Coastlines are the interface between the terrestrial and the marine and as such 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. Cove Point N. J. migration tude to longshore drift.
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  • Waves at high tide cutting into beach cliff. Note how flat the top of the cliff is and what is being eroded. These are old beach deposits that were uplifted and are now being eroded. Ths photo is from Cabo San Pulmo, Baja, Mexico.
  • waves form beaches and make and/or shape beach sediment.
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  • Waves are sculpting the gravel and sand into cusps along the Cabo San Pulmo beach, which in turn influences how the waves run up the shoreface.
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  • Due to the constant wave tumbling and abrasion by other cobbles and grains the beach gravel becomes very well rounded and polished.
  • Link to avi video of surf zone.
• 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.
  • influenced by moon and suns gravitational pull, but also coastline configuration
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  • USGS tidal gauge in New Jersey, along with a tidal gauge history. Image source: http://pubs.usgs.gov/fs/2007/3064/
• river sedimentation ('deltaic' forces): supplier of sediment.
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  • Image from the USGS of the Mississippi and Mekong deltas side by side. Note there very different appearance, but in both cases they represent bodies of sediment that have built out into the sea as the river continually supplies sediment through time. Image source: http://deltas.usgs.gov/
• uplift vs. subsidence (tectonism).
• mass wasting: wave undercutting, often accelerated during storms.
• biologic (esp. reefs, mangrove swamps).
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  • To the left is a picture of mangroves that trap sediment (note all the mud exposed at lower tide) and form islands in warmer and low relief coastal environments. All of the holes in the mud are associated with some burrowing animal, and are one manifestation of the significant biodiversity and activity that characterize these ecosystems. To the right is part of a coral reef, which acts as a wave barrier and a sediment producer. The white sand in the foreground is largely sediment from the breakdown of the reef material. Photos from USGS site: http://sofia.usgs.gov/virtual_tour/kids/ecosys.html
• offshore currents.
• ice.
• eolian processes: wind blown sands, coppice dunes.
• eustatic (global sea level) changes.
• humanity.

• deltas.
• barrier island complexes.
• emergent shorelines.

Deltaic complexes:

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• 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.

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• 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.
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• Diagram from USGS site http://3dparks.wr.usgs.gov/nyc/shoreline/beaches.htm that shows many of the components of a barrier island, with older, now submerged deposits when sea level was at a lower level.
• 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?

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