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SEDIMENT TRANSPORT AND ACCUMULATION IN A FJORD BASIN,
GLACIER BAY, ALASKA1,2
CHARLESM. HOSKIN3 AND DAVID C. BURRELL
Department of Geology and Institute of Marine Science; and Institute of Marine Science,
University of Alaska, College, Alaska 99701
ABSTRACT
Sediment transport and accumulation were studied over several years to define the sedimentary environment in a fan-terminated, active valley glacier and adjacent fjord at Queen Inlet, Glacier Bay National
Monument, Alaska. Recently exposed ice-contact sediment at the glacier snout is entrained during summer
and early fall by meltwater streams crossing a subaerial-intertidal outwash fan. Suspended sediment in the
meltwater (sediment loads exceed 1 g/liter at the inlet head) subsequently yields a cold, surface sediment
plume overlying warmer saline water in the fjord basin. Mixing of these layers produces flocculation and
settling occurs in discrete layers; each layer is considered to represent one tidal cycle. No gravel is present
in fjord floor sediment, although both colluvium and outwash fan sediments contain gravel. This gravel distribution eliminates sliding, slumping of the outwash fan, and ice rafting as major contributors to fjord basin
sediment in Queen Inlet. Piston cores of muddy fjord basin sediment show cyclical, thin, black horizons,
thought to be annually produced. Spacing of these marker horizons indicates that sediment accumulation
may exceed 1 m/year at the inlet head. The fjord floor is cut by sinuous valleys with natural levees, terraces,
and sandy silt axial sediment. These valleys are believed to be the result of sediment-transporting bottom
currents.
INTRODUCTION
The modern valley glacier-fjord regimen
is a microcosm of the detrital phase of the
sedimentary cycle. Source, transport, and
accumulation are contained in a natural
package of logistically manageable dimensions in a virtually closed system. This
paper examines the processes and products
of accumulationin the fjord basin of Queen
Inlet, Glacier Bay National Monument, in
southeastern Alaska (fig. 1). We have monitored Queen Inlet for over 5 years, commencing in the summer of 1966. The regimen of Queen Inlet is particularly well suited for sediment transport studies because
(a) there is only one volumetrically important source of sedimentary particles (ice-
contact deposits at the glacier snout) with
the tremendousadvantageof having no well1 Manuscript received April 27, 1971; revised
March 28, 1972.
2 Contribution no. 148 from the Institute of Marine Science, University of Alaska.
3 Present address: Box 5345, Southern Station,
University of Southern Mississippi, Hattiesburg,
Mississippi 39401.
[JOURNAL OF GEOLOGY, 1972, Vol. 80, p. 539-551]
@ 1972. The University of Chicago. All rights reserved.
developed grain-size modes (Slatt 1971),
(b) transport (meltwater streams) resembles an on-or-off mechanism with maximum
flux in summer and zero flux in winter,
which supplies two grain-size populations
(suspended load and bedload), and (c)
separate bodies of sediment, recognizable
by grain-size composition, accumulate in
the fjord basin. For detailed results of
grain-size analyses for 32 Shipek grabs and
three piston cores, see Hoskin and Burrell
(1968, table 1, p. 102-104).
PHYSIOGRAPHY
GENERAL
Queen Inlet (fig. 2) is a typical fjord
with high, steep walls, a valley glacier, and
an outwash fan and meltwater streams
which connect CarrollGlacier-via an intertidal zone-to the marine portion of the
fjord. The present long-term climatic conditions are causing most glaciers to retreat
in Glacier Bay
(Goldthwait
1966),
yet
Carroll Glacier, now the principal glacier
of Queen Inlet, advanced by as much as
1 mile during the period 1964-1968 (Field
1969), and this advance has since continued. Less than 1 mile now (1970) separates
539
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540
CHARLESM. HOSKIN AND DAVID C. BURRELL
1360
136°
1320
FIG. 1.-Location of Queen Inlet within Glacier Bay National Monument, Southeast Alaska
the glacier snout and tidewater. The physiographic map of Queen Inlet (fig. 2) was
made from bathymetric (PDR) profiles
taken in the summer of 1967. Bedrock
(mostly foliated granitic rocks and carbonates; MacKevett et al. 1971, pi. 1) forms
steeply sloping subaerial and submarine
walls which continue at the inlet floor beneath a sediment fill of unknown thickness.
