stream_lab - Stream Processes, Landscapes, MassWastage, and...

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Unformatted text preview: Stream Processes, Landscapes, MassWastage, and FloodHazards .CONTRIBUTING AUTHORS. Pamela J.W. Gore. GeorgiaPerimeter College Richard Macomber.LonglslandUniversity-Brooklyn W. CherukupalliE. (CUNY) Nehru. Brooklyn College OBJECTIVES A . B . . r l r l ( . t ( )u \ ' l { ) } n i r r . r r . n r , r f , . r n r l \ t r r ( o t F r i n r , l t , ( l f . . r r l ' , r f d I n l . 4 ) r r r\ t r r . r n r \ , r n dh . \ . 1 1 . \ . h l p . \ . ( h r n n e l . r I r r s L . r t i . n \ .d r . r l n r s . p n l l . ' r ) \ , , rr rr i l l r ( , . r o s i o n . r l . r n ( l \ i f r , . r d def(isili()rr.rl itLrr.5 thr\ o..rtf lr B. Lnrl.r.l,rn(l rrLNi(n.rlin,l nr,r,,s,rn.rr. P r ( r i \ { \ i h . r t(\ . u r . r t \ i , r ! . 1 , r l , r l l , .. r n , l b f a b l e r , )r \ . r l u r l . f u h \ i r \ h i Lh l h f r , r l l , i , r f t r r , r l ilr! C . B c n l ' 1 . 1 , ,n r i f i n J n i i r : . t h t r ' \ t r n r , , r r l ( ! \ l h.,/nr1. il(inI lhf l Lui lti\ f r,(;(\rgr,r 1\l{nD . ^ ( - r r , l r l f l . h r l , r t . . r ( r rr n r i ) f t r r , r l r o.n t . ( \ r lr h f r \ l l l l h t r \ l \ ) f r . f i r u t o r ' l ( r \ i , . . r n d \ h . r tt o d , , i i \ ( \ r , r r ( . . r L r r l r li n i t l o r n l,i,r,,i r/,r Ih.str{,rtrr.Nill{{nlinLrckr ,lo\ lot.r\ long r\ lhr\ rc.ei\..r snt(r \uptl! Ironl r d d L t r { r r irl i i n . n r (l l i n g r n L \ \ ., , r l , ^ , r l , } , r . r c u n ( ] \ , 1 i[ l f r t h i r l \ { p ( i n l L ,, r \ t r f . r n 1\ r . rf ( ! 1 \ , . r \ 1 , . r f n . l L r r r , / ' r ' r , r I r , r li i r i , r r r . 1 \ \ n r L r r JIl .i I u n s . i ) t l ( \ i . o n i ) L r . u r l \ l h f o u r h , i Ut l \ r , f . ! / r j r , r r | l / , 1 , r , 1 , , , rr r r g l \ t 5 L r r e f-. ) t l ( n \ r n r l \ , r l( e r i . l i nl i n r r \ ( , i l h f \ . i r . s u . h . r , ||rn\ \',r\if. ('f \ l)(!r,nos ' rrl t tn 'l n,r But .rll r f r . , . l n l ' h . r \( , t l r ( l \ i t u r t i r l h i f l o o d ( ( ) \f r r l L t r \ t h e r r h . f f . i r I l t \ \ j , r l n n r r L cm o r r h n r . r r r r { ) l \ , r t \ j n t l r . f 1 ,r,. -'ir '. 1., r\ ,,r,. , .1../..1 5 i r r r n r \ n f L , r l \ 1 , h r : i n . r l . r r r { N tr n f { i n . r n t n i i t . r L r r ln g r . t ( i i r , r r J , i ' 1 r , , r i s r , I r A i s . r \ ( n t h t n r L t l I h . ' \ . n \ l r n r ( ) n , \ l i n r i r t I n ' | r l h . l , I r r l t h . r n\ \ n ) d , ! g l a c i r r . r , r o r e . r | rr , r r r . . T h . \ \ l i n r . n l i \ r r . r n s N r l r t l . r r r dr \ e f l r i . r l l \ ! l r f r \ i n l \ h . i ( a r l 1 L nr t r \ . . r l l d a l l u , \ i u n r . \ i l u \ r u n r\ r ! r , i , t . o i S r l r \ . 1 . , r n ( 1 . ' r l t . . l n d . l . r \ r l e p o . i t c ( l1 n i l ( \ \ l f l . r i n \ , f o r n t l r , r r \ .( h . r r n c t r r a r s . d f l i . r . , r f d . r l l u \ r . r lL r f . l f r s L i f . s I I I h t r . n , r . . , t r , , r n rl r c . r . r * r r r t l r r .r.r1I ,,i ., . ; : , . I . r t f r r n ( ! r s t h . I r r N i r n r p o ' 1 . r g ( f l \ t l r . r l\ h . r p c L n f i h \ \ r f i . r . f l r r ( l I f u s e d i n r , r $ . t { )h ' r n . r n s . r n d MATERIALS l ' r f c i l , r , r n \ . r ;l . b o r . r l r ) 1 1 o n , l n r i k . I r j l r r t ( n l f u l i t o r , l: in.h lenrlh (n \trif{. rnd f(\ k.l ,t.f.,N!.r)|(, INTRODUCTION Il.rllsln .