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Physiographic Setting Subcomponent (GC)


Unit name Description
Abyssal/Submarine Fan A low, outspread, relatively flat-to-gently sloping mass of loose material—shaped like an open fan or a segment of a cone—deposited by a flow of water at the place where it issues from a narrower or steeper-gradient area into a broader area, valley, flat, or other feature. Abyssal fans form at the mouths of submarine canyons, and fans are also the result of turbidities (that is, gravity-driven, underwater avalanches).
Barrier Reef A long, narrow coral reef, roughly parallel to the shore and separated from it by a lagoon of considerable depth and width. This reef may enclose a volcanic island (either wholly or in part), or it may lie a great distance from a continental coast (such as the Great Barrier Reef). Generally, barrier reefs follow the coasts for long distances—often with short interruptions that are called passes or channels. Three principle examples of this type of feature are Australia's Great Barrier Reef, the New Caledonia Barrier Reef, and the Meso-American Barrier Reef system—although similar features exist elsewhere.
Bight A broad bend or curve in a generally open coast. Examples include the South Atlantic Bight and the Southern California Bight. These are distinguished from Embayment/Bays by the shallower angle between the apex of the bight and the adjacent coasts, although the term <i>Bay</i> has been used to name these features (e.g., Bay of Campeche).
Borderland An area of the continental margin (between the shoreline and the continental slope) that is topographically more complex than the continental shelf. This feature is characterized by ridges and basins, some of which are below the depth of the continental shelf.
Continental/Island Rise An area that lies at the deepest part of a continental or island margin between the continental slope and the abyssal plain. The rise is a gentle incline (with slopes of 0.5° to 1°) and it has generally smooth topography—although it may bear submarine canyons.
Continental/Island Shelf That part of the continental margin that is between the shoreline and the continental slope (or a depth or 200 meters when there is no noticeable continental slope); it is characterized by its very gentle slope of 0.1°. Island shelves are analogous to the continental shelves, but surround islands.
Continental/Island Shore Complex This feature includes the land-water interface zone and contains geoforms across a diversity of scales. For CMECS, the supratidal zone forms the landward limit of geoforms found within the shore complex setting. This setting does not include the land-water interface along tidal rivers that may extend a considerable distance inland.
Continental/Island Slope That part of the continental margin that is between the continental shelf and the continental rise (if there is one); it is characterized by its relatively steep slope of 1.5 - 6°. Island slopes are analogous to the continental slopes, but occur around islands.
Embayment/Bay A water body with some level of enclosure by land at different spatial scales. These can be wide, curving indentations in the coast, arms of the sea, or bodies of water almost surrounded by land. These features can be small—with considerable freshwater and terrestrial influence—or large and generally oceanic in character.
Fjord A long, narrow, glacially eroded inlet or arm of the sea. They are often U-shaped, steep-walled, and deep. Because of their depth, they tend to have low surface-area-to-volume ratios. They have moderate watershed-to-water-area ratios and low-to-moderate riverine inputs. Fjords often have a geologic sill formation at the seaward end caused by glacial action. This morphology—combined with a low exchange of bottom waters with the ocean—can result in formation of hypoxic bottom waters.
Inland/Enclosed Sea A large, water body almost completely surrounded by land. Salinities range from fresh through marine. The term <i>inland</i> is used to describe situations where the water body is connected to an adjacent large water body by a narrow strait, channel, canal, or river. Examples of this type of setting are the Mediterranean and Black Seas. The Great Lakes, due to their connectivity to the Atlantic Ocean via the St. Lawrence River also fall into this category.
Lagoonal Estuary This class of estuary tends to be shallow, highly enclosed, and have reduced exchange with the ocean. They often experience high evaporation, and they tend to be quiescent in terms of wind, current, and wave energy. Lagoonal estuaries usually have a very high surface-to-volume ratio, a low-to-moderate watershed-to-water-area ratio, and can have a high wetland-to-water ratio. The flushing times tend to be long relative to riverine estuaries and embayments because the restricted exchange with the marine-end member and the reduced river input lengthen residence times. As such, there tends to be more benthic-pelagic interaction, enhanced by generally shallow bathymetry. Additionally, exchange with surrounding landscapes (often riparian wetland and palustrine systems) tends to be enhanced and more highly coupled than in other types of estuaries.<br/><br/>Occasionally, a lagoon may be produced by the temporary sealing of a river estuary by a barrier. Such lagoons are usually seasonal and exist until the river breaches the barrier; these lagoons occur in regions of low or sporadic rainfall.
Major River Delta The nearly flat, alluvial tract of land at the mouth of a river, which commonly forms a triangular or fan-shaped plain. It is crossed by many distributaries, and the delta is the result of sediment accumulation from the river. Deltas are distinguished from alluvial fans by their flatter slope. Examples of this feature include the Mississippi Delta, the Nile Delta, and the Ganges Delta. All deltas are dynamic areas of mixed-water flow and salinity.
Marine Basin Floor Basin floors refer broadly to the areas of the seafloor between the base of the continental margin (usually the foot of the continental rise) and the mid-ocean ridge. Occasionally, this large region is subdivided into smaller basins based on local bathymetry.
Ocean Bank/Plateau A mound-like or ridge-like elevated area on the seafloor; it may have a modest-to-substantial extent. Although submerged, this feature can reach close to sea level (e.g., Bahama Banks).
Riverine Estuary This class of estuary tends to be linear and seasonally turbid (especially in upper reaches), and it can be subjected to high current speeds. These estuaries are sedimentary and depositional, so they may be associated with a delta, bar, barrier island, and other depositional features. These estuaries also tend to be highly flushed (with a wide and variable salinity range) and seasonally stratified. Riverine estuaries have moderate surface-to-volume ratios with a high watershed-to-water-area ratio—and they can have very high wetland-to-water-area ratios as well. These estuaries are often characterized by a V-shaped channel configuration and a salt wedge.<br/><br/>High inputs of land drainage can promote increased primary productivity, which may be confined to the water column in the upper reach, due to low transparency in the water column. Surrounding wetlands may be extensive and healthy, given the sediment supply and nutrient input. This marsh perimeter may be important in taking up the excess nutrients that are introduced to the system. Physically, the system may tend to be stratified during periods of high riverine input, and the input of marine waters may be enhanced by countercurrent flow.
Shelf Basin Basins occurring on the continental shelf formed by offshore faulting activity.
Shelf Break The slope discontinuity (rapid change in gradient) of 3° or greater that occurs at the outer edge of the continental shelf. This boundary generally occurs at a depth between 100-200 meters and forms the boundary between the Marine Offshore and Oceanic Subsystems.
Sound (a) A relatively long, narrow waterway connecting two larger bodies of water (or two parts of the same water body), or an arm of the sea forming a channel between the mainland and an island (e.g., Puget Sound, WA). A sound is generally wider and more extensive than a strait. (b) A long, large, rather broad inlet of the ocean, which generally extends parallel to the coast (e.g., Long Island Sound, NY).
Submarine Canyon A general term for all linear, steep-sided valleys on the seafloor. These canyons can be associated with terrestrial or nearshore river inputs, such as in the Hudson or Mississippi canyons.
Trench Trenches in the physiographic setting subcomponent occur at a smaller spatial scale than the hemispheric-sized trenches in the tectonic setting. Both types of trenches share similar morphology, but physiographic setting Trenches are not necessarily associated with plate subduction.