Both Triangle and Composite Islands are
outcrops of bedrock, and some rough bottom topography at the inlet head may be
submarine outcrops of the same material.
Lateral moraines are subaerially exposed
on the northwest inlet wall just above sea
level. The sill which restricts the southwest
entrance (figs. 2, 5) has not been studied
in detail. The entrance southeast of Composite Island has no such restriction. From
seismic reflection profiles, Von Huene
(1966, p. 300) considered the baymouth
sill in Nuka Bay (Kenai Peninsula, Alaska)
to be glacial drift and sills within Nuka
Bay to be basement rock (Von Huene
1966, p. 293; p. 294, fig. 2). Holtedahl
(1967, p. 190) favors a bedrock origin for
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541
SEDIMENT TRANSPORT AND ACCUMULATION IN A FJORD
QUEEN INLET
East
West
-0
20
40
S60
S80
-100
fMS
0
0.5
1.0
n.m.
FIG. 3.-Precision depth recorderprofiles for
traversesshownin fig. 2. Channeldepthsbelow
the
FIG.2.-Physiographic representationof Queen
Inlet showingthe inlet-floorvalleys. The intertidal mean low water in fathoms: n.l. = natural levee,
zone is stippled; numberedtraversesare the PDR t = terrace.
profiles of fig. 3; * = locations of the analyzed
channel sediment samples of fig. 11; X = major channels of surface streams is not yet clear.
lateralstreamdeltas.
Two streams have built gravelly deltas
(labeled X, fig. 2) into the fjord basin, but
the sills in Hardangerfjord of western Nor- careful echo sounding around each delta
way. An extensive terminal moraine and has revealed no channels, and therefore no
outwash fan have developed in front of connection is believed to exist between
Carroll Glacier.
these two surface streams and the inletfloor valleys. Meltwater streams crossing
INLET-FLOOR VALLEYS
the outwash fan in the vicinity of Triangle
There are at least two inlet-long depres- Island could connect with the inlet-floor
sions in the floor of Queen Inlet which are valleys, but lacking the necessary data from
here termed "inlet-floor valleys." Two val- side-looking echo sounders, their relationleys are clearly evident in transverse sec- ship is not known (fig. 2, question marks).
tions north of profile 6 (figs. 2, 3). Only
Most transverse profiles show terraces
one valley appears in the next profile south within the valleys and natural levees where
(7) and it is believed that the two valleys
the valleys join the adjacent flat fjord
merge as shown in figure 2. The valleys are
floor. Buffington (1952) has noted that subsomewhat sinuous in plan, and less than
marine valleys with levees are perfectly
30 m wide at the inlet head, increasing to
analogous to their subaerial counterparts.
about 120 m near the inlet mouth. The valley walls are steep (see fig. 3), but actual Such valleys have not been previously reslopes may not be determined from the corded from fjords and are of considerable
wide-beam echo soundings obtained to date. interest because they are believed to be
The valleys are between 3.7 and 12.7 m evidence for sediment-transporting bottom
deep. The relationship between the head currents. Echo-sounding studies in adjacent
(north) of the inlet-floor valleys and the Glacier Bay fjords (predominantly with
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CHARLES M. HOSKIN AND DAVID C. BURRELL
542
tidal glaciers) have revealed no inlet-floor There is no freshwaterinflow from Carroll
Glacier during the long subarctic winter.
valleys.
Thermohaline
mixing of the fjord waters
HYDROGRAPHY
is induced by surface cooling and, during
Hydrographic and suspended-sediment
this period, the fjord is essentially unstratiprofiles have been obtained at the head of
fied and homogeneous. Spring insolation
Queen Inlet at various seasons over a 5- effects upon
the upper water column is
year period. Figure 4 illustrates the seasonshown by the April profile of figure 4. A
al vertical temperature distribution of the
strong, shallow thermohaline (figs. 4, 6)
reference locality, station Ql-10 (fig. 5).
is developed with the glacial meltwater
inflow during the summer and early fall,
and surface warming of the marine water
helps stabilize this surface stratification.
