JOURNAL
OF GEOPHYSICAL
RESEARCH,
VOL.
92, NO. C3, PAGES 2875-2881, MARCH
15, 1987
Turbidity Currents and Submarine Channel Formation
in Rupert Inlet, British Columbia
1. Surge Observations
ALEX
E. HAY
Department of Physicsand NewfoundlandInstitute for Cold Ocean Science,Memorial University of Newfoundland
St. John's,Newfoundland,Canada
Acoustic backscatter images obtained at 107 and 200 kHz of surge-type turbidity currents resulting
from mine tailing dischargeare presented.Excessdensitiesin the head of the order of 100 kg m -3 are
estimated from differencesin acoustic backscatter intensity and in the amplitude of the bottom-reflected
signal. These excessdensities are comparable to estimates based on surge height and speed, the speed
being determined by assuminga universal head shape. Unlike gravity current surgesfrom an impulsively
started steady source, the surge-type turbidity flows consist of a high concentration slug of short duration followed by a longer-lived wake in which sediment concentrations are lower by 2-3 orders of
magnitude. The profile of the high concentration slug resemblesthose for density slugs on small bottom
slopesobtained in laboratory experiments.Discrete scatterers,probably fish, are observed to avoid the
surges.
1.
INTRODUCTION
Turbidity currents are an important sediment transport
mechanism in aqueous environments. They are generally
thought to be responsiblefor one of the major featuresof the
seafloor: the submarine fan and fan valley systemsissuing
from the mouths of submarinecanyons.They also representa
hazard which in appropriate conditions can place man's
underwater activities at considerablerisk. Testimony to their
destructivepower and the potential damage to seabedstructures is provided by instancesof submarine cable breakage
[e.g., Heezen and Ewing, 1952] and the bending of steel rods
and the lossof instruments[Inntan et al., 1976].
Few direct observationsof turbidity currents have been obtained in the field, however.This is particularly true of surgetype flows. The lack of observationsis attributable partly to
the intermittent occurrenceof theseeventsand partly to the
high probability that conventionalinstrumentation would be
lost. The purpose of this article is to present the results of a
field investigationof surge-typeflows using a techniquefor
which there is no risk of loss or damage. The surgesare of
considerably larger scale than is normally achievable in the
laboratory, and the results are relevant to the problem of
sedimenttransport by turbidity currentsin general.
turbidity current associatedwith the dischargeand by surgetype turbidity currents (see Hay et al. [1983a] and Hay [this
issue]). The surge-type flows are believed to result from the
failure of the submarinechannelbanks and levees[Hay et al.,
1983b].
2.
ACOUSTIC OBSERVATIONS
The channelizationof the tailing deposit in Rupert Inlet
underwent a successionof several phases.The observations
discussedhere were made during the so-called meander and
apron phases.Thesephasesare discussedbriefly by Hay [this
issue], but the reader is referred to Hay et al. [1983a] for
details.
Only a single surge was observedduring the meandering
channelphase.This is the August1976eventdiscussed
by Hay
et al. [1982].Theevent•vasdetected
for a 1.5-hour
periodin
successiveacoustic sounding transects across the straight
lower reach.Initially characterizedby a sharp upper interface,
weakened bottom echo, and minimal overspill onto the adjacent levees,the upper interface was observedto become more
diffuse,the bottom echoto regainstrength,and the overspilled
material to spread laterally with time. In addition, a second
cloud of sediment was observed to the south of the channel
and was ascribedto overspillfrom an upstreammeander.
During the apron phase,three eventswere detectedat 2344,
107 and 200 kHz. It is shown that estimatesof surgeproperties, including probable speedsand excessdensity, can be ex- 0225, and 0525 PST, on September 12, 13, and 15, respectracted from the acousticrecords.These quantities are used in tively, at station 2 (Figure 1). The 107- and 200-kHz records
the companion paper [Hay, this issue] to estimate the excess for the first two of theseeventsare shownin Figures2 and 3.
here. Figure 2
masstransported per surgeand the surgerecurrencefrequency The third was lessdistinctand is not discussed
in Rupert Inlet. The surge shapesin vertical section are com- shows the head regions for the two events in detail. The repared with those which have often been assumedin the litera- cordsare characterizedby intensebackscatterfrom the surge.
