Table 7 (cont'd). Classification and description of geomorphic units used for differentiating ecosections
within Fort Greely.
Geomorphic unit
Description
Glaciofluvial
Old deposits formed by meltwater streams beyond the terminal glacial margin that are no longer
Outwash Terrace
affected by the current fluvial regime. Sediments are composed of moderately to well-sorted, clean-
Deposit (Gfot)
washed bedload sand and gravel with some boulders. A thin layer (<40 cm) of wind-blown silt is often
present at the surface. Due to the lack of a loamy mantle, permafrost usually is absent.
Moraine, Ice-
Residual accumulations of glacial till and remnant ice deposited by ablation at the lateral and terminal
cored (Gmi)
margins of modern active glaciers. The moraines are highly unstable, with steep slopes and abundant
collapse features. Substantial portions are unvegetated. Moraines usually are frozen and ice-rich.
Moraine, Young
Relatively young moraines with steeper knob and basin topography with a poorly integrated drainage
(Gmy)
network. The deposits are composed of glacial till material deposited at the terminal or lateral margins
of a glacier that has since retreated or disappeared. Younger moraines have less basin filling.
Sediments are highly variable ranging from poorly sorted sand and subangular gravel with some
boulders to sorted coarser subrounded material. Permafrost distribution is very patchy.
Moarine, Old
Similar to above except older moraines have subdued topography with broader knobs and swales
(Gmo)
and more integrated drainage network. Soils show more leaching and horizon development,
permafrost is patchy.
Lacustrine (L)
Silt and clay materials deposited in both glacial and non-glacial lakes. Lake sediments generally are
well stratified into very thin laminations, but may also include coarse-grained sediments associated
with shorelines and fluvial sediments in deltas and fans.
Human Made
All deposits or surface modifications resulting from human activity, including fills and embankments,
Deposits
cuts and excavations, and accumulations of mine tailings.
Drainage Fen
Minerotrophic peatland forms (also called channel fens) that have a generally flat and featureless
(Ofd)
surface that slopes gently in the direction of drainage. The fens are confined to narrow, well-defined
drainages in gently rolling topography. The underlying peat deposit is poorly to moderately well
decomposed and ranges in thickness from 40 cm to 2 m.
Shore Fen/
A fen with an anchored surface mat that forms the shore of a pond or lake. The rooting zone is
Lacustrine (Ofs)
affected by lake water. The thick (>40 cm) organic deposit is dominated by fibric sedge peat.
Basin Bog
Ombrotrophic bogs with thick (>40 cm) organic matter accumulations developed in basins with
essentially closed drainage receiving their water from precipitation and immediate surroundings. The
surface is flat and the water table is near the surface. Organic matter is dominated by fibric peat of
Sphagnum mosses and ericaceous woody material but may be underlain by sedge peat.
Collapse Scar
A circular or oval-shaped wet depression formed from thermal degradation of ice-rich permafrost. The
Bog
depression is poor in nutrients, water input is from precipitation. This unit is associated with head-
waters and abandoned floodplain cover deposits, peat is fibric derived mostly from Sphagnum
mosses. These features were not mapped because of their small size and low abundance.
Veneer Bog
Extensive peat deposits (>40 cm thick) that occur more or less uniformly over gently sloping hills and
(Obf)
valleys. The bog surface is virtually unaffected by the groundwater from the surrounding mineral soils
and thus is acidic and low in nutrients. Water is near the surface. The dominant materials are weakly
to moderately decomposed Sphagnum and woody peat, sometimes underlain by sedge peat.
Upper Perennial
Permanently flooded channels of freshwater rivers where the gradient is relatively high and discharge
River, Non-glacial
and water quality are not affected by glacial meltwater. Water sources are not differentiated and can
include surface runoff, deep groundwater, and black water from bogs. Rivers generally experience
peak flooding during spring breakup and late summer and lowest water levels during mid-summer.
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