Runoff peaks in early September with the
combinedcontributionsof maximumglacial
melt and enhanced precipitation. Carroll
Glacier terminates prior to the intertidal
area (fig. 5), so that meltwater enters the
fjord as a cold surface prism. More commonly (in southeast Alaska), the valley
glaciers are in direct contact with the marine water; these are the "iceberg fjords"
of Pickard (1967). For this latter class of
fjord, fresh water enters the fjord in a more
3
5
4
2
6
7
diffused fashion and the resulting circulaT C
tion patterns, at least adjacent to the glaFIG. 4.-Annual low-water temperature districier face, are poorly understood.
bution at station QI-10 of fig. 5.
Figure 6 plots salinity values concomitant with the temperatureprofiles of figure
4. These illustrate the classic fjord hydrogQUEEN INLET
raphy, with primary summer mixing and
ACONA 099
SEPT. 70
099 JULY 70
076 SEPT. 68
038 APRIL67
S
Ol-10
LW
4
8
12
16
20
24
28
32
S %.
FIG. 5.-Location of reference station Ql-10 and
longitudinal profile of fig. 7.
FIG. 6.-Annual low-water salinity distribution
at station QI-10 of fig. 5.
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SEDIMENT TRANSPORT AND ACCUMULATION IN A FJORD
circulation restricted to the upper layers
(e.g., Cameronand Pritchard 1963, p. 313).
Data obtained for both tidal velocities and
freshwater inflow in Queen Inlet to date
are somewhat crude. However, it would
appear that the surface-layer water circulation is more strongly influenced by tidal
mixing and marine entrainment during the
early part of the summer season, becoming
progressively river-dominated toward the
fall; that is, a progressionfrom a standard
type-B estuary toward type A (Pritchard
1955). In September the Queen Inlet halocline is restricted to the surface 10-15 m
(fig. 6). At this time, saline entrainment,
and hence the nontidal component of the
balancing return flow of subsurface marine
water up the inlet, would be minimal.
McAlister et al. (1959) have given depths
of 0-6 m and 6-35 m, respectively, for the
surface outflow and inflow (from mouth to
head) for the Silver Bay fjord (fig. 1, near
Sitka) at an equivalent time when river
runoff predominatedover tidal mixing. The
July halocline of figure 6, when surface
tidal mixing is of relatively enhanced importance, extends to a depth greater than
30 m, and the "base" of the upper fjord
FIG. 7.-Temperature
in July.
543
"circulation cell" lies deeper also. The net
nontidal velocities are, however, well below
the September values because of the reduced river flow. Surface wind mixing, due
to intense foehn-type winds from the glacier, might well be sporadically important
but has not been observed in this particular
inlet.
Figure 7 gives the July low water-early
flood temperature structure for the longitudinal section shown in figure 5 (stations
99-7-99-2). The profile to the left of the
vertical broken line is a "backwater"region
adjacent to the sill. At the maximum flood
stage, the fresh water is backed up north
of stations 99-2 and 99-1 (QI-10). This
latter station (location of the profiles given
in figs. 4, 6, 9, and 10) therefore "sees"
the surface prism each tidal cycle. Figure 7
shows warmer (> 5.7° C) and more saline
(> 30.7%0) Glacier Bay water partially
penetrating the density structure. At the
head of the inlet (i.e., in the vicinity of
station QI-10), the subhalocline water is
essentially homogenousand "marine."With
the characteristic fjord depth/width ratio,
and the absence of a complete entrance sill,
deep tidal water movements are very slight,
distribution along the profile shown in fig. 5. Low-water-early flood tidal stage
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544
CHARLES M. HOSKIN AND DAVID C. BURRELL
and the principal nontidal circulation is
confined to the surface waters as noted.
However, there is a progressive slight dilution and warming of the deep waters at
the inlet head during the summer (figs. 4,
6). This is a reflection of the summer-fall
subsurface trends within the contiguous
Glacier Bay (which is itself a complete
fjord system); the summer hydrographic
patterns developed within Glacier Bay have
been discussed by Quinlan (1970). It
should be noted that the subsurface water
column of "iceberg"fjords is far less stable,
as might be expected, than for Queen Inlet
where fresh water is added only on the surface. Pickard (1967), for example, has recorded considerably higher dissolved oxygen contents at depth for the former type.
This enhanced vertical diffusivity seems to
occur regardlessof the fjord geometry.
