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Transition from debris flow to hyperconcentrated flowin a submarine channel (the Cretaceous Cerro ToroFormation, southern Chile)

Y. K. Sohn,1 M. Y. Choe2 and H. R. Jo2

1Department of Earth and Environmental Sciences, Gyeongsang National University, Chinju 660–701, 2Polar Sciences Laboratory, Korea

Ocean Research and Development Institute, PO Box 29, Ansan 425–600, Korea

Introduction

Debris flow is an important sediment-transport mechanism in subaerial andsubaqueous environments. Its proper-ties change almost continuously assediment and water are added to orsubtracted from it (Smith and Lowe,1991; Vallance, 2000). In subaerialenvironments, debris flows are com-monly diluted into hyperconcentratedflows when they encounter a stream-flow (Pierson and Costa, 1987; Costa,1988). A transition facies is producedduring these events, comprising bothdebris-flow and hyperconcentrated-flow deposits in one sedimentationunit (Pierson and Scott, 1985; Scott,1988; Scott et al., 1995; Sohn et al.,1999) (Fig. 1A,B). In subaqueousenvironments, debris flows are muchmore vulnerable to flow dilutionbecause of larger flow resistance(Norem et al., 1990), lack of surfacetension effects by interstitial water(Mulder and Alexander, 2001) andprompt disintegration of debris in thecase of hydroplaning debris flows

(Mohrig et al., 1998). Sohn (2000b)has suggested that submarine debrisflows can be efficiently diluted whenthey hydroplane, and that two differ-ent associations of debris-flowdeposits and diluted-flow deposits(turbidites) can be produced depend-ing on whether a debris flow hydro-planes or not (Fig. 1C,D). This studyreports another example of flow tran-sitions in a submarine environment,which involved progressive dilution ofdebris flows into hyperconcentratedflows and turbidity currents. Thisstudy suggests that the transition fromdebris flows to hyperconcentratedflows can occur in the submarineenvironment in a manner similar tothe subaerial counterparts but underdifferent conditions.

Geological setting

A foreland basin (Magallanes Basin)developed to the east of the Andeanproto-cordillera during the MesozoicAndean Orogeny (Dalziel and Brown,1989). The basin consisted of a N–S-trending foredeep along the westernmargin and a gently sloping forelandramp in its central and eastern parts(Biddle et al., 1986; Wilson, 1991)(Fig. 2B). Throughout the Late Cre-taceous, arc- and cordillera-derivedsediments were dispersed along the

foredeep, resulting in deposition of thedeep-marine Cerro Toro Formation(Winn and Dott, 1979; Wilson, 1991).The formation is composed of about2000 m of hemipelagic mudstones andthin-bedded turbidites as well as thicklenses of submarine channel conglom-erates named the Lago Sofia lens(Scott, 1966; Winn and Dott, 1979)(Fig. 2C).The Lago Sofia conglomerates are

hundreds of metres thick, kilometreswide and extend for more than120 km from north to south (Winnand Dott, 1979), representing one ofthe largest submarine channel systemsin the world (Jo et al., 2001). Theconglomerates occur as isolated chan-nel-fill bodies in the northern part,generally less than 100 m thick andintercalated between much thickerfine-grained facies, whereas they con-stitute vertically stacked and laterallyinterconnected channel-fill bodies inthe south, more than 300 m thick(Fig. 3). The overall distribution,geometry and north-to-south palaeo-flow pattern of the conglomeratessuggest that the channel system con-sisted of tributaries in the north,which joined to form an axial trunkchannel in the south. The Lago Sofiaconglomerates can be divided into twomajor groups of facies: disorganizedto variably graded conglomerates with

