The formation of ice-marginalembankments into ice- dammedlakes in the easternPuget Lowland, Washington,U.S.A., duringthe late Pleistocene

DEREK B. BOOTH

BORE\S 3i?,li;?illii;#XTtX'.'ft:*:ti3T::fi:;Tt'JTl""il':115li::';:*::.jl':t:',li?'i:1: Oslo. ISSN 0300-9483.

Large embankments, typically several kilometers in lateral extent and many tens of meters high, choke the mouths of each alpine valley of the central CascadeRange, Washington Stale, U.S.A.. at or near their junctions with the Puget Lowland. They comprise till and bedded gravel, sand, and silt, aggraded into ice- dammed lakes. The embankments lie within the late-PleistoceneCordilleran ice-sheetlimit and so do not mark the location ofthe ice-maximum terminus. Reconstruction ofthe subglacial hydraulic potential field indicates that these ice-dammed lakes would have drained subglacially via spillways located near the junc- tion of each alpine valley and the Lowland. Physical processes tended to stabilize the grounding line for each ice tongue close to its respective spillway location. Because sedimentation rates are highest adjacent to the grounding line, subaqueous sedimentation formed a growing embankment there. In some valleys, subsequent subaerial lake drainage or decay of the active-ice dam resulted in late-stage deposition of del- tas or valley trains. This analysis of ice-water behavior is based on physical principles that should be gener- ally applicable to any environment where glaciers terminate against ice-dammed bodies of water.

Derek B. Booth, Il.S. Geological Survey, Quaternary Research Center, University of Washington AK-60, Seattle, Washington 98195, U.S.A.; 6th February, 1985 (revised 7th October, 1985)

A striking characteristicof the topography along time that the Puget lobe occupiedthe Lowland the western slopes of the CascadeRange of during the Fraserglaciation. WashingtonState, U.S.A., is the presenceof Eleven valley-constrictingembankments are constrictions in river valleys as they pass from recognizedin this area. Although a few early their bedrock-walledalpine reaches into the Pu- workersbelieved that theseembankments were get Lowland (Figs.1,2). Theseconstrictive land- depositedby alpineice flowing downvalley,most forms are not bedrock ridgesbut rather comprise studies of embankmentmorphology and clast glacial, fluvial, and lacustrinesedimentary mate- provenancehave demonstrated that the sediment rial. They are here termed.'embankments'to was derived from the Puget lobe (Cary & Carl- avoid the common genetic implications of alter- ston 1937; Mackin 1941; Knoll 1967;Williams native nomenclaturesuch as 'morainalembank- 1971; Hirsch 1975). These studies also docu- ments'or'delta-moraines' that hasbeen applied mented the presenceof extensiveice-marginal to these features. All lie within the limits and lakes,impounded by the Puget lobe, that filled near the margin of the Pugetlobe of the Cordille- the lower reachesof the alpinevalleys. A classic ran ice sheet that occupied the Puget Lowland studyby Mackin (19a1)of one of the major em- mostrecently about 15,000years ago, duringthe bankment systemscharacterized it as a set of Vashonstade of the Fraserglaciation (Armstrong greatglaciofluvial deltas that progradedinto the et al. 1965\. Most of the embankmentsediments adjacentalpine-valley lakes, veneered by till on are virtually unweathered, indicating transport the ice-proximal faces. He believed that they and deposition during this late-glacial time formed at the maximum stand of the Vashon-age (Booth 1986).A slightly earlier advanceof al- ice sheet and were composedwholly of Vashon- pine glaciers that originated in the Cascade agesediment. His work outlined the fundamental Range is inferred to have climaxed and waned relationship between the ice sheet, alpine gla- before the Vashon maximum (Cary & Carlston ciers, and sedimentationassociated with theseice 1937;Mackin 1941;Williams t97l;Porter 1976). massesthat has guided all subsequentgeologic The lower reaches of alpine valleys were thus studyin this region. free of alpine-glacierice during much or all of the This study addressesseveral characteristicsof 248 Derek B. Booth BOREAS 15 (1986)

1 220 I 2 1030' Bo

Fig. 2. Aerial view of the Wallace embankment (see Fig. 1 for location). View is to the east. The Wallace River has incised through embankment sediments adjacent to the south bedrock wall of the valley in postglacial time.

erate wherever a glacier terminatesin an ice- dammed lake. Proposedprocesses of aqueous deposition adjacent to Pleistoceneice sheets have received considerable recent attention a1 several localities in eastern and central North America (e.g.Dreimanis 1982; Shaw 1982; Eyles & Eyles 1983;Barnett 1985;Heiny 1985;Kulig 1985).The examplesfrom the Puget Lowland should prove quite relevant to these and other geographicallydiverse localities. Despite rela- tively limited exposuresof their geologic mate- rials, renderingdetailed lithofacies schemes such as proposedby Miall (1977)or Eyles & Eyles 16 km (1983) inappropriate,these featuresprovide a 0- unique opportunity to study ice-marginal pro- 10 mi cessesin an area where lake geometry, drainage routes,and configurationofthe ice sheetare par- ,..1Pugetlowland ticularlywell constrained.

Description

WASHINGTON The eleven embankmentsin the study area (Fig. 1) have severalcommon characteristics.They oc- cupy alpine valleys, typically at or just abovethe Fig. 1. Index map of geographicallocalities. Ernbankments aie junction of the valley with the Lowland proper. marked with stars. Vashon-ageice limit is shown with small Their tops are from 100 to several hundred me- dots (Booth 1986),which approximatesthe boundary between the Puget Lowland and the CascadeRanse. ters above the valley floor and cover 1-1.0km2. All appear to have filled their respectivevalleys from sideto side(Fig. 2). Post-depositionalriver these embankments,particularly their common erosionhas incised them along the valley axis and valley-mouthlocations and the variety of sedi- typically has removed much upvalley material. mentscomposing them. The analysisis basedin Less commonly, the downvalleyfaces have been part on availablegeologic data but stressesthe modified as well (Fig. 3). physicalbehavior of glacier ice near its margin Embankment sediments comprise diamicfon and the attendantdepositional processes that op- and beddedgravel, sand, and silt in variable pro- BOREAS 1s (1986) Ice-marginalembankments 249

nonfluvial sedimentsare typically weakly strat- ified and lie in abrupt contact with the overlying material. Three examples,treated in detail, exemplify both their similarities and differences.The South Fork Tolt embankmentis composedof thin, dis- continuousfluvial depositscovering a rounded ridge of primarily glacially transported sedi- ments.The Middle-SouthForks Snoqualmie em- - bankments,by contrast,are characterizedby a planar surfaceof fluvial sand and gravel that ex- tendsboth upvalleyand laterally along the moun- tain front for manykilometers. The Pilchuck-Sul- tan embankmentshares important characteristics of both; it is a particularlyuseful examplebe- causeof good exposureand extensivesubsurface data.

