In this article, Bretz describes two glaciers that reached then drained through the northern part of the Columbia basalt plateau. Based on the physical evidence, Bretz attempts to determine when the earlier Spokane glaciation occurred relative to the Wisconsin glaciation.
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Bretz, J Harlen

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Eastern Washington UniversityEWU Digital CommonsPublications from Special Collections University Archives & Special Collections10-1924Age of the Spokane glaciationJ Harlen BretzFollow this and additional works at: http://dc.ewu.edu/spc_pubsThis Book is brought to you for free and open access by the University Archives & Special Collections at EWU Digital Commons. It has been acceptedfor inclusion in Publications from Special Collections by an authorized administrator of EWU Digital Commons. For more information, please contactjotto@ewu.edu.Recommended CitationBretz, J Harlen, "Age of the Spokane glaciation" (1924). Publications from Special Collections. 4.http://dc.ewu.edu/spc_pubs/4Bretz The age of Spokane glaciation [FROM Tmt AMl>RICAN JOURNAL OF SCil!NCE VOL. VIII, October, 1924.J THE AGE OF THE SPOKANE GLACIATION. By J. HARLEN BR.!tTZ. o.P. RY A Tr. Jt 14.1 XHOO~ l riL ,t :. l.bi-t. 2 ,. ·~ ------ -- -- - .~~-. , C -< l ./ II . Hretz-Ane of 8JJOka11e Uiaf'iatio11. .. c\_uT. X.XYllI.- '1'/i e Age of /lie Spoka11e Ulacialio11; /Jy ,J liAHu~x B1rnTz. The northern par t of the Columbia basalt p la teau in '\Yashington has been glaciated at least twice. Dm ing both glaciations the drainage fr om the southern margin of the ice sheet ,ms deflected southwar d across the pla-teau. During the earlier or Spokane glaciation the vol-ume of the waters was Yery great and the plateau 's southward slope was seyerely scom ed along dozens of huge channels.1 During the later or '\Visconsin glacia-tion, the Yolume of escaping waters appears to haYe been far less. Due to this lesser Yolume and the failure of the later ice sheet to reach as far a· the earlier , only two of the older glacial clraiuao·e ways were used. Because of th e nearl y horizontal position of th e ba ·alt sheets over most of the pla teau and. the preYailing col-umnar structure, the high-gradien t glacial streams pro-duced almo t Yertically wall ed channels, many of th em canyons in their proportions. The unifo rmity in the character of the flows aud the nearly uniform onthward slope of ahout 25 feet to the mile oYer th e whole area cleterminell 1111iformity in this feature of nearly Yertical eliffs throughout the area affected. Sinee th e glacial rivers cear-, ecl to flow, th ese g reat channels kwe carried very in significant streams, most of them intermittent affairs which flow only a few months iu the year. Great numhers of lakes and p onds . ti exist on the irregnla rly eroded floors, unfill ed nd undrained by subsequent Rtream action. The prin pal change in the abandoned waterways has been the break-ing- clown of th e steep cliffs and th e accmrrnla hon of talus at their bases. The prismatic strnctnre of the ha salL provides an ahnnclance of Yertical join ts :ilong wl1ieh the rock hrealrn . Th e cliff fa ces thus r 0ma in nen rly verlira l dnring their r el reat. They decr ease in heig·lil hy lrnrial of th e lower por[i onR ns the talus mount s. The fall011 material iR chie(lv fro st-riven dnring· th e winters. Of und er-cutting-, th er0 is 11one. Vegetati on on eliff face R iR 11 nee:ligihl e fador. ('Ji mi C'al <1 0composi-, The Chn nrwlrd S(•ablan cls of the Columhia Plateau, .J Ilarlen Bretz, .fon r. nrol. , \'Ol. 31, pp. 61 7-11-19, 19~3. .J JT. lJret::-~lge of Spoka11e Glaciation. tion is occnni11g far more slow(,· than medwnieal t1isin-tegrntion. Th0 only atl<litioual factor 01 importanl'e in di1uuption of the basalt is nne<]_ual hen t iu.2,· aml cooling. The climnte of the plateau today it; t;erni-arid, the min-fall ranging from ahout 10 incites annuall:· in the south-west to :20 inche in the northeaRt. Seasonal arnl amrnal temperature rnnges do not Y;1 rr much o,·e r