ABSTRACT

It is important to understand the exact process whereby verylarge amounts of sediment are transported. This paper reportspeculiar conglomerate beds reflecting the transition of sub-marine debris flows into hyperconcentrated flows, somethingthat has been well documented only in subaerial debris-flowevents until now. Voluminous debris flows generated along aCretaceous submarine channel, southern Chile, transformedimmediately into multiphase flows. Their deposits overlie flutedor grooved surfaces and comprise a lower division of clast-supported and imbricated pebble–cobble conglomerate withbasal inverse grading and an upper division of clast- to matrix-supported, disorganized conglomerate with abundant intrafor-

mational clasts. The conglomerate beds suggest temporalsuccession of turbidity current, gravelly hyperconcentratedflow, and mud-rich debris flow phases. The multiphase flowsresulted from progressive dilution of gravelly but cohesivedebris flows that could hydroplane, in contrast to the flowtransitions in subaerial environments, which involve mostlynon-cohesive debris flows. This finding has significant implica-tions for the definition, classification, and hazard assessment ofsubmarine mass-movement processes and characterization ofsubmarine reservoir rocks.

Terra Nova, 14, 405–415, 2002

Correspondence: Y. K. Sohn, Department

of Earth and Environmental Sciences,

Gyeongsang National University, Chinju

660–701, Korea. Tel.: +82 557516005;

fax: +82 557572015; e-mail: yksohn@

nongae.gsnu.ac.kr

� 2002 Blackwell Science Ltd 405

a muddy matrix and stratified orcross-stratified conglomerates with asandy matrix (Fig. 4). The former areinterpreted as deposits of multiphasedebris flows composed of a series ofdistinct flow types, whereas the lattershow laterally inclined stratification,foreset stratification and hollow-fillstructures, reminiscent of terrestrial

fluvial deposits and suggestive of tur-bidity-current processes.

Characteristics of multiphasedebris-flow deposits

The multiphase debris-flow depositsare generally several metres thick,commonly in excess of 10 m in thick-

ness. They are easily distinguishedfrom the stratified conglomeratesbecause of a total lack of internalstratification, sharp bed boundariesand the muddy nature of the mat-rix (Fig. 4). They show a gradualpinch-out geometry on km-long expo-sures. The multiphase debris-flowdeposits have certain sedimentary

Fig. 1 Four possible models of multiphase flows generated by dilution of debris flows in subaerial and subaqueous settings.(A) A subaerial debris flow, diluted at the leading edge by a streamflow, comprises a preceding hyperconcentrated flow and afollowing debris flow, resulting in hyperconcentrated flow deposits overlain by debris-flow deposits (Pierson and Scott, 1985; Scott,1988; Scott et al., 1995). (B) Incremental aggradation from subaerial debris flows, coarsest in the flow head and progressively moredilute and finer-grained toward the tail, results in a debris-flow deposit successively overlain by hyperconcentrated flow andstreamflow deposits (Sohn et al., 1999). (C) Subaqueous debris flows, non-hydroplaning because of extremely permeable fronts,are subject to mainly surface transformation. The surface-transformed suspended-sediment flows and debris-fall blocks canoutpace the parental debris flows, resulting in outsized clast-bearing turbidites beneath debris-flow deposits (Sohn, 2000b).(D) Subaqueous debris flows with impermeable fronts can hydroplane and their flow fronts can be repetitively detached anddiluted to form voluminous turbidity currents. The turbidity currents outpace or are outrun by the debris flows, resulting inextensive turbidites beneath and above the parental debris-flow deposits (Sohn, 2000b).

Debris flow and hyperconcentrated flow in a submarine channel • Y. K. Sohn et al. Terra Nova, Vol 14, No. 5, 405–415.............................................................................................................................................................

406 � 2002 Blackwell Science Ltd

characteristics in common irrespectiveof their locations in the submarinechannel system. They are, however,more abundant in the northern areawhere the channel-fill bodies areinterpreted to represent tributaries,whereas they are less abundant than

the stratified conglomerates in thesouthern area (Fig. 3). The down-stream decrease in the proportion ofthe multiphase debris-flow deposits isinterpreted to be due to a higherfrequency of debris-flow processes inthe tributaries rather than to down-

stream continuation and transforma-tion of the debris flows into turbiditycurrents. Measurements of clast im-brication show that the debris-flowdeposits have highly variable palaeo-flow patterns, commonly at high an-gles to the overall trend of the channel

Fig. 2 (A) Location map of the study area. (B) Depositional setting of the Magallanes Basin during the Middle to Late Cretaceous,formed by flexural subsidence due to thrust loading to the east of the uplifted Andean protocordillera. (C) Distribution of the LagoSofia conglomerates, shown in a dark grey tone. Overall palaeoflow patterns in the conglomerates, compiled from Scott (1966),Winn and Dott (1979) and the authors’ own measurements, are indicated by large arrows.

