Table 3 (cont'd). Description of geomorphic units within Ft. Wainwright, central Alaska, 1998.
Geomorphic unit
Description
Glaciofluvial
Deposits formed by meltwater streams beyond the terminal glacial margin. They are similar in character to alluvial fan
Outwash
deposits described above and lack significant accumulations of fine-grained cover deposits. These deposits are found
Abandoned
where Wood River exits the mountains and were formed during the Riley Creek Glaciation.
Riverbed (GForb)
Glaciofluvial
Fine-grained material deposited by overbank flooding events on glaciofluvial outwash fans. Sediments range from
Outwash
sandy silts to clay material deposited in slackwater environments. Permafrost is present in most areas except where
Abandoned
active thermal degradation is occurring. The outwash fan is characterizied by numerous groundwater seeps and near
Cover (GFocb)
linear headwater streams that form a dense fluvial pattern on the surface. This unit is found on the lower portion of the outwash
fan associated with the Wood River.
Dissected Glacio-
Similar to above except the surface is dissected and frequently forms terraces above the surrounding deposits.
fluvial Outwash
Thermokarst features are prevalent. The deposits probably were formed during the Healy glaciation.
Cover (GFoct)
Lacustrine (L)
Silt and clay materials deposited in both glacial and nonglacial 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.
Collapse Scar
A thick (>40 cm) organic deposit associated with minerotrophic groundwater movement. The mat of live, fibrous roots
Fen (usually
and loosely consolidated poorly decomposed organic material forms a floating mat, underlain by water or loose fluid
Off/Fpac/Fpr)
peat. The fen surface in near (<10 cm) the water level. The deposits are associated with the degradation of ice-rich permafrost.
Drainage Fen
Minerotrophic peatland forms (also called channel fens) that have a generally flat and featureless surface that slopes
(usually Ofd/
gently in the direction of drainage. The fens are confined to narrow, well-defined drainages in gently rolling topogra-
Fpac)
phy. 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 affected by lake water.
Lacustrine (Ofs/L)
Veneer Bog
Bogs have thick (>40 cm) accumulations of organic matter and the water table is usually at or near the surface. The bog
(usually Obf/Fsl
surface is virtually unaffected by the nutrient-rich groundwaters from the surrounding mineral soils and, thus, is acidic
or Bxr)
and low in nutrients. The dominant materials are weakly to moderately decomposed Sphagnum and woody peat,
underlain at times by sedge peat. Veneer bogs are extensive peat deposits that occur more or less uniformly over gently sloping
hills and valleys.
Collapse Scar
A circular or oval-shaped wet depression formed from thermal degradation of ice-rich permafrost. The depression is
Bog (usually
poor in nutrients because it is not connected to minerotrophic fens. This unit is associated with abandoned floodplain
Obc/Fpac)
cover deposits and frequently is mapped as part of a geomorphic complex because of their small size and abundance.
Flat Bog
A bog having a flat, featureless surface and occurs in broad poorly drained depressions or abandoned floodplains. This
(usually
unit is difficult to distinguish without detailed soil information and is usually included in the Abandoned Floodplain
Obf/Fpac)
Cover Deposit.
Peat Plateau
A bog with thick accumulations of peat over fine-grained mineral soil, rising abruptly about 1 m from the surrounding
Bog (usually
unfrozen fen. The peat was originally deposited in a nonpermafrost environment and is often associated with collapse
Obpp/Fpac)
scar bogs and fens. This unit is difficult to distinguish in the study area without detailed soil information and usually is
grouped with Abandoned Floodplain Cover Deposits. This unit is tentatively used for a problematic situation where birch
forests are growing on degrading permafrost situations. A thick (0.50.8 m) surface of peat has accumulated at the surface.
Shore Bog
A nonfloating bog forming at the shore of a pond or lake. The bog surface is elevated at least 0.5 m above the level of
(usually Obs/L)
the lake. The bog often encroaches over the lake.
Human Made
Gravel fill in roads and pads, also cut and fill material associated with roads.
Deposits (H)
14
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