the rt>gion. The presence of mm1~· mi11or \\·atcr eonrsc,- in the mature topography of the loess-<·on'n'd portions of the plateau irnlica ies a former he,ff in precipita iion hn t their spac-ini2: arnl d0gree of tle,·elopment show no more 11<>tc,rnrthy climatic tlifferences th roughout the nrea than JIOW exist. The rate of retreat of the cliffs therefore ]ins heen apprnxinrntely the same thrnughout the area dming- the Rame time. There liaYe hee11, of conrne, c limn tic find ua tions n ffect-iug the area as a whole since the denlopmt-nt of each group of chmrnels. Bui, so far as the ph)·siogrnphic record goes, such changes luwe not introclncetl different clominnnt factors in the <lestrnction of the cliffs. lnsola-tion and frost action l1cn-e remainetl in control. '1 he onl~· effect of con. eqnence has 1>00n to cliange the rair of wnstag·e of the Yerticnl faces of columnar hasal1. The cliffs of 1lte older ehmmC'l1-, ha,·e \\·,u·d Pc1 during an i11ter-gfaeial rpoch, a g-lal'ial L']><>C'h ([he 1Yisconsi11) arnl post-gfaeial time. ':Phe C'liffs left hr the ddinagr of the later epoch htlYe hrokeu down onl:· <luring post-glal'ial t inw. The rate of wastng:0 of the oltler ('liffs therrfore haR Yarircl nt clifferC'1ll tinws. Si11ee, ho,vm·er, then' i!-l no ,rn~· of detennining (hp changes in rntt', thiR i1Pm is ig·norecl in the solution of the 1>rohkm emrniclerecl in tl1is paper. Tt 1irohal>l~· woultl make hut little difference "·ith lhC' reRult. It seems safe, the l'Pf or 0, t o assume i lrn t (hat port im1 of fhe J)lat0an which hea r the P leistocene ri,·er eonrsrs lias not had J1ot0worthv climatic eonirnsis dctt>rmi11prl hY cliffen•1H·Ps i11 laiitn;le, aHitll(le or lll'oximit~· t o hnnrn1in g; highlnrnls si11ee these riYrrs flowe<l. Thrn' a r e thousarnlR of mil es of eli ffs fo m wd <l m in p: the <'n r li('l' epoeh arnl h nrnlre<ls of m il eR of cli ffs fonne tl or elen r r<l of talus dt>pos itR du ri ng· the Inte r epoeh. '!'he talus in 010 cl1a rn wls ahnrnlonrcl Riner 1hr Rpolrnnr C']lOC'h Rtan c1 s unifonn l)' nhoni threr l'onrtl1 s of t he total hPip:ht of 01 e ori e:inal eliffs ; tha t in the ehnrn1 els 11 se1l 1lul'ing the J II. Bretz-Age of Spokane Glaciation. ·wisconsin epoch stand uniformly about half lhe total height of the original cliffs\ The angle of repose in the talus piles lies between 3lr and 35 degrees. The post-Wisconsin talus is 35 degrees; the post-Spokane in some places is fully as steep, in others it is nearer 30 degrees. Among the cliffs of each group, there are exceptions to the ratios used in the following solution. But they are few and in most case seem adequately explained by exceptional local conditions.2 The problem may be stated as follows . Given :-(1) A region with nearly horizontal strata, uniformly possessing prismatic jointing, twice during the Pleistocene cr ossed by huge, short-liYecl, hig;lt-µ; rmlient riYers which eroded nearly vertically walled channels and canyons; (2) the retreat of the cliffs of these water-ways, with maintenance of nearly ver tical faceR, and accumulation of talus at their bases as tho only change of consequence in them since their formation; (3) the channels active during each of the two epochs identified by (a) the field eYidence of the glaciated areas, and (b) the greater accumulation of talus in the older channels; ( 4) tho talus in .the older channels three fourths the height of the original cliffs, that in the later channels half tho height of t ho original cliffs. T o find ;-the relative lapse of time since each glacia-t ion. The solution is based wholly on the ratio of height of tahrn to height of cli ff. To make a concrete prohlem, a Yer lical cliff orio·imd l>' 1000 feet high is taken, and talus fill s J<"l, J 1, %, 3-'f. %, % and % of this or~e;inal height arc assumed. Two factors whose numoncal values arc 'In some places the original structure of the basalt Yarics from the prevailing monotonous columnar joii!ting .. Ash beds, sconaceou. phases, ellipsoidal structures, prommcnt platmess m the columns, unusu~l size of columns; all are variant