Table 3 (cont'd).
Geomorphic unit
Description
Abandoned
Vertical accretion deposits of a floodplain that no longer is associated with the present fluvial regime or where flooding
Floodplain
is sufficiently infrequent that fluvial sediments form a negligible component of surface material. The abandoned flood-
Cover Deposit
plain is an older, commonly frozen portion of a floodplain, particularly in permafrost areas, which can include a mix-
(Fpac/Fpr)
ture of fluvial, eolian, and organic materials. A typical profile includes 0.31.5 m of organic material with few thin mineral
layers, and 12 m of fine-grained cover deposits over gravelly riverbed material. Organic deposits (>40 cm) are difficult to
distinguish from this unit, so this unit often includes thick accumulations of peat at the surface.
Abandoned
Generally coarse-grained fluvial materials deposited within channels of recently abandoned channels of meandering
Floodplain
rivers. This unit is found in the riverbeds of formerly meandering streams in the Willow Creek and Crooked Creek
Meander River-
Lowlands that have recently been abandoned as groundwater flow has increased and surface flow has decreased. In
bed (Fparm)
many places, the old channels have filled with fine-grained deposits, which then are classified as abandoned floodplain cover
deposits.
Abandoned
Generally coarse-grained riverbed materials in recently abandoned floodplains that lack significant accumulations of
Floodplain
fine-grained cover deposits. The braided pattern of the old channels still are evident. The old channels generally have
Braided Flood-
an organic-rich, fine-grained cover deposits, while the old riverbars have gravel near the surface. Permafrost generally
plain Riverbed
is absent. This unit occurs in the Bear Creek and Eielson Lowlands.
Deposit gravel
(Fparb)
Abandoned
This geomorphic complex includes ice-rich abandoned floodplain cover deposits and organic fen deposits that have
Floodplain
formed in areas of thermal degradation of the cover deposits. See descriptions of the separate deposits.
Cover + Organic
Fen (Fpac + Off)
Abandoned-
This geomorphic complex includes ice-rich abandoned floodplain cover deposits and organic bog deposits that have
Floodplain
formed in areas of thermal degradation of the cover deposits. See descriptions of the separate deposits.
Cover + Organic
Bog (Fpac + Obc)
Headwater
Small, shallow deposits formed in the headwater of small creeks. Deposits may range from boulders in narrow, incised
Floodplain (Fh)
channels to fine-grained material in broader floodplains. This unit is found in the Yukon-Tanana Uplands district.
Alluvial Fan
Alluvial fans are gently sloping cone-shaped deposits of coarse-grained alluvium formed where a stream course ex-
Abandoned
tends onto a relatively level plain. Abandoned riverbed deposits on fans contain coarse-grained material and frequently
Riverbed
include cobbles and boulders. Significant fine-grained cover deposits are lacking. This unit is found in the Dry Creek
Deposit (Ffrb)
Fan area.
Alluvial Fan
Fine-grained cover deposits associated with overbank flooding on alluvial fans. The material is ice-rich and
Abandoned
thermokarst features are prevalent. This unit is found in the Dry Creek Fan area.
Cover Deposit
(Ffcb/Ffr)
Dissected Alluvial Similar to above except that the surface is dissected, reflecting older deposits. This unit is found in the Dry Creek Fan area.
Fan Cover Deposit
(Ffct/Ffr)
Lowland
Fine-grained, organic-rich materials moved downslope by slopewash, solifluction, and in some cases, piping and, thus,
Retransported
are influenced by both fluvial and gravity processes. Loess also may be incorporated in these deposits. On airphotos,
Deposits (Fsl)
the surface has a feather pattern indicative of small-scale fluvial processes and typically occur on the lower portion of slopes.
The material generally is frozen and ice rich. This unit is associated with upland areas.
Upland
Generally silty to sandy material with occasion gravel-sized fragments that occur in horizontally stratified deposits
Retransported
indicative of fluvial origin. This unit generally occurs at the upper portion of lower slopes and forms a transition zone
Deposits (Fsu)
between residual soils and lowland retransported deposits.
Undifferentiated
Granular deposits in areas of nonglacial floodplains, granular alluvial fans, and glacial outwash plains that have an
Fluvial/Glacio-
unspecified origin. In proglacial environments, glaciofluvial deposits grade into nonglacial fluvial deposits, and this
fluvial Deposit
class is utilized in these transitional areas. In the study area, FG is used when designating subsurface fluvial layers.
(FG)
13
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