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RiverTerraceMappingofRushRiver,Sibley
County,MNBy
KylePinke
Athesissubmittedinpartialfulfillmentoftherequirementsforthedegreeof
BachelorofArts
(Geology)
At
GUSTAVUSADOLPHUSCOLLEGE
2017
RiverTerraceMappingofRushRiver,SibleyCounty,MN
ByKylePinke
UnderthesupervisionofProfessorLauraTriplett
Abstract
Approximately10,000yearsago,GlacialRiverWarrencarvedoutthemodern
MinnesotaRiverValley.WhentheMinnesotaRiverlateroccupiedthatvalley,it
workedtoachieveastateofequilibrium.Duringthisprocess,thefeaturesofthe
riverbegintoreflecttheamountofwaterandtheamountofsedimentbeing
transported.TheMinnesotaRiver’stributariesinturnrespondedtothenewbase
levelofthedeepenedMinnesotaRivervalley.Thetributariescarveddownthrough
thesubstrate,producingterracesthatwereleftbehindhighonthestreamvalley
walls.RushRiver,about3milessouthofHendersonMN,isonesuchtributary.In
thisstudy,threeseparateterracelevelswerelocatedandmappedwithintheRush
Riverravine.ThemappingoftheseterracesalongtheRushRiverValleycantellus
aboutpastevents,likethetimingofbaselevelchangesoftheMinnesotaRiverorthe
GlacialRiverWarren.Theterracescanalsoserveminingandexcavatingcompanies.
Bymappingtheseterracesandnotingtheirconsistency,wecanhelpcompanies
determineiftheareaisworthexcavatingforearthmaterialsforconstruction
purposes.
Acknowledgements Iwouldliketothankallthosewhocontributedtheirhelpandguidanceforthisproject.Dr.JamesWelshandDr.JulieBartleyforintroducingtheideatomaptheterracelevelsandtheirinputthroughoutthelengthoftheproject.ThankstoDr.LauraTriplettforassistancewithfieldworkandforherinputwithmappingandespeciallythewritingportionofthisproject.IwouldalsoliketothankRussKruegerforhisassistancewithArcGISprocesses.
IwouldliketothanktheGustavusAdolphusGeologyDepartmentforprovidingmewithadequatetoolsforfieldwork,andthetechnologyneededtocompletetheproject.
ThankyoutomyparentsforgrantingmethegiftoflifeandalloftheopportunitiesthatledmetodevelopintowhoIamtoday.
ContentsIntroduction…………………………………………………………………………………pg.6
GeologicSetting……………………………………………………………………………pg.10
WatershedCharacteristics……………………………………………………………pg.11
ResearchMethods………………………………………………………………………..pg.12
Results…………………………………………………………………………………………pg.13
Discussion……………………………………………………………………………………pg.21
Conclusion……………………………………………………………………………………pg.23
References……………………………………………………………………………………pg.25
FiguresandTablesFigure1………………………………………………………………………………….pg.6
Figure2………………………………………………………………………………….pg.7
Figure3………………………………………………………………………………….pg.9
Figure4………………………………………………………………………………….pg.14
Figure5………………………………………………………………………………….pg.16
Figure6………………………………………………………………………………….pg.17
Figure7………………………………………………………………………………….pg.19
Figure8………………………………………………………………………………….pg.20
Figure9………………………………………………………………………………….pg.20
Introduction
Attheendofthemostrecentglacialinterval,GlacialLakeAgassizcontained
enormousvolumesofglacialmeltwater,trappedagainsttheretreatingicesheetto
thenorthwest(OjakangasandMatsch,1982).Whenthemorainedamcontaining
thelakefailed,thereleaseofwatercarvedachannelandcreatedtheGlacialRiver
Warren(Figure1).GlacialRiverWarrenistheancestoroftheMinnesotaRiver.
OvertimeGlacialRiverWarrenanditstributariescarvedthroughtillintobedrock,
creatingawidechannelandassociatedfloodplains(Johnson,1998).
