Transcript Coasts

Coasts
Areas where the land
meets the sea…..
A shore (or shoreline) is the place where
the land meets water (between low tide
line and high tide line), but a coast
includes a larger zone affected by this
boundary. A beach is a zone of loose
sediment that covers part or all of a shore
on a depositional coast.
Coastal Regions/Zones
Seaward – toward the sea/ocean
 Inland – toward the land
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Coastal Regions/Zones
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Foreshore – seaward of the berm crest;
active zone of the beach. Extends from
beach scarp to low tide mark.
– (berm crest = highest point on the beach)
– (beach scarp = high tide line)
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Backshore – inland of the berm crest,
extending to the farthest point where
beach sand had been deposited
Coastal Regions/Zones
Nearshore – area of breaking waves
 Offshore – area beyond breaking waves
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Coastal Regions/Zones
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Beach
Coast
Shore
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Nearshore
Offshore
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Backshore
Foreshore
Coastal Regions/Zones
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Beach
Coast
Shore
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Nearshore
Offshore
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Backshore
Foreshore
Classifying Coasts
Coasts are influenced by many factors.
It is most useful to classify coasts based
on predominant events that occur there, such as:
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Erosion
 Deposition
Classifying Coasts
Another way to classify coasts is by tectonic
activity.
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Active (active margin)
 Passive (passive margin)
Classifying Coasts
A third way to classify coasts is by what is
influencing or shaping them: either land
processes or marine processes
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Primary (land processes)
 Secondary (marine processes)
Classifying Coasts
The last way we can classify coasts is by
changes in sea level.
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Emergent Coast
 Submergent Coast
EROSIONAL COASTS
The Twelve Apostles - sea stacks along the
southern coast of Australia – are part of an
erosional coast.
Erosional Coastlines
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Well-developed cliffs
Recent tectonic activity (active margins)
Wave erosion increases with
– More shore exposed to open ocean
– Smaller tidal range
– Weaker bedrock
Features of Erosional Coastlines
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Headlands – areas of the shore that stick
out farther than others
Features of Erosional Coastlines
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Wave-cut cliff (sea cliffs) – slope abruptly
from land into the ocean; usually formed
from the collapse of undercut notches
Features of Erosional Coastlines
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Wave-cut platform– smooth, nearly level
terrace just offshore, marking the
submerged limit of rapid marine erosion.
Created by wave action
Features of Erosional Coastlines
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Sea cave – cave formed by wave action in
zones of weakness in sea cliffs
Features of Erosional Coastlines
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Sea arches - a natural opening eroded out
of a cliff face by marine processes
Features of Erosional Coastlines
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Sea stacks - steep column or columns of
rock in the sea near a coast formed by
wave action
Features of Erosional Coastlines
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Blowhole - a cavity located at the end of a
sea cave which exits above the cave.
When a wave enters the mouth of the cave
it will be funneled up towards the blowhole,
which can result in quite spectacular blasts
of water from the top of the blowhole
http://www.oce
anfootage.com/
stockfootage/Bl
ow_Hole
(Blow Hole,
Hawaii
Coastline)
Erosional Coastline
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Sea Cave
Sea Arch
Sea Stack
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Sea Cliff
Blowhole
Headland
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Wave-Cut Platform
Beach
Erosional Coastline
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Sea Cave
Sea Arch
Sea Stack
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Sea Cliff
Blowhole
Headland
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Wave-Cut Platform
Beach
DEPOSITIONAL COASTS
Depositional Coastlines
Created mainly by sediment eroded
from another coastline (longshore drift)
 Passive margins
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Features of depositional coastlines
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Spit - a linear accumulation of sediment
that is attached to land at one end,
formed by longshore current.