SUSPENDED-SEDIMENT
SURFACE
REGIME
PLUME
During late August-September, glacier
meltwater covers large areas of the mudflats (fig. 8) in ill-defined streams. In early
summer this water is confined to several
major courses (principally between Triangle Island and the east shore), but these
have changed over the years with the advance of Carroll Glacier. It is impossible to
monitor quantitatively the freshwater inflow with any degree of accuracy, but the
contribution from Carroll Glacier certainly
far exceeds that from any lateral stream.
This runoff transports considerable quantities of sediment from the glacier, moraine,
and intertidal mud-flat areas into the fjord;
thus, the surface prism described above is,
in fact, a distinctive sediment-ladenplume,
which may maintain its identity (at low
water) for several miles down the inlet.
Figure 8 illustrates a quasi-synoptic distribution of the plume at this tidal stage at
the head of Queen Inlet in September.The
suspended-sediment load (fig. 8, S.L.) is
always in excess of 1 g/liter at the mudflat-marine boundary; the sample given in
figure 8 is for just one of the many streams
emptying into the fjord. The major glacial
streams at this time were located on either
side of Triangle Island, with the principal
plume transport concentrated on the west
side of the fjord, as is the case in highlatitude (N) estuaries.
FLOCCULATION
FIG. 8.-Quasi-synoptic distribution of the sediment plume at low water in September. See text for
discussion of boundaries A and B. The temperature
(T), salinity (Sal), and suspended-sediment load
(S.L.) data are for the surface 5-10 cm.
SITE
Boundary A of figure 8 is the highly distinctive flocculation front of the plume.
This has been shown by laboratory experiment to occur with mixing to approximately 4 %o salinity. We concur with Schubel
(1971) that there is much ignorance concerning the mechanism of agglomeration
of suspended sediments in estuaries, but
the active fjord environment may well be
one of the few examples where use of the
term "flocculation" per se is correct. The
exceedingly high sediment concentrations
within the freshwater plume ensure that
flocculationproceedsrapidly, once initiated,
with increase in ionic strength of the water;
hence the sharp leading edge (fig. 8, A) of
the plume. There is (as noted also by
Schubel) no established method for determining the degree of such sediment agglomeration. Our work (see below) utiliz-
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545
SEDIMENT TRANSPORT AND ACCUMULATION IN A FJORD
ing electronic (Coulter Counter) procedures
appears to yield size spectra of the primary
particles only. Settling rates of the flocs
under shipboardlaboratoryconditions indicated that most were in excess of 100 4,
that is, fine sand-silt size-range. Electron
micrographs of undisturbed bottom-Sediment samples show typical, randomlyorientated floc textures (N. R. O'Brien, personal
communication, 1970). Between boundaries A and B of figure 8, the settling sediment is close to the surface and still visible,
so that load samples from this zone and the
primary plume area are not dissimilar.
Boundary B in reality marks an indistinct
zone when visual contact with the sediment
is finally lost. The samples of figure 8 were
collected by small boat, and the boundary
positions fixed by radar ranging from the
research vessel.
ment-load values obtained contemporaneously) were taken at station QI-10 at a
time of maximum freshwater runoff. These
data required approximately 30 min for
collection, bracketingthe tidal stages shown.
It is believed that each of these layers
represents an individual tidal flocculation;
that is, for any given locality at the head
of the inlet, a flocculated sediment layer is
produced every tidal sweep of the surface
plume approximately on a 12-hour cycle.
The suspended-sediment band spacing is
much increased earlier in the summer (and
later in the fall) compared with the highrunoffperiod data of figure 9. For example,
figure 10 gives the load distribution for
July 1970. Only one major subsurfaceband
is apparent.If the formationof these layers
is in phase with the tidal cycle, then net
vertical settling rates from 1.0 to 5.0 m/
hour, respectively, for the September and
SETTLING OF FLOCCULES
July conditions are indicated (figs. 9, 10).
Vertical profiles of suspended-sediment Such seasonal variations in the band spacdistribution at stations within the area oc- ings are consistent with the hydrographic
cupied by the plume at low, but not high, conditions discussed above. During periods
water (e.g., station Q1-10) show that this
material is present within the water column
(ppm) 8 SAL.(%o)
VOLUMECONCENTRATION
20
50
in discrete layers. Figure 9 is illustrative
30
10
40
in this respect; here transmissivity data
(which corresponds very closely to sedi-
(m)
20
50
100
60
100
140
180
220
LOAD (mg/1)
RELATIVE % TRANSMISSION
FIG. 9.-Distribution
patterns of particulate
sediment over tidal cycle at station Q1-10 in September.
