WilliamA. Long, Geologislretired, 123 F verffontDrive, Cashmere, Washlngton 98815

A Probable Sixth Leavenworth Glacial Substage in the lcicle-ChiwaukumCreeks Area, North ,

Abstract In the valleysofthe Icicte-Chiwaukuncreeks area on the easternslope of the North CascadeRang€, noraines wirh pronounced constructionaltopography are representativeo{ fie last glaciation, the Leavenworthglaciation. Recessionfron the Leaven' worth maxirnuln was follo{ed bv severall€ss€r stillstands or readvanc€s.The Larch Lake moraine at the h€ad of Chiwaulun Creek reaches1737 In altitude and lies betweenthe Leaven{orlh V rnoraineand noraines of Neoglacialag€. On and behind the Larch LaIe moraine the ca. 11,250-year-oldGlacier Peaktephra is found beneaththe 6900-year-oldMazama ssh. Moraines with preseF/ation,form, and relativeposition nearly identicalto that ofth€ Larch L!*e moraineoccur in the lcicle Creekdrainage beyond the fallout limit of the Peak tephra. tsecausethe Larch Lake noraine was built prior to late'glacialeruptions of Glacier Peak but after the LeavenworrhV subslage,ir appa.€ntly representsa previously unrecognizedsubstage termed

lntroduction their confines, suggestingthat they are Neo- glacial in age. The LeavenworthV and inter- Icicle and ChiwaukumCreeks are in the southern mediatemoraines have a thin soil which supports WenatcheeRiver drainage,Chelan County (Fig- old-growthconifers, but the Neoglacialmoraines ure l). AlongIcicle Creek multiple-end moraines have only incipient soil profiles and sparse with pronouncedconstiuctional topography and vegetation. The intermediate moraines could associatedoutwash bodies permit subdivision of representeither a previouslyunrecognized sixth the latest glaciation(Leavenvorth) into four Leavenworthsubstage or a post-Leavenwoh ad- substages(Long and Porter 1968,Porter 1969). vance.A reasonablesolution to the problemwas Waitt (1977) found a fourth Leavenworth-age found in l9B7 in neighboringChiwaukum Creek morainea mile behindthe LeavenworthIII in valley. lower valley. Recessionfrom the Leavenworthmaximum was followed by several Observations lesserreadvances. Claciers during the Leaven- worth I, II, III, and IV substageswere long valley The maximurnlength of the Icicle Creekglacier (longest glacier 48 km). During the of Leavenworth V age, as measured from LeavenworthV substagethey were short valley JosephineLake at the sourceof Icicle Creek,was glaciers (longest glacier 12 km in Eightmile 10.5km, comparedto 48 km for the Leavenworth Creek). I. A morainethought to be the terminal moraine As describedby Porter (1969),the type ofthe LeavenworthV glacierin IcicleCreek lies LeavenworlhV deposir is an arcuate moraine at the junction of Icicle Creekand Doughgod complexbuilt by the Rat Creekglacier at the Creekat 945 m altitude(Figure l). junctionof Icicle Creekand Rat Creek.The in- Page(1939) described a moraine-likemass ner of tno morainesforms a continuousloop, just below the mouth of Glacier Creek that con- crossedby Rat Creek at its lowest point ar 549 sist.of angularschist blocls piJed up in trans. m altitude,and is the lowestLeavenworth V versefashion across the valley.This masswas morainein Icicle Creekdrainage. Distribution thoughtb1 Pageto be a recessionalmoraine. or of LeavenworthV morainesin Icicle Creekis one markingthe terminationof the glacieroc- shownon the locationmap of Icicle and Chi- cupyingupper ChiwaukumCanyon. Leavenworth waukumCreek drainages (Figure l). V alongupper ChiwaukumCreek apparently While mapping LeavenrrorthV deposits terminatedhere at ll58 m, about I km below alougIcicle Creek,I recognizedrnoraines behind the mouth of GlacierCreek. the LeavenworthV morainesbut belowthose in The moraineforms a continuousloop which the highestcirques. The highestmoraines are is incisedby ChiwaukurnCreek to a depth of very fresh, as are the bedrock surfaceswithin aboutB m (visibleon USDAserial photographs