Figure1.GlacialLakeAgassizwithaSouthernoutletcreatedbythelossofanaturalicedamdrainingwaterwhichcreatedtheGlacialRiverWarrenwhichisthepresentdayMinnesotaRiver.(TheInstituteforMinnesotaArchaeology)
RushRiverislocatedinSibleyCounty(Figure2.)about3milessouthofHenderson,
Minnesota(Figure3).Theriverisestimatedtohaveformed10,000yearsagoafter
meltwatersfromtheLaurentideIceSheetformedLakeAgassiz.Whenthelake
brokethroughanaturaldam,amassive
outflowofwater–TheGlacialRiverWarren–
carvedthelandscapeofsouthernMinnesota
creatingahugevalleythatwasultimately
occupiedbytheMinnesotaRiver(Fisher
2003).Whenwateraccumulatesinuplands,
itwillflowtothelowestspotpossibleorbase
levelduetogravity.Thebaselevelofariver
isthelowestpointtowhichwatercanflow.
Forexample,iftherewereaperiodofmassive
amountsofflowintheMinnesotaRiver,more
andmoresedimentwouldbemoved
downstreamcausingmoreincision.Inturn,tributariestotheMinnesotaRiver
wouldalsobegintodown-cutandinciseinresponsetothebaselevelchangeofthe
MinnesotaRiver.Thisperiodofincreasedincisioncouldthenberecordedby
terraces,whereinformationaboutpasteventscanbeobtained.
Terracescomposedofsandandgravelareremnantsofformerfloodplains;
theymanifestgeomorphicallyasstep-likefeaturesattheedgesofrivervalleys.
Becausebaseleveldroppedastheriverinciseditsvalley,highterracesaretypically
Figure2.SibleyCountyhighlightedinred.
olderandtheyoungestterraceshavelowerelevationandsitclosetothemodern
riverchannel.Overtimeaswaterfloweddowntributarystreams,headward
erosionlengthenedtheravinesupstream,eventuallydevelopingnewtributaries
andravines.WhenGlacialRiverWarrencausedlocalbaseleveltodropthese
tributarieswouldsimilarlyhavecutdownward,leavingterracesattheedgesof
theirpaleochannels(Bock,2010).
OneexampleofatributarywithterracesisSevenMileCreek,atributaryto
theMinnesotaRiverthatislocatedabout5milessouthofSaintPeter,Minnesota.
Thatcreekanditsravinesystemhavebeenextensivelystudiedinthepastand
presentinhopestobetterunderstandissuesofhydrologyandpollution.Thisarea
ofMinnesotaisheavilyusedinagriculturesoissuesofsedimentsuppliesandrunoff
fromfertilizersmakethistributaryafitcandidateforpollutioncontrolstudiesin
ordertolearnmoreaboutwhypollutionandsedimentsuppliesaresoheavyinthe
Minnesota
River,MississippiRiver,andultimatelyintotheGulfofMexico.RushRiver,located
inSibleyCountyabout3milessouthofHenderson,Minnesota,isananalogous
systemtoSevenMileCreekalsoleadingintotheMinnesotaRiver.
TheRushRiverareahasnotyetbeenstudiedasextensivelyasSevenMile
Creek.LocatingandmappingriverterracesatRushRiverwillopenawindowinto
Figure3.ShowsthelocationofHenderson,MNinrelationtoRushRiverandtheMinnesotaRiver
thepastandgiveusknowledgeoftheevolutionofthetributaryravinesofthepost
MinnesotaRiver.Riverterracesareimportantlandformsbecausetheycanprovide
depositsofaggregateusedforconstructionpurposesaswellassanddeposits.They
canprovideinformationabouthydrologyforfloodmanagementandplanning
purposesaswellaslonger-termenvironmentalchangesdrivenbycombinationsof
climateandanthropogenicchanges.
InBock’sthesisaboutSevenMileCreek,hewrotethatweneedtoadddata
fromotherravinesmuchlikeSevenMileCreek(2010).Iwishtoaddtothedata
collectedbymimickinghisstudyatRushRiver.Then,thetwotributariescanbe
compared.
