Table 7. Classification and description of geomorphic units used for differentiating ecosections within
Fort Greely.
Geomorphic unit
Description
Weathered
Highly fractured or poorly consolidated bedrock that can have soil-like properties, but has more
Bedrock (Bxw)
evidence of primary structures than residual soil. Ground surface has abundance of exposed rock
blocks. In the study area, this unit is limited to alpine areas where soil formation is minimal.
Residual Soil over Completely weathered material formed from underlying bedrock that has soil-like properties and little
Weathered
or no original primary structure remaining. Typically, particle size increases as it grades into
Bedrock (Bxr)
angular weathered bedrock below. Thin (<40 cm) deposits of colluvial, eolian, or slopewash deposits
may be present. Permafrost generally is absent on south facing slopes, present on north-facing
slopes.
Solifluction
Saturated soil material and rock fragments formed by downslope, viscous flow of the active layer. The
Deposits (Cs)
unit is identified by the distinct lobate surface mounds.
Talus (Ct)
Angular rubble or rock fragments that have accumulated by gravity at the base of cliffs and steep
slopes.
Lowland Loess
Windblown silt deposited on poorly drained lowland locations in complex depositional environments
(Ell)
near large river floodplains. The deposit may contain a mixture of eolian sand, retransported, and
organic deposits in close association with the deposits of massive silt. The soil is normally frozen with
a high ice content and small collapse-scar bogs are common.
Upland Loess
Windblown silt deposited on well-drained upland slopes. Gully pattern associated with these easily
(Elu)
eroded deposits is usually present. Massive silt deposits lack horizontal stratification and coarse
fragments. Deposit must be at least 40 cm thick. Permafrost is absent.
Frozen Upland
Similar to upland loess except that it is frozen. Areas on north-facing slopes and at high elevations
Loess (Elux)
are more susceptible to permafrost formation.
Meander
Meandering channels that wind freely in regular to irregular, well-developed, S-shaped curves.
Floodplain
Channels range from highly sinuous to only slightly meandering. Riverbed material can range from
Riverbed (Fmr)
gravel to gravelly sand and lateral accretion deposits along point bars typically are sandier. Perma-
frost is absent.
Meander Active-
Low portions of the overbank environment in proximity to the river channel that are subject to
floodplain Cover
frequent flooding. Sediments typically are composed of silts and fine sands and have a laminar,
Deposit (Fmca)
interbedded structure formed by changes in velocity and deposition during waxing and waning floods.
Frequent deposition prevents organic matter accumulation. Fine-grained material must be >40 cm
thick and organic layers compose less than 10% of the thickness. Permafrost is absent.
Meander Inactive- Higher portions of the overbank environment in proximity to the river channel that are subject to
floodplain Cover
infrequent flooding (approx. every 525 years). Sediments typically are composed of interbedded
Deposit (Fmci)
organic material, silts, and fine sands. Cover material is >40 cm thick and organic layers compose10
90% of the thickness. Permafrost is absent.
Abandoned-
Vertical accretion deposits of a floodplain that no longer is associated with the present fluvial regime
floodplain Cover
or where flooding is sufficiently infrequent that fluvial sediments form a negligible component of
Deposit (Fpac)
surface material. Surface materials include a mixture of fluvial, eolian, and organic materials but
typically are highly organic. The deposit is >40 cm thick and organic layers compose >90% of the top
40 cm. Organic deposits (>40 cm) are difficult to distinguish from this unit, so this unit often includes
thick accumulations of peat at the surface. Permafrost usually is present.
Headwater
Small, shallow deposits formed in the upland headwaters of small creeks. Associated with steep
Floodplain, Steep
(>4%) stream gradients, entrenched channels, and step-pool bed morphology. Due to high energy
Undifferentiated
and debris transport, deposits range from boulders in narrow, incised channels to fine-grained
(Fhsu)
material in broader floodplains. Channel and overbank deposits are not differentiated. Permafrost is
absent.
Headwater
Small, shallow deposits formed in the headwaters of small creeks in lowland areas. The moderate to
Floodplain,
low stream gradients (<4%) are associated with "bog" streams and places where small streams
Lowland Undiff.
originating from upland areas cross low-lying flat areas. Deposits usually range from gravelly sand to
(Fhlu)
fine-grained and organic-rich silt. Permafrost usually is absent.
Headwater
Small, shallow deposits formed in the riverbeds of steep headwater streams in upland areas.
Floodplain, Steep
Deposits typically have abundant boulders and cobbles and are often constrained by bedrock.
Riverbed (Fhsr)
46
Previous Page