\lth.r!rrrI m m d r ( j f t h L r r i . ( j t h . ri n , ] r n o l h e r \ \ s . r l ( J , l ' r ' n ! h r , rt h . l . I r ( l ! , r f . . n r n . \ r l \ r n t o t h e g r o L r n (.l r n , l b . L r ) r n . ' s, , { r , r / , n r / , l l , ) l ) ( ! I t o r \ t | -., ' t1.,.\.,\i,t' r1..r'.1'.r,'.,. , ,-,., PART STREAM 1: PROCESSES AND LANDSCAPES It.rrll n trnr.r lr.f \,)r pcrro|.rll\\ itn.\\\l .r drrr hjru f.rlnn('fnr \{herr'Lli(1 thc $.rtercol ,ril llurin{ (lf.rr hln* r.lnrlornrt..L)nrc th. $ rrtr ,i' 175 176 . taboratotyren patterndevlopson conicalhills, suchas volcanoesand somestructuraldomes. . Annul.r pallem-re5emble5 serie5 in(oma of plete concentric rings of streams. This pa$ern developsin beltsof easilvweathered rock of structuraldomesand basinslike thoseillustrated 9.11. in Figure seps slowlv into the ground. But most of the water flows over the ground beforeit can seepin. It flows over fields,streets, and sidewalksa5sheets water of severalmillimetersor cenhmeters deep.This is called Sheetflo('movesdownshpe in response the to pull of gravity,so the sheets water flo$' from strts of and sidewalksto ditchesand streettutters. From the i'ater flows downhill ink) ditchesand storm swers, small streams. Small streamsmergeto form larger largerstreamsmergeto form rivrs,and streams, rivers flo$ into lakesand oceans. This entire drainage system,from the smallestuplnhd strcams(headloalerc), to larter streams(hirulnfies),to the la$est river (r,nin str.ant nLain or riL,er), calleda stramdrainagesysis tem (Fiture 10.1A). Drainage Basins and Divides The entire area of land that is drained by one stream,or an entires[eam drainagesystem, calleda drainage is basin.And the linearboundaries that sparate one drainagebasinfrom anotherarecalleddivide6. Somedivides are easyto recognize maps as on ridge crests. Hoi{'ever,in regionsof lower relief or rollinS hills, divides are more like narow strips of land that di(ide on gentleslopefrom another For this reason, divides cannotalwavsbe mapped as dislincl lincs on maps. fhey are.'ftcn reprsentcd by dashedlines. You ma], have heard ofsomcthing calleda ronii n.rldl dti,ide, rvhich is.l narrow strip of land dividing surfacwaiers that drain in oppositedirectionsacross th continent.The continentaldivide in North America is arl imaginarv line along the crestof the Rocky Mountains.Waterthat falls eastof the line drainseastwandinto the Atlantic Ocean,and water that falls west of the line drains westward into the Pacific Therefore, Ocean. North America'scontinentaldivide is sometimes called "The Creat Divide." Stream DrainagePatterns Streamdrainate systems form characte stic patterns ofdrainage,dependingon the rlifand geologyof the land. The commonpattemsbelow ar illustrated in Figure10.2: . Dendritic pattem-resembles the branchingof a tree.Waterflow is from the branchliketributaiies to the trunklike main streamor riYer.This pattem is commonwhre a streamcuts into horizontal layersof rock or sediment.It alsodevelopswhere a stneam cuts into homoSeneous rock (crystalline igneousrock) or sediment(sand). . Distributary pattem-resembles radiating branches a tree.Waterflow is from the trunkof like main streamto many small tributariesthat neverietum to the main stream. This pattern is typically developedat the mouth ofa rivet lrherc it forms a delta or alluvial fan. . Rectantularpattm-rsembles a network of intrconnected rectanSls