Note that the most intensebackscatteris indicatedby light
ture and are found to be quite different.
The experiments were conducted in Rupert Inlet, British gray shading,like that from the bottom immediatelyahead of
Columbia, which servesas the receivingbasin for tailing dis- the nose.This arisesfrom the Fineline feature of the receiver,
charged by Island Copper Mine. Submarine channel systems through which signalsabove a thresholdsetting are reprewere formed in the tailing depositboth by the continuousflow sentedby a uniform light gray shading.Following each surge
is a lower-amplitude echo from a diffusewake, the thicknessot
which tendsto increasewith time. During the passageof the
Copyright 1987 by the American GeophysicalUnion.
thicker event (Figures2a, 3a, and 3b) the amplitude of the
bottom echo is attenuated. Peak surge thicknessesare 2-5 m.
Paper number 6C0654.
0148-0227/87/006C-0654$05.00
The surgespass the observationpoint in 4-6 min, and the
The results consist of acoustic
backscatter
observations
at
2875
2876
HAY: TURBIDITYCURRENTSIN SUBMARINE
CHANNELS--SURGE
OBSERVATIONS
0
•
•.Oo
400rn
-•
•o
----4
.........
100-'L-
•
'
110
....
115•
...._
•
....
Fig. 1. Tailing deposit bathymetry in September 1978. Contours in meters. Anchor station locations are shown as solid
circles.
echo from the wake persists for 0.5-1.5 hours (not shown).
These characteristicsare similar to those of the August 1976
surge.
A contour plot of the backscattered signal amplitude recorded at 200 kHz during the passageof the September 13
event is presented in Figure 4. The contour levels are in volts.
Figure 4 was constructedafter analog to digital conversionof
the backscattered signal, which was recorded on a HewlettPackard model 3960 instrumentation tape recorder. The corresponding echogram (Figure 3b) has been discussedpreviously. This was the only event of the three for which any
part of the head region was recorded on tape, and even then
the recorder was started after the passageof the nose (compare Figures 3a and 3b). Figure 5 is a time seriesof the backscatter amplitude records through the courseof the event. The
same general features are present in Figures 4 and 5 as in the
echogram,and these featuresmay now be discussedquantitatively. The high-amplitude backscatter (> 1 V) from the head
near time zero at the beginning of the recording, the lowamplitude (< 0.25 V) echo from the bottom at the same time,
the rapid decrease with time of the backscatter from the
shrinking body and wake, and the recoveryof the strength of
the bottom echo with time are all apparent.
The behavior in relation to the surgesof discretescatterers
in the water column is interesting.Both of the acousticimages
in Figure 2, particularly Figure 2b, give the distinct impression
that these scatterersmove upward to avoid the surge. It is
reasonable to assume that these targets are individual biota,
possibly fish. It appears that they sensethe oncoming surge
and swim out of its path.
3.
DISCUSSION
Several properties of surge-type flows can be derived from
the preceding results. The thicknessof the head is an obvious
example. The other properties are the surge speed and excess
density and the surge shape,which is discussedfirst.