F,g. J. North Fork Snoqualmie embankment (outlined). Post- South Fork Tblt embankment deoositional erosion is evident both in the transverseincision by th; North Fork Snoqualmie River (N 1/2 section 20) and by The South Fork Tolt embankmentoccupies an by recessionalmeltwater modification of the ice-proximal face areaof about2 km2,forming a broadnorth-rising flowing south down the valley of Deep Creek (Sections 18-19)' Topography from USGS Mount Si 15' quadrangle. Ice-maxi- ridgewith maximumrelief of 150m (500ft) (Fig. mum limit shown by black dots; altitude in feet. 4,A). Tiuncatedsedimentary lavers on its steep easternface indicate postglacialerosion of the embankment by the South Fork Tolt River. portions. Fluvial sediment,deposited as either Through the southernpart of the embankment, proglacialoutwash or deltatopset beds, typically recentexcavations have exposed a 100-mvertical forms much or all of their upper surfaces.The sectionof glacial,glaciolacustrine, and glacioflu- coresof theseembankments are more heterogen- vial sediments. eousand includesignificant amounts of subaque- This sectionis subdividedinto threeunits (Fig. ously or subglaciallydeposited sediment. These 48). The lowest(unit 1) is an oxidizedbouldery

.\ )o3. ? 3 ,{-ixp/szoo.2 Unit '<;"-=-.../' bedded sand and qravel 47042'30"=

Unit2 crudely bedded d iamicton

Unit I ox. di amicton

*A C-

2km o# 1mi

Fig. 4. South Fork Tolt embankment. A: Topography from USGS Mount Si 15'quadrangle (embankment is outlined). Ice-maxi- mum limit shown by black dots; altitude in feet. B: Stratigraphy of embankment sediments exposed downstream of dam. Contacts between units are not necessarily horizontal and so span a range of altitudes within the represented region. C: Pebbly silt diamicton with crude horizontal bedding (location shown on Fig. 4.A; altitude 520 m (1'710 ft)).

17 Boreasl5:3. 1986 250 Derek B. Booth BOREAS ls (1986) B 5OO m

',i::":sand and gravel 350- l4c 4OOm 36:i 300- 35O m Unit I Unit 2 unweath. bedded t'il I sand and silt OOm

Frg. 5. Middle-South Forks Snoqualmie embankment com- plex. A: Topography from t2 ,l USGS Mount Si and Bandera l-5' quadrangles. Ice-maximum limit shown by black dots; alti- ./-- tude in feet (outlined area in- cludes embankment and its SW continuation past Cedar ( Butte). B: Stratigraphy of em- bankment 2,km sediments in the vi- | ,-roo u' , 12f 40' cinity of the Holocene channel 0ffi of the South Fork Snoqualmie lmi River. diamicton containing lenses 5-30 cm thick of 2,Fig.48; Fig. 4C), 50 to 100m thick, overlies compactmedium sand. Clast lithology and de- the lowestunit. This material constitutesthe bulk gree of weathering indicate probable deposition of the embankmentand definesthe shapeof its by an ice sheetof pre-Fraserage (Booth 1986). upper surface. Gravel-sizedclasts are round to A massiveto crudely bedded diamicton (unit subangular, commonly striated, and of mixed BOREAS ls (1986) Ice-marginalembankments 25I

Iithology. The clastshave no apparent preferred silt depositsdominating beyond about 4 km from orientation. The diamicton differs from typical the ice-proximalface of the embankments.At the Puget-Lowlandlodgment till in that it has a far Middle Fork embankment,this face is character- lower degreeof compactionand a slightly higher izedby ice-contacttopography and moderatelyto clay contentin the matrix (c. l0%; cf. Crandell poorly sorted gravel, sand, and silt and an ab- 1963;Mulline aux 1970; Dethier era/. 1981).Sub- senceof recognizablelodgment till. A more com- horizontalpebble-poor zones, 5-20 cm thick that plex record is revealed at the South Fork em- extend laterally for several meters, are inter- bankment(Fig. 58), perhapsowing to more ex- spersed throughout the diamicton. Larger dis- tensive exposure. Low on its ice-proximal face,- continuous subhorizontalsand layers, extending an areaof fine-grained,horizontally bedded sand to, a and silt is exposed(unit 1). Wood in this sedi- 1J:0 m, are clustered in, but not limited tnC zone 2A40 m thick in the middle of the unit. ment, in part converted to lignite, yielded a Horizontal layering and planar contactsthrough- date of >50,000years B.P. (Porter 1976;sample out the exposureshow that no significant flow- number UW-243). Drag folds and thrust faults, at ing, slumping, or glacitectonic deformation of an altitudeof about300 m (1,000ft) nearthe top sediment occurred during or following deposi- of the deposit,indicate shearing of beds to the tion. In one locality west of the south abutment east,presumably by overridingice. Unweathered of the dam, silt and clay laminaedrape over, and (i.e. Vashon)till (unit 2, Fig. 58), whichrests di- are depressed locally several centimeters be- rectly on striated bedrock, is exposedonly along neath, clasts(dropstones) as large as 15 cm in the river topographically below the older sedi- diameter. mentarymaterial. This till must havebeen depos- A surfaceunit (unit 3, Fig. 48) of oxidizedgla- ited in a valley incised through pre-Vashonsedi- ciofluvialrecessional outwash, generally less than ment. 2 m thick, overliesthe diamicton.It drapesmost The uppermost sediment of this embankment of the embankmentand thickensto form a con- (unit 3, Fig. 58) is part of an extensivereces- structionalsurface only on the western(ice-prox- siohal outwash deposit over 100 m thick in this imal) slopes below about 500 m (1,600 ft) alti- area. As Mackin (1941)first inferred, much of tude, where the sedimentsmerge with fluvial de- this fluvial sedimentmay have been depositedas positsof the late ice recession(Booth 1986). deltas into ice-marginallakes. Deltaic prograda- tion, coupled with ice-marginretreat, resulted in depositionof deltaic and lacustrinesediments up Middle and South Forks Snoqualmie the Middle and South Fork valleys that merge embankments with a valley-train fluvial deposit southwest of A nearly continuous, flat-surfacedembankment cedar Butte (Fig. 5A). complex that chokes the valley mouths of the An analogoushistory is inferred for at least Middle Fork and South Fork of the Snoqualmie oneother embankmentin this area.The morpho- River (Fig. 54) can be traced south for nearly 1-5 logy of the Skykomishembankment (Fig. 6) is km alongthe mountainfront. It blocksthe Cedar controlled by an extensive deposit of late-stage River valley and terminates against ice-contact fluvial sedimentthat extendsmany kilometers sediment at the northeast edge of the Taylor upvalley.Poorly exposedbeneath this material, Creek valley (Frizzell et al. 1984).Its surface al- however,is both a basalpebble-poor diamicton titude descendsfrom about 510 m (L,670ft) on and a recessionalmoraine of Vashonage (Booth the proximal side of the Middle Fork embank- 1e86). ment to 500 m (1,640ft) at the South Fork em- (1,560 of Thylor bankmentto 475m f0 northeast Pilc huc k -S ultan embankment Creek. Approximately one-third of this gradient is probably due to isostaticrebound since degla- Deposits constituting the embankment at the ciation (Thorson1981). headof the PilchuckRiver (Figs.7A and 7B) are Most of the sedimentexposed in roadcuts and exoosedin excavationsassociated with the con- streambanksis gravel and sand, subrounded to struction and subsequent raising of adjacent well rounded, with better sorted sand layers and CulmbackDam. They are augmentedby exten- lensesthroughout. Both median and maximum sive subsurfaceexploration (ConverseWard Da- grain sizesgradually decreaseup the Middle and vis Dixon 1979; Shaffer 1983). The basal em- South Fork valleys, with pebble-poor lacustrine bankment sedimentsare encounteredin two drill 252 Derek B. Booth BOREAS 15 (1986)

