Physical Geology lecture outline
- Coastal Processes
Coastlines as interfaces between the terrestrial
and the marine: very dynamic locations.
What are processes that move sediment, shape
coastal landforms, and determine the geologic evolution of coastlines?
- waves:
- what determines wave size?
- the importance of wave base.
- prevailing wind directions and longshore
drift.
- storms:
- deeper reach through increased wave base.
- come in a range of sizes.
- return flow of storm surge also transports
sediment deep offshore to create distinctive layer - a storm
bed. This often represents a permanent sediment loss from shoreline
system.
- can consider storm energy levels.
- tides.
- river sedimentation ('deltaic' forces): supplier
of sediment.
- uplift vs. subsidence (tectonism).
- mass wasting: wave undercutting, often accelerated
during storms.
- biologic (esp. reefs, mangrove swamps).
- offshore currents.
- ice.
- eolian processes: wind blown sands, coppice
dunes.
- eustatic changes.
- humanity.
There is a great diversity
of coastlines. We will look at just three types:
Deltaic complexes:

- Image of a delta building out into a fjord
in Svalbard. Since this fjord was occupied by ice some 15,000
years ago or less, we know this delta has built out in that time
period. Note the active portion to the left where transport and
deposition is occuring via a braided stream. The oldest portion
of the delta surface is the darker surface, where tundra vegetation
has had a chance to establish itself. The braided stream has
wandered back and forth over the delta surface with time. Note
also the thin narrow beach ridge that has trapped small ponds
behind it. What process is it that forms the smooth beach ridge,
and why doesn't the delta have a birds-foot shape? Remember that
this is in a more sheltered fjord.
- definition of a delta: body of sediment that
forms where a river meets a lake or the sea.
- how can deltas be classified?
- cross section view and progradation and coarsening
upwards sequence.
- evolution of in map view, lobe switching
and abandonment.
- subsidence and mass wasting as contributing
processes.
- the Atchafalaya and the Mississippi delta dynamics.
- stream table example.
Barrier Island
complexes:
- common with low profile sandy slopes, e.g.
associated with coastal plains.
- ridge fundamentally caused by wave action
piling up sediment and vegetation working to stabilize it.
- better known examples: Padre Island, Galveston,
Hilton Head - common along the Gulf Coast and southern half of
east coast.

air photo mosaic images of barrier
island complexes SE of Savannah Georgia taken from USGS (terraserver
site).
air photo mosaic form USGS (terraserver site) of Gulf
coast barrier island SW of Houston.
false color satellite
image of thin barrier island complexes along North Carolina coast.
- geomorphic components of the system: offshore
sand bars, shoreface, dunes, spillover fans, tidal channels,
lagoonal area.
- character of sediments in different portions?
- dynamics of change? barrier island migrations
and regressions and transgressions.
- storm deposits:
- storms transport sediment back into the lagoonal
area via spillover fans.
- storms transport debris semi-permanently
offshore.
- brings up question of what is more important
to the shape and character of the Barrier Island - day to day
events and dynamics (e.g. tidal events) or rare events such as
the 100 year hurricane. Could compare, for example, the volume
of sediment moved by each during the time span under consideration.
- what will cause barrier island dynamics to
change and migrations to occur? sediment budget, storm energy,
tectonic and eustatic changes.
Emergent coastlines:
- some associated features - sea cliffs, sea
stacks, sea caves, sea arches.
- importance of wave cut terrace formation
and mass wasting.
- examples: sections of California's coast
line, large parts of the Arctic due to rebound from glacial retreat
and unloading.
- why discrete 'steps' seen?

This is a photo of some sea cliffs that surround Bear
Island (Bjørnøya) on the Barents Shelf. The upper
flat surface was due to erosion by an ice sheet. Since then waves
have cut back into the bedrock to create these sea cliffs. The
bays form along material that is easier to erode while the headlands
are more resistant.

In this photo, also from Bear
Island, the surface zone outlines a shallow and relatively flat
area that is being cut by constant wave action - i.e. a wave cut
terrace in the process of being formed. Note the sea cliffs in
the back, with some talus at their base. Here the process of undercutting
and mass wasting are important.
In this photo from Bear Island a sea arch has formed
as the waves have cut through a rock fin of dipping strata with
softer shales beneath harder sandstones. This is one of a number
of erosional features such as sea stacks and sea caves, that form
along erosional and emergent coastlines. The rebound of the crust
after the glaciers melted away makes many coastlines in the Arctic
area emergent.

This is a photo from a mountain top looking down on curved beach
ridges in Svalbard. There are literally scores of beach ridges
here, marking the gradual rise of the land out of the sea. Each
beach ridge is made up of coarse gravel, and it is possible to
fine driftwood and whalebones in some of them. The uplift is due
to glacial rebound and associated unloading. An active surf zone
can be seen on the far shore and the process continues, although
probably at a decreasing rate.
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