Coastal Geomorphology Flashcards
What is a continental shelf?
An underwater platform of fluvial sediment that forms following sea level rise
How is a continental shelf formed?
As sea level rises above the shallow downstream part of a fluvial system, it becomes essentially a platform beneath sea level. Over time sediment continues to be piled on top of this shelf
What are quaternary sediments in terms of continental shelves?
The sediment that has been deposited on top of a new shallow continental shelf
What is progradation?
This is when the build up of sediment on the shallow continental shelf builds up so much that the top rises out of the water to form a delta.
What are the external inputs to coastal systems?
Sediments, Geology, External forcings (tectonics or anthropogenic)
What are the processes of a coastal system?
Erosion, transportation and deposition
How do the external inputs and processes of a coastal system interact with each other and sediment transport?
The external inputs affect the processes of which they then both separately affect sediment transport mechanisms.
How does sediment transport mechanisms affect morphology?
They affect the morphology of the coastal environment which then feeds back in to determining the processes of the system
What is stratigraphy within coastal systems?
The long term features of coastal systems that are affected by the culmination of all the other mechanisms.
What are the two coastal systems and how are they created?
Estuarian: fluvial sediment input is weaker than coastal removal
Deltaic: fluvial sediment input is greater than coastal removal
What are the two ocean forces shaping coastal systems?
Waves and Tides
How are waves created?
The energy derives from either wind or seismic activity then when eddies approach the coastal system and encounter the ocean floor within half of their wavelength they begin to trip growing in height and eventually collapsing
What is wavelength?
The distance between the two peaks of a swell
How do waves exert energy and subsequently erosion upon a coastal system?
Friction when they encounter the ocean floor within distance half their wavelength and when they collapse and scrape the shore
How are tides determined?
Gravitational relationship between the sun and moon
What are the two types of tide and how are they caused?
Spring Tides: Strongest wave caused when the gravitational energy of sun and moon are aligned to each other relative to the earth
Neap Tides: Weak tides caused when the sun and moon are perpendicular to each other relative to the earth
What is the tidal range?
The difference between te high and low water levels during a tidal cycle.
What is tidal range affected by?
Bathymetry (depth), Width of Continental Shelf, Coastal configuration, distance from amphidromic points (places of no tide)
Does the UK have a large or small tidal range?
Large
What is important to remember about transition from neap to spring tides?
It is continuous - there is not strict switch between the two
How can the impacts of tidal range be enhanced or mitigated?
Storm surges and local conditions
How is a coastal system distinguished as either being tidal or wave dominated?
If tidal range is less than 2m then it is wave dominated if the range is greater than 4m it is tide dominated
How you determine an erosional or depositional coastal system?
Erosional: Energy>Sediment input
Depositional: Energy
What are other determinants on coastal erosion other than simply the amount of wave or tidal energy?
Wave Environment (height, storms severity and frequency)
Coastal Lithology
Coastal morphology (planform configuration, cliff height, angle to ocean, bathymetry)
Tidal, biological and climatological
What are some erosional costal landforms?
Cliffs, which may retreat
Wave-cut platforms
What is the main depositional coastal landforms?
Beaches
What affects the gradient of beaches?
Gradient is determined by sediment size. Large sediment leads to steep beaches because they are hard to move and can only be moved through a steep gradient. Better to think of the opposite sediment size
What are three planform coastal features?
Barrier Islands
Estuaries
Saltmarshes and Mudflats
What is a barrier island?
Island barriers between a lagoon and ocean. They are typically linear shape with low gradient and an opening between the two masses of water
What is an estuary?
Formed behind barrier islands these are lowland areas drowned by post-glacial sea level rise. They consist of fresh and salt waterand receive sediment from fluvial, coastal and local sources.
What is a unique determinant of deposition in estuaries?
Salinity - the input of saltwater encourages some molecules such as clay to stick together
What is flocculation?
The process of molecules sticking together due to salinity changes
What are the points of most energy within an estuary and those that have the least?
Most: Ocean Mouth and River Mouth
Least: Middle
What part of the estuary has little sediment and why?
Middle because there is little energy to transport it there
What are saltmarshes and mudlfats?
landforms that occur at the intertidal boundary between the continent and ocean.
Why are there creeks within saltmarshes and mudfalts?
Penetration of tides
What allows the saltmarshes and mudflats to accumulate sediment?
Vegetation traps the sediment transported in by the tides
What are saltmarshes and mudflats sensitive to most?
Sea level change because it affects the amount of sediment they receive to grow
What are the coastal sediment supply controls?
Catchment characteristics (relief, size, lithology, tectonics) Climate Soil Vegetation Human activity
What are the coastal sediment dispersal controls?
River flow characteristics River Sediment load Strength of Estuarine Tidal currents Strength of offshore currents Bouyancy of river water Wave environment
What are the three delta types?
Elongate: Dominated by fluvial processes which allows for progradation.
Estuarine: Dominated by tidal processes that create lots of large channels. There is also sufficient energy to cut back the delta
Cuspate: Dominated by wave energy that cuts deposits back rapidly
Give an example of al three delta types?
Elongate: Mississippi
Estuarine: Ganges-Brahmaputra
Cuspate: Tiber
What is the important relationship between all three delta types?
Most deltas are a form of all three types and so have elements of them all
How does dam construction affect sediment supply?
Dams act as sediment sinks and prevent it from flowing further downstream and assisting with delta formation
What is a major threat that is posed by dam construction related to climate change?
Climate change will lead to significant sea level rise in certain low lying areas. If deltas are deprived of sediment through dams then the inundation of low lying areas will be faster as there is no natural defences. Some of these areas are heavily occupied by humans.
What are some of the threats to coastal systems due to anthropogenic activity?
Changing sediment input, precipitation, sea level change, land and shelf subsidence, coastal erosion, subsurface abstraction, increased population