Terra Nova, Vol 14, No. 5, 405–415 Y. K. Sohn et al. • Debris flow and hyperconcentrated flow in a submarine channel.............................................................................................................................................................


segments (Fig. 5A,C). This suggeststhat the debris flows originated fromfailure of nearby channel banks orslopes flanking the channel system,and their flow paths were influencedby local topographic relief. On theother hand, the stratified conglomer-ates show a fairly uniform palaeoflowpattern, approximately following theoverall trend of the channel axes(Fig. 5B,D).The majority of multiphase debris-

flow beds show prominent normalgrading composed of clast-supportedpebbles and cobbles in their lower partand loosely clast-supported or matrix-supported pebbles in their upper part(Figs 6A and 7). The lower part com-monly shows upcurrent-dipping[a(p)a(i)] imbrication of gravel andwell-developed inverse grading nearthe base (Fig. 6B). The lower bedcontact is generally erosional, occa-sionally showing gigantic flute orgroove casts (Fig. 6C). The upper partof the bed shows disorganized fabricand characteristically contains abun-dant intraformational clasts, rangingfrom fine pebble-size mudstone chipsto several metre-long sandstoneblocks (Fig. 6D). Some of the bedsare capped by decimetre-thick layersof abundant mudstone chips set in amudstone or sandy mudstone matrix.The matrix consists of poorly sortedmuddy sand, containing about 30vol.% sand. There is no significantmatrix difference between the lowerand the upper parts of individual beds(Fig. 8A,B). Rarely, the matrix isricher in mud (Fig. 8C,D) or is com-posed of mainly mud in the upper partof the bed (Fig. 8E,F).

Depositional processes

The internal succession of texturesand structures compiled from a num-ber of beds suggests temporal changes

Fig. 3 Measured sections from the LagoPehoe (A) and the Lago Sofia (B) areas.The Lago Pehoe section is characterizedby several isolated units of conglomer-ates intercalated between much thickerfine-grained facies, whereas the LagoSofia section comprises a much thickersequence of conglomerates and thick-bedded sandstones, generally lackingfine-grained facies.



Fig

.4

Photographandsketch

ofanoutcropin

theLagunaGoicsectioncharacterized

byastack

ofverythick-bedded

debris-flow

conglomerates(M

G),whichare

richer

ingravel

clastsin

theirlower

parts(norm

allygraded)andcontain

intraform

ationalmegaclasts.Stratified

conglomerates(G

1&

G2)appearlight-colouredbecause

oftheirsandymatrix

and

show

planarto

inclined

stratificationandhollow-fillgeometry.Theexposure

suggests

thatthechannel

wasincisedmainly

byturbiditycurrents

andthen

filled

byaseries

of

voluminousdebrisflowsprobably

producedbychannel-bankfailures.Palaeoflowdirectioninferred

from

clastim

bricationandorientationofthehollowaxes

istoward

theleftand

obliquelyinto

thepage.

Afigure

(circled)gives

thescale

oftheexposure.



in flow type associated with the pas-sage of a multiphase flow (Fig. 9). Theerosional lower contact with well-developed flute and groove casts indi-cates an initial erosional event causedby a turbulent flow. The erosion wasimmediately followed by depositionfrom a gravelly flow. The basal inversegrading and imbrication of gravel inthe lower division suggest high rates

of shear strain, active clast collisionsand immediate deposition of the gra-vel without rolling or prolonged fric-tion-dominated movement on the bed(Walker, 1975; Lowe, 1982). The kin-etic energy for the high shear strainand active clast collision in the grav-elly flow was probably supplied froman overriding turbulent flow. Thewhole flow responsible for the lower

division is therefore interpreted tohave been bipartite or stratified, com-prising a high-concentration gravellydispersion or a traction carpet at itsbase and an overlying lower-concen-trated and turbulent suspension. Thiskind of flow is comparable to hyper-concentrated flows in subaerial envi-ronments (Costa, 1988; Smith, 1986;Pierson and Costa, 1987; Sohn et al.,

Fig. 5 Contrasting palaeoflow patterns between multiphase debris-flow conglomerates (A,C) and stratified conglomerates (B,D)obtained from the Laguna Goic section (A,B) and the Lago Sofia section (C,D). The debris-flow conglomerates have highlyvariable palaeoflow patterns, compared with the uniform palaeoflow pattern of the stratified conglomerates.



