Table 2. Processes of recharge and discharge in Anchorage Lowland.

Table 1. Characteristics of surficial deposits.

Figure 6. Interbedded alluvial sediments as might be produced by periodic discharge events (sand and gravel) and silt deposition in abandoned channels.

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Table 2. Processes of recharge and discharge in Anchorage Lowland.

Recharge

Discharge

Unconfined aquifer

Stream infiltration (losing reaches)

Stream channels (gaining reaches)

Rain/snowmelt percolation

Seeps/springs

Discharge along mountain front

Confined aquifer

Percolation from unconfined aquifer

Percolation to unconfined aquifer

Seeps from fractured bedrock

under high hydrostatic head

Discharge along mountain front

Lateral discharge into unconfined zone

artesian flow to surface or bluffs

where confining layer is intersected

Elmendorf Moraine. An older ground moraine of

cier margins have a distinctly hummocky mor-

Late Wisconsin age lies at depth south of the

phology caused by the meltout of glacier ice,

cantonment area.* It appears sporadically at the

which was buried beneath them (Fig. 5). This

surface, where it protrudes through younger

melting commonly disturbs the overlying sedi-

glacioestuarine and alluvial fan deposits, and

ments and further complicates the stratigraphy.

likely underlies the sediments across much of

Several types of kame deposits can be recognized;

Fort Richardson.

most are generally composed of thin beds of sand,

silt, diamicton, and gravel, with varying degrees

Glacioalluvial, alluvial, and alluvial fan deposits

of bedding and sorting. Irregular hills from melt-

Glacioalluvial. These are a suite of deposit

out include those near the margin of the Elmen-

types, including kame-channel, meltwater-

dorf Moraine, within the Elmendorf Moraine

channel, and outwash-train deposits, consisting

north of Clunie Creek and at the margin of the

of water-laid sediments deposited in front of a

Anchorage Lowland downslope of major moun-

glacier (Fig. 5; App. A). Meltwater-channel

tain valleys (Plate 1). These deposits are moder-

deposits are composed of well-bedded and well-

ately loose, but compact in the center of some

sorted sand and gravel, which may include some

hills and commonly may merge with end- and

finer-grained material that was deposited in a

lateral-moraine deposits. They are often charac-

shallow backwater. Thin organic horizons are

terized by sharp crests and more rounded hum-

also common on the surface of fine-grained

mocks, moderate to steeply dipping slopes, and

deposits. Thickness is highly variable, often 1 m

sometimes are truncated by stream channels.

to a few meters, but in places channel deposits may

Kame-terrace deposits were formed by water

be thin and patchy, allowing ground moraine or

running along the glacier margin. Long, narrow

bedrock to crop out at the channel floor. Stratified

landforms with smoothly sloping surfaces

sand and pebble- to cobble-size gravel form out-

develop. Prominent scarps may remain where

wash-train deposits, which accumulated in front

deposition was in contact with the glacier. Kame-

of the Elmendorf Moraine and downstream from

fan deposits, which also form at the glacier mar-

Chugach valley glaciers. Most of these latter

gin, range from several to a few tens of meters in

deposits now occur mainly in terraces along

thickness. Their topography is generally smooth,

former channels. Kame-channel deposits are

and surfaces are relatively moderate, with gentle

composed of sand and pebble- to cobble-size

slopes increasing in steepness towards their ice

gravel, similar to outwash-train deposits. Some

source.

silt and clay may now fill paleo-topographic

Alluvial. Both modern and ancient alluvial

depressions. Thickness is generally at least a few

deposits are found on Fort Richardson. They

meters and the deposits have a hummocky sur-

occur along present day streams and floodplains

face that may be incised with low relief channels.

(Fig. 1; Plate 1), often incised into older glacioal-

Kame-channel deposits are common at the transi-

luvial and alluvial fan deposits. The deposits are

tion between high-relief kame and ground-

commonly well-bedded and well-sorted sands

moraine deposits.

and gravels of variable thickness (a few to tens of

Glacioalluvial sediments deposited along gla-

meters). Clasts are rounded to well rounded.

Both modern and ancient stream deposits have

nearly flat to gentle slopes. Scarps 1 m to several

meters high may locally separate deposits from

* Personal communication with H.R. Schmoll, USGS, 1996.

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