FIG. 10.-Particulate sediment-load distribution
(closed circles) and volume concentration (crosses;
see text) at low water at station Ql-10 in July; open
circles = salinity profile.
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546
CHARLES M. HOSKIN AND DAVID C. BURRELL
of low freshwater inflow, when the upper
part of the inlet has the characteristics of
a partially mixed estuary, the rapidly settling sediment is mixed and dispersed more
vertically. Conversely, at the time of maximum runoff, the net downward velocity of
the sediment is decreased because of the
greatly increased surface outflow, but the
surface hydrography is that of river-dominated flow. This means that the circulation cell is shallow, vertical mixing is minimal, and the marine reservoir beneath the
halocline is relatively stagnant. Under these
conditions, the discreteness of the floc layers may be maintained through the bulk of
the water column. It should be noted that
there are no anomalous density stratifications beneath the halocline. The relevant
velocity profiles for the comparable Silver
Bay fjord have been given by Rattray
(1967, p. 55-56). Under high-runoff conditions in Queen Inlet, the subhalocline
current velocities obtained to date (of the
order of 5 cm/sec or less) are outside the
operating range of the measuring system
used.
FLOCCULE
SIZE
The sediment volume-concentration profile given in figure 10 was obtained by a
Coulter Counter electronic sizing technique
(Burrell and Hadley 1971). This procedure
is applicable only to the silt-size fraction
(4-64 /i) of the suspended sediment. The
covariance of the volume and load plots
thus indicates that this size component is
representative of the total sediment. The
density range given by these values is 2.73.5 g/cm3. If we assume the true density
of this silicate material (the organic carbon
content of the deposited sediment at station
Q1-10 is < 0.1%) to be something less
than 2.0, it would appear that less than
50% of this sediment has been rejected by
the sizing technique and hence lies outside
the silt-size range. Major silt-size modes for
suspended sediment samples taken from the
high-load bands within the water column
lie in the range 7.0-7.6 p (7.8-5.2 /). This
does not exactly coincide with the inletfloor major size mode range (see below),
but this discrepancy may be due to the
totally different sizing techniques used. It
must be reemphasized that these data refer
to primary particles and not floc agglomerates.
ACCUMULATED SEDIMENTS
SOURCE
The size-frequency distribution of recently exposed ice-contact sediment (muddy sandy gravel; terminology of Folk 1954)
at the snout of Carroll Glacier has been
examined in detail by Slatt (1970, 1971).
This material is the principal source of
sediment now being redistributed and accumulating in other environments in Queen
Inlet. Slatt (1970) has shown the grainsize composition of the ice-contact sediment to be gravel > sand > silt > clay,
and he (Slatt 1971) has shown from pebble
roundness measurements that some of this
material may be reworked outwash.
INTERTIDAL
OUTWASH
FAN
Entrainment of the ice-contact sediment
by meltwater results in strong grain-size
fractionation. Boulder gravel is concentrated as lag material in the terminal
moraine, and pebble gravel and sand are
deposited from the meltwater streams,
forming the bulk of the outwash fan (4
samples from the intertidal portion of the
fan average 2 gravel, 91 sand, and 7 mud,
% w/w); mud and some sand are transported across the fan into the marine environment.
Temporary deposition and subsequent
erosion are frequently occurring processes
in the outwash fan. Silt and clay dispersed
in meltwater streams flocculate as they mix
with salt water in the fjord basin. Flood
tides transport the suspended floccules onto
the outwash fan, and the settling lag effect
(Kuenen 1961) results in accumulation of
mud in the intertidal zone during the meltwater season. A piston core taken from this
mud deposit in September 1967 showed a
thickness of 81 cm, with an average mud
content of 94% w/w. In winter, meltwater
stream flow ceases, and mud is no longer
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SEDIMENT TRANSPORT AND ACCUMULATION IN A FJORD
available from that source. However, the
tides continue to rework the outwash fan;
by April 1968 mud was gone from the fan
and the site where the core was taken 6
months earlier. In other environments,such
as the Dutch tidal flats (Kuenen 1961) and
some estuaries (Chesapeake Bay; Schubel
1971), mud is accumulated through the
filter-feedingactivity of invertebrateorganisms. This is thought to be of little importance in Queen Inlet because so few living
organisms have been observed; carbonate
shells and shell fragments have not been
seen in the 37 submarinesamples analyzed.