squares. and This pattem often dvelops over rocks that are fractured or faulted in two main directionsat nearly dght (and breakthe bedrockinto rectanSrlaror anSles squareblocks). . Trellis pattem-resembles a rosetrellis,where parallelmain streams intersected nearly are at right antles by their tributaries. This pattrn commonly developswhere a river cuts through a seriesof ridgesand valleys. . Radial pattem-resembles the spokesof a wheel. Water drains from the inside of the pattem, where the "spokes"nearly meet,to the outsideofthe pattem (wherethe spokesare farthestapart).This Stream Weatheling,Transportation, and Deposition Threemain processes at $'ork in every stream. are W?irlldli,i.q occurswhere the streamphvsicallyerodes and disintegrates Earth materialsand where it chemi cally decomposes dissohesEarth materialsto form or sedimentand aqueouschemicalsolutions.T/rrspola tio, ofthese weatheredmaterialsoccurswhen they are dragged,bounced,and carried(assupended grainsor chemicals the water) downstream. in Deposi lio, occursifthe velocityof the streamdrops (allowing sediments settleout of the water)or if partsof to the streamevaporate(allowing minral crystalsand oxide residues form). to The smallest valleysin a drainagebasinoccurat its highestelvarions, uplan&.In the uplands,a or stredm\ pornt of ongln, or had,may be at d sprintor at the startof narrow runoff channels developed during ninstorms. Weatherint is a dominant process here, and the stream channelsdeepen and erode uphill through time, a process calldheedwardero8ion. k r r F F r i atsnlrrt . P L : \ r , r ; 1!, E i l F r r Nd,rou bon..rP.l .--.-- F SYSIEM ''. '. '-; ,k .11 FLATBOTTON']LVALLET L] \1 IN I,IEANDEF STFEAi,I NG CHAt!\EL F. ,'i, ,I I . -._i -:-- ILTlTBOIIOI"JED VALLEY !.,]TH BI-]A DED !d\\r r\rlf.'a\ OIFFI OAD . Etdd r 'I Alwun Foodl - F I G U A E 0 1 G e n e r a l z e c h a r a c t e rl c f e a t u r e s i s t r e a m l r i i a g e s l s t c f r : s 1 r e a f i ra r d s l r e a n l i s o c s. c h a n n e l s . r r o w sn d c a i e c u r r e n l i o w n m a i n s t . e a m c l r a n n e sA F e a i L r r e s a s t r e a m . l r rr r a ( . A ol system B-Stream channe types as obserled n rrrap! evi C Featlres or r nrearderfg st,{nr !a e y D - F e a l l r e s o f . l y p c a l b r ad e a s t r e a m B ' : d e d s l r e a m s i . r e o p . s e d n F r r . f o ( . . j S i r . r r . s . 177 ".1 valley.Along the h'ay,somne$' materialsareweatheredand depocrts form tcmpordril). th( main bur process i{'ork is transportation. at The end of a river valley is the mouth of the river, where it entersa lake,ocean, dry basin.At this locaor tion, the river water is dispersed into a wider area,its velocitydrops,and sedimentsettles ofsuspension out to form an alluvial deposit.Ifthe river water entersa dry basin,then itwilevaporat and precipitate layers of mineral crystalsand oxide residues. RiverValley Forms and Processes The form or shapeof a river valey variesraith these Ceology-th Seologyover which the stream flo$ s affects the stream's ability to find or $'eatherits course. Gradient-the slopeof the sheamchannelalonSa lengthof its cou6e. CradientSenerally is selected rI.easuJed feet per mile. For example, if a stream in descnds feetover a distance 40 miles,then 20 of its gradientis 20 feet/40 miles,or 0.5foot/mile. You can estimate the gradient of a stream b), studying the spacing of contolrs on a topo8raphic the map. Or you canpreciseltcalculate