Three schematic profiles for surge-type turbidity currents
are shown in Figure 6. That in Figure 6a is based upon the
acoustic images in Figure 2 and consistsof a head region of
high concentration followed by a body of rapidly decreasing
thickness
and a low concentration
wake. The thickness
of the
wake increases with distance away from the head because of
either sustained vertical turbulent diffusion or the positive
buoyancy of the water advectedfrom shallower depths by the
surge. This profile of the head and shrinking body region is
very similar to those obtained in laboratory experiments by
Shwartz et al. [1973] and Beghin et al. [1981, Figure 2a-I with
density slugson small slopes(< 5ø).The profiles in Figures 6b
and 6c are adapted from Middleton and Hampton [1976-1and
Komar [1977-1,respectively.Both are based on laboratory experiments in which the dischargeat the source was essentially
steady. In both, the head is followed by a body region in
which excessdensity and flow thickness are assumed to be
sufficiently constant so that uniform flow dynamics may be
used in the body. The observations presented here do not
support the existence of such a region in naturally occurring
turbidity currents. That is not to say that such regionsdo not
exist. Clearly, the shape of a surge must depend critically on
conditions at the source and along its path. In actual fact a
continuum of surge shapesspanning the range shown in Figures 6a-6c may be possible.
Now consider the question of surge speed and excessdensity and how to extract information on these quantities from
the acoustic data. Several methods are used, and because each
involves the use of some approximation, the degreeof success
will be judged from the extent to which the estimatesare
mutually consistent.Speed and excessdensity are, of course,
linked dynamically, so we begin with a brief discussionof the
form that this link takes for slug-shapedsurges.
The problem of gravity currents of finite length on a sloping
bottom has been discussedby Hay [1983a], who obtained an
expressionfor the nosespeedUo of the form
Uo = (g'Ho/2)•/211
+ C sin/?]
(1)
where H o is the maximum thicknessof the head and g'=
(Ap/po)g,g being the accelerationdue to gravity, Po the density of the ambient fluid, and Ap the excessdensity in the
surge. C is a constant of order unity. Equation (1) was shown
to apply to gravity currents driven both by a steady source
and to slugsof densefluid of finite length and to be consistent
with laboratory experiments.BecauseC is of order 1, the effect
of bottom slope is weak, and for small slopes there is little
differencebetweenthe nose velocitiesfor gravity surgesdriven
either by a continuous sourceor by a sourceof finite duration.
For slopeslessthan 5ø, (1) differs little from the usual relation
[e.g., Middleton, 1966; Benjamin, 1968; Komar, 1977]:
Uo = 0.75[g'Ho]•/2
(2)
HAY.' TURBIDITY CURRENTS IN SUBMARINE CHANNELS--SURGE OBSERVATIONS
2877
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c
bottom
•fish"
nose
i
I
i
i
!
D
__•
•m•
••
I
;mm
mm mmmm
mm
mm
mmm
mmm
m•
mmm
mmm
m
I
I
I
I
Fig. 2. Acoustic
images
at 107kHz of theheadregions
of twosurge-type
turbiditycurrents
on(a)September
13,1978,
and(b)September
12,1978.(c)and(d)Thelocationof thebottomechoanddiscrete
scatterers
(probably
fish)evading
the
surges
in Figures2a and2b.Theverticalscale(inmeters)andhorizontalscale(inminutes)
areshown.
and therefore(2) will be usedfor the order of magnitudeesti- tween the leading edgeand the point of maximum thickness
(Figure6a),is about 1.5.Shouldthis relationhold in the presmates required here.
Estimatesof the surgespeedmay be made directly from the ent instance,the nose velocity would be given by
acousticrecordsif a universal shape for the head is assumed.
U o = 1.5Ho/At
(3)
A universal shape for the head of a density surge has been
suggestedon the basis of laboratory experiments[Keulegan,
1957, 1958; Middleton, 1966; Simpson,1969]. This shape is where At is the elapsedtime between the leading edge of the
suchthat the ratio x/H o, x being the horizontaldistancebe- surgeand its creston the acousticrecord (5-10 s). This implies
2878
HAY.' TURBIDITY CURRENTSIN SUBMARINECHANNELS--SURGE OBSERVATIONS
..................
,:x:c:•:•.... .:.:
.........................
........... . .......................
..::........ . .................
.
..........
.::,.:>............
.
