||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).
||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.
||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).
||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.
||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
||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.
||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
||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.
||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.
||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.
||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.
||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
||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
||Basins occurring on the continental shelf formed by offshore faulting activity.
||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
||(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).
||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.
||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.