Figure 6. Interbedded alluvial sediments as might be produced by periodic dis-
charge events (sand and gravel) and silt deposition in abandoned channels.
(After Selly 1976.)
tain View fan extends from the Chugach Moun-
different periods, forming a series of terraces that
tains to Knik Arm in the area between the Port of
represent several periods of downcutting.
Anchorage and Turnagain Heights and lies below
Alluvial deposits on the east side of the
most of the Fort Richardson cantonment (Miller
Anchorage Lowland are composed primarily of
and Dobrovolny 1959). This particular fan has
well-bedded and well-sorted sand and gravel
multiple levels (nested or composite morph-
derived from local mountain-valley sources. Con-
ology), reflecting a complex history of formation
tacts are generally well defined and the morph-
by recurrent, sudden breakout discharges from
ology reflects alternating periods of deposition
an ancient glacial lake in the Eagle River Valley, in
and incision. Well-developed terraces are com-
a manner similar to Lake George discharging into
mon at all levels, with the nested fans emanating
the Knik River (Post and Mayo 1971). The result is
from incised channels. These fans formed both
a complex assemblage of flood and interflood
before and after the incursion of the Eagle River,
deposits (Fig. 6) that reach a thickness of 15 to 18
while some of the higher-level deposits are prob-
m and are composed of a cobble gravel near the
ably similar in age to outwash of the Elmendorf
head of the fan (see Hunter et al. 1997). Further
and older glacial advances.
west and downslope, the size of material decreases
Alluvial fan. Fan deposits are common across
from gravelly sand to fine sand. A high percent-
the area. Important deposits include 1) a large fan
age of fines (1015%) is described in borehole logs
emanating from the Eagle River Valley, 2) smaller
from the cantonment area (USACE 1996b), the
fans from local valley sources, and 3) fans along
the edge of the Elmendorf Moraine. Alluvial fans
amount increasing with depth.* Locally (e.g.,
are composed of well stratified and sorted sand
Ruff Road Fire Training Area, E & E 1996), sand
and gravel.
and gravel may be interbedded with fine silt and
The largest of these deposits on Fort Richard-
clay.
son is the Mountain View fan, which emerges
Also there is a series of small, well-developed
from the Chugach Mountains at the south edge of
the Eagle River Valley (Fig. 4; Plate 1). The Moun-
* Personal communication with H.R. Schmoll, USGS, 1996.
9
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