exact81adient by measuring hoiv much a stream desends along a measured segmentofits cours. \ \\// \ ,,' Baselevel-the loi{'estlevl that a streamcan theoretically erode.For example,baselevel is achieved ra'herea stream entrs a lake or ocd. Al lhal pornl iheerosional poserof thestredm rzeroand depositionalprocsses occur. Discharge-the late of steam flow at a giren time and location. Discharyeis measuredin u'ater vo1um per unit of time, such as cubic persecafi,]. lect Load-the amorntof sedimentthat is transported by a stream.ln the uplands,most stramshav relativelysteepgradients, the streams so cutnar' valleys.Near the headrow-bottomed,V-shaped waters,most sheamscarry only a minor load. Tributariesand the main nver transportthe loa.l. The load is depositedat the mouth ofthe river, whereitenters a lake,ocean, dry basin. or From the headwaters the mouth oIa stream, to the Sradientdecreases, discharSe increases, valand lys generaly widen. AlonS the wat the load of the the streammay exceed abilit) ofthe water to carry it and accumulate sdimentary as depositsalont the dver margins,or banls. Floodplainsdevelopwhen alluvium accumulats landward of the river banls, during floods (Figurs10.1A,10.18). Floodint also may erodethe valley walls. I .-/a --:\_ r" t\ ;l l'\ *uoi", \ patlerns in FIGURE 10.2 Slream drainage observed map (ae al)view. Streams alsoweathertheir oh,n valleysalong weaknesses the rocks(fractures, in faults),solublelayers of rock (saltlayers,limestones), where thereis and the lcast resistanceto erosion and abrasion. Rock comprisedof hard minerals(Figure2.16)are generally more resistanito erosionand Iorm ridSesor other hill tops. Rockscomprisdof soft mineralsare generally less resistant to erosion and form valleys. Headwatervalleysmr8einto laer tributary vallevs.and the\e e\ entuall) merte into d larger ri! er 174 J! ,'i I 36". FIGUFE10,3:Lake Scoll Kansas "1 l:24,000 -_ !a:: _ _/: -i 1,4 ,'"" LPI 4 1., . 3 .l :tl 5 4 :[ 15 T4 -],, B E AVER '- 23 r ++ __- - *,*- *, !-r',rsu$r6sJF*qstNskllt(tN)lt::-Jx I l{re Strcan Pro.esses, Ldflils.apes, Mass Wostage, anil Flood Hazads . 179 n ! Still farther downstream, gradientdecreases the evenmor as discharge and load increase. The stream valleysdevelopvery wide, flat floodplainswith sinuous channels. These channels may become highly sin(Iiguresl0.lB. C). Erosion uous. meandering or whi<h dre o<curson lhe outeredge;f meanders, calledcutbanks.At the sametime, point bardeposits accumulate along the inneredge ofmeanders,Proerosionof cutbanksand deposihonof point Sressive ba$ makesmeanders"migrate" over time. Channels may cut new paths during floods.This can cut off the outer edge of a meandet abandoning it to becomea crescent-shaped oxbow lake (Figure 10.1C). When !ow-gradient/high-dischaestreams become overloaded with sediment, they rnay form braided streampattems.Theseconsistofbraided channels wiih linear underwatersandbaE (channel bars)and islands(Figures10.18, D). Some stream valleys have level surfaces that are higher than the present floodplain. These are remnants of older floodplains that have ben dissected (cut by younter streams) and ar calledstreamterracs.Sometimesseveral levels of stream terraces may be developedalont a stream,resemblinS steps. Where a stream enters a lake, ocan,or dry basin, its velocity decreasesdramatically. The stream drops its sedimentload, which accumulates a triangular as or fan-shapd deposit. In a lake or ocean,such a depositis