Fig. 6. Skykomish embankment (outlined). Pebble-poordiamicton is exposed in section24 just southof the highway;the ridgein section18 (alti- tude 610 m (2,001ft)) is a bouldery moraine. To- pographyfrom USGS Index 15' quadrangle.Ice- maximum limit shown by black dots; altitude in feet. holes near the downstream toe of the embank- of this unit extend at least3 km upvalleyof the ment. Thesesediments consist of more than 100 mainembankment crest. m of fluvial sand and gravel that fill part of the This unit is coveredby beddedgravel and sand bedrock valley of a pre-VashonSultan River be- (unit 3, Fig. 78) that is at least100 m thick on the neaththe presentembankment (unit 1, Fig. 78). northern part of the embankment.This fluvial The upper surface of the sand and gravel, at an sedimentforms a nearly continuouskame terrace altitude of about 410 m (1,350ft), is 20-30 m that beginsat the 700-m (2,300-ft)altitude at a above the present altitude of the bedrock lip bedrock notch on the north wall of the Pilchuck through which the Sultan River now drains into valley,continues upvalley as a featureonly a few the Sultan gorge. This upper surfacemay repre- tensof meterswide, and broadensabruptly at the sent a pre-Vashon-agefloodplain of the Sultan embankmentitself. The gradient of the construc- River, an interpretationthat also implies drain- tional surfaceis about 12 nlkm (65 ftlmi), which age through the Sultan gorge during pre-Vashon projectssouth to the altitudeof a spillwayat Ol- time. Alternatively, the surfacemay represent ney Pass(Fig. 7A). the level of proglacial fluvial deposition during the Vashonadvance only (Shaffer1983). Beddedsilt and pebblysilty diamicton(unit 2, Fig. 78) overlie the fluvial sediment. On the Reconstructionof the ice-mareinal southdam abutmentthe unit is only 5-10 m thick environment and variesfrom rather typicalmassive and stony Ice-dammed lakes Vashontill (clastcontent about25'/") to a poorly sorted,pebble-poor deposit containing discontin- The occupation of the Puget Lowland by the Cor- uoussilt layers1-2 cm thick and a few gravel-rich dilleran ice sheet required major readjustments lenses.On the north abutment it thickens to in the prevailing westward and northwestward nearly 100 m. In this area, clastsconstitute less drainage out of the Cascade Range. Rivers were than 5"h of this unit (Fig. 7C); thosepresent are first diverted south along the advancing ice mar- subangularto well rounded, 0.5-4 cm in dia- gin. Eventually, the ice reached the eastern edge meter, and commonly striated.The matrix pri- of the Lowland, covering all ice-free routes. Gla- marily consistsof fine silt. Faint color changes cial lakes then formed in the lower reachesof the and slightlycoarser texture definesubhorizontal west-draining alpine valleys of the Cascades layersin this silt up to l0 cm thick and several (Cary & Carlston 1937; Mackin 1941; Williams metersin lateral extent. Lensesof fine sand as 1971.;Porter 1976; Booth 1985, 1986). much as I m thick are also present.Poor expo- Ice-marginallakes of similar sizeand geometry suresfarther east suggest that erosionalremnants are common in modern glacial environments BOREAS 15(1986) Ice-marginalembankments 253

48('00'

12 40' 2km oF+ lml

Unit 3 bedded sand 70- and grave'l 9Om Uflit 2 silty dianicton, lO m bedded sand and silt

Unit I bedded sand and qravel

Frg. Z. Pilchuck-sultanembankment. A: Topographyfrom USGS Index and Silverton 15' quadrangles(embankment is outlined). Ice-maximumlimit shown by black dots; altitude in feet. B: Stratigraphyof embankmentsediments north of Culmback Darn (adaptedfrom Shaffer1983). C: Pebble-poorsilty diamicton; zonesof horizontallybedded silt are presentabove and below shovel (location shown on Fig. 7A; altitude 440 m (1,2140ft)). 254 Derek B. Booth BOREAS 15 (1986)

(Stone 1963;Post & Mayo 1971).These lakes bard 1980;Eyles et a|.1982;Shaw 1982; Eyles & typicallydrain either throughsubaerial spillways Eyles1984). upvalleyof the ice or beneaththe dammingice it- self (reportsof long-termlake drainageover the Interaction of ice and water at the ice ice surfaceare notablyrare). margin In valleysadjacent to the PugetLowland, bed- rock dividesupvalley of the maximumice margin Although the sedimentologicalevidence supports standwell abovethe altitudeof the dammingice. the existenceof lacustrineenvironments adjacent Thus, drainageof eachlake could only be over, to and beneaththe ice sheet,these data alone under, or aroundthe ice dam (seebelow). Even cannot conclusively delineate this environment at lower ice stands,only the SultanRiver valley (cf. Karrow et al. 1984;Christe-Blick 1985).Fur- had exposeda spillwayover the bedrockdivide thermore, they offer little insight into the con- (at Olney Pass;see Fig. 7A) that permittedsub- figuration of the ice sheet, the controls on lake- aerial lake drainagewhile ice still blocked the surface altitude, or the determination of where valley mouths.All other valleysdrained via the andunder what conditionssedimentation will oc- ice dam for as long as active glacier ice remained cur. These deficienciescan be corrected by ana- at their mouths. lyzing the mechanicsof ice and water along a gla- cier margin.This analysisnot only independently confirms the presenceof this inferred environ- Sedimentological processes in ice-marginal ment, but also showswhy environments embankmentsformed almost exclusivelyat valley mouths, why they are The origin of depositssimilar to the stratified, ubiquitousin this region, and whetherthey rep- pebbly silt and diamict units in both the South resent climatically induced stillstands of the ice Fork Tolt and Pilchuck-Sultanembankments margin. (unit 2, Figs.4B and 78) has beendiscussed by many authors(e.g. Dreimanis 1979;Evenson el Ice limits. - Evidence for maximum extent of ice al.1977;May1977; Gibbard 1980;Eyles & Eyles into alpine valleys that enter the eastern Puget 1983;McCabe et al. 1984;Barnett 1985; Heiny Lowland is not well expressedon the steepvalley 1985).Common to all hypothesesis an inferred sidewalls.The distribution of glacial erosion and environment of subaqueousdeposition, indi erratics on the adjacent interfluves (Booth cated in particular by laterally continuous, non- 1986),however, indicates the vertical extent of deformed stratification that presumably pre- theseice tongues.These data show that ice, at cludesdeposition (lodgment) by ice slidingover maximum, stood from L00 to over 6(X)m above its bed. the altitude of the present embankmentsurfaces All of the characteristicsof the diamictunits in and in places nearly 700 m above the inferred thesePuget-Lowland embankments are compa- Vashon-agevalley floor (Table1). Embankment tible with, thoughnot demandingof, sedimenta- altitudes bear no systematicrelationship to adja- tion processescharacterized by fallout of debris cent ice-maximumaltitudes, and thus embank- from the baseof meltingice combinedwith sedi- mentsrepresent neither the positionof maximum ment influx from subglacialstreams and the set- ice advance (Knoll 1967) (because600-m-thick tling of suspendedlacustrine sediments. The vari- ice would have continued advancing beyond able sedimentload of ice and subglacialwater them) nor a synchronoushalt of the whole ice yields irregularly distributedpebble-poor layers front during retreat. and lenseswithin a more uniform lithology of fine-grainedsuspended material. Tiaction cur- Marginal lakesand subglacialhydrology. - Once rentsassociated with waterflow into or out of the a marginallake is impoundedby ice, the lake's lake locallyproduce stratified and sortedcoarse- maximum surfacealtitude equalsthe maximum grained layers. The absenceof sediment-flow hydraulicpotential that its drainageroute must featuresrules out significantdeposition by sub- cross(Nye 1976).For subaerialdrainage, this po- aqueousflowtill (Evensonet al. 1977).The lack tential is simplythe altitudeof the spillway.For of overconsolidationor glaciodynamicstructures subglacialdrainage paths, the hydraulicpotential (DreimanisI976) near the top of most of these has two components:the bed altitude of the deposits implies that the ice may have only channel and the pressureof the overlying ice grounded rarely againstthese sediments(Gib- (Shreve1972). These are analogousto the eleva- -j ' BOREAS 15 (1986) Ice-marginalembankments 255

Tablel.Embankment altitudes,inferred glacial-agevalley-floor altitudes, and reconstructedice-surface altitudes in the PugetLow- land.