Overthecourseofthisstudy,usingmethodsfrompreviousstudiesofriver
terraces,ImadevarioustripstoRushRivertolocateterracesandconfirmtheir
compositionsinordertomapthevariouslevelsofterraceswithintheRushRiver
Ravine.
GeologicSetting
WhenglacierscamethroughthisareaofMinnesotaforthelasttime,ending
around10,000yearsago,theyleftthickdepositsofglacialtillontopofPaleozoic
sedimentarybedrock.Thetillisspatiallyheterogeneous,withvariousstratigraphic
layersandunitsasdescribedbyLusardietal.(2012).Becausetheglacialtillisso
clayrichitisabletoholdtogethermuchstrongerthanifitwererichinsand-sized
particles.Sinceitissoclayrich,theRushRiverravineisabletokeepitssteepvalley
wallsintact.Thisisimportantasitalsohelpskeepterracesintactandwell
preserved.AlsolocatedwithintheRushRivervalleyareunitsofquaternary
alluvium,quaternarycolluviumandalluvialterracedeposits.Alluviumisasanda
gravelunitwithsiltandclaythathavebeendepositedbythemodernRushRiverin
channelsandfloodplains.Colluviumisaunitthatconsistsofclaytoboulders.This
unitisdepositedonsteepslopesbyweatheringandgravitationalprocesses
(Jenningsetal.2012).Thealluvialterracedepositsarecomprisedofasandand
gravellysandunitwithsiltandclay.Thisunitiswellsortedandtheyformanearly
levelsurfacewithsomeareasofstreamlinedbarsandshallowchannels(Jenningset
al.2012).Theunitliesabovethemodernfloodplain.
WatershedCharacteristics
SincetheGlacialRiverWarrencamethroughthisarea,RushRiverandits
tributarieshavebeenslowlyincisingthroughtheglacialtillandunderlyingrock
layers,tryingtoreachbaselevel.Inmorerecentyearsinadvancementsof
agricultureanddrainagetechniques,floodplainsandwetlandshavebeenalteredor
losttheirabilitytostorefloodwaters.Becausedrainagetilingspeedsuptheprocess
ofdrainingwaterflushedoutintodrainageditchesorriversatahighrateofspeed
causingincreasedflooding,erosionandsedimentloadedwater(Fennessyetal).
ResearchMethods
Thedatacollectedcamefromamixtureoffieldworkandobservationsmade
atoutcropsandlandformswithinthepark.Informationwasgatheredinafield
notebookandphotographsweretakenforvisualization.Informationfromthefield
suchasthecompositionoftheterracesaswellasgatheredfrommapsfromthe
MinnesotaGeologicSurveyforSibleyCounty(Jenningsetal.2012)wasusedto
verifylocationsofterraces.Thisinformationwasrecordedonafieldbasemap.
ThesemapsarecontourmapsthatarederivedfromLightDetectionandRanging
(LiDAR)takenfromtheMinnesotaGeospatialCommonsforSibleyCounty
(MNDNR).Themapgivesdetailsofdifferentelevations;terracesatdifferent
elevationscandistinguishseparateunits.ThroughoutRushRiverCountyPark,
terraceswereidentifiedandtheirlocationwasrecordedonthebasemaps.Sand
distributionmodelsfromtheMinnesotaGeospatialCommonsdeterminedtheir
extentforSibleyCounty(Lusardietal.2012).Oncetheinitialfielddatawasinput
intoArcMap,additionalterraceregionswereinterpretedbasedontheirsimilar
appearancetoknownterracestructuresinArcMapaswellasusinginformationof
differentunitsfromtheSurficialGeologyofSibleyCountyMapfromtheMinnesota
GeologicSurvey(Jenningsetal.2012)Fromthedatacollected,mapsofterraces
alongRushRiverweremadeusingArcGIStovisuallyshowthelocationandwhat
uniteachterracebelongsto.Becausethereisnotimescaleoftheeventsthat
happenedtocreatetheterraces,theywerebrokendownbylocationandelevation.