FJORD BASIN
General.-There is a remarkable partition between sandy silt (grain-size modes
of 2.3 4, 205 4; 4.5 4, 44 p) in inlet-floor
valleys and mud (grain-size mode of 6.5 4,
11 p) on the predominantlyflat floor of the
inlet. This is most clearly seen in the form
of size-frequencydistributionsfor these two
sediments (fig. 11). Neither sediment has
a simple Gaussian distribution; both are
bi- or polymodal and fine skewed, with
inlet-floor valley sandy silt and flat-bottom
channelsedimentin
inletfloorvalleys
n=12
40
30
QUEEN INLET
20
mud on flat bottom
10
0
2 3
Sand
4 5 6 7
Mud
2 3 4 5 6
Sand
7 8 9 10
Mud
FIG. 11.--Size-frequency distribution for sediment from the inlet-floor valleys (fig. 2) and for flatbottom samples.
547
mud being leptokurtic and mesokurtic, respectively. These grain-size distributions
are open-ended, as no technique conveniently generates data for fractions finer
than 10 4, 0.98 i, which amounts to an
average of 37% w/w for the flat-bottom
mud. It is suggested that the textural differences between flat-bottommud and inletfloor valley sandy silt indicate provenance
by two distinct processes. The overflow and
underflow concept developed by Gould
(1951) for the Colorado River and Lake
Mead may be applicable here. Overflows
correspond to the surface-sediment plume
(above). The inlet-floor valleys with their
natural levees, terraces,and coarser-grained
axial sediment are strong evidence for underflows, but attempts to measure current
flow directly within the inlet-floor valleys
have not provedsuccessful to date.
Underflows.-It has been observed that
many other Alaskan fjords with nontidal
glaciers do not have the feature we term
"inlet-floor valleys." We suggest that the
inlet-floor valleys are formed and maintained by underflows related to meltwater
and sediment discharge. Clearly, more data
are needed, but as the geometry and dimensions of the outwash fan in Queen
Inlet, to our knowledge, are not duplicated
in other fjords of Glacier Bay, they may be
key factors in underflowgeneration.
If the sediment load of the outwash
streams was great enough, the streams
might continue to flow along the fjord bottom, but Bates (1953) has pointed out that
few streams have sufficient load to sink
beneath the usually denser seawater. Queen
Inlet seawater, with a temperatureof 6° C
and 31 %o salinity, has a density of
1.0243 g/cm3 (Zerbe and Taylor 1953).
Measurements of suspended-sedimentload
made in September 1969 in the largest
meltwater stream in Queen Inlet (upstream
from the high-tide mark) had a load
range of 11.722-14.504, and an average
load of 12.769 g/liter, at a water temperatureof 0.5° C (Slatt 1970, appendix C,
p. 111). These suspended-sediment loads
result in meltwater stream densities of
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548
CHARLES M. HOSKIN AND DAVID C. BURRELL
1.0073-1.0090 g/cm3, with the average suspended-sediment load corresponding to a
stream density of 1.0079 g/cm3. As calculations show that a suspended-sediment
load of 39 g/liter is required to equal the
density of local seawater, the meltwater
stream cannot sink due to the suspendedsediment load in transit at that time, and
thereforemust form an overflow.Suspended
load in meltwater streams varies with time
of day and season, as documentedby Rainwater and Guy (1961) for the Chamberlin
Glacier in the eastern Brooks Range, Alaska. The Queen Inlet meltwater streams at
other times might have greater suspendedsediment loads, but such data are not available. U.S. Geological Survey water-supply
papers contain no suspended-sedimentload
data for the Glacier Bay area. To show
that suspended-sedimentloads in Alaskan
meltwater rivers do exceed the density of
Alaskan coastal seawater, we cite data from
the Susitna River of south-central Alaska,
which drains valley glaciers on the south
slope of the Alaska Range. Suspended-sediment loads at two different stations on the
Susitna River exceeded 72 g/liter on July
16, 1965 and 68 g/liter on September 6,
1965 (U.S. Department of the Interior
1970).