tructures. Subsequent stream '".ork 111 a few places has removed some of the talus, subsequent aggradatw,'. of C'ha111'.el fl oors in some places makes the apparent rat10 of talus hc_,ght to ('],IT height greater than the adual, winclhlown dust anrl sanrl "': one tract (D rumheller Channels, south of Moses Lake) has added consHlerably to tho talus acrumulation, anti sl<'cply tiltctl flows in an?ther pln<·c ,Clower Grnncl <:onlcc) havo appnren!ly 1ktenninP1l unusually rapHl growth ol talus. Al l these Yrtriants wPre C'OnsitlPrrrl <luring the fielrl sturly. The total mi leage of rlifl's drparting from the ratios usetl is. so small that the writN hcl ic,·cs the method of attar·k anti the conelus1on here reached as to relati,·e ages not to he invalitlatctl hy their existenre. ) ' J H. Bretz-Age of Spokane Glaciation. sought, enter into !he problem; (1) the amount of mate-rial in the talus for each stage, and ( :l) 1.hc m·erage height of the cliff face during the time consumed for eaeh stage. This time will Yary clirectl:- as the ,·olume orodccl and in,-ers<-1ly as the exposed aYerage face. ;< .. . . ... 1000 fe e t· . ... .... .. ... . > :<. :,:):) -r eet- ·· · · ~: .A . - - - - - - - - - - - - - -,------------..--J I I I I I tl1 0 1 11< .soo-h .. . .. .. '> I . I . I : I r., ---------- ·---~------------- "- ' I I '< 1 I I N :X urnerical solutions were obtained for the se,·en c1iffer-ent fills for three ca es.3 Case A-Angle of repose 30 degreeR, en( nncl fill of equal density; Case B-Angle of repose 33 degrees, cul mid fill of equal density; Ca. e C .Ang·lo of repose ;33 clegree., fill GO pen•eJl( ns cl en so as en t. 3 I am grratly inrkhte,1 to P,·ofpssor 0. <:. ClilTonl, of .\rmour lnslilnlc of Te<"hnolog~-, who has prnpos<•1l the assumptions 011 \\hi,·h th,• time rntios are ral1·nlak1l, formulate,\ the 111athematil'al prOl'e<lure nnd 111:1,l,• th~ ,·om-putations lwre presented. ,, I 11 I I 'i JI J II. Bretz-Age of Spoka11e Glaciation. J ll. Bretz-..:lf/1' of Spokane c:taciatio11. 3-!l To show the method used, case A is worked out in detail for a fill half way up on the cliff. Tu fi o·ure Fill TABLE I Area hlcan Exposme 1 let the orio·ina l height of the cliff he 1000 feet, and 13,..._;, 12000 8-191 ' :-, 1fs = 125' V •q. ft. Case A was soh·ccl for the heights shown in Table I let Ji be as shown, 1;,1, = 250' 5-!' 42000 766' x be the (li.stni1ee the eliff has retreated ,d1cn the % = 375, l2l' 80000 660' talus has acc11n111lated to half the original height of the ~:? = 50Q: 216' 122000 ~-~1: __ ~3; cliff, 'Is= 62u 3:37' 159000 " y be the horizontal distance between the presc11t cliff % = 750' 486' 190000 390' face and the lower margin of the talus, and Ys = 875' 680' 219000 322' z he the l10rizonlal di.stanee the tnlm; has extell<led As already stated the time i1wokecl in attainment of beyornl the original foot of the cliff. any stage of talus gro,dh will Yary directly a . the Yol-(1) lOOOx therefore = ,>00y :2 . , ume eroded and i1ffersely as the exposed aYCrage face. Since both 1000.x ~ncl 300)'/2 contam an are_n o[ ~Yerl_a~) . __ J. 122000 :12000 } -108000 .6760 = 16 ,1 = 500': 1252 which is mostly solHl roe k but partly talus i1ll, tills a1 ea t500 .t12o - 1 879 :56:~ - · may be ignored and _ Thus the time of one fill is to the time of another fill as (2). 500:s: + :s:hl_2 = (,)00-h)z/2 . . " ., .. , . , hY the squares of the heights filled. Tli~ relafrrn values of Smee angle of repose of th e fill is 0 0 de,..,i cc,;, then · t for the stages usecl in this computa hon a re as follows: trigonome~ry Ys = 125' = It 58 = 625' = 25t (:3) )'=-a00\l3,and 1;.'.;_=250'= -!t ~,.= 750' =36t (.J.) z-300\ 3-x . %=:37.3'= 9t 7;;= 875'=-t9t Frnm small triangle whieh is part of the croclPcl arc~ 1:? = 500' = 16t 8/,= 1000' = 6:lct (3) tan 30 degrees h /x, ?r h = tan 3o x, or h x \ ° Case B, in which the angle of repose wa taken to be Suhstituting fm; h ancl z m (2) - ;-;) 12 35 degrees and the cut and fill to be of equal density, (G) 300x+x~/2\ 3-(300\ 3-:s:) (.JOO-x \ hasthesamesoluiionasCaseAexceptthatian 33 takes Clea ring , ., the place of tan 30 . Table II contains solutions for (7) 1000.x +x~/:2\ 3 :230000\! 