Eig. 3. Acousticimagesillustratinghead and wake regionsof surge-typeturbidity currentson September13, 1978at
(a) 107 and (b) 2• kHz; and on September12, 1978 at (c) 107 and (• 2• kHz. Figures3a and 3c are from the same
recordsas Figures2a and 2b but coverlongertime intervals.The arrowsdenotethe positionof the noseat the left sideof
each image.
nosevelocitiesrangingfrom 30 to 120 cm s- • for the surges dimensionalizedby H o, exhibited a weak surge Reynolds
numberdependence
(=0.61Re -ø'z3, Re beingthe surgeReynEquation (2) and the above estimatesof U o give valuesof olds number). Since the nose overhang arisesfrom the no-slip
Ap rangingfrom 8 to 50 kg m-3 for theseevents.Thesevalues condition at the bottom, the dependenceof nose elevation on
observed.
are quite reasonable, being much less than the 10-20% by
volume concentrations at which grain-to-grain contact is expected to become important [Komar, 1969], and 2-3 orders of
magnitude larger than the concentrations measured in the discharge plume at this time [Hay, this issue, Figure A2]. Fur-
Reynolds number (i.e., viscosity) is not unexpected.At the
sametime, U o is known to dependon noseelevation [Benjamin, 1968], so there may be some variation of x/H o with
Reynolds number. It is assumedhere that such variations are
small.)
thermore, as will be seen, these concentration estimates are
The data in Figures 4 and 5 suggestthat another estimate of
consistent with that derived from the digitally processed the concentration of suspended material might be derived
acoustic backscatter data.
from the changesin amplitude of the bottom echo and of the
(Nevertheless,more recent laboratory work [Simpson,1972] signal backscattered from the surge. The obvious difficulty
suggeststhat a universal head shape may not exist. Simpson with the former method is that the acousticimpedance of the
found that the elevation of the nose above bottom, when nonbottom is likely to changeduring the passageof the event. It is
HAY' TURBIDITY CURRENTS IN SUBMARINE CHANNELS--SURGE
OBSERVATIONS
2879
135-
14o-
I-- 145-
z
i,J 150-
155-
160-
TIME
(rain)
Fig. 4. Contour plot for recorded backscatter amplitude at 200 kHz for the September 13 event (see also Figure 3b).
Contours are in volts. The bottom echo is indicated. The flow is from right to left, and the trailing part of the head and
shrinking body region are on the left between 0 and 5 min and about 143 and 148 ms equivalent depth. (Equivalent depth
is the two-way travel time of sound. Actual depth in meters equals equivalent depth times 0.74 m/ms.)
quite possiblethat the reasonfor the apparentattenuationof long as it may be presumedthat the particleradii in the surge
the bottom echo during the surgeis simply that the bottom no
longer existsas an interface acrosswhich there is a marked
changein acousticimpedance;that is, the density of the fluidsolid mixture undergoes continuous transition from values
within the surge far from the bed to the value for the stationary sedimentwithin the bed. This is most likely to be true
during the passageof the noseitself becauseof upward vertical velocities associated with recirculation in the head [Simp-
are comparableto those found in the turbidites. In this case
the expressionfor the viscousattenuationcoefficientsimplifies
to [Urick, 1948]
3.9 x 10- 4e/a
(5)
at 200 kHz, where e is the volume fraction occupiedby solids
and a is the particle radius in millimeters and where a speedof
soundof 1500 m s- • has been assumed.Making the further
son, 1982]. In that part of the surgetrailing the head region,
assumption that e and a are constant in the vertical, then
however, it is probable that the bottom is again a discrete
acousticinterface.The procedure that will be followed there(6)
2A = 2%H • 3.9 x 10-3e/a
fore is to usethe amplitude of the bottom echoto estimatethe
concentration change in this trailing region and then to use where a flow thickness H of 5 m has been used (Figure 4).
the signal backscatteredfrom the surge to extrapolate this
From Figure 5, p and p' at 4 and 6 min are proportional to
concentration estimate into the head.