As the inlet-floor valleys appear to begin
where the meltwater streams leave the outwash fan and join the fjord basin, it is
tempting to postulate that the stream flow
separates, with the bedload part continuing
to flow down the slope of the submarine
outwash fan (which exceeds 2.50) and then
along the fjord floor. This would occur if
the bedload material were sufficient to exceed the density of local seawater; unfortunately, measurements of stream bedload
are difficult to obtain and are not now
available for Queen Inlet. The outwash fan
(gravel and sand) has been built by meltwater streams,and therefore,bedload transport must be considerable. Another possibility is that meltwater stream-bed material continually accumulates just seaward
of the stream mouth. Periodically, this material may slide down the slope of the out-
wash fan into the fjord basin, thereby generating an underflow. The latter may be
analogous to the underwater sand falls of
Southern California submarine canyons as
illustrated by Shepard and Dill (1966, fig.
55).
Holtedahl (1965) has clearly documented turbidity currentsas important sediment
transporters in Hardangerfjord, Norway.
It is uncertain whether turbidity currents
are active in Queen Inlet, as graded beds
have not been seen in the few short (3-4
m) cores available from the inlet-floor valleys. Also, the floor of Hardangerfjordis
flat (Holtedahl 1965, figs. 37 and 39),
whereas the inlet-floor valleys in Queen
Inlet may suggest activity of some process
other than turbidity currents. It is not yet
known whether the sediment-transporting
bottom flows in Queen Inlet are continuous
or sporadic; most probably they are not
continuous.However, as mud floccules sediment over the entire fjord basin during the
time of meltwater flow, and as only sandy
silt is found in the inlet-floor valleys, the
flows must occur fairly frequently.
Slumps.-Slumping in the ordinary sense
(and as distinct from sliding, above) is not
believed to be an important process in
Queen Inlet. Slumpingin other fjords forms
mounds of sediment at the juncture between the fjord floor and wall (Von Huene
1966, in Nuka Bay, Alaska; and Cone et al.
1963, in Hardangerfjord, Norway); these
mounds have not been seen in Queen Inlet.
It is also important to note that slump
deposits in Hardangerfjordare not located
near river mouths (Holtedahl 1965, p. 129).
A further argument against slumping in
Queen Inlet concerns the distribution of
gravel (particles > 2,000 p). Gravel is
abundant in subaerial inlet wall colluvium
(average 49% w/w) and the intertidal
portion of the outwash fan (average 2%
w/w). Gravel has not been found in 14
grabs of sandy silt from inlet-floor valleys
or from eight grabs and seven cores of mud
from the flat fjord floor. Lack of gravel
in the fjord basin argues for an absence of
slumping.
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SEDIMENT TRANSPORT AND ACCUMULATION IN A FJORD
Ice rafting.-Major sediment transport
by ice rafting (identified by gravel supply)
either from Carroll Glacier within Queen
Inlet or from other inlets into Queen Inlet
may be discounted by lack of gravel in the
fjord basin. Ice rafting is important in
areas adjacent to Queen Inlet, since gravelrich bottom sediment (70-80% w/w) has
been recovered from upper Glacier Bay inlets. Ovenshine (1970) has provided additional documentationof this process.
Sedimentation rates.-Exceedingly high
rates of sediment accumulationat the heads
of many Alaskan fjords have been proposed, but direct rate measurements are
generally not available. If sediment thickness data from seismic reflection profiles is
used, accumulation is assumed to have occurred during the period 10,000 years B.P.
to today (Von Huene 1966, fig. 2, and
p. 295), the accumulationrate for the basin
at the head of Nuka Bay is of the order of
0.45 m/year. Jordan (1962) interpreted
changing bathymetric profiles within several Alaskan fjords in terms of accumulation of glacial sediment. Caution must accompany such interpretations, however, as
changing bathymetry may partially reflect
movement of the glacier and, possibly, the
different sounding and navigation techniques used.
Sediment accumulationin the fjord basin
by settling from the surface plume occurs
mainly through the summer-fall seasons
(our field observations, 1966-1970), but
this periodicity is not obviously apparent
from grain-size characteristics of the bottom-sediment column. Three-meter piston
cores of fjord bottom mud contain essentially uniform sediment (1 sand, 66 silt,
33 clay, % w/w), with thin and nonsystematic sand layers a few grain diameters
thick. Interestingly, all mud cores do contain thin layers (few millimeters) of intensely black mud-sized particles. We have
found these black layers in other inlets in
Glacier Bay, and in Endicott Arm (fig. 1;
D. E. Buckley, personal communication,
1968). Grid coring of Queen Inlet (fig. 12)
has shown that the black layers are re-
549
FIG. 12.-Locations of black marker horizons in
piston-core profiles, indexed in meters from sediment surface. Dotted lines show position of inletfloor valleys.
peated on an approximatelyregularpattern
within each core; we believe that these
black layers are produced on some seasonal
pattern. Regular annual production, a priori, would seem most likely. Spacing between black layers, accepting the seasonal
origin, would indicate sediment accumulation rates in excess of 1 m/year at the head
of Queen Inlet-high values, but possible.
