UNIVERSITY OF SOUTH ALABAMA
Last Time
Coastal Geomorphology 1
Basic classification (substrate and “energy”)
Processes (waves and currents)
Topographic Features (lab prep)
GY 301: Geomorphology
Lecture 7:
Coastal Plain
Topography:
Terraces
Coastal Geomorphology
Coastal Geomorphology
There are two main controls on coastal geomorphology:
Although diverse, you can group most shorelines into one of 3
broad types:
1) Geological materials available on the shoreline
●Outcrop (rock)
●Gravel
●Sand
●Mud
1) Rocky (high energy [waves, tides, currents]; outcrop/rocks)
2) Beaches (high energy [waves]; sand and gravel)
3) Estuaries (low-high energy [tides]; mud)
2) “energy” of shoreline
●waves
●currents
●tides
●storms
Bay of Fundy, Canada
The irregular shape of rocky coastlines is a consequence of wave
refraction; the bending of waves as they approach a shoreline.
Waves tend to bend toward headlands
which focuses strong erosive forces
around their periphery.
Sandy Shorelines
From Walker, R.G. and James, N.P. (1992). Facies Models: Response to
Sea Level Change. Geological Association of Canada, 409p.
Rocky Coastline
They come in many forms:
●Barrier Islands
●Spits
●Strandlines
●Beaches (open/sheltered)
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Sandy Shorelines
Wave refraction will
result in longshore
currents and
longshore drift
Today’s Agenda
Coastal Geomorphology 2: Terraces
Some definitions and types of terraces
Terraces on topographic maps
Sea level changes and terrace development
Coastal Terraces
Terraces: relatively flat plains formed by deposition or less
commonly, by precipitation (hydrothermal processes)
Coastal Terraces
Terraces: relatively flat plains formed by deposition or less
commonly, by precipitation (hydrothermal processes)
Tuffa/Sinter Terraces:
silica (opaline) precipitated
from
hot
water
in
hydrothermal pools/geysers
Tuffa deposits at Yellowstone National Park
Coastal Terraces
Coastal Terraces
Terraces: relatively flat plains formed by deposition or less
commonly, by precipitation (hydrothermal processes)
Terraces: relatively flat plains formed by deposition or less
commonly, by precipitation (hydrothermal processes)
Tuffa/Sinter Terraces:
silica (opaline) precipitated
from
hot
water
in
hydrothermal pools/geysers
Beach Terraces:
Sediment deposited at the
high and/or low tide levels
in beach environments
Pink Terraces, Tawawera, New Zealand (c. 1890)
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Coastal Terraces
Coastal Terraces
Terraces: relatively flat plains formed by deposition or less
commonly, by precipitation (hydrothermal processes)
Terraces: relatively flat plains formed by deposition or less
commonly, by precipitation (hydrothermal processes)
Beach Terraces:
Sediment deposited at the
high and/or low tide levels
in beach environments
Beach Terraces:
Sediment deposited at the
high and/or low tide levels
in beach environments
High tide terrace, shingle beach, Canterbury, New Zealand
Low tide terrace, Banks Peninsula New Zealand
Coastal Terraces
Coastal Terraces
Terraces: relatively flat plains formed by deposition or less
commonly, by precipitation (hydrothermal processes)
Glacial Terraces: Sediment deposited primarily by melt water or
behind ice-dams in glaciated environments
Glacial Terraces:
Sediment deposited primarily by
melt water or behind ice-dams in
glaciated environments
Glacial outwash, Northern Canada
Glacial outwash, Northern Canada
Coastal Terraces
Coastal Terraces
Glacial Terraces: Sediment deposited primarily by melt water or
behind ice-dams in glaciated environments
Terraces: relatively flat plains formed by deposition or less
commonly, by precipitation (hydrothermal processes)
River Terraces:
Sediment deposited
primarily on flood plains
of rivers. Directly related
to base level.
River terrace
Channel
River terrace
Glacial outwash, Northern Canada
Stream bed model; channel incised river terrace
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Coastal Terraces
Coastal Terraces
Terraces: relatively flat plains formed by deposition or less
commonly, by precipitation (hydrothermal processes)
Base level: The lowest level that a river can erode down to
(incise). It is controlled by the elevation of water bodies that the
river flows into.
River Terraces:
Sediment deposited
primarily on flood plains
of rivers. Directly related
to base level.
Dam
Two river terraces, United Kingdom
Coastal Terraces
Coastal Terraces
Base level: The lowest level that a river can erode down to
(incise). It is controlled by the elevation of water bodies that the
river flows into.
Base level: The lowest level that a river can erode down to
(incise). It is controlled by the elevation of water bodies that the
river flows into.
Base Level
Base Level
Dam
Vertical exaggeration = 50X
Dam
Base Level
Coastal Terraces
Sea level is the ultimate base level……
Coastal Terraces
Sea level is the ultimate base level……
…… and it is never truly constant
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Coastal Terraces
Coastal Terraces
Sea level is the ultimate base level……
Sea level is the ultimate base level……
…… and it is never truly constant
Base level rises
…… and it is never truly constant
Base level falls
Transgression
Regression
Coastal Terraces
Coastal Terraces
Consequently, different terraces can be deposited at different
elevations over time.
Consequently, different terraces can be deposited at different
elevations over time.
Two river terraces, United Kingdom
Coastal Terraces
Coastal Terraces
There is one more variable in the terrace equation that must be
recognized: uplift
There is one more variable in the terrace equation that must be
recognized: uplift
Tectonically active areas
may rapidly elevate and
rotate terraces.
Tectonically active areas
may rapidly elevate and
rotate terraces.
Uplifted beach terrace, Wanganui New Zealand
Uplifted river terraces, Central Asia
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Coastal Terraces
Coastal Terraces
There is one more variable in the terrace equation that must be
recognized: uplift
Late Pleistocene-Holocene sea level curve
But this is good!
It allows us to
synchronize
world-wide
eustatic events.
Coastal Terraces
Terraces on Topographic Maps
C14 dating and other
techniques are used
to establish the age
of each terrace
Weeks Bay
West to east cross-section across Weeks Bay
Schematic, no vertical scale implied
West
East
Terraces on Topographic Maps
Terraces
X
Citronelle Fm.
XI
IX
>39,000 yrs
B.P
XIII XIV XV
6000 yrs B.P
(Tertiary)
“Ecor Rouge” Fm. (Tertiary)
3 km
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Terraces on Topographic Maps
Terraces on Topographic (& Geological) Maps
Upcoming Stuff
Homework
Finish lab 3 (due Friday)
Next Lecture:
GIS and planning (& maybe environmental
applications)
Friday’s Lab:
See homework bump
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