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A ProbableSixth LeavenworthGlacial Substage 97 1986 llight). A large swampy area behind the CupLake Moraine moraine may have been a lake. A well-defined As describedby Merrill (1966, segmentof moraine remains against the south p. 8), a moraine dammingCup Lake at an valley wall and rises 45 m above the swamp. altitudeof 1964m (6443 ft), which he provisionally Evidently the central part of the moraine has assigned a Neoglacialage, Iies in the highest been eroded, thereby exposing its broad base, cirqueof the ChiwaukumCreek drainage (Figure 4). The whichdses as much as lOm abovethe swampand Larch Lakemoraine separates the Larch Lakecirque consistsof fresh rubble and angular blocks up from toSmindiameter. the stream draining Cup Lake. The Cup Lakemoraine is very bouldery,exceedingly ftesh, A sharp-crested,well-developed lateral and showslittle or no soil development.Lichen moraine (altitude 1675 m) lies 90 m above rhe coveron moraineboulders is discontinuousand nest end of ChiwaukumLake. This rnoraine, othervegetation is absent.The CupLake cirque recognizedby Merrill (1966),is hereinrerpreted hasonly smalltalus cones, in contrastto much as the right-lateral moraine of the Leavenworth larger talus conesjust downstreamon the east- V glacier.From its (1830 m) altitude, north facingvalley wall. Because the Mazamaash ap- aspect,and large size ofthe JasonLakes cirque, parently is absenton or behind the morainebut it is clearthat ice from JasonLakes joined the is presenton the steepslope immediately beyond ChiwaukumCreek glacier over Honour Lake at it, and becausethere is no hint of a streamnotch, a point only 2 km above the mouth of Glacier the Cup Lake moraineis consideredto be late Creek (Figure 2). The Glacier Creek glacier Neoglacial(late Little ) in age. joined the Chiwaukum Creek glacier farther downvalleyand wasthe mostimpofiant tributary. Discussion The tephra layerswere identified in the field as LarchLake lvloraine GlacierPeak lapilli purniceand Mazamasilty ash on the basisof grain size,color, distribution and Larch Lake is a tarn at an altitude of lB52 m stratigraphicposition. Three principal layersof (6048ft) behinda multipleterminal moraine in pumiceoustephras, resulting from multiple erup- the ChiwaukumCreek valley-head cirque (Figure tionsof the GlacierPeak volcano in late-elacial 2). The Larch Lake moraine reaches an altitude lime,corer much of thelandscape in the"astern of 1737 m and lies B km upvalley from the Norrh CascadeRange (Porter 1978).In this area LeavenworthV moraine. At Larch Lake a yel- the Glacier Peak tephra, as shown by Porter Iowish-brownpumiceous tephra layer underlies (19?8),consists largely of lapilli pumice;rhe grain a thick pale-brownfine ash in a surfacelocaliry size decreasesaway from the volcano,with fine just behind the innermost moraine.A strati- ash being predominant only along the distal graphicsection was obtained in a wet meaoow marginsof the depositand east ofrhe Columbia insidethe Larch Lake moraine at the tephrasam- River. Available 'aC dates indicate rhat the ple site (Figure 2). Glacier Peak tephras were depositedabour I 1,250year B.P. (Porter As shownin Figure 3, the baseof the section et al. l9B3).The lapilli pumiceat Larch Lakecould is in dark gray,Iayered lacustrine silt, the deposit only havecome from GlacierPeak, because lapilli pumice of a smalllake formerly dammedby the moraine. layersfrom any other sourcehave The silt is overlainby 30 cm of tephra consisting not beenrecognized in this part of the North Cascades. of yellowish-brownand strong brown (whenwet) pumice lapilli up to 8 mm in diameter. The Ar the Larch Lake locality, the 6900-year-old tephrais coveredby 43 cm of dark gray sandand Mazama tephra is a fine volcanic ash, light- gravel and 30 cm of black sandy organic sedi- yellowish-brownor tan in color whendry, and ap- ment. Above is 70 cm of strong orange to parentlyreworked and concentratedto a thick- yellowish-brown(when wet) fine ash capped by nessof 70 cm. The only volcanicash megascop- about 30 cm of fine loamy sandwith many roots. ically similar to the Mazama that could be The unusualthickness of the volcanicash layers mistaken for it is rhe 3400-year-oldMounr St. is most likely due to fluvial reworking and con- HelensYn ash,which generallyis found only as centration of the ashes. a rhin silt layer abovethe Mazamain this part of

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A Probable Sixth LeavenworthGlacial Substase 99 Orgonic lilter- leoves,twigs, ond roott Dork brow. loomr mony rools Lightgroy, loose,line loomy 30nd, mony roots

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Figure 3. Shatigraphic successionat a wet meadowinside Larch Lake noraine at head of Chiwaulum Creek (SeeFig'rte 2 fo. location).