Embankment Valley-floor altitude (m)'z Embankment Ice Ice altitude (m)r height3 altitudea thicknesss (m) (n) (m)

Pilchuck-Sultan 680/480 3m 410 390 290t90 1060 380/580 Olney 510 370 510 490 2.4 1050 ffi Wallace 800 590 610 590 2to 980 180 Skykomish 5401160 720 130 130 410t30 860 32I/7n Proctor 7ffi 630 650 630 130 910 150 North Fork Tolt 550 430 460 450 100 880 330 south Fork Tolt 610/600 500 540 s00 110/100 860 250t2ffi North Fork Snoqualmie600/600 no 4% 390 zrcnfi 850 250t250 CalliganLake 7lO 550 680 s90 120 840 130 Lake Hancock 700 550 660 610 90 830 130 Middle-South Forks Snoqualmie 490 230 360 n0 220 780 290

1 First number is the present embankment altitude. Second number is available data on the altitude of the highest non-fluvial sedi- ment depositedsubglacially and/or subaqueously. t Euid"nci for valley-floor altitude includesthe top of bedrock or pre-Frasermaterial (minimum altitude) and the baseof reces- sionalor postglaciil deposits(maximum altitude). The bestestimate assumes a concave-upvalleyprofile and is probably accurate in all casesto within 50 m. I Equals the differencebetween the embankmentaltitude and the best valley altitude' a Booth (1986) s Equals the differencebetween ice and embankmentaltitudes.

tion head and pressurehead, respectively,com- The hydraulic potential beneath ice tongues mon in groundwaterterminologY. that extendedinto alpine valleysin the study area The hydraulic potential (or total head) at any thus increasedupglacier (to the west and north- point on the glacier bed can be expressedas an west, towardsthe center of the ice sheet).This altitude,ignoring any dynamiccomponent due to wasthe directionof greaterice-surface altitudes, sliding of the ice (Booth 1984a): more than compensating(via eqn. 1) for the des- cent of the valley floors in this (upglacier) direc- (1) drainage H : zr + @,lq-)h, tion. Any potentialroute of subglacial down these valleys thus faced steadily rising hy' where 11 : the hydraulic potential, zr: bed alti- draulic potentials.At the edgeof the Lowland, tude, p, : ice density,q, : water density,and ft however, potential subglacial drainage routes : thicknessof ice. werenot constrainedby valleywalls and so could In these terms, .FIequals the altitude to which turn southward, in a direction of decreasingice- water would rise in a boreholethat penetratesthe surface altitudes, to follow paths where the hy- glacier to its bed. The hydraulic potential in- draulic potential decreasedmonotonically (cf. creaseswith increasingice thicknessand de- Fig. 8). A maximumvalue was therefore defined creaseswith decreasingbed altitude. The gra- for the potential along each complete drainage dient of H specifiesthe direction of water flow route, betweentheir'confined' west-flowingand (i.e. from regionsof high11 to low 11).Note from 'unconfined'south-flowing legs, which must have equation1, however,that any changein 11is pri- beenexceeded before the water impoundedin a marily determinedby changesin the altitude of valley could drain. The locationof thesemaxi- the ice surface;bed altitude exertsan influence mum potentials,near to where each valley en- only one-eleventhas great (Shreve1972,1985; tered the Lowland proper, defined the position Nye 1976).The hydraulicpotential at the baseof of an effectivespillway for eachlake. the ice can thereforebe reconstructed(Fig. 8) Where subglaciallake drainageflowed over from the reconstructedtopography of the ice sur- sucha spillwayupglacier from the snoutof each f'aceand the glacierbed (approximatelythe pres- local ice tongue,some ice betweenthe spillway ent groundtopographY). and the glaciermargin probably began to float as 256 Derek B. Booth BOREAS ls (1986)

Waterflow into a marginallake will eventually raisethe water-surfacealtitude to equalthe spill- way potential.If the spillway,and thusthe drain- age,is subaerialover a bedrockdivide, lake level is stableat this point. If drainageis subglacial,a more complex sequenceof eventsmodeled by Nye (1976)typically results in total or near-total drainageof the lake (Clarke 1982). Subglacial water flow melts a tunnel, whoserate of expan- sion due to melting initially exceedsits closure rate due to ice deformation.The hydraulicpoten- tial along the tunnel thus loses its component from the ice overburdenand dropsprecipitously

NORTH 4t"ts to equal the bed altitude. Drainageshould now FORK TOLT proceed catastrophicallyas a jcikulhlaup until lake level falls to the altitude of the highestbed SOUTH FORK TOLT spillwayalong the drainageroute (2, in eqn. 1) or until ice finally resealsthe tunnel during waning flow. Refilling of the lake begins the process anew(e.g. Stone 1963; Post & Mayo 1971;Mot- tershead & Collins 1976; Sturm & Benson CALLIGAN 1985).The lakesalong the easternmargin of the Pugetlobe probably refilled in a few tens of years HANCOCK

ot*------ikt

MIDDLE-SOUTH FORKS . SNooUALMIE

Fig. 8. Contour map of subglacial hydraulic equipotentials cal- culated using equation 1, contour interval 15 m. Ground sur- face digitized from 7.5' and 15' topographic maps; ice-surface reconstruction from Booth (1984a: fig. 3.8). Embankment lo- cations are marked with open stars, subglacial spillways by heavy dots.

the altitude of the impoundedlake approached the value of the spillway'shydraulic potential. Suchlacustrine ice shelveshave been observed in someareas (Nye 1976;Stone 1963; Post & Mayo 1971, lakes no. 6 and 27; Sturm & Benson 1985)though are absentor ill-definedin others (e.g. Holdsworth1973; Bindschadler & Rasmus- sen 1983).An ice shelf will alwaystend to ad- vance into standing water becauseits unsup- ported portion abovewater level exertsa longi- tudinal stressgreater than the water pressure acting on the submergedice face (Weertman 1957;Thomas 1973).The shelf thicknessneces- sary for appreciablestrain rates, observedin Ant- arctica to be 150-300m (Robin 1979;Thomas 1979),was exceededduring the Vashonstade in mostof the major alpinevalleys entering the Pu- get Lowland (Table1). Therefore,shelf ice adja- Frg. 9. Boulder gravel depositedby episodic drainage out of centto the Pugetlobe probably advanced beyond glacial Lake Skykomish(see Fig. 1 for location). Note person the groundingline into theseice-marginal lakes. a

