Coasts are highly varied and complex
systems. The number and variety of coastal classifications is large and
often
subject to an author's personal bias or background. Here are a few.
Descriptive Classifications
- Army Corps of Engineers ,1977
- Rocky Coasts with limited beach
- Straight Barrier island shoreline
- Short Barrier island shoreline
Genetic Classification
Genetic classifications are based on
influencing factor such as geologic history and sea-level changes, tectonic
environment, glaciation, sediment
supply, wave and tidal regime etc.
Relative sea level changes
(eustatic and isostatic).
Johnson (1919)
- Submergent: Fjord or ria coast (Chesapeake Bay, Martha's
Vineyard)
- Emergent: Tidal flats and barrier islands
- Neutral
- Problems: Most coasts do not reflect present conditions
but past condition
- Example:
- coast of ME is emerging but has some the best examples
of submergent coastal features
- Most of the east Coast is submerging, but has the
features of an emergent coast (e.g. barrier islands)
- Concept: Lagtime=Length of time, following a
change in conditions, required to reach a new equilibrium. In a
coastal region lagtime is a function of energy input and
sediment mobility.
modification
by coastal
processes and geologic history. Shepard
(1973)
Primary coast: Unmodified--morphology controlled by
recent geologic history
- Land erosion coasts
- Ria coast drown river valleys: indented--shape controlled
by drainage basin pattern
- Drowned glaciated coast (e.g. Deep coastal valleys--fiords)
Examples:
- Drowned karst topography
- Subaerial deposition coasts
- River deposition coasts
- Deltaic coasts (single delta complex)
- Compound delta coasts
- Compound alluvial fan coasts
- Glacial deposition coasts
- Partially submerged moraines
- Partially submerged drumlins (Boston Harbor
drumlins)
- Partially submerged drift features
- Wind deposition coasts
- Landslide coast
- volcanic coasts
- shaped by diastrophic movements (faulted coasts)
- Ice coasts
Secondary Coasts (modified
by coastal processes)
- Wave erosion coasts
- Wave straightened cliffs
- Differentially eroded coasts
- Marine deposition coasts
- Barrier beach
- Barrier island
- Barrier spit
- Bay barrier
- Coasts built by organisms
- coral reef coasts (fringing reef, barrier reef, atoll,
keys, etc.)
More about reefs:
- Serpulid reef coasts
- Oyster reef coasts
- Mangrove coast
- marsh grass coast
Pros and cons of Shepard's classsification: His classification is
thorough, but cumbersome. Also many coasts may fall under more than
one classification.
Tectonic
Classification of
Coasts
Hydrographic
regime (Energy-based classification)
Davies, 1964: Classification based on tidal energy
- Microtidal coasts (tidal range
= 0-2 meters)
- Mesotidal coasts (tidal range
= 2-4 meters)
- Macrotidal coast (tidal range
>4 meters)
- Assumptions (not always true)
- Microtidal = wave dominant
- Macrotidal = tide dominate
- Mesotidal = mixed energy
Hayes,
1979: Classification based on wave and tidal energy
Hayes' classification builds upon Davies' classification
and quantifies the relative input of wave and tidal energy. See
lecture on hydrographic regime.
Summary
Evolving from the attempts to classify coasts in an understanding
of the factors that control their morphology, such as tectonic
environment, climate, hydrographic regime, geologic history, and
coastal fluvial processes. All of these factors are discuss in
greater detail in the next
lecture.
Sites to Explore
Lindley
Hanson/email
Department
of Geological Sciences, Salem State
College, Salem, MA
