arches & Sea Stacks

○ Wave-Cut & Marine Terraces

○ Coastal Cliffs

Where do they come from?How do we use them?

6B – Slide 2

EstuaryOcean

Land

Estuaries

○ bodies of water partially surrounded by land

○ many names: bay, harbor, sound, mouth of a river, lagoon, etc.

○ where fresh & salty water meet

○ major cause of currents: tides

Estu

ary

Estuary

Land

HarborOcean

6B – Slide 3Estuaries & Humans

○ contain more life than the nearby ocean. Why?more nutrients:● washed off the land from 2+ sides● “trapped” in the estuary by the surrounding landNutrients are used by…

Used for shipping, industry,

recreation, waste

disposal, etc…

“Nurseries”

Also: salinity, water depth

6B – Slide 4Wetlands

○ covered by waterpart of the time, primarily due to tides(also: freshwater runoff from the land)

○ 2 kinds of coastal wetlands:

Where are each found?

common along the shorelines

of estuaries

salt marshes & mangrove forests

What do they look like?

6B – Slide 5Benefits of Wetlands

○ flood control: rain & storm surge○ protect shoreline from erosion by waves○ filter pollutants out of runoff: keep them

out of the ocean (= cleaner ocean)○ “nurseries” for marine life. How? Why?

like estuaries, plants absorb nutrients in runoff and…Also: salinity, hiding places

Pollutants are less biologically dangerous

in the sediments.

Major Food Source:

“Detritus”

6B – Slide 6Deltas○ 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,Sacramento-San Joaquin

6B – Slide 7Humans and Deltas

○ 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”

6B – Slide 8Barrier Islands

○ 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

Estu

ary

Ocean

Main-Land

BarrierIslands

Living on Barrier Islands

Bar

rier I

slan

d

Barrier Is

land

Barrier Is

land

6B – Slide 9

Photographs of Headlands and Coves

Cove

Cove Cove

CoveCove

Cove Cove

Cove

Headland

Headland

Headland

Headland

6B – Slide 10Headlands and Coves

○ waves erode the “softer” rockin-between the “harder” rock more quickly, pushing back the land and creating coves

○ the places with “harder” rockare left sticking out into the ocean: in other words, they become headlands

At First

Wave Crests

Examples of “harder”and “softer” rocks?

#3

Note: wave refraction

6B – Slide 11Sea 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)

Land

At First #2 #3 #4 #5

Wave Crests

Ocean Note: wave refraction

Arch

Sea Stack

Sea StackHeadland

6B – Slide 12Wave-Cut Terraces○ Waves erode

the shoreline, pushing back the cliffs and leaving behind a broad, flatarea called a wave-cut terrace.

What is a terrace?

After ErosionPushed Back

Wave-Cut Terrace

Cliff

Before Erosion

Wave-Cut Terrace

Wave-Cut Terrace

Marine Terrace

6B – Slide 13Marine Terraces I○ If sea level sinks dramatically, the flat area

is out of the water at the top of a cliff. It is now called a marine terrace.

After UpliftMarine TerraceBefore Uplift

Wave-Cut Terrace

What could cause a change

in sea level?

Marine Terrace

Marine Terrace

6B – Slide 14

PalosVerdesfromPoint

Vincente

Marine Terrace #3

Marine Terrace #2Marine Terrace #1

Marine Terrace #1

Marine Terrace #2

Marine Terraces II

○ Waves will begin eroding a new wave-cut terrace, producing a new cliff.

Why no longer flat?

After Uplift & More Erosion

Marine Terrace

Wave-Cut Terrace

6B – Slide 15Coastal Cliffs formed on the Bottom of the Ocean

Note the Layers

Evidence?

Sediments vs. Sedimentary Rocks: What’s the difference?

6B – Slide 16Formation of Coastal Cliffs

Layers

CoastalCliffs

FaultUplift

Riversand Runoff

Layers

Bodies of Organisms

Layers

Riversand Runoff

Layerof Sediments

#1 #2

#3 #4