reduced the pond bottom elevations an additional,
RESULTS OF PREVIOUS PHYSICAL
but unknown, amount, as it did in the Portage
SYSTEM INVESTIGATIONS
area of Turnagain Arm (Ovenshine et al. 1976a).
Our previous investigations have focused on
Post-seismic adjustments have resulted in an
characterizing the processes and factors affect-
episodic uplift (Savage and Plafker 1991), which,
ing the physical environment of ERF (Tables 1
according to tide-gauge data, was initially rapid
to 4) and evaluating the fate and transport of
WP, both of which are critical to developing a
Table 2. Erosional processes.
conceptual model for identifying appropriate
methods of WP remediation and site restora-
a. Summer.
tion (Lawson et al. 1996).
Morphological
The processes of erosion, transport and depo-
unit
Processes
sition vary across ERF, with responses to mul-
Marshes
Currents (rare)
Wind waves (rare)
tiple internal and external factors over seasons,
Ponds
Wind waves
Tidal currents
years and decades (Table 1). External controls
Wind currents
Debris impacts (e.g., logs)
on the physical system are difficult to define
Ducks and other
Bioturbation
because their effects may last several decades or
bottom-feeding
organisms
more and exert considerable control on internal
Gullies
Currents
Ground water
factors that influence process relationships. The
tidal
piping
effects of earthquakes and other tectonic activ-
runoff
sapping
ity are difficult to predict; however, their im-
Overland flow
Gravitational slope processes
sheet
slump
pact on the ERF physical system may be enor-
rill
block collapse
mous.
Wind waves
sediment gravity flow
The 1964 Alaskan Earthquake (magnitude 9.2
Mudflats
Currents
Debris impacts (e.g., logs)
on the Richter scale) resulted in both sedimen-
wind
Rain drop impact
tidal
Bioturbation
tary and tectonic subsidence, which modified
Overland flow
the site's elevation and the processes operating
sheet
therein (e.g., Ovenshine et al. 1976a; Brown et
rill
Levees
Currents
Debris impacts
al. 1977; Combellick 1990, 1991, 1994; Savage
tidal
Wind waves
and Plafker 1991). A tectonic drop of about 0.6
river
0.7 m relative to mean sea level was recorded in
Coast
Current scour
Debris impacts
the Anchorage region (Brown et al. 1977). Sub-
Wind waves
Overland flow
sidence caused by sediment liquefaction and
solidification during the earthquake probably
b. Winter.
Marshes
Ice plucking
Table 1. Controls on physical
Ponds
Freeze-on and ice plucking
processes.
Ice shove
Ice scour
Gullies
Plunge pool undercutting
Factor
Freezethaw cycling
Internal
Ice segregation and thaw
River
Ice directed current scour
Tides
Mudflats
Ice plucking
Glacial sedimentwater sources
Ice shove (floatingexpansion)
Substrate material properties
Ice scour
Vegetation
Ice cover confined scour
Sediment influxefflux
Freezethaw cycling
Weatherclimate
Levees
Ice scour
Human activity
Freezethaw cycling
Ground water conditions
Ice shove
External
Ice-directed current scour
Earthquakes
Coast
Ice plucking
Tectonic activity
Ice shove (floatingexpansion)
Eustatic sea level rise
Ice scour
Isostatic rebound
Ice block confined scour
Subarctic climate
Freezethaw cycling
Current scour
Glaciers
Surface and ground water systems
Wind waves
5
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