calleda dlta.A similar fan-shaped deposit of streamsedimmtalso occurswhere a steep-Bradient stream abruptly ente6 a wide level plain, creating an alluvial fan. c, The mudstonebedrcckof theseuplandsis overlainby alluvium (sandand gravel)that was deposited about 10,000-12,000 yearsagoby streams draining from meltint glaciers (prior to diss(tion of the surface as it appeaG today). It G the upper surface of this alluvium that has the attitude describd in a and b above. What is the probable source area for th water and sdiments that formed this alluvial deposit? Explain your reasoning. (Hirlj Kansasis just east of the Creat Divide.) 3. Reconsider uplandsand upland alluvium disthe cussedin Question2- The extensive sheetof upland alluvium was probably depositdby braided streams(Figurcs10.1B, D). a. l\fhat drainagepattern shown in Fitur 10.2is currently develoPed this area? in b. What doesthismodem drainagepattem sugBestabout th attitud of bedrock layer (the mudstonebeneaththe upland alluvium) in this area? Explain your reasoning. 4. Examine the landscape of the Waldron, Arkansas quadrangle(Figur10.4). Wlat drainagepattem is developed in this arca, and what does it sutgest about the attitude of bedrock layers in dris area? Explain.(Hirt: Referto Fi8ure9.9and 9.11.) PART STREAMPROCESSES 2: AND LANDSCAPES NEARVOLTAIRE, NORTHDAKOTA Refer to the Voltaire, North Dakota quadrangle (Figure 10.5) and stermgram (Figure10.6). Qlrcstions 5. Glaciers (composedof a mixtur of ice, gravel, sand, and mud) were pEsent in this region at the end of the Pleistocenelce Age. When the glaciers melted about 11,@12000 years a8o, a thick layer of sand and gravel was deposited on top of the bdrock and sbeamsbegan forming from lhe glacial meltwater. Therefor,streamshave been eroding and shaping this landscapefor about 11,000-12000 years.Notice how well developed the meanders and floodplains lhe SourisRiverare. of The landscape around lake Scott, Kansas (Figure10.3) about the sameage (i.e., is 10,00G| 2.000yearsold). What factorsmight explain the differences in form of the stream valleys of this region and the Lake Scott region? Qlestions arecontinud on page186. Questions 1. Referto the topographicmap of the Lake Scott quadrangle, Kansas(Figure10.3). e. Draw and labela dashdline on this map that is the divide betweenBattendorfCanyon(NE% sec.9) and the smallercanyonthat runs from the SWZ sect.9to the "B" in the word "TIMBER" (ha]Jmile north of the center of sec. 16). b. Draw and label a dashedline at the boundary of the Garvin Canyondrainagebasin. 2. Notrce that th upland surface of the Lake Scott, Kansasquadrangle is not horizontal. a. In what gneral direction does water flow over the upland su ace? b. What is the gradient of this upland surface? (Showyour mathematical calculation.) 10.5: Voltate, FIGUBE NonhDakota 0 A Yl .5 Y? 1 k lometer 1 mie 1:24,000 Conlourinlrual= 5 fl. J( a. ,,0 i-'{[ ffi t4, 'r\.: 4 --,..5-,:- ...."/ /l 7 i4 fi if, i;r )ii; 1 E FIGUFE 0.7: .n s Monlana 012 t 1:62,500 ,. Contolr nterual=4011 it"... 23 I I*' 1,.' 1,5 "'i.-r i ,t ! '. @ . . . -., i' l ,69\.. il' I .I '' 1 .L : "':. 1- 186 c tabotatoty rea Questiotrs 13, What was the sourcof the sdiments that have accumulated the CedarCrcekAlluvial Fan? on 14. What is the approximate stream gradient of: r. The main stream in the foFsted southeastern comer of the map GiSure 10-7)and stereogram (FiSure10.8)? b. Most streams on the Cedar Creek Alluvial Fan? c. The Madison River? 