Ice-marginalembankments 257 BOREAS 15 (1986) itself (Booth 1984a),and so this processrepeated ICE SHELF lne numeroustimes during the Vashonstade' oi"ai.t.O path of theseoutburst floods is etched as in the land'scapeof the easternPuget Lowland a 4O-km-longtrough up to 1 km wide and over is ioo-r a".p [uootti 198'4b)'a portion-of.which (now oc- depictedaiong the westedge of Fig' I I Snoqualmie .rrpi"O Uy th-e North Fork of the grounding clear."f t:il- basal niu.t;. Attnougtrlargely swept liner, in one areaby a 4uu- --till ment, the trough is choked t,'E r-,ni.t sectioi of fluvially transportedbou-lder basal, tl gravelwith clastsup to 3 m in diameter(Fig' 9)' neftout',i,' tri " B""uur" no subierial drainage routes out of V* the upper Cascadevalleys existed-during tl9 re- shonmaximum, each ice-dammed lake in this gion would have experiencedsubglacial drainage of E.rtlng to-" (usuatty extensive) period .its ICE ice GROUNDED existe"nce.Lake drainageover or aroundeach dam is precluded on both theoretical and em- pirical grounds. Becausewater is more dense ihun ice",its hydraulic potential will exceedthat of ice at the bed before the water surface ever risesaboue the ice level (an obviousprerequisite an to supraglacialflow). Subaerialflow around -confined ice dam by steep valley walls (Mackin 1941)is equallyimplausible, requiring the.water gra- to flow .ottttuiy to the prevailing hydraulic dient (see below). These physical constralnts are boine out by the absenceof reported su- gla- praglaciallake-drainage systems on modern is ii.ri. Ceotogicevidenie in the PugetLowland equally in accord with these physical expecta- at tions;incised channels adjacent to eachvalley or near the maximum ice-marginposition are no- ICEBERG tably absent,implying a lack of significantsub- aerial marginal drainage along the steep lnter- fluves. Even at progressivelylower ice stands' o"fy n the Sultan River valley would subae.rial patls have been uncovered(the farthest upvalley teing Olney Pass;see Fig' 7A)' The rematrung valleysdrained subglacially for as long.asactrve basal \ffi glacier ice remained in their lower reaches' ill]fr"tr ffirli' i! i,iilf,ii

Sedimentationinto ice-dammed marginal lakes Fie. 10. Possibleice-termini configurationsand processesof till deiosition in glaciolacustrineenvironments (adapted fromVor; Processes rei et ol. t983). More detailed discriminationof depositional 4) in the Plget-lobe permits a vari- processes(e.g. Eyles & Eyles 1983: fig. The glaciolacustrineenvironment is inhibited by insuffrcient exposure of the sedi- general- embankmenti ety o"fpotential depositional processes' mentsthemselves. With a stablegounding line beneaththe ice of accumu- h'fig. 10. Theseinclude basalmeltout shelf depictedin the upper diagram,waterlain till will #O of a floating shelf or berg' sub- late over time to form a ridge regardlessof the topography ,"di*".tt 6eneath substrate. glacier snout' subglacial the cross-hatched ;;;;"t flowtill off the 258 Derek B. Booth BOREAS 15 (19861 or supraglacialtransport of sedimentby running ation upvalley of the groundingline, however, water into the lake, and settlementof suspended should havelittle effect on the primary pattern of lacustrinesediment (variously discussed singly or sedimentation,namely a pronounceddecrease in in combinationby Rust & Romanelli1975; May sedimentationaway from the grounding line. 1977;Evenson et al. 1977;Fecht & Thllman1978; ThesePuget-Lowland embankments thus reflect Dreimanis 1979,1982; Gibbard 1980;Hicock er anticipateddepositional processes focused near al. 1978;Hillaire-Marcel et al. 1981;Orheim & the groundingline of a glacieradjacent to a mar- Elverhoi1981; Powell 1981; Eyles & Eyles1983; ginal lake. Vorren et al. 1983;McCabe et al. 1984).Contin- ued aggradation,lowering of lake level, and/or Location and stability of the grounding exposureof a subaerialspillway will permit sub- line sequentdeltaic or subaerialfluvial sedimentation As the site of maximumsubaqueous sedimenta- as well. Theseprocesses are not mutuallyexclu- tion, the positionof the groundingline controls sive;most studies have recognized their closeas- the patternof deposition.Formation of a discrete sociationin evensingle exposures. The ratesand embankmentrequires that the glaciermargin ter- dominantsites of sedimentation,however, may minatein or againststanding water and maintain differ for eachprocess. a relativelystable grounding line for a consider- Sedimentationby most subaqueousprocesses able time (Rust & Romanelli i975). A stable is concentratedat the groundingline (Orheim & groundingline requires,either singly or in combi- Elverhoi 1981),because the glacieris the primary nation: (1) a long-term climatically controlled sourceof sediment.Except in the presenceof lo- stillstandof the ice margin,coupled with either a calizedfast currents near the ice margin, all but fixed water level or one that never rises high the finest suspendedsediment should be deposi- enoughto float a portion of the ice; (2) presence ted here (Edwards 1978;Eyles & Eyles 1983). of a pre-existingtopographic rise or shoal;(3) re- The resultingdeposit commonly forms shoalsor sistanceto ice advanceby confining topography; ridges beneath the ice at the grounding line. or (4) a processthat incorporatesthe interde- These linear ridges have been repeatedlyob- pendenceof the thicknessof an ice dam with the servedor inferred beneathmodern glaciersand water depth in an impoundedlake. ice shelves(Holdsworth 1973;Barnett & Holds- worth 1974;Post 1975;Rust & Romanelli1975; (l) Climatically controlledstillstand. - In the Pu- Edwards1978; Hillaire-Marcel et al. 1981.;Powell get Lowland, evidencedoes not seemto support 1981;Sturm & Benson1985). this alternative (Thorson 1980; Booth 1986). Alternative processesthat distribute subaque- Limiting radiocarbon dates on the Vashon stade oussediment over a wider areaate likely to be in- from the centralLowland (Rigg & Gould 1957; effectivein a confinedice-marginal lake. Because Mullineaux et al. 1965)require rapid averagead- the debriscontent of ice tendsto be highestat its vanceand retreat ratesof the terminusof about base(Pessl & Frederick1981), basal melting will 100m/a throughoutthe glaciation.Commensur- yield the greatestvolume of sedimentnear the ate motionof the lateralice marginswould be ex- groundingline regardlessof how far ice floatsor pectedto havefollowed suit. A singlestillstand at extendsinto the basin (cf. Anderson et al. 1980). or near ice maximum (Mackin 1941)cannot ex- Basedon study of modernAlaskan glaciers, the plain the formationof theseembankments (Thble volumeof supraglacialdebris available for more 1) becausethe variation in ice thicknessabove distaltransport is negligibleby comparisonto the them impliesgreat variability in the lengthof the basalcomponent (Evensonet al. 1985).Further- ice-maximumtongue beyond them. No geologic more, rafting by icebergsis restrictedto those evidencein the Lowland suggeststhe likelihood monthswhen the lakesurface is unfrozen(Holds- of elevensuch halts, neededto climaticallysta- worth 1973). bilize eachof the ice tonguesat the presentsites Suddenlowering of lake level during a period of their respectiveembankments. of episodicdrainage tends to destabilizean ice shelfand hastensits breakupinto bergs(e.g. Post (2) Pre-existingshoals. - From the record of mul- & Mayo 1971:lake no. 5 photo). Slowerrefilling tipfe glaciationsin the Lowland (Armstrong et al. of the lake would havea similar,though less pro- 1965)and the ubiquitous presenceof Vashon-age nounced effect (Holdsworth 1.973;Barnett & embankments, pre-existing valley blockades Holdsworth1974). Such changes in ice configur- were probably presentwhen the Vashonice sheet BOREAS 1s (1986) arrived. Older glacialsediments are indeed ob- served at the core of several of these embank- ments(e.g. Porter 1976;Figs. 48, 5C). This ex- planation, however, merely displacesback in time the questionof why depositionis localized. It is also inapplicable for those embankments weredeep exposures or drill coresreveal no such material. The effect of shoalsmay neverthelessbecome important during the formation of a new em- bankment.Once sedimentbegins accumulating, the growth of an incipient embankmentwill tend (Post and 4 to stabilize the grounding line t975) i.3 further localize deposition there. ,u\f uoe (3) Confining topographiceffects. - The position of most of the embankmentsat valley mouths empiricallyshows the importanceof the valley- wall configuration.Its conceptuallymost simple consequenceis to induce resistanceto ice-front advance,thereby halting any advance of the groundingline aswell. As an ice tongue advances into a valley, it must thicken and steepenat the 2km valley entranceto compensatefor the added lat- eral drag (Nye 1965).The convergentupvalley geometrytypical of most valleysamplifies this ef- Fig. 11. Calligan and Hancock embmkments (outlined). To- fect (Mercer 1961;Funder 1972).It the valley is pographyfrom USGS Mount Si 15' quadrangle.Ice-maximum by black dots; altitude in feet. perchedabove the Lowland, suchas those shown limit shown in Fig. 11, this pausewill last even longerwhile ice thickensat the valley mouth. The secondcon- sequenceof valley-wall configuration is reflected Wherever the altitude of the lake surfaceequals indirectly in its contribution to the location of the or exceedsthe hydraulic potential at the bed, the subglacialspillways (discussed below). ice floats. The exact extent and configuration of the lake ice is irrelevant, for although the ice (4) Interdependenceof ice thicknessand water front will advance as a shelf if it is sufficiently depth. - Although an ice margin and grounding thick (Weertman 1974;Sanderson 1979), the lo- line may stabilize under the special conditions cation of the grounding line does not depend on mentioned above, these conditions cannot ac- the position of the ice front. count for deposition of all embankmentsalong Rising water can float ever-increasingthick- the Cascadefront, becausethey do not all satisfy nessesof ice, causingthe grounding line to mi- one or more of the precedingrequirements. The grate upglacier. As lake level approachesthe hy- morphological and sedimentologicaldata from draulic potential of the subglacial spillway and theseembankments can be understood,however, drainage becomesimminent, the grounding line by consideringthe mechanicsand interaction of lies acrossthe ice tongue just downglacierof this ice, subglacialtopography, ice-marginal water, spillway (Fig. 12). Subsequentdrainage may al- and transportedsediment. low the grounding line to migrate upvalley some As thickening ice seals subaerial drainage distance,but repeatedcycles of depositionduring routesout of a basin,rising lake water, unavoid- lake filling will tend to stabilizethe ice front. This able in a blocked basin, must eventuallyfloat the is partially due to both the effect of shoals(Post glacier snout prior to (or simultaneouswith) lake 1975)and the shapeof natural reservoirs.Water drainage.The locationofthe groundingline then level risesmost slowly, and so the grounding line becomesa function of the depth of impounded migrates most gradually, when these lakes are water and the hydraulic potential at the bed. filled near to their maximum depths. Thus the Wherever the altitude of the lake surfaceequals grounding line will remain longest at positions 260 Derek B. Booth BOREAS 15 (1986)