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A Probable Sixth LeavenworthGlacial Substase the Cascades.Because the lowermosttephra laver worthV ageand the Cup Lakemoraine of Neo- at a depthof 170cm is an airfall lapiili pumic" glacial age,it occupiesa relativeposition similar easily idenrifiable as from Glacier Peak, the to that of the Brisingamenmoraine. The Brisin- Larch Lake moraine must be older than about gamen moraine predates the 6900-year-old I1,250years B.P. Mazamaashfall, whereas the Larch Lakemoraine Waiteet aL(1982) described lwo moraine sets predatesthe ca. 11,250-year-oldGlacier Peak in the upper EnchantmentLakes Basin of the tephra.Thus, nhilc lhe Lar,^hLake moraine can Stuart Range, which drains into Creek be assignedto latest Leavenworthtime, the tributary to lower Icicle Creek (Figure 1), Each Brisingamenmoraine could represent either an moraine records an episodeof glacier advance earlyHolocene glacier advance, as suggested by after the end of the Leavenworthglaciation. The Waitt et aL (1982)or, if correlativewith the Larch outermoraine set, the Brisingamen,lies at 2310 Lakemoraine, it couldrepresent a late Leaven- m, aboutI km behindand 1760m abovethe type wo h event. LearenworthV moraineat the mouthof iiar Creek.Apparently there are no morainesbetween Conclusions the Brisingamen moraine and the Rat Creek moraine. The inner moraine set, the Brynhild, Whetherthe Larch Lake morainerepresenrs a liesimmediately beyond Snow Creek Glacier. It stillstandor readvanceof Leavenworthice is not is only slightlyweathered, lacks a soil, and is clear,but the moraine'snearly complete closure almostdevoid of lichens.The Brynhild rnoraines and position on the no hwest-facingthreshold evidentlypostdate Mount St. Helenstephra Wn of a largevalley-head cirque delimitsrhe ice that (500years old; l4B0AD), which lies only beyond built it. Becausethe Larch Lake moraine lies the inner moraine set, and therefore are behind the LeavenworthV moraine in Chi- Neoglacialin age.The Brisingamenmoraine is waukumCreek and hasGlacier Peak tephra on weathered,and on and behind it the 6900-years- and behind it, the moraine was buih someume old Mazamaash is presentbeneath the Mount before lare-glacial eruptions of Glacier Peak St. Helens Yn (3400 years old) and Wn tephra volcanoabout 11,250years ago, but after the layers.Tephra from Glacier Peak eruptions was LeavenworthV substage.The Larch Lake mo- not found in the EnchantmentLakes Basin, raine thereforeprobably represents a previously which apparentlylies south of the recognized undescribedsixth Leavenworthsubstage. limits of GlacierPeak tephra. Waitt e, aL (1982) notedthat despitemore than seyen millennia of weathering,the rock surfacebehind the Bris- Acknowledgments ingamenmoraine is measurablyless weathered I gratefullyacknowledge assistance of DanielS. than the surfacebeyond, which waslast glaciated Long (MontanaState University,Bozeman) in during the Leavenworth (Rat V Creek)advance determiningthe thicknessand characterof the about13,000 years ago. These data led them to subzonesin the soil profile at the Larch Lake assign probable a ageof earlyHolocene to the tephra samplesite, the United StatesForest Sei- Brisingamenmoraine. viceat Leavenworthfor the loanofaerial photo- As the LarchLake moraine lies between the graphs,and of reviewersof this manuscript for ChiwaukumCreek moraine of probableLeaven- helpful comments.

LiteratureCited Page,B. M. 1939.Multiple alpine glaciarion in the Leav€n, worth area, Washinsron.J. C€ol. 47:785-815. Long, W. A., and S. C. Porr€r. 1968.Reyision of the alpine Porter, S. C. 1969. Pleistocenegeology of rhe east-cenrral glacialsequence in the Leavenworiharea, Washingron CascadeRange, Washinsron: Cuidebook for Third (abst),1n Abstracrsfor 1967: Geol. Soc. Amer. SD. Pacific Coast lriends of rh€ Pleislocenefield con- PapPrr t5. p. 3J8. ference.University of Vashington, Seaule. Merrill, D. E. 1966.Clacial seologyofrhe ChiwaukumCreek -. 1978.Glacier P€ak t€phra in rhe North Cascad€ draimge basinand vicinily. UniversityofWashinglon, Range,Washington: Stratigraphy, distribution, and Seattle. M.S. Thesis. relationshipto late-glacialevena. Quar. Res. l0:3041.

102 Long Porter, S. C., K. L. Pierce, and T. D. Hamihon. 1983.Lat€ Waitt, R. B., J.. 1977.Cuidebook to Quaternarygeology of Wisconsinnounlain glaciationin the westernUnited the Colunbia, Wenarchee, Peshastin, and upper Srares,/tr Porte., S. C. (ed.). Late Qualernary En, Yakima valleys, west-cerr.al Washington. U.S. viroDmeDtsofthe United States.Volume I, The Late Geolosical Suryey 0pen-File Report 7? 753, 25 p. Pleistocene.University of Minnesota Press, Min- Waitt, R. 8., Jr., J. C. YouDr,and P. T. Davis.1982. Resional neapolis.Pp. 7l-111. significanceofan earlyHolocen€ moraine in Enchant, menl LakesB6in, North CascadeRang€, V6hinglon. Receiued5 tuly 19BB Quar.Res. l7:191,210. Acceptedfor publication l3 December l9BB

A Probable Sixth LeavenworthClacial Substaee r03