15. l,Vhat drainage pattems (shown in Figure 10.2)are a. The forested southeastem corner of the stereo8ram (Figure10.8)? b. The CedarCreekAlluvial Fan? c. The valley of the Madison River (northwestem portion of Figure 10.7)? 15. How are the stream gradients and drainate pattems described above(Questions and 15) 14 related? r7. How did the CedarCreekAlluvial Fan folm? l l' t: 6. On Figures10.5and 10.6, note the swampy (hachuredcontours oxbow lakesand depressions on Figure 10.5) the SourisRiver floodplain. in Theseshow that the river channelhas changed courserepeatedly. Explain how itscourshas chanted at the oxbow just eastof Westgaard Cemetery(northeast map center, of NE%sct.3, Figure 10.5). 7. Do the hachured contours and other oxbows of the SoudsFjver Valleyshow that this same process occurredelsewhere has along the valley? If so, then suggest one location. 8. What is one locationalong the courseofthe SourisRiver where the samethingmay happenin the future if the course of the channel is not controlled by entineers? 9. lmagine what the topographicprofile look like along X-X'. (Referlo the.tereogramin Fiturc 10.6to help you with this.)Notice the relatively flat areas ofthe profile such as thosein Sw%sec. 33 and SEk sec.4(Figure10.5). a. What are thesefeatures called? b. How did they form? c. How could vegetationbe used to map the lo.ation of the modem floodplain? 10. In SE% sec.3(FiSure10.5), streamtrends a northeast-southeast. What is the name ofthis type of streamand how did it probablyfom? q ll. Notice the marsh in sec. and the depresrionon PART STREAMEROSION 4: AND MASS WASTAGE AT NIAGARAFALLS Mass wast4e is the downslope movement of Earth materials such as soil, rcck, and other debris. lt is comrnon along steep slopes such as those created wher rivers cut into the land. Somemass wastage occu6 along th steep slopes of the river valleys. Howevr,masswastagecan also occurin the bed of the river itselt as it does at Niagara Falls. The Niagam River flows from Lake Erie to Lake Ontario (Fi8ur10.9). The gorgeof the Niagarapresnts Sood evidence of the erosion of a caprock falls, Niatara Falls(FiSure10.10). edgeof the falls is The composed of the resistant Lockport Dolostone. The retreatof the falls is due to undercuttingof mudstones that support the Lockport Dolostone. Water cascadinSfrom the lip of the falls enters the plunge pool with tremendous force, and the turbulent rdater easilyerodesthe soft mudstones. With the erosionof the mudstones, the Lockport Dolostone collapses. Questions 18. Geologjcevidenceindicatesthat the Niagara fuver beSan to cut its gorge about 11,000 years ago as the Laurentide lce Sheetreheated from the a .' !i i t c ,' which il is lNated.WhatEas thisdepression beforeit became marsh? a 12. How might the discharge ofthe SourisRiver have chanSd over the past 12,000 years? Why? t, , J PART STREAMPROCESSES 3: AND LANDSCAPES NEARENNIS. MONTANA Somerivers are subjectto larte floods,either seasonal orperiodic.In mountains,this flooding is due to snow melt; in deserts is causedby thunderstorms. it During such times,rivers transportxceptionally largevolumesof sediment. This causes characteristic features, two ofwhich are braided(anastomosint) channels and alluvial fans.Both fatures relatively are commonin add mountainousregionssuch as the (Both Ennis,Montanaareain Figures10.7and 10.8. features also can occur wherever conditions are ri8ht, even at construction sitesl) "t .t L { t\ I r , I \ I F Str.,r' r'lo..sns, Ldrds.,r/es,.lrass tlhstuS., atrli Ilootl Iti:tltls . 