ine Aconto?;,1 trI'3J;riff,]acier[r.Erl'?i;.iiff'1.. grounding1 ine and/or 1ake z Ice margin Subglacial Ar:l H:',"llF[7'lsu'u?]ii'll,ni. tq soi 1I way (ep'isodic)

Flg. 12. Reconstructionof subglacialwater-flow paths and spillwayin a hypotheticalvalley dammedby active glacialice. A: Sub- glacialbed topography;contour interval 100m. B: Ice-surfacetopography; contour interval 10 m. C: Subglacialhydraulic equipo- tentials; contour interval 10 m. Grounding line for a given lake level defined by the position of the equipotentialcontour whose value equalsthe lake-surfacealtitude. The maximum lake altitude will be determinedby the potential of the subglacialspitlway. Deposition of embankmentsediments occurs in the shadedarea, at greatestrates near to the maximum upglaciergrounding-line position. Note gradient of the hydraulic potential adjacentto ice margin on the steepsideslopes; extensive marginal drainagenot physicallypossible in theseareas. D: Cross-sectionalview ofice dam, impoundedlake, and subaqueousembankment sediment. Observedranges of embankmentheights and maximum ice thicknessesin the easternPuget Lowland are shown (from Thble 1). BOREAS 15 (1986) Ice-marginalembankments 261 closestto that of the spillway.Continued sedi- their examplewas controlled by a subaerialspill- mentation there will tend to stabilizethat lo- way at an altitude too low to float the ice. This cation. process,however, was active following the ice- Subglacialspillways are located in the Lowland dammedstage of depositionat severalof the Pu- just south of the mouth of most valleys(Figs. 8 get embankments(e.g. Pilchuck-Sultan,Sky- and 1.2).This geometryfocuses subaqueous de- komish, North Fork Tolt, and North Fork Sno- position at the valley mouths and explainsthe qualmie).as reflectedby planartopset surfaces tendencyfor embankmentsto form in theseposi- and rarely observed upvalley-dippingforsets. tions. These spillway locations, and thus the Other generalizedice-contact lacustrine environ- - groundingJinepositions, are quite insensitiveto ments, such as describedby Koteff (197a), all changesin the ice thickness(which can be easily have subaerialspillways distinct from the dam- if somewhattediously checked by alternativere- mingice. The locationof depositionin suchcases constructionswith thinner ice usingeqn. 1). De- is thereforedetermined by the positionof the ice position during advance,maximum, and retreat front itself during temporary stillstands.This stagestherefore will be at virtually the samelo- contrastswith the Pugetembankments, whose lo- cation. cations were determined by a grounding line The Sultan River, by contrast,has a spillway fixed by the pattern of subglacialhydraulic po- that is not in the Lowland proper (Fig. 7A). The tentials and resultant subglacialspillways. Al- embankmentin this valley alsooccupies an atyp- though focusedon a particular geographicre- ical position. As predictedby this analysis,the gion, this analysisshould apply to any locality diamicton(unit 2 of Fig. 78) of this embankment wheremodern or Pleistoceneglaciers have termi- in the main Pilchuck-Sultanvalley was deposited nated againstice-dammed, subglacially draining at a point just upvalleyof where the subglacial water bodies. potential(in the main valley)equals the potential this study were collected (located the Sultangorge; cf. Acknowledgments. - The field data for of the spillway in as part of a regional mapping project for the U.S. Geological Fig. 7A). Survey (Booth 1986; Frizzell et al. 1984). I would like to par- ticularly thank Stephen C. Porter and Fred Pessl, Jr., who led me to more careful consideration of many of the ideas pre- Other models sented here. and Bernard Hallet, Mark E. Shaffer, Rowland W. Tabor, Richard B. Waitt, Jr., Charles F. Raymond, and The physicalprocesses described here are similar Garry K. C. Clarke for invaluable discussions.B. Hallet, S. C. to thoseinvoked by Hillaire-Marcelet al. (1'981) Porter, J. J. Clague, and M. E. Shaffer critically reviewed the for formation of 're-equilibrationmoraines', lo- manuscnpt. calizeddeposits at ice-watermargins during uni- form retreat of the easternLaurentide ice sheet. Their model implicitly assumessedimentation is fully only during periods when' the ice References groundedin shallowwater, with neither a float- ing nor an activelycalving margin. The processes Anderson. J. B., Kurtz, D. D., Domack, E. W. & Balshaw, K. that activelycontribute sediments to thisenviron- M. 19U0: Glacial and glacial marine sediments of the Ant- arctic continental shelf. "/. Geol. 88,399-414. ment, however,will be active at the grounding Armstrong, J. E., Crandell, D. R., Easterbrook, D. J. & No- line regardlessof the configurationof the ice far- ble. J. B. 1965: Late Pleistocenestratigraphy and chronology ther downglacier.This resolvestheir acknowl- in southwestern British Columbia and northwestern Wash- edged difficulty (Hillaire-Marcel et al. 1981':212) ington. Geol. Soc. Am. Bull.76,321-330. Barnett. D. M. & Holdsworth, G. L974: Origin, morphology, in explaininglarge sedimentvolumes, hypoth- and chronology of sublacustrine moraines, Generator Lake, esizedto accumulateonly during the few years Baffin Island, Northwest Territories. Canada. Can. J. Earth that the ice front actuallyterminates at a specific Sci. 11. 380-408. locality. Barnett. P. J. 19tl-5:A model of glacial-glaciolacustrine sedi- mentation, Lake Erie basin. Geol. Soc. Am., Abstr. with Other settingsproposed for depositionof flu- Progr. 17(5),279. vial and ice-contactsediment in other localities Bindschadler, R. A. & Rasmussen, L. A. 1983: Finite-differ- are clearlynot applicableto the initial formation ence model predictions of the drastic retreat of Columbia the Puget embankments.Deltaic sedimenta- Glacier, Alaska. U.S. Geological Suruey Professional Paper of 1258-D. 17 pp. tion into a proglaciallake, describedby Orom- Booth, D. B. 1984a: Glacier dynamics and the formation of gla- belli & Gnaccolini (1978), lacks a significant cial landforms in the eastern Puget Lowland, Washington. basal-meltoutcomponent because water depthin Seattle, University of Washington, Ph.D. thesis. 217 pp. 262 Derek B. Booth BOREAS ls (1986)