Intervalsofaround50ft.werenotedforeachterracelevel.FurtherstudiesofRush
Riverarerequiredinordertobetterdatetheterracelevels.Hypothesesofevents
thatoccurredovertimearethebestdatingmethodsusedinthisstudy.
Results
ByusingacombinationofArcGIS,DEMdata,contourelevationmaps,the
SurficialGeologymapfromtheMinnesotaGeologicalSurvey(Jenningsetal.2012),
andfieldwork,terraceswerelocatedandtheirextentwasmapped.Threeterrace
levelswereidentifiedalongtheRushRiverravine.Thethreeterracelevelsare
distinctfromeachotherfromelevationsof970-740ft.abovesealevel.
Figure4.ThecoloredsectionsarethelocationsofterraceswithintheRushRiverravine.Terracelevelsaremeasuredinelevationabovesealevel.
Locatedwithinalloftheterraceunitsinthepreviouspage(Figure4.)are
sandandgravellysandunitswithsiltandclay.Theseunitsarewellsorted,fining
upward.Theterracelevelsformanearlylevelsurfacewithsomeareasof
streamlinedbarsandshallowchannels.Therearelocationsfilledwithfine-grained
sediment,whichlieabovethemodernfloodplain.
TerraceLevel1-thisterracelevelismappedyellowincolor.Theelevationatwhich
theseterracesarelocatedis970ft.inelevationabovesealevel.Thisterracelevel
sitsatornearthetopoftheRushRiverravine
TerraceLevel2-thisterracelevelismappedblueincolor.Theelevationofthe
surfaceoftheterraceis860ft.inelevationabovesealevel.
TerraceLevel3-thisterracelevelismappedgreenincolor.Theelevationofthe
surfaceterraceis790ft.abovesealevel.
Althoughwedonothavedatesofwhentheseterraceswereformed,wedo
havegeologicinformationofwhattypesofmaterialsthatwaterfromRushRiverhas
hadtocarvethroughforthousandsofyears.BelowisaroughsketchofaCross
SectionofRushRiver.
Figure5.AroughsketchofthecrosssectionoftheRushRiverRavine.(Notdrawntoscale)
ThecrosssectionsketchofRushRiver(Figure5.)givesageneraldescription
ofthematerialsthatRushRiverhaserodedordepositedduringits~10,000year
evolution.
Figure6.Threedistinctterracelevelsshownwith10ft.contourlines.Terracelevelsaremeasuredatelevationabovesealevelinfeet.
Theelevationcontoursareshownat10ft.intervals(Figure6).Fromthetop
oftheoldestterracelevelstothebottomoftheyoungestterraceslevelsthereisa
distanceofabout230feet,withinthat230feetterracesweremappedbasedon
pointsofequalelevation.Basedontheseelevationdifferencesbetweenterrace
levels,itispossibletobegintointerpretpreviousenvironments,suchaswhen
periodsofhigherorloweramountsofdowncuttingandincisionwereoccurring
withinthearea.
Figure7.AlluviumandColluviummappedwiththe3distinctterracelevelsoftheRushRiverravine.Showingrelationofterracelevelsandunitsofalluviumandcolluvium.
Alluvium(Figure8.)isaunitconsistingofsandandgravelwithsiltandclay.
Fine-grainedsediments,whicharedepositedbymodernstreamsinchannelsand
floodplains.
Colluvium(Figure9.)isaunitthatconsistsofclaytoboulders.Thisunitis
mostlyfine-grainedsedimenttosandandgravel.Depositedonsteepslopesby
weatheringprocesses.
Figure8.ExampleofquaternaryalluviumdepositsinthefloodplainofRushRiver.RushRiverislocatedontheleftinthispicture.
Figure9.ExampleofquaternarycolluviumwithintheRushRiverravine.Thereissoilalongwithotherfinegrainedsedimentsandlargergravelsizeparticlesdepositedonaslopeoftheravineduetoweatheringandgravitationalprocesses.
