aine in bluffs on Knik Arm (Miller and Dobrovol-
Pond and bog deposits (peat and organic-rich
ny 1959, Cederstrom et al. 1964). The Bootlegger
silt, minor woody horizons, and interbeds of ash-
Cove Formation is exposed principally in the
sized tephra) are widespread in the Elmendorf
southern part of the Anchorage Lowland near
Moraine, the floor of Eagle River Valley, and
Campbell Creek and along numerous sea and
locally in lateral moraines. Bog deposits may
stream bluffs, where it is commonly concealed
overlie silt, clay, marl, or fine-grained sand that
beneath other deposits (Plate 1). It is likely that a
first accumulated in small lakes or along stream
sandy facies of the Bootlegger occurs along the
channels. These deposits commonly reach 4 m in
former basin margin and locally interfingers with
thickness, but may locally exceed 10 m.
deposits of the Elmendorf Moraine. This is a tran-
sitional zone, where coarse clastic sediments
GLACIAL GEOLOGICAL HISTORY
were contemporaneously deposited adjacent to
fans and streams.
Glacial deposits in the Anchorage area have
traditionally been divided into broad age groups
Lacustrine and glaciolacustrine deposits
that span much of the Quaternary Period (e.g.,
Lacustrine deposits accumulate in bodies of
Miller and Dobrovolny 1959; Karlstrom 1964;
water ranging from large lakes to small ponds,
Reger and Updike 1983, 1989; Reger et al. 1995).
and include water bodies closely associated with
The earlier studies thought that at least five major
former glaciers as well as those formed after their
glaciations affected the Cook Inlet region, extend-
retreat. Kame-fan deposits are transitional between
ing back more than 200 ka BP (Ulery and Updike
glacioalluvial and glaciolacustrine deposits and
1983). Their chronological control was derived
are found where ice dams temporarily impound-
from relative age dating techniques and minimal
ed water along the glacier margin. Thicker glaci-
conventional radiocarbon data. More recently,
olacustrine deposits accumulate in large lakes in
Yehle and Schmoll (1987a,b, 1988, 1989), Yehle et
valleys blocked by the glacier. Deltas commonly
al. (1990, 1991, 1992), and Schmoll et al. (1996)
prograde into the lakes where outwash streams
have attributed most of the surficial deposits to
enter them. Other lacustrine deposits originate in
multiple advances and retreats of the last glacia-
lakes behind moraines or landslides. Deposits
tion (Late Wisconsinan). Rapid changes from gla-
similar in nature also originate in ponds that fill
cial to marine and terrestrial environments pro-
topographic depressions, such as in hummocky
duced abrupt shifts in depositional processes.
ground moraine. Bogs form as ponds fill in with
These rapid changes, taking place as the glacier
organic material and may accumulate thick lay-
margin fluctuated over both the short and long
ers of peat.
term, may account for some of the seven or more
Glaciolacustrine deposits consist of interbed-
glaciations interpreted from the borehole data by
ded clay, silt, and sand, and may include occa-
Trainer and Waller (1965) and Schmoll and Barn-
sional layers of gravel or diamicton. The deposits
well (1984).
range from well to poorly sorted and contacts are
Below, we review the glacial history of Anchor-
generally well defined. Surface topography is
age according to Schmoll et al. (1996) and Reger et
generally smooth, with gentle slopes that
al. (1995). An understanding of how the glaciers
increase in steepness towards valley margins.
fluctuated and deposited their sediments is
The silt and clay are moderately stable, except in
required for us to develop a conceptual strati-
contact with colluvium on valley walls, where
graphic model of the cantonment area. Such an
they are susceptible to stream erosion and failure.
overarching idea is required to evaluate the
Along the Elmendorf Moraine, lake deposits
hydrogeology of Fort Richardson, so that ground
reach thicknesses of 5 to 10 m and may be much
water flow patterns and contaminant transport
thicker beneath alluvial and peat deposits that
can be evaluated, because detailed geological
form the floor of the upper part of Eagle River
data on the subsurface are generally not avail-
Valley. Correlative deposits are found in major
able. So, the conceptual model is therefore based
mountain valleys from Eklutna River south to the
on knowledge of the glacial history and sedimen-
Eagle River Valley. Older deposits occur along
tary processes (Lawson 1979, 1981, 1982, 1988;
Ship Creek, the lower slopes of Peters Creek, and
Boulton 1968, 1970, 1971, 1972, 1975; Powell 1980,
the South Fork Eagle River up to an elevation of
1981, 1984a,b; Hunter et al. 1996a,b).
100 m asl and reach a thickness of about 10 m in
The sequence of events during the last glacia-
the bluffs of Thunder Bird Creek.
tion is as follows.
11
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