Fig

.6

(A)Overallnorm

allygraded

multiphase

debris-flow

conglomerate,2–3m

thick,composedofaclast-supported

andbasalinversely

graded

lower

divisionandamatrix-

supported

anddisorganized

upper

division.Theupper

divisioncontainsabundantmudstoneintraclasts,

ofwhichthelargestoneis

outlined.(B)Clast-supported

andinverse-

to-norm

allygraded

lower

divisionofamultiphase

debris-flow

conglomerate,about10m

thick,showingwell-developed

imbricationofcoarsegravel

clasts.A

graphic

logofthe

conglomerateisshownin

Fig.7(F).Thestickis90cm

long.(C

)Base

ofamultiphase

debris-flowconglomerate,>

10m

thick,showinggiganticflutecasts.(D

)Middle-to-upper

part

oftheconglomeratebed

shownin

Fig.7(A

),containingabundantsandstoneintraclasts.Thelargestintraclastin

thelower

leftis7m

longandhasaloaded

andflame-likeboundary.



1999), high-density turbidity currents(Lowe, 1982; Postma et al., 1988) orconcentrated density flows (Mulderand Alexander, 2001) in subaqueousenvironments.Some units that lack either the basal

inverse grading or clast imbrication inthe lower division (Fig. 7) were prob-ably emplaced by a flow in whichfrictional shear stresses were domin-ant (Sohn, 1997, 2000a) or graininertial stresses did not overcome thelubricational and repulsive forces ori-ginating from a viscous muddy matrix(Coussot and Ancey, 1999). Themassive or normally graded interval

directly above the basal inversely gra-ded interval (e.g. Fig. 6B) is inter-preted to have resulted from rapidsettling of coarse gravel in (intermit-tent) suspension in the lower part ofthe flow (Lowe, 1982).A number of sedimentary features

in the upper division, including com-mon matrix-supported texture, disor-ganized clast fabric and the presenceof large floating intraformationalclasts, are generally indicative of cohe-sive debris flows that underwent avery low rate of laminar shearingpossibly with a rigid plug (Johnson,1984; Shultz, 1984). The development

of normal grading in the upper divi-sion of some units is most likely due toincremental aggradation from a debrisflow that was progressively finer-grained toward the rear part (Vallanceand Scott, 1997; Sohn et al., 1999).The multiphase flow event, com-

posed of turbidity currents, hypercon-centrated flows and cohesive debrisflows, is interpreted to have resultedfrom progressive dilution of a parentaldebris flow. The flow dilution is inter-preted to have involved repetitivedetachment and disintegration ofgravel-rich fronts of a hydroplaningdebris flow (Mohrig et al., 1998)

Fig. 7 Graphic logs of several multiphase debris-flow conglomerates with variations in the clast-supported, imbricated, and basalinversely graded intervals.



Fig. 8 Positive prints of thin sections from the matrix of three debris-flow conglomerate beds. Thin sections A and B are from thebase and top of the same bed, respectively; so are the thin sections C,D and E,F. Most beds do not show a significant difference inmatrix grain size between the lower and the upper parts (A,B). Others have slightly muddier (C,D) or completely muddy (E,F)matrix in the upper part. All scale bars are 1 cm long.