Levelsurfaceslocatedbelow740ft.andslopinghillswithcolluviumdeposits
arenotconsideredterracesinthisstudy(Figure7.).Althoughtheyhavesimilar
characteristicsofterraces,locationsbelow740ft.withintheravineareconsidered
tobewithinthemodernfloodplainorhaveendedupintheareaduetoweathering
processes.
Discussion
ThenumerousterracespresentwithintheRushRivervalleysuggestthatthe
streamhasgonethroughmanyperiodsofdowncutting.Whendidtheseperiodsof
downcuttingoccurandwhatfactorscontrolledthem?Onehypothesisofmineis
thatterracelevel1isdifferentfromtheothers.Thisterracelevelisinterpretedto
betheoldestterracelevelwithintheRushRiverRavine.Ibelievethatthisterrace
levelwasformedduringperiodsofpost-glacialmelt,butpriortotheGlacialRiver
Warrencarvingthroughthisarea.BecausetheseterracelevelslieabovetheRush
Riverravine,itispossiblethattherewerepre-GlacialRiverWarrenflowsofwater
inthisarea.Duringthistime,therewaslittletonovegetationduetotheglaciers
thathadjustreshapedthelandscape.Aftertheglaciersmeltedaway,theyleft
massivedepositsofglacialtill.Thisloosesedimentwithnovegetationtoholdit
togetherwouldhavebeeneasilyshapedbyfluvialprocesses.Elevationsdecrease
fromthewesttotheeast,whichisthesamedirection,thatRushRiverdrainsinto
theMinnesotaRiver,leadingonetobelievethatthenaturalflowofwaterpriorto
RushRiverbeingformedisthesimilarwesttoeastdirection.Theseterracelevels
werepreservedwhileRushRiverorothererosionalprocesseswashedoutother
terraceswithinthislevelduringthedrainingofGlacialLakeAgassiz.
Terracelevel2reflectsahigherbaselevelthatexistedastheGlacialRiver
Warrenwasstillcarvingthevalleyshortlyafterdeglaciation.Aterraceheightof
around50ft.isasignificantdistance.Geologistsdonotknowhowlongittook
GlacialRiverWarrentocarvetheentiredepthoftheMinnesotaRiverValley.There
mayhavebeenmultiplephasesofoutburstfloodsanddowncuttingwithassociated
pausesbetweenfloodevents.Duringthosepauses,tributarieslikeRushRiver
wouldhavehadtimetodevelopfloodplainsthatwouldlaterbecometerraces.Thus,
thisterracelevelmayindicateaperiod,howevershort,duringwhichGlacialRiver
Warren–and,thus,thelocalbaslevelforRushRiver–wasstableatahigher
elevation.
Terracelevel3wasformedinmorerecentyears,sometimeafterthefinal
drainingofLakeAgassiz.Thisterracelevelisinterpretedtobetheyoungestof
terracelevelswithintheravine.Olderterraceswerecontrolledbynaturalfactors
butyoungerterracedevelopmentmayhavebeeninfluencedbyanthropogenic
events.Onehypothesiswouldbewithmoreandmoredraintilebeingplaced
underground,waterdrainingfromthesetilereachtherivermuchfastercausing
higherratesoferosionandflooding.RelativetonormalflowofRushRiver,thereis
evidenceoflargescalefloodingeventsthatcovertheselowareas.Thisterracelevel
couldtellusmoreabouterosionratesaswellastheeffectsthatthesepracticeshave
beenhavingonourriversystemsandtheamountofwaterbeingdrainedinthe
area.
Althoughwedonothaveagesoftheseterracesandarethuslimitedinwhat
wecaninterpret,wecancomparetheseterraceswiththoseofSevenMileCreek.