187 Sh8b(Bo*n) 0r MA. RABIVER GOAGE g 2 b 3 6 'T 250 FIGURE10.10 Schematicof NiagaraFallsand geologrc unrtsoi the N agara escarpr.ent. PART FLOOD 5: HAZARD MAPPING, ASSESSMENT, RISKS AND The watcf lc\ cl and disch,rrge n rivcr fluctuntes of from da) to da), rlcek to $ cel, and month to nonth. Thcsechanges mensured a.e at.{irsnrs slirlrrrs,l\ith a permancntsttcrlevel indicat()rand rccorder (h.l t\,picilAugustdav in do$ ntovlnSl. Louis,Missouri, the MississippiRiler normallv hasa dischi rge of .rbout 130,000 cubic fert of rvatcrp('r s('cond and 11'nter levclsrlcll bclo$ th('bont docksnnd con.retc (retnining i, r,rrs w.rlls). FIo{e\ or at thr penkof an historic le93 flood, tho rivi'r discharge.i mr)rethan I million cubi( fectof waii'r pcr sc.ond (eight timcs thc no|n,ll amount),sseFt awav docks,and rcachcd i!.rter levelsat thc very ed8of thc highestle\1es. When the \\'at('rli\el ofa ri|cr is b.'lot\ th. rivcr's banks,the river is at a normal stag.When the $.rle. l,a ul * u\ en h rtl. thr bdn}., rl-Ffl\ c' r- .rl bankfull stage. And $ henihe watrr lc!elex.crd\ ( erflows)tho banks,the nvcr is ai a flood stag. E,rrh in Iuly 1991, TroFicalStorm Albcrb ortered Ceorgiaand r.'mainedin a fixc(t position for sc\cral d.ys. Moro thnn 20 inchesof r.rin f(,ll in southeasturn C(.orBi.o\er thosothr('ed.r\'sand causedsevcrc fl(x)dnrgalonSth.' Flint and OcmulgecI{ive.s.Monlezuma rvnsonc of thc to\^,ns along ihc Flint lti|cr' ih.rt r!.ls floodod. FIGUnE 10.9 Mapof the N agara Gorge reglon oi Canada the Un(edSlaies. and area.It startednt ihe NiagaraEs(arpment(li'Bur(' 10.9). Dascd this geochronohgr ind th lcngth on o{ the gorgc,cnlculate a\erager.rteof falls the rcrrcar cm/\'car. 'n 19. Nnme somc fa(tors thnt could .ius. th. falls h) reireatat n task r rate. 20. Nnme soniefacbrs that could c.use th fdiis to rctre.t morc slowll: 21. \iagari F.rllsis ab('ut3; knr north of Lakc F.ric, and ii is rctreatinS south$ard. If th( falls t{erc kr continueits retreatat the avrrag.' calculaicd in Question18,hos miny yearsfrom nos ilould thc falls re.rch l.akc Erx ? I r: r r r r r r ,i- F r r @ I tr r r.o 'p'' dd\L'd ' L.'Po i. lr I F I G U B E . 1 0 M o n o cn e . N o t a i o d s r a l e t ! . r o m b s 9 T h e m o n o c n e s a t o d n c r i n e dn o n t o n e d r e c to n A r a t en v o n e a r y h o rz o n t a m b s f r o ma m o r es t e e p r y nc ned nrb. Note the symbo s lsed to nd cale honzonta strata (rock ayers rornralonsi. F F r r r r r F r L_--....-- FIGUBE9.9 P uforng iolds. A-Belore eroson B ue imag nary p a.e s lne haxzantaldatutnpta.e, irom !r h ch a I dala are measlred B-Afier erosoi Erocledp ung,ng fo ds are erposed ai the and surlace Not ce the oltcrop p a t l e r n s l l l r el o d s a n d l h e s y n r b o t h a l h a v eb e e nu s d o s r: tr FIGUnE9.11 Dome and bas n Bolh of these struciuresare bow shaped n three d mensons a n d a p p e a r a s r e a l v e y c r c ! a r " b u l l s e y e p a l t e r n s n m a p s A - A d o m e s c o n v e xl b o w e d o upward)and has lhe olcleststrata n ts center B-A basrn s concave(boweddownw.r.l) :rfd has the you.gest strata n ls center 167 ...
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This note was uploaded on 04/17/2008 for the course ERTH 1020 taught by Professor Joepyle during the Spring '08 term at Rensselaer Polytechnic Institute.

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