Features of depositional coastlines
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Baymouth Bar (Bay barrier) – formed
when a spit extends across the mouth
of a bay, closing it off
Features of depositional coastlines
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Lagoon – shallow body of seawater
isolated from the ocean. Formed when
a bay is completely closed off by a bar
Features of depositional coastlines
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Barrier islands – narrow, exposed sand
bars parallel to but separate from land
Features of depositional coastlines
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Inlet – narrow passage to the ocean;
break in a spit or between barrier
islands
Features of depositional coastlines
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Sea island – were once part of the
mainland, but rising sea level has cut
them off
Features of depositional coastlines
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Tombolo – bridge of sediment
connecting a sea island to the mainland
Features of depositional coastlines
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Delta – coast built out by large amounts
of sediment washing off land (usually
from a river)
Features of Depositional Coastlilnes
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Sand Spit
Baymouth Bar
Barrier Island
Tombolo
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Beach
Lagoon
Sea Island
Inlet
Features of Depositional Coastlilnes
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Sand Spit
Baymouth Bar
Barrier Island
Tombolo
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Beach
Lagoon
Sea Island
Inlet
BEACHES
Features of depositional coastlines
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Beach
– Backshore, foreshore, nearshore, offshore
– dunes
– berm
– berm crest
– beach scarp
– longshore trough
– longshore bars
Features of a Beach
Dunes – ridges of sediment behind the
beach which protect land from waves
 Sand carried/deposited by wind
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Features of a Beach
Berm – an accumulation of sediment
that runs parallel to shore and marks
the normal limit of sand deposition by
wave action
 Sand carried/deposited by waves
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Features of a Beach
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berm crest – the peaked top of the
highest berm; usually the highest point
on a beach
Features of a Beach
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Beach scarp – a wall in the base of the
berm carved by wave action at high tide
Features of a Beach
longshore trough – underwater trough
(depression) parallel to shore caused by
wave action and backwash
 longshore bars – submerged or exposed
accumulations of sand below the low-tide
line (nearshore)
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Features of a Beach
Features of a Beach
Dunes
 Berms
 Berm Crest
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Longshore Trough
 Longshore Bar
 Beach Scarp
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Features of a Beach
Dunes
 Berms
 Berm Crest
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Longshore Trough
 Longshore Bar
 Beach Scarp
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Features of a beach
Coasts
Primary/Secondary
Primary Coasts
A primary coast is in almost the
same condition as it was when sea
level stabilized after the last ice age.
Primary coasts form as a result of
land processes.
Primary coasts:
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Are often rough
and irregular.
 The ocean has not
had time to modify
the terrestrial
features provided
by changes in sea
level.
Examples of Primary Coasts
Deltas (built out by land processes)
 lava coasts (Volcanic coasts)
 drowned river valleys
 fault coasts (Coasts shaped by earth
movements)
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Examples of Primary Coasts –
Delta: Nile River; Mississippi River
Examples of Primary Coasts –
Volcanic Crater Coast: Hanauma Bay, HI
Examples of Primary Coasts –
Drowned River Valley: Chesapeake Bay
Examples of Primary Coasts –
Faulted Coasts: Bolinas Bay and Tomales
Bay (along western California coast).
Secondary Coasts
A
secondary coast has been
significantly changed by wave
action since sea level stabilized.
 Secondary coasts form as a result
of marine processes.
Processes that shape secondary coasts
Waves and currents
 Stream erosion
 Abrasion of wind-driven particles
 Freeze/thaw cycles
 Slumping
 water chemistry
 coral-building marine animals
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Examples of Secondary Coasts
Barrier Islands
 Cliffed Coasts
 Reefs/atolls
 mangrove swamps
 Sandy beaches
 salt marshes
 Erosional coasts
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Examples of Secondary Coasts –
Barrier Islands: Outer Banks
Examples of Secondary Coasts –
Cliffed Coasts: Maine
Examples of Secondary Coasts –
Coral Reefs/atolls
Examples of Secondary Coasts –
Mangroves: Florida
Examples of Secondary Coasts –
Sandy Beaches: Caribbean
Examples of Secondary Coasts –
Marshes: East Coast
Examples of Secondary Coasts –
Erosional Coasts
Emergent vs. Submergent Coasts
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Emergent Coast
– the amount of
exposed coast is
increasing: sea level
is lowering.
– Due to evaporation,
freezing, plate
tectonics, etc.
Emergent vs. Submergent Coasts
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Emergent Coast
– the amount of
exposed coast is
increasing: sea level
is lowering.
– Due to evaporation,
freezing, plate
tectonics, etc.
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Submergent Coast
– the amount of
exposed coast is
decreasing: sea level
is rising.
– Due to precipitation,
melting of glacial ice,
deforestation, etc.
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Go back to warmup and label each
coast as either primary or secondary
Coastal Zones
Nearshore
 Offshore
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Backshore
 Foreshore
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