(Fig. 1D). An assessment of the den-siometric Froude number shows thatmetre-thick debris flows, experiencinga shear strain rate above 1 s)1, canhydroplane even at a very low slopegradient. The muddy sand matrix ofthe debris flows is also interpreted tohave been sufficiently impermeable toallow for hydroplaning. The abun-dance of coarse gravel in the hyper-concentrated flow deposits alsosuggests a full-scale dilution of thegravel-rich fronts of debris flows, mostlikely involving disintegration ofhydroplaning flow fronts rather thanjust stripping of debris-flow surfaces(i.e. surface transformation) (Sohn,2000b). The presence of a mud-chip-rich interval at the top of someunits suggests that the majority ofthe flow-transformed materials werecarried and deposited in front of theparental debris flow.

Comparison with subaerial debrisflow-hyperconcentrated flowtransitions

Subaerial debris flows behave in dis-tinctly different manners dependingon the matrix properties. Cohesivedebris flows, containing more than3–5 wt.% clay, travel long distanceswithout transforming into hypercon-centrated flows or water floods butremain as debris flows to their termini.

On the other hand, non-cohesive deb-ris flows, containing lesser amountsof clay, have a higher rate of flowattenuation with overrun streamflowsand transform easily into dilute flowtypes, despite the similarities indeposit geometry and internal sedi-mentary characteristics and possibleoverlap of particle-support mecha-nisms with the cohesive debris flows(Scott, 1988; Scott et al., 1995). Thebehavioral differences between thecohesive and the non-cohesive flowsare interpreted to be due to thedifferences in the degree of clast inter-action and segregation and the misci-bility of the flow with associatedstreamflow, which are strongly con-trolled by the clayey matrix (Scottet al., 1995).In subaqueous environments, non-

cohesive debris flows may transforminto dilute flow types as readily assubaerial ones because of easierentrainment of ambient water andrapid loss of integrity of the flows insubaqueous settings (Postma et al.,1988; Mulder and Alexander, 2001).Sohn (2000b) reported, however, anexample of a non-cohesive debrisflow, which neither hydroplanedbecause of an extremely permeablematrix nor was subject to vigoroussurface transformation because of anarmour of gravel on the flow surface(Fig. 1C).

As for cohesive debris flows,Mohriget al. (1998) showed experimentallythat they can become efficiently dilu-ted in subaqueous settings becausetheir impermeable (muddy) matrixfacilitates hydroplaning via sustaininghigh pressures underneath the loftedflow head. Sohn (2000b) reported apossible example of a multiphase deb-ris-flow deposit, which originatedfrom a cohesive hydroplaning debrisflow (Fig. 1D), in only a few kilome-tres from its source area. Several otherstudies are also suggestive of thereadiness of transformation of cohe-sive debris flows in subaqueous set-tings (e.g. Larsen and Steel, 1978;Postma, 1984; Postma and Roep,1985). The debris flows in the LagoSofia submarine channel are alsointerpreted to have been initiatedwithin the submarine-channel tractby the failure of nearby channel banksor slopes and transformed immedi-ately into multiphase flows in spite oftheir cohesive nature. The ready trans-formation of cohesive debris flows insubaqueous setting is in marked con-trast to subaerial cohesive debrisflows, which can maintain theircoherence and textural uniformityover 100 km (Scott, 1988; Scott et al.,1995).

Conclusions

Voluminous debris flows were initi-ated ubiquitously along the tract ofthe Cretaceous Lago Sofia submarinechannel system, southern Chile. Theycould hydroplane because of themuddy (impermeable) nature of thematrix and transform immediatelyinto multiphase flows, consisting of aturbidity current and a hyperconcen-trated flow advancing in front of theparental debris flow. The turbiditycurrent carved flutes and grooves onthe substrate, above which depositionoccurred successively from a hyper-concentrated flow and a cohesive deb-ris flow, resulting in a transition faciesthat is comparable to those producedby a subaerial debris flow – hypercon-centrated flow event. The subaqueousmultiphase flow event differs from thesubaerial variety in that it involved acohesive debris flow. Cohesive debrisflows are inferred to transform intodilute flow types more easily in sub-aqueous settings because their imper-meable matrix aids hydroplaning,

Fig. 9 A synthetic depositional sequence compiled from a number of multiphasedebris-flow conglomerates with brief descriptions and interpretations.



which is an efficient mechanism offlow dilution in subaqueous environ-ments. The documentation of thepossible transition from submarinedebris flows to turbidity currents withan intervening intermediate flow type(hyperconcentrated flow) has signifi-cant implications for hazard assess-ment of submarine mass-movementprocesses, characterization of submar-ine reservoir rocks, and the definitionand classification of subaqueous sedi-ment gravity flows, which have beenan ongoing issue of debate in thesedimentological community (Shan-mugam, 1996; Sohn, 1999; Mulderand Alexander, 2001).