Booth, D. B. 1984b: Ice-sheet reconstruction and erosion by (eds.): Polar geomorphology. Inst. Brit. Geogr. Spec. pub. 4, Subglacial meltwater in the eastern Puget l,owland, Wash- 3HZ. ington. Geol. Soc. Am., Abstr. with Progr. 16(6), 450. Gibbard, P. 1980: The origin of stratified Catfish Creek till by Booth, D. B. 1985: Surficial geology of the Granite Falls 15- basal mefting. Boreas Q,7l--85. minute quadrangle, Snohomish County, Washington. U.S. Heiny. J. S. 1985:Glaciogenic sediment sequencesand inferred Geological Survey Open-File Report 85-517, scale 1:50,000. ice margin fluctuations in the Lake Michigan basin- Geol- Booth, D. B. 1986: Surficial geology of the Skykomish and Soc. Am., Abstr. with Progr. 17(5),292. Snoqualmie Rivers area, Snohomish and King Counties, Hicock. S. R., Dreimanis, A. & Brosten, B. E. 1981: Subma- Washington. U.S. Geological Survey Miscellaneorc Investi- rine flowtills at Victoria, British Columbia. Can. J. Earth Sci gations Map I - 1745, scale 1:50,000. /8, 7l-80. Cary. A. S. & Carlston, C. W. 1937: Notes on Vashon stage Hillaire-Marcel, C., Occhietti, S. & Vincent, J. S. 19g1: Sa- glaciation of the South Fork of the Skykomish River valley, kami moraine, Quebec: a 50O-km-long moraine without cli- Washington. Northwesl Science I I, 6l-62. matic control. Geology 9,210-214. Christe-Blick, N. 1985: Depositional processes and environ- Hirsch. R. M. 1975: Glacial geology and geomorphology of the ments inferred from glacial rocks: interpretive ambiguity, ob- upper Cedar River watershed, Cascade Range, Washington servational inadequacy, inappropriate models and strategies Seattle. University of Washington, M.S. thesis. 48 pp. for future research. Geol. Soc. Am., Abstr. with Progr. Holdsworth. G. 1973: Ice calving into the proglacial Generator r7(5),283. Lake. Baffin Island, Northwest Territories, Canada. J- Glac. Clarke. G. K. C. 1982: Glacier outburst floods from 'Hazard r2.235-250. Lake', Yukon Territory, and the problem of flood magnitude Karrow,P. F., Dreimanis,A., Sharpe,D. R., Gravenor,C. P., prediction. J. Glac. 28,3-21. Eyles,C. H. & Eyles,N. 1984:Comment and reply on'Sedi- Converse Ward Davis Dixon 1979: Final geotechnical invest! mentationin a largelake: A reinterpretationof the latePleis- gation. raising of Culmback Dam, Sultan River Project, tocenestratigraphy at ScarboroughBluffs, Ontario, Canada.' Stage ll. Unpublished report for Public Utility District No. 1 Ceology12, 185-190. of Snohomish County, Washington. Knoll. K. M. 1967:Surficial geology of the Tolt River area, Crandell. D. R. 1963: Surficial geology and geomorphology of Washington.Seattle, University of Washington,M.S. thesis. the Lake Tapps quadrangle, Washington. U.S. Geological 9l pp. Survev Professional Paper 388A. 84 pp. Koteff, C. 1974:The morphologicsequence concept and degla- Dethier. D. P.. Safioles, S. A. & Pevear, D. R. 1981: Com- ciationof southernNew England./n Coates,D. R. (ed.): position of till from the Clear Lake quadrangle, Skagit and Clacial Geomorphology,121-144. State University of New Snohomish Couoties. Washington. U.S. Geological Survey York. Binghampton. Open-File Report 8l-517. 55 pp. Kulig. J. J. 1985:Detailed sedimentological analysis of glaci- Dreimanis. A. 1976: Tills: their origin and properties. 1n Leg- genic sediments deposited in central Alberta. Geol. Soc. get. R. F. (ed.): Glacial Tills, an Interdisciplinary Study, 1l- Am., Abstr. with Progr. l7(5),297. 49. Ottawa. Ontario. Mackin.J. H. t94l: Glacialgeology of the Snoqualmie-Cedar Dreimanis. A. 1979:The problem of waterlain tills. In Schluch- area.Washington. J. Geol. 49, 449481. ter. C. (ed.): Moraines and Varves, 167-177. A. Balkema, May. R. W. 1977:Facies model for sedimentationin the glacio- R0ttcrdam. lacustrineenvironment. Boreas 6. 175-180. Dreimanis. A. 1982:Two origins of the stratified Catfish Creek McCabe,A. M.. Dardis.G. F. & Hanvey,P. M. 1984:Sedi- Till of Plum Point. Ontario, Canada. Boreas 11, 173-180. mentologyof a latePleistocene submarine-moraine complex, Edwards. M. B. 1978: Glacial environments. 1n Reading. H. CountyDown, Northernlreland. J. Sed.Pet. 54,716-730. G. (ed.): Sedimentary Environments and Facies, 416_4'38. Mercer,J. H. l96l: The responseof fjord glaciersto changesin Blackwell. Oxford. the firn limit. L CIac.3,850-858. Evcnson. E. B.. Clinch, J. M. & Stephens.G. C. 1985:Debris Miall, A. D. 1977:A review of the braided river depositional delivery. deposition and reworking at Alaskan glacier mar- environment.Earth Sci.Rev. 13,142. gins. Geol. Soc. Am. Abstr. with Progr. 17(5), 286. Mottershead,D. N. & Collin, R. L. 1976:A studyof glacier- Evenson. E. B., Dreimanis, A. & Newsome, J. W. 1977:Sub- dammedlakes over 75 years - Brimkjelen,southern Norway. aquatic tlow tills: a new interpretation for the genesisof some J. Clac.17.491-505. laminated till deposits. Boreas 6, 115-133. Mullineaux.D. R. 1970:Geology of the Renton,Auburn, and Eyles. C. H. & Eyles. N. 1983:Sedimentation in a large lake: a Black Diamond quadrangles.King County, Washington. reinterpretation of the Late Pleistocenestratigraphy at Scar- U.S. Geologkal SurveyProfessional Paper 672.92 pp. borough Bluffs. Ontario. Canada. Geology 11,146-152. Mullineaux,D. R., Waldron,H. H. & Rubin, M. 1965:Stra- Eyles. C. H. & Eyles. N. 1984: Glaciomarine sediments of the tigraphy and chronologyof late interglacialand early Vashon lslc of Man as a key to late Pleistocene stratigraphic investi- glacialtime in the Seattlearea, Washington.U.S. Geological gations in the Irish Sea Basin. Geology 12,359*364. SurveyBulletin 11944. lO pp. Eyles. N.. Sladen. J. A. & Gilroy, S. 1982: A depositional mo- Nye, J. F. 1965:The flow of a glacierin a channelof rec- del for stratigraphic complexes and facies superimposition in tangular.elliptical, or paraboliccross-section. J- Glac. 5, lodgement tills. Boreas 11, 317-333. 661-690. Fecht, K. R. & Tallman, A. M. 1978: Bergmounds along the Nye. J. F. 1976:Water flow in glaciers:jokulhlaups, tunnels, western margin of the channeled scablands, south-central and veins.l. Glac.17,181-207. Washington. Geol. Soc.Am., Abstr. with Progr. 10(7),400. Orheim.O. & Elverhoi,A. 1981:Model for submarineglacial Frizzell.Y. A.. Jr.. Thbor. R. W., Booth, D. B. & Waitt, R. deposition.Annals of Glaciology2, 123-128. B.. Jr. 1984: Preliminary geologic map of the Snoqualmie Orombelli,G. & Gnaccolini,M. 1978:Sedimentation in pro- I : 100,000 quadrangle. Washington. U. S. Geological Survey glaciallakes: a Wurmianexample from the Italian Alps. Z. Open-File Report 84493. Geomorph. N. F. 22, 417-425. Funder. S- 1972: Deglaciation of the Scoresby Sundfjord re- Pessl.F., Jr. & Frederick.J. E. 1981:Sediment source for melt- gion. northeast Greenland. /n Price, R. J. & Sugden, D. E. water deposits.Annals of Glaciology2, 92-96. BOREAS 15(1986) Ice-marginalembankments 263 l)orter. S. C. 1976:Plcistrxcne glaciation in the soulhcrnpart Shreve.R. L. l9li5: Eskcr characleristicsin tcrms of glacier of thc North CascadeRange. Washington. Ceo!. Soc.Am. physics.Katahdin esker sl'slcm. Mainc. Geol. Soc.Ant. Bull. BullcrinU7.6l-75. 9(). 639446. Post.A. S. t975: Preliminaryhydrography and historictermi- Stonc. K. H. 1963: Alaskan ice-dammcdlakcs. Assoc. of nal chungcsof ColumbiaClacicr. Alaska. U.S. Geological AnrcricanGeogr., Annals J.l, 332-3.19. Surrct Hvdrologic InrcstigationsAtlas 559. 3 sheets. Sturm,M. & Benson,C. S. 1985:A historyof jSkulhlaupsfrom Posl.A. S. & Mayo.L. R. l97l: Clacierdammed lakes and StrandlineLake, Alaska.l. Glac.3l,27?-28o. outburst floods in Alaska. U.S. Gcological Surve-vH;"dro" Thomas.R. H. t973:The crecpof iceshclves: thcory. J. C/oc. logic lnrestigarionsArlas 155. lll pp, ,2. 4.s-53. Poucll. R. D. l9til: A model for scdimentationby tidcwater Thomas.R. H. 1979:The dynamicsof marinc ice shccts.J: gfacicrs.; rncls of Glociologl' 2, 129-134. Glac. 24. 167-177. Rigg.G. B. & Gould. H. R. 1957:Age of Clacier Peakerup- Thorson.R. M. l9ft0:lce shcctglaciation ofthe Pugethrrvland. tion and chronologyof postglacialpcal dcposilsin Washing- Washington.during the Vashonstade. Quat. Rcs. I'1,tt13' ton and surroundingareas. Am. J. $ci.255.341-363. 321. Robin. C. de Q. 1979:Formation. flow. and disintegralionof Thorson.R. M. l9lll: Isostaticeffccts of the lastglaciation in ice shefves.l. Gloc. 24.259-271. the Pugel lowland. Washington. U.S. Geological Survev Rust.B. R. & Romanelli.R. l9?5:Late Quaternary suhaque- Open-FilcReport 81-370. l|.X..lpp. ous oulwashdcposits ncar Ottawa. Canada,/, Jopling.A. Vrrren. T. O.. Hald. M.. Edvardsen.M. & Lind-Hanscn,O. V. & McDonald. B. C. (eds-):Glaciofluvial and glaciola" W. 1983:Glacigcnic sediments and sedimenlarycnviron' cuslrincsedimcnlation. Soc. Econ. Paleo.Min. Spec.Publ. mcntsof continentalshelves: general principles with a case 2-t. t77-192. studyfrom the Norwegianshelf. /n Ehlcn. J. (ed.l; Glacial Sandcnon.T. J. O. 1979:Equilibrium profile of iceshelves. J. Dcpositsin North-west Europc. 6l-73- A. Balkcma, Rot- Clac. 22.43-5*460. lerdam. Shaffcr.M. E. l9tl3: Repon on geohydrologicinvestigation of Wecnman.J. 1957:Dcformation of floaringice shelves'J. PilcbuckPlug. raisingof CulmbackDam, SultanRiver Pro- GIac.3.3tA2. jcct. Stagcll. Scatlle.Convcrse Consultants. lnc., unpub- Weertman.J. 1974:Stability of rhejunction of an icesheel and lishcdreport for R. W. Beckand Associalesand PublicUtil- an ice shelf.J. Glac. 13.Tll. it1,District No. I of SnohomishCounty. Washington. 54 pp. Williams.V. S. l97l: Glacialgeology of the drainagebasin of Shaq'.J. l9ti2: Mcltout till in the Edmontonar€a. Alberta. thc MiddlcFork of the SnoqualmieRiver. Scattle. Universit) Canada.Can. t. Earrh Sci./9, l-5411-1569. of Washington.M.S. thesis.4-5 pp. Shreve.R. L. 1972:Movemcnt of $,aterin slaciers."1. Glac. I I, l(1.5-214.

