Surface Mapping of Sand & Graveland LiDAR Applications

Christopher Maike

Surface mapping is a fundamental aspect of the North Dakota Geological Survey (NDGS). The production ofmaps allows thecommunitytounderstandtherocks,sediments,structures,andother geologic features in an area. Geologicmaps further thescientificunderstandingofNorthDakotageologyandprovideanadded economic value for the knowledge of natural resources.TheadditionofLiDAR(lightdetectionandranging) imageryhasallowed geologists to observe small-scale features that maynothavebeenobservedbefore. TheNDGSisgeneratingdigitalelevationmodelsderivedfromtheStateWaterCommissionLiDARDatasettosupportitssurficialmapping,landslidemapping,andothergeologicalinvestigations.

The construction of high-resolution digital elevation model(DEM)mapsfromtheLiDARdataisinstrumentalinthefutureofmapping at theNDGS. Thesemaps are thebuildingblocks foravarietyofmappingprojects. AdistinctadvantageofLiDAR isthe three-dimensional visualization of topography allowing forclearer interpretationsof landforms,which allows geologists tospatiallyanalyzethesurfaceandidentifysubtleglacialfeatures.Approximately75%percentofNorthDakotaiscoveredbyglacialdeposits;therefore,theidentificationofspecificglacially-derivedlandformsissignificantforgeologistsintheevaluationofpotentialsandandgraveldeposits. In particular, there are specific glacial landforms that containcommercialgradesandandgravel.Examplesoftheselandformsare eskers, kames, beaches on the shorelines of former glacialmeltwaterlakes,andoutwashplains.Aneskerisalongsinuousridge with stratified drift containing identifiable cross-beddingthatcommonlyformedwithinanice-walledtunnelinorbeneathaglacier(fig.1).Gravelandsandweredepositedwithinthetunnelas the glacier was retreating and deposited the sinuous ridgefound on landscapes today (fig. 2). A kame contains stratified

drift and looks like a hill on themodern landscape (fig. 3). Akame deposit originally formed within a depression on the top of aglacier,andastheglaciermeltedandretreated,thesedimentwas deposited on the landscape appearing as a hill, invertedfrom its original form (fig. 4). Beach ridges that formed along

Figure 1. Ontheleft:Thisillustrationshowsameltwaterchannelwithinaglacier.Thehighenergyofthewaterwithinthetunnelallowssandandgraveltobedeposited.Ontheright:Thedepositedsandandgravelformsaridge,calledanesker,astheicemeltsaway.

Figure 2. This map dis-plays an example of anesker viewed on LiDARimagery. The esker pic-tured is the Dahlen es-ker locatednearDahlen,NorthDakota.

Background Picture: Twenty feet of sand and gravel overlain by five feet of till in Williams County, North Dakota.

Figure 3. Thismap dis-plays an example of akame viewed on LiDARimagery. The kame islocatednearPickardville,North Dakota, approxi-mately 6 miles east of McClusky.

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the shores of meltwater lakes are a rich source of sand for commercial use and can be found throughout the glaciatedpartofNorthDakota.ThelargestoftheseareassociatedwithglacialLakeAgassiz. ThelakeexistedinNorthDakotafromapproximately11,700yearsagountil9,000yearsagoandleftbehinditsrichlakesedimentforfarmingintheRedRiverValleyandanextensivecomplexofbeachridgesalongitswesternedge.Glacialmeltwatertransported sediment away from the ice margin forming plains referred to as outwash plains, which containstratified and cross-bedded sand and gravel deposits.Thehighenergyoftheoutwashcausessmallerparticleslike clay and silt to remain in the water column and be washeddownstream,resultinginthepristinedepositionofsandandgravel.

NDGSgeologistsareable to identifypotentialsandandgravel deposits from the geomorphology within LiDARdata.Followingthis,ageologistwillfieldcheckthedatatomakesuretheinterpretationisconsistent.Techniquessuchashandauguring,orusingasoilprobetopenetratethesubsurface,willbeusedtovalidatethesandorgraveldeposit. If thegeologistvalidatesthedeposit, theareaof the landform can be delineated and the volume ofsediment calculated from the LiDAR data. This giveslandownersandminingcompaniesvaluableinformationfor landmanagement and natural resource evaluation.After a sand or gravel deposit is discovered there aremanydifferentlabtechniquesthatareusedtoevaluatechemistry, grain size, roundness, and sphericity. This isan important step that helps companies determine the economicneedofaparticularsandandgraveldeposit.

In addition to glacial deposits, wind-blown (eolian)depositsaresignificantsourcesforsand.Dunesthatmaybetoosubtletoseeonaconventionalaerialphotograph ortopographicmapsareeasilyidentifiedonLiDAR.Theirdistinctivemorphologyisclearlyevidentonthelandscapeastheobliqueviewinfigure5displayssoeffectively.

LiDAR has become a very important tool for mapping at theNDGS. Ithasmadegreatadvancements inthe identificationofsandandgraveldepositsandhassimplifiedthecalculationsforquantifyingthevolumeofthesedeposits.Formoreinformationon the technicaldetails of LiDAR, there is anarticle in the July2016issueoftheNDGSGeoNews(Maike,2016).

References:Anderson, F.J., 2016, Geomorphology of Dune Sand Resources

in Southwestern Sargent County: North Dakota Geological SurveyGeologicInvestigationNo.190.

Maike,C.A.,2016,LiDAR:Whatisitandhowdoweuseit?:NorthDakotaGeologicalSurveyGeoNews,July2016.

Figure 4. This illustration shows the formation of a kame. Above:sediment begins to accumulate within a depression on the surface of a glacier.Below:astheicemeltsthesedimentslumpsontothegroundandformsahill-likeshape.

Figure 5. ObliqueLiDARimageshowingdunemorphologyinsouthwestSargentCounty, North Dakota. The three-dimensional image displays the surfaceexpression and varying relief of the eolian system. This deposit would be anexceptionalresourceforfuturesanduse(Anderson,2016).

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