Acknowledgments

This research was conducted as part of theproject �The Studies on Natural Environ-ment and Conservation of Polar Regions(BSPP00001-03)�, which was granted toKorea Ocean Research and DevelopmentInstitute by the Ministry of MaritimeAffairs and Fisheries, Korea. This manu-script was improved by thoughtful andcritical reviews by Drs R. Steel, F. Surlykand G. Postma. All the help is gratefullyacknowledged.

References

Biddle, K.T., Uliana, M.A., Mitchum,R.M.J., Fitzgerald, M.G. and Wright,R.C., 1986. The stratigraphic and struc-tural evolution of the central and easternMagallanes Basin, southern SouthAmerica. In: Foreland Basins (P.A. Allenand P. Homewood, eds), Int. Assoc.Sedimentol. Spec. Publ., 8, 41–61.

Costa, J.E., 1988. Rheologic, geomorphic,and sedimentologic differentiation ofwater floods, hyperconcentrated flows,and debris flows. In: Flood Geomorphol-ogy (V.R. Baker, R.C. Kochel and P.C.Patton, eds), pp. 113–122. John Wiley &Sons, Inc., Chichester.

Coussot, P. and Ancey, C., 1999. Rheo-physical classification of concentratedsuspensions and granular pastes. Phys.Rev. E, 59, 4445–4457.

Dalziel, I.W.D. and Brown, R.L., 1989.Tectonic denudation of the Darwin me-tamorphic core complexes in the Andesof Tierra del Fuego, southernmost Chile:implications for Cordilleran orogenesis.Geology, 17, 699–703.

Jo, H.R., Choe, M.Y. and Sohn, Y.K.,2001. Drainage pattern and fluvialarchitecture of a gigantic gravelly sub-marine channel: the Cretaceous LagoSofia conglomerate, southern Chile. In:Seventh International Conference on Flu-vial Sedimentology, Prog. With Abstract.,

Conservation and Survey Division. Uni-versity of Nebraska, Open-File Report 60(J.A. Mason, R.F. Diffendal, Jr andR.M. Joeckel, eds), pp. 144. Universityof Nebraska, Lincoln.

Johnson, A.M., 1984. Debris flow. In:Slope Instability (D. Brunsden and D.B.Prior, eds), pp. 257–361. John Wiley &Sons, Chichester.

Larsen, V. and Steel, R.J., 1978. Thesedimentary history of a debris-flowdominated, Devonian alluvial fan- astudy of textural inversion. Sedimentol-ogy, 25, 37–59.

Lowe, D.R., 1982. Sediment gravity flows.II. Depositional models with specialreference to the deposits of high-densityturbidity currents. J. Sediment. Petrol.,52, 279–297.

Mohrig, D., Whipple, K.X., Hondzo, M.,Ellis, C. and Parker, G., 1998. Hydro-planing of subaqueous debris flows. Bull.Geol. Soc. Am., 110, 387–394.

Mulder, T. and Alexander, J., 2001. Thephysical character of subaqueous sedi-mentary density flows and their deposits.Sedimentology, 48, 269–299.

Norem, H., Locat, J. and Schieldrop,B., 1990. An approach to the physicsand the modeling of submarineflowslides. Mar. Geotechnol., 9,93–111.

Pierson, T.C. and Costa, J.E., 1987. Arheologic classification of subaerial sedi-ment-water flows. In: Debris Flows ⁄Avalanches: Processes, Recognition, andMitigation (J.E. Costa and G.F. Wiecz-orek, eds). GSA Rev. Engng. Geol., 7,1–12.

Pierson, T.C. and Scott, K.M., 1985.Downstream dilution of a lahar: trans-ition from debris flow to hyperconcen-trated streamflow. Water Resour. Res.,21, 1511–1524.