2.2 and 4.3 ¾, respectively,which gives
Supposethat this is the caseand the bottom reflectioncoefficient is constant by t = 4 min (Figures 3b, 4, and 5). Let p
e/a- e'/a'= 1.7 x 102m- •
and p' representthe pressureamplitude of the bottom echo at
t- 4 and 6 min, respectively.These times correspondto the Further assuming that a = a'= 30 /•m gives e-d=
5.2
end of the shrinking body region and the beginning of the
x 10-3. The excess
densityis givenby (Po'- Po)e, wherePo'
longer-livedwake. The ratio p'/p is given by
is the grain density of the particles. This change in p therefore
log (p'/p)= 2(A -- A')
(4)
where A representsthe vertical integral of the additional attenuation due to the presence of suspended matter [Hay,
1983b] and is given by A = 2•H, H being the thicknessof the
current
and
•
the linear
attenuation
coefficient
due to the
particles in suspension.The magnitude of • depends on the
relative sizesof the particles and the acousticwavelength. At
200 kHz the acoustic wavelength is about 7.5 mm. The particles in suspensionare assumedto be no larger on average
than those found in the Rupert Inlet turbidites: about 30- to
60-/•m diameter [Hay et al., 1983b]. The acousticwavelength
therefore greatly exceeds the particle circumference. This
means that thermal
attenuation
and attenuation
due to scat-
corresponds
to a changein excess
densityof about9 kg m-3
It remains to estimate the excessdensity in the head. This
may be done roughly if it is assumed initially that the excess
densityat t = 6 min is much lessthan the 9 kg m -3 change
calculated above. We use the known proportionality of the
mean backscattered voltage to the square root of suspended
solids concentration [e.g., Hay, 1983b-I. The mean amplitude
of the backscatter
at t - 0 is about
3 times that at t = 4 min
(Figure 5). The excessdensity in the head is roughly 9 times
that at t = 4 min,or 80 kg m-3. Using(2) with H o - 4 m, this
corresponds
to a nosevelocityof 1.3 m s-x, which is in reasonableagreementwith the value of 1.2 m s- • estimatedfor
this surge on the basis of an assumeduniversal head shape.
This agreement supports the assumption that the excessden-
tering can be ignored [Hay and Burling, 1982], leaving only
sity at t = 6 min is muchlessthan 9 kg m-3 and leadsus to
viscous attenuation
conclude that in the wake the maximum suspendedsediment
concentrations are likely to be at least 2 orders of magnitude
to be considered.
The
thickness
of the
viscousboundary layer at the surfaceof each grain (about 1.4
/•m at 200 kHz) is much lessthan the particle radius, again, as
lower
than those in the head.
2880
HAY: TURBIDITY CURRENTSIN SUBMARINECHANNELs--SURGE OBSERVATIONS
200
kHz: NAY = 0
13 September,1978
0.0
2.o
4.o
AMPLITUDE SCALE
139.51
E
6.0
(volts)
--
-
•
-r
i..- 146.34Q.
uJ
0.5
ms
•
Bottom
z
..J
153.17
=)
_
o
160.0
-
I
0.0
I
I
0.66
I
I
1.33
I
I
2.0
I
I
I
I
2.66
3.33
I
I
I
I
I
I
I
I
4.0
4.66
5.33
6.0
13.99
14.65
15.32
15.99
TIME (min.)
139.51
'r
I--
-
146.34 Bottom
Q.
UJ
CI
_
I-Z
..j
153.17
=}
_
o
160.0
--
9.99
10.65
11.32
11.99
12.65
TIME
13.32
(min.)
Fig. 5. Time seriesof 200 kHz backscatteramplitudefor the September13 event.See also Figures3 and 4. Each
verticaltracerepresents
backscatteramplitudeas a functionof two-waytraveltime (equivalentdepth).Zero backscatter
is
indicatedby the short verticalline at the top and bottom of each trace, and this zero level is positionedalong the
horizontal axisat the point in time at whichthe trace was acquired.The receiveroutput saturatedat about 6 V.
4.