l\i A) BOREAS BOOK REVIEWS \\-

MATTI ERONEN

Sutcliffe. Antony J. 1985:On the Tiack of lce Age Mamnab. well illustrated with many black-and-*'hitepholographs, draw- 224pp..Brirish Museum (Natural History). PriceGBP 12.95' ings, maps, and diagrams.The book is aimed primarily at sPe- cialists working on different fields related 1o Quaternary re- This book is a comprehensivetreatment of the biological and search,but it should also appealto a wider audience- physicaldevelopments during the Quaternaryperiod. Although Although Antony J. Sutcliffeis an expert in mammalianpal- the lce Age mammalian fauna referred to in the title fiSure aeonrology,he skilfulty provides an oven'ieu of all the main prominently rhroughout the entire book, many different as- lines of modern Ouaternary researchin this book. He opens pectsof environmentalchanges during the Quaternarytime are with a discussionof Quatemary climatic variations and their also discussed.Both the title and tbe aPpearanc€of the book consequencesand follows with a fascinatingdescription of the are 'selling': on the dust jaclet, for example, there is a col- early interpretations of fossil remains. For example, early ourful picture of an lce Age landscapewith a herd of woolly workersidentified animal bonesunearthed in rhe Pastcenluries mammoths.Five such colour plates depicting different Pleisto- as remainsof such fanciful creaturesas dragonsand unicorns- ccne sccnescan be found inside the book, which as a whole is The next chapler is concernedwith our prescnt knowledgc of