3 - lOOOx + x'\ " three heights of the talus under Case B. (8) 2000x = 2.)0000 \ 1 :3 Case C, in whieh !he angle of repose is taken to be (0) x 123\ :~ or :2JG feet. _ 35 degrees and the fill to he GO 11crrent as (lcnse ns the (10) from (:>) h xj-\/3 or 12.J fret cut, has io lHffe GO llOO area of fill taken to equal area (J1) _\.rca of e'ut or of fill=500(12,>\ :1) + 123 (l:23\ 13) of cut in the equation of areas for finding the Yalue of x. 2 or 12°000 ~q. ft. . Thus, for 11~ fill Since we arr here ronsiclcring· onl>' the pa_ri cle_posIIPcl .:;oox+xh/2=60/100 (500/tan. 33°-x) (;iOO-h) 2 in front of the orig·inal rliff fare and am ignoniig·_ ihe This wa. rompuiccl for the same three heig·hls of talu OYerlap arra (sec (1) ), th~ a,:crage cxposm:e or ~}.('!~ht used in C'aRc Ball(] the Yalucs of x, area arnl mean expoR-of the cliff far(' for il1l' l1aH height ,;tag·c of Lilns gi <n\ tli ure ohtainc<l are also shown in tahlc IT. is 300 + h /2 or 3G3 feel. 1 , p. fr .. 0 . C'lifToril foun,l that the eon tad. between talus. anil l,nriril ,]"ff'.: a'\/110 1,nr·thola. Jh <·n.kulus hr ohtains the nrl'a l<'ft fnn,letr tlw1 ' i i. , • : f i' l 1 . ·hn <T]c to "Pt tlw n rl'a o c·u • :n11 F ,·111·,·r, sniJtrn.ds tills , om t ,r " 10 c 're , ,. ,. .·' I f· . ' to g-rt the 'ill ,livid,•s this n,·,•a I>\' the distnn,·t' bn!'k from the o11g11t PX,t~~ed surl'·H·rs TABLE II Area A n C ill H(J. ft. 35000 2:;ooo 51' ,J J.6' 3q_9, 42000 lOJOOO 7~000 )fran l~xpo~ure ,.--A B C ifiW 7RW nYPr:t"<' exposed s1;rf:1c·e. Ynlues _of nrenst _rut an,\_.°, o·l;,tion l;rrr~\'itl; If, = 250' tl . ~1 t . e 1 liff,•r from those 111 tl,c ngonorne I H s . . 1/., - 500' Jl:.~:('11~;,t;\,'t ;lw ,·on'.poim,l r:iti1Js yit'l,l the snmc proport1011al relation ~ ~ 750, that is obtamecl by tngonometry. AM. Joun. SC'I.-F!FTn SERIES, VOL. V]II, No. 4fi.-0C'TOHE!t, 102.1. 2:1 157000 119000 !'Hi~' f>(i:~' 390' :mo· 216' l 7B.4' 155..J' 122000 680' 401.4.' 350.1' 190000 760' 5-16' 365' I :3+:2 J IT. Jfretz-Age of Spokane Glaciatio11. In cases B and l' the solution of the compound ratio for times shows tlla t for cnch case Urn results come out as in Case A. 'J'lie limes of fill are direclly proportional to the squares of /lie heights filled. IlaYing obtaine<l ihe ,;ame reRults for different angles of repose and for different densities of fills, it seems fair to assume that, though both enter into the distance cut back, these factors do not ,·ary with the ratios ohtained, whateYer their Yalues may be. The field c,·iclcnce irnli. Cates that their Yalues arc constant throughout the area. The application of the rule obtained to the physio-graphic problem of this paper giYes us a lapse of time Rince the Spokane glaciation (36t) two and a fomth times as great as i.lrnt since the Wisconsin glaciation (161 ) . Assuming that the '.Yisconsin glaciation of the nodhcrn part of the Columbia plateau is late \\Tisconsi11, aR the Yer~· strong morainic exprN,sion of its drift sl1ect r-:ng-gests, this ratio would make the Spokane µ;laciation cquiYalcnt to either the Towan or early \"\Tisconsin. The record of prodigious cimrntities of ,rntC'r <liRchargecl at the maximum of the Snokanc glaciation iR Yer~· unlike the record of Rlngg·ish Iowan ablation in i.he :.[iRsiR;;ippi Valley. On the othC'r hand, the Rcanty till deposits and total lack of terminal moraine on tl1e area co,·erccl hy the Spokane ice iR w17 unlike the early '.YiRccmRin drift.' If, and when. n clrfinitc ratio for earl-v and late:> ,YiRconsin and poRt-\YiRCOllRill time is oh!ainccl in the ;.[iRRiRRippi Valley. the Spokane glaciation may he conelated defi. nitcl>· in the:> accrptcfl Rchcmc. University of Chicago, Chicag-o, Ill. ' 'I. 1e I l~im~l/1 /II II m /1 I I I I 19 220581 (O!j_-CIRCULATING Spc: Ctosro • • 4 ~-' .1t ~1ul:Jm~G SpC NO,, . i .1 1 G QE176 Bretz S7B7 The age of Spokane glaciation 

Age of the Spokane glaciation

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Age of the Spokane glaciation

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