SUMMARY AND CONCLUSIONS
In summary,remoteacousticimageshave beenusedto estimate the properties of surge-typeturbidity currents. Flow
becauseof the positivebuoyancyof the water advectedfrom
shallower depths by the surge.
These acoustic images of surge-type turbidity currents,
which are presumedto have been generatedby failure of the
tailing deposit,are consistentwith the resultsobtainedin labof suspended
sedimentconcentrationin the head region are oratory experimentswith slugsof densefluid on small slopes,
extracted by using the changesin acousticbackscatterinten- which also consistof a head followed by a rapidly shrinking
sity and in the amplitude of the signal reflectedfrom the body. This meansthat flow in the body region of thesesurges
bottom.A typicalexcessdensityestimateis 100 kg m-3, cannot be described by steady, uniform flow density current
which is roughly consistentwith independentestimatesbased theory, as has been commonly assumedfor surge-typeturbidon surge speedand thickness.The surgespeedswere deter- ity currents elsewhere.Becausenaturally occurring turbidity
mined from the acousticimages,assuminga universalhead currents are known to be generated at least in some casesby
thickness.is,of course,obtained directly. Reasonableestimates
discontinuoussourcessuch as earthquake-generatedsediment
failure, these results raise questions about the conditions
under which steadyflow conditionsmay be assumed.In addition, surge-typeflows wi[h rapidly shrinkingbodiesand their
centrations in the wake are estimated to be 2-3 orders of
associatedwakes may affect the nature of the depositedturbimagnitudebelow thosein the head and shrinkingbody. The dite in ways which remain to be explored.
These resultsrepresentone of the few instancesin which
wake persistsabout 10 times longer and probably transports
much finer-grainedand much lesssedimentthan the head.It direct observationshave been obtained of surge-typeturbidity
also increasesin thicknesswith time at a fixed point, possibly currents in a submarine channel systemwhich is in the process
shape.
No elongate body region of constant thicknesswas observed. Instead, the head is followed by a rapidly shrinking
body (or tail) and a long-livedlow concentrationwake. Con-
HAY: TURBIDITY CURRENTS IN SUBMARINE CHANNELS--SURGE OBSERVATIONS
(a)
2881
Benjamin, T. B., Gravity currents and related phenomena, J. Fluid
-- _
Mech., 31,209-248,
PO
1968.
Hay, A. E., On the frontal speedsof internal gravity surgeson sloping
boundaries, J. Geophys.Res.,88, 751-754, 1983a.
Hay, A. E., On the remote acoustic detection of suspendedsediment
at long wavelengths,J. Geophys.Res.,88, 7525-7542, 1983b.
Hay, A. E., Turbidity currents and submarine channel formation in
Rupert Inlet, British Columbia, 2, The roles of continuous and
surge-typeflow, J. Geophys.Res., this issue.
Hay, A. E., and R. W. Burling, On sound scattering and attenuation
in suspensions,with marine applications, J. Acoust. Soc. Am., 72,
lOW
d--en'•it;
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(b)
950-959, 1982.
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body
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Hay, A. E., R. W. Burling, and J. W. Murray, Remote acousticdetection of a turbidity current surge,Science,217(4562), 833-835, 1982.
Hay, A. E., J. W. Murray, and R. W. Burling, Submarine channelsin
Rupert Inlet, British Columbia, I, Morphology, Sediment.Geol., 36,
289-315, 1983a.
Hay, A. E., J. W. Murray, and R. W. Burling, Submarine channelsin
Rupert Inlet, British Columbia, II, Sediments and sedimentary
structures, Sediment. Geol., 36, 317-339, 1983b.
Heezen, B.C., and M. Ewing, Turbidity currents and submarine
slumps and the 1929 Grand Banks earthquake, Am. J. Sci., 250,
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body
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849-873, 1952.
Inman, D. L., C. D. Nordstrom, and R. E. Flick, Currents in sub-
marine canyons: An air-sea-land interaction, Annu. Rev. Fluid
Mech., 8, 275-310, 1976.
