Glacial Geology and Stratigraphy of Fort Richardson, Alaska
A Review of Available Data on the Hydrogeology
LEWIS E. HUNTER, DANIEL E. LAWSON, SUSAN R. BIGL, PEGGY B. ROBINSON, AND JOEL D. SCHLAGEL
INTRODUCTION
cial diamicton) that extends underneath the fan
deposits and probably below the Bootlegger
The distribution of surficial deposits across
Cove Formation, a fine-grained silt deposited in
Fort Richardson is well known, based on more
an estuarine environment (e.g., Miller and Dobrov-
than 40 years of investigations (e.g., Miller and
olny 1959, Reger et al. 1995, Schmoll et al. 1996).
Dobrovolny 1959; Cederstrom et al. 1964; Karl-
The Bootlegger deposits and the ground moraine
strom 1964; Schmoll and Dobrovolny 1972a;
form an irregular surface upon which younger
Reger and Updike 1983, 1989; Yehle and Schmoll
glacioalluvial sediments were deposited. Both the
1987a,b, 1989; Yehle et al. 1990, 1992; Reger et al.
fine-grained diamicton of the ground moraine and
1995; Schmoll et al. 1996). Most of the Fort Rich-
the Bootlegger Cove Formation have much lower
ardson cantonment is situated on a large glacioal-
hydraulic conductivities than the overlying gravel
luvial fan, which originates at the mouth of the
and may confine ground water into multiple
Eagle River Valley near the city of Eagle River
aquifers. Older gravel horizons that lie beneath
(Fig. 1, Plate 1). The fan slopes gently to the west
these deposits form confined aquifers that appear
southwest, underlying parts of Elmendorf Air
to be hydraulically linked throughout the
Force Base and downtown Anchorage, and is
Anchorage area (Cederstrom et al. 1964).
truncated to the west by sea bluffs along the Knik
This report summarizes the results of the ini-
Arm. The fan is composed of outwash deposited
tial phase of our hydrogeological study of Fort
by ice-marginal streams and outburst floods that
Richardson. Our goal was to synthesize existing
occurred when ice-dammed lakes in the Eagle
surficial geology and stratigraphy information
River Valley drained (Schmoll et al. 1996). The
relevant to Fort Richardson, including a review of
glacioalluvial fan is bordered on the north by the
the glacial history of the Anchorage area. These
Elmendorf Moraine, a low relief ridge that trends
data were then to be integrated into a conceptual
east to west across the region. The moraine
stratigraphic model to provide a basis for future
formed about 13,000 14C years ago (Schmoll et al.
environmental studies and to help explain
1972, 1996; Reger et al. 1995). Hummocky end-
ground water behavior below the cantonment.
and ground-moraine deposits mixed with out-
The reason for this work is that the stratigraphic
wash, estuarine, lacustrine, and bog deposits are
models typically used for environmental investi-
found north and northwest of the Elmendorf
gations on Fort Richardson are generally over-
Moraine.
simplified, potentially leading to a false impres-
Along the southern margin of the fan and fur-
sion of subsurface conditions. This in turn could
ther to the south, several low hills of ground
cause unwarranted conclusions to be drawn about
moraine protrude through younger glacial depos-
the stratigraphy and its influence on ground water
its of various origins from the most recent glacia-
movement, affecting proper management deci-
tion of this area (Plate 1). The streamlined hills
sions, and leading to ineffectual environmental
located between the post housing area and Glenn
cleanup efforts and compliance. This report doc-
Highway are such features (e.g., Birch Hill).
uments the complexity of the stratigraphy on the
These hills are composed of ground moraine (gla-
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