Spacing between black layers gradually decreases toward the mouth of Queen Inlet
(fig. 12), and this is interpreted to mean
that sediment is supplied by the outwash
streams at the inlet head. It should be
noted also that, at the head of the inlet,
the band spacing is greater for the western
profile; increased deposition on this side of
the fjord would be consistent with the sediment-plume distribution discussed above.
Lack of increased spacing between black
layers in core 2634 (fig. 12), mile west
of a gravelly delta built by a surface stream,
shows no important sediment input via underflowsto the fjord basin from this stream.
Some sediment escapes into Glacier Bay,
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550
CHARLES M. HOSKIN AND DAVID C. BURRELL
as we have observed the surface-sediment
plume south of Composite Island at low
tide. Suspended sediment may be transported into Queen Inlet by the tides, but
no data are available on this point.
The origin of the black layers is not
known at present, and the layers do not
correlate with any other discernable properties of the cores. Chemically reduced
bands analogous to the varved deposits of
British Columbia fjords 600 miles to the
south (Gross et al. 1963) are not a likely
interpretation because neither Queen Inlet
(nor any other Alaskan fjord) has been
shown to go anoxic. All sediment Eh measurements-admittedly crude in this poorly
poised environment-have indicated an oxidizing environmentthrough at least the top
meter of bottom mud. Organic carbon profiles (method of Menzel and Vaccaro 1964)
also have shown no significant enhancement in the black horizons. However, the
accuracy of these data is limited because
of the high inorganic carbonate content
(glacially abraded limestone and dolomite)
and the thinness of the layers. Further
chemical study is in progress.
from the intertidal portion of the outwash
fan. The bulk of Queen Inlet bottom sediment is texturally uniform mud, both areally and with depth-at least down to 3 m.
Piston cores show thin, black marker horizons which are judged from spacing increments to be seasonally, and possibly annually, produced. Spacing between black
layers increases toward the juncture of the
meltwater streams and the fjord head,
which suggests mud is most abundantly
supplied by the meltwater streams. Spacing
of black layers does not increase in the
vicinity of other surface streams, showing
their lack of significant sediment input.
Accumulationrate of mud (uncorrectedfor
water content and compaction) may exceed
1 m/year at the inlet head, decreasing to
about 0.4 m/year near the inlet mouth.
Sand deposited by meltwater streams has
built an extensive outwash fan, which continues to grow seaward. Sand is also supplied to the fjord basin, perhaps by the
underflow mechanism of Gould (1951).
Sinuous inlet-floor valleys with natural
levees, terraces, and sandy silt axial sediment are evidence for some form of sediment-transportingbottom flow.
SUMMARY
Gravel is present in the outwash fan and
This study of sediment transport and subaerial inlet wall colluvium, but has not
accumulation in an iceberg-free fjord has been recovered from the fjord floor, which
shown that mud and sand are entrained discounts slumping, land sliding, and ice
from glacier snout ice-cored deposits during rafting as sediment suppliers in Queen Inthe summer-fall season. Size sorting during let.
transport in meltwater streams results in
ACKNOWLEDGMENTS.-Some of these data
separationof mud and sand.
Mud is supplied to the fjord dispersed were presented initially at the American Geoand suspended as a thin surface plume over physical Union meeting, Portland, October
the marine surface. Mixing with saline 1969. The work has been supported in part by
U.S. Atomic Energy Commission contract
water causes flocculation, and the floccules
AT(04-3)-310, with ship time provided on the
settle through the water column in discrete R/V Acona under NSF grant GP5515. We are
layers. It is suggested that each of these grateful to our colleagues for many forms of
layers represents one tidal cycle. Mud is help, and to Dr. O. T. Ovenshine for much
also seasonally deposited and reworked appreciated critical comments.
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