Keulegan, G. H., An experimental study of the motion of saline water
from locks into fresh water channels, Rep. 5168, 21 pp., Natl. Bur.
Stand., Gaithersburg, Md., 1957.
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Keulegan, G. H., The motion of saline fronts in still water, Rep. 5831,
29 pp., Natl. Bur. Stand., Gaithersburg, Md., 1958.
Fig. 6. Schematicprofilesof surge-typeturbidity currentsflowing Komar, P. D., The channelized flow of turbidity currents with applidown an incline (shown here in a horizontal orientation for concation to the Monterey deep-sea fan channel, J. Geophys.Res., 74,
venience)based on (a) the acousticimagesin Figures 2 and 3, (b)
4544-4558, 1969.
sketches
by MiddletonandHampton[1976], and (c) Komar [1977].
Komar, P. D., Computer simulation of turbidity current flow and the
study of deep-seachannelsand fan sedimentation,in The Sea, vol.
of active development.The quantitative estimatesare neces6, edited by E. D. Goldberg, I. N. McCave, J. J. O'Brien, and J. H.
Steele,pp. 603-622, John Wiley, New York, 1977.
sarily approximate but appear to be self-consistentwhen independentchecksare made. Further support for theseestimates Middleton, G. V., Experiments on density currents, I, Motion of the
head, Can. J. Earth Sci., 3, 523-546, 1966.
is providedby Hay [this issue],who estimatesthe surgerecurMiddleton, G. V., and M. A. Hampton, Subaqueoussediment transrencefrequencyfrom the resultspresentedhere and finds that
port and deposition by sedimentgravity flows, in Marine Sediment
it agreeswith the recurrencefrequencyestimated from the
Transport and EnvironmentalManagement, edited by D. J. Stanley
and D. J.P. Swift, pp. 197-218, John Wiley, New York, 1976.
number of turbidites in cores. Finally, it has been demonstratedthat acousticremote sensinghas considerablepotential Shwartz, J., W. van de Watering, K. Landa, and S. Reed, Jr., Hydrodynamic study of density surgesand turbidity flows, Rep. 805-1,
for the quantitativestudy of this potentiallydestructivephepp. 1-45, Hydronautics, Inc., Laurel, Md., 1973.
nomenon.
Simpson, J. E., A comparison between laboratory and atmospheric
density currents, Q. J. R. Meteorol. Soc.,95, 758-765, 1969.
Acknowledgments.I am grateful to my thesissupervisors,R. W.
Simpson,J. E., Effectsof the lower boundary on the head of a gravity
Burling and J. W. Murray at the University of British Columbia
current, J. Fluid Mech., 53, 759-768, 1972.
(UBC), to the captains and crew of CSS Vector, and to the technical
Simpson, J. E., Gravity currents in the laboratory, atmosphere and
staff and other graduate studentsat UBC who assistedme in the field.
ocean, Annu. Rev. Fluid Mech., 14, 213-214, 1982.
I thank the personnelat Island Copper Mine for their cooperation. Urick, R. J., The absorption of sound in suspensionsof irregular
The studywas supportedby strategicgrant G0208 (to R. W. Burling
particles, J. Acoust.Soc. Am., 20, 283-289, 1948.
and J. W. Murray) and grant A8446 from the Natural Sciencesand
Engineering Research Council, Canada. I was supported while at
A. E. Hay, Department of Physicsand Newfoundland Institute for
UBC by a MacMillan Family scholarship.Newfoundland Institute Cold Ocean Science, Memorial University of Newfoundland, St.
for Cold Ocean Science contribution
119.
John's, Newfoundland, Canada A1B 3X7.
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REFERENCES
Beghin, P., E. J. Hopfinger, and R. E. Britter, Gravitational convection from instantaneous sourceson inclined boundaries, J. Fluid
Mech., 107, 407-422, 1981.
(Received April 15, 1986;
acceptedAugust 26, 1986.)