Bockalsolocatedthreeterracelevels.And,issimilarinbothtributaryvalleys,one
terracelevelofaround59feetinSevenMileCreekissimilartoTerrace2inthe
RushRivervalley,whichisatabout50feet.Havingacorrelationinterracelevelsin
bothSevenMileandinRushRiverisstrongevidencethattherewasaperiodof
stabilityoftheGlacialRiverWarrenatthisterraceelevation:thesetwostreamshad
timetodevelopfloodplainsatthatelevation.
Becausetheagesoftheseterracelevelsaswellasthefactorscontrolling
theirdevelopmentareunknownitisdifficulttopinpointthetimesthatthese
terraceswereformed.However,IbelievemyinterpretationscorrelatewithBock’s,
physicallyexploringtheareatoidentifyterracelevelswashelpfulinensuring
accuracy.Furtherinvestigationcouldhelpdetermineifhumaninteractionhasin
factbeenaffectingterracedevelopment,andavaluablefutureeffortwouldbeto
collectdatesoftheterracematerialstodetermineifhumandevelopmentaffected
terraceprocesses.
Conclusion
BymappingtheterracelevelswithintheRushRivervalleyabetter
understandingofthecurrentandhistorichydrologyoftheareahasbeenobtained.
Themappingshowsevidenceofpost-glaciationbutpre-GlacialRiverWarrenflows
wherethereisalluvialsedimentlyingabovetheravine.Thereisalsoevidenceof
theperiodwhereRushRiverwastryingtoreachbaselevelwiththeMinnesota
RiverduringthedrainingofGlacialLakeAgassizwhentheGlacialRiverWarren
carvedthroughthearea.Finally,Ibelievethereisevidenceofanthroprogenic
influencetoyoungerterracedevelopmentwithintheravineduetohigheramounts
ofwaterbeingdischargedfromdrainagetiling.
References
AeroMetric,Inc.LiDARElevation,MinnesotaRiverBasin,SouthwestMinnesota,
2010MinnesotaDepartmentofNaturalResources(MNDNR)Bock,Jeremy.“GeologyandGeomorphologyofSevenMileCreekPark.”Thesis.
GustavusAdolphusCollege,2010.GeologyandGeomorphologyofSevenMileCreekPark.Web.
Fennessy,Siobhan,andChristopherCraft."AgriculturalConservationPractices
IncreaseWetlandServicesintheGlaciatedInteriorPlains."(n.d.):n.pag.EcologicalSocietyofAmerica.Web.3Dec.2015.<http://www.indiana.edu/~craftlab/publications/09-0269.1.pdf>.
Fisher,T.(2003).ChronologyofglacialLakeAgassizmeltwaterroutedtotheGulfof
Mexico.QuaternaryResearch,59(2),271-276.doi:10.1016/S0033-5894(03)00011-5
Jennings,CarrieE.,BarbaraA.Lusardi,andAngelaS.Gowan.,2012,"Surficial
Geology."CountyAtlasofSibleyCounty,Minnesota.Vol.C-24.N.p.:TheU.S.GeologicalSurvey,n.d.N.pag.Print.PartA.
Johnson,MarkD.,Davis,DavidM.,andPederson,JoelL.TerracesoftheMinnesotaRiverValleyandtheCharacterofGlacialRiverWarrenDowncutting.MinnesotaGeologicalSurvey.p.121-1301998
Lusardi,BarbaraA.,R.S.Lively,andAngelaS.Gowan.,2012,"SandDistribution
Model."GeologicAtlasofSibleyCounty,Minnesota.Vol.C-24.N.p.:TheU.S.GeologicalSurvey,n.d.N.pag.Print.PartA.
Matsch,C.L.,1972,QuaternarygeologyofsouthwesternMinnesota,inSims,P.K.,
andMorey,G.B.,eds.,GeologyofMinnesota:acentennialvolume:St.Paul, Minnesota,MinnesotaGeologicalSurvey,p.548-560
Ojakangas,RichardW.andMatsch,CharlesL.(1982)Minnesota’sGeology.` Minneapolis,MN:UniversityofMinnesotaPress
"UpperMississippiGlacialLandscapes."TheInstituteforMinnesotaArchaeology,
1999.Web.