Stage 1 corresponds to full glacial conditions
up the Susitna Valley (Reger et al. 1995). Mar-
ine submergence during the initial phase of
reached prior to 20,000 years BP. Glaciers
flowed out of the Chugach and Talkeetna
ice retreat was about 140 m above mean sea
Mountains, where they coalesced and flowed
level and was probably followed by isostatic
into the Cook InletSusitna Lowland. Ice
uplift shortly after the ice retreated. Coastal
filled Knik Arm, overtopping some of the
processes active along the Hillside area and
ridges along the Chugach Mountains, and
Fort Richardson moraine would have eroded
flowed into the isostatically depressed Cook
these older morainal sediments up to the level
Inlet. Lateral moraine deposits from this
of submergence.
time correspond to the Rabbit Creek
Stage 7 is a major readvance of the ice margin
Moraines.
around 13,50014,000 14C years BP into Knik
Stage 2 is the retreat from full glacial condi-
Arm. This advance probably occurred behind
a marine shoal that protected most of the gla-
tions, probably beginning around 18,000 to
cier 's terminus from tidewater conditions
20,000 14C years BP. A marine transgression
(e.g., Post 1975, Mayo 1988) (Fig. 8). The upper-
(sea inundation) accompanied retreat to an
most units of the Bootlegger Cove Formation
unknown position in Cook Inlet.
were deposited then. These units contain
Stage 3 is a stillstand or minor readvance of
sand layers and generally coarsen upwards
the glaciers, with multiple fluctuations in the
(Miller and Dobrovolny 1959, Karlstrom 1964,
ice margin that resulted in deposition of
Yehle et al. 1986), apparently recording the
some of the Fort Richardson moraines.
increased proximity of the ice or a shoaling, or
Marine conditions extended to Rabbit Creek
both, during ice advance. Termination of this
and South Fork Campbell Creek about this
advance constructed the Elmendorf Moraine.
time.
Reger et al. (1995) estimate that at the end of
Stage 4 is a retreat of unknown distance,
the Elmendorf advance, land began to emerge
which allowed a marine incursion that
from the sea at about 13,500 14C years BP.
extended north to at least the North Fork
Land emergence, ice shove, and glacial tec-
Campbell Creek and Chester Creek areas.
tonic uplift of sediments was probably attrib-
The lowermost sediments composing the
utable to a combination of high sedimentation
Bootlegger Cove Formation were deposited
rates near the glacier margin and isostatic
during this incursion.
uplift after the ice receded.
Stage 5 is a readvance that deposited the
Ice or moraine dams at the mouth of the Eagle
Dishno Pond moraines in the eastern low-
River Valley periodically broke, causing rapid
land area (Plate 1). Marine conditions
drainage of lakes impounded in the valley. Such
remained in the Campbell Creek and Ches-
catastrophic flooding would cause intense, local
ter Creek areas, with additional marine sedi-
scour as water was deflected across the front of the
ments deposited to form additional Bootleg-
Elmendorf Moraine. Recurrence of these events
ger sediments.
likely produced the Mountain View fan that origi-
nates at a narrow gap between the Elmendorf Mor-
Stage 6 corresponds to the final retreat of the
aine and Chugach Mountains near the city of Eagle
ice from the Dishno Pond moraines and pro-
River. The fan forms a sand and gravel plain that
gressive recession up-valley out of the lower
extends across the Anchorage Lowland to Knik
Knik Arm. Ice-rafted debris in the base of the
arm (Fig. 4). As ice began to retreat from the
Bootlegger Cove Formation indicates tide-
Elmendorf Moraine, ancestral channels of the
water conditions and glaciers calving ice-
Eagle River were reoccupied as new channels
bergs into the sea (Schmidt 1963) around
became incised, providing lower elevation drain-
14,900 350 14C years BP (Schmoll et al.
ages and shorter routes to the Knik Arm.
1972, Reger et al. 1995). Reger et al. (1995)
concluded that the Bootlegger Cove Forma-
Stage 8 represents a rapid retreat of ice from
tion was deposited between about 15,000
the Elmendorf moraine. The hummocky top-
and 13,000 14C years BP. The extent of ice
ography in the Susitna Valley and upper Knik
retreat up Knik Arm is not known; however,
Arm are indicative of ice stagnation and
marine silt equivalent to the Bootlegger
downwasting. Reger et al. (1995) suggest that
Cove Formation can be found about 60 km
ice margin retreat probably reached the
12
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