Postma, G., 1984. Slumps and theirdeposits in fan delta front and slope.Geology, 12, 27–30.

Postma, G., Nemec, W. and Kleinspehn,K., 1988. Large floating clasts in turbi-dites: a mechanism for their emplace-ment. Sediment. Geol., 58, 47–61.

Postma, G. and Roep, T.B., 1985. Resed-imented conglomerates in the bottomsetsof Gilbert-type gravel deltas. J. Sedi-ment. Petrol., 55, 874–885.

Scott, K.M., 1966. Sedimentology anddispersal pattern of a Cretaceous flyschsequence, Patagonian Andes, southernChile. Bull. Am. Ass. Petrol. Geol., 50,72–107.

Scott, K.M., 1988. Origins, behavior, andsedimentology of lahars and lahar-run-out flows in the Toutle-Cowlitz RiverSystem. US Geol. Surv. Prof. Paper,1447-A, 1–74.

Scott, K.M., Vallance, J.W. and Pringle,P.T., 1995. Sedimentology, behavior,and hazards of debris flows at Mount

Rainier, Washington. US Geol. Surv.Prof. Paper, 1547, 1–56.

Shanmugam, G., 1996. High-density tur-bidity currents: are they sandy debrisflows? J. Sediment. Res., 66, 2–10.

Shultz, A.W., 1984. Subaerial debris flowdeposition in the Upper Paleozoic CutlerFormation, western Colorado. J. Sedi-ment. Petrol., 54, 759–772.

Smith, G.A., 1986. Coarse-grained non-marine volcaniclastic sediment: Termin-ology and depositional process. Bull.Geol. Soc. Am., 97, 1–10.

Smith, G.A. and Lowe, D.R., 1991. Lah-ars: Volcano-hydrologic events anddeposition in the debris flow-hyper-concentrated flow continuum. In: Sedi-mentation in Volcanic Settings (R.V.Fisher and G.A. Smith, eds). Soc. Sedim.Geol. (SEPM). Spec. Publ., 45, 59–70.

Sohn, Y.K., 1997. On traction-carpetsedimentation. J. Sediment. Res., 67,502–509.

Sohn, Y.K., 1999. Rapid development ofgravelly high-density turbidity currentsin marine Gilbert-type fan deltas, LoretoBasin, Baja California Sur, Mexico-Dis-cussion. Sedimentology, 46, 757–761.

Sohn, Y.K., 2000a. Coarse-grained debris-flow deposits in the Miocene fan deltas,SE Korea: a scaling analysis. Sediment.Geol., 130, 45–64.

Sohn, Y.K., 2000b. Depositional processesof submarine debris flows in the Miocenefan deltas, Pohang Basin, SE Korea withspecial reference to flow transformation.J. Sediment. Res., 70, 491–503.

Sohn, Y.K., Rhee, C.W. and Kim, B.C.,1999. Debris flow and hyperconcentrat-ed flood-flow deposits in an alluvial fan,NW part of the Cretaceous YongdongBasin, central Korea. J. Geol., 107,111–132.

Vallance, J.W., 2000. Lahars. In: Encyclo-pedia of Volcanoes (H. Sigurdsson, B.F.Houghton, S.R. McNutt, H. Rymer andJ. Stix, eds), pp. 601–616. AcademicPress, San Diego.

Vallance, J.W. and Scott, K.M., 1997. TheOsceola Mudflow from Mount Rainier:Sedimentology and hazard implicationsof a huge clay-rich debris flow. Bull.Geol. Soc. Am., 109, 143–163.

Walker, R.G., 1975. Generalized faciesmodels for resedimented conglomeratesof turbidite association. Bull. Geol. Soc.Am., 86, 737–748.

Wilson, T.J., 1991. Transition from back-arc to foreland basin development in thesouthernmost Andes. Bull. Geol. Soc.Am., 103, 98–111.

Winn, R.D. Jr and Dott, R.H. Jr, 1979.Deep-water fan-channel conglomeratesof Late Cretaceous age, southern Chile.Sedimentology, 26, 203–228.

Received 7 February 2002; revised versionaccepted 18 July 2002



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