Talus slope characterization in Tasiapik Valley (subarctic Québec): Evidence of past and present slope processes

(1)

HAL Id: hal-03170489

https://hal.archives-ouvertes.fr/hal-03170489

Submitted on 16 Mar 2021

HAL

is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire

HAL, est

destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Talus slope characterization in Tasiapik Valley (subarctic Québec): Evidence of past and present slope processes

Samuel Veilleux, Najat Bhiry, Armelle Decaulne

To cite this version:

Samuel Veilleux, Najat Bhiry, Armelle Decaulne. Talus slope characterization in Tasiapik Valley

(subarctic Québec): Evidence of past and present slope processes. Geomorphology, Elsevier, 2020,

349, pp.106911. �10.1016/j.geomorph.2019.106911�. �hal-03170489�

(2)

ContentslistsavailableatScienceDirect

Geomorphology

j o ur na l h o me p a g e :w w w . e l s e v i e r . c o m / l o c a t e / g e o m o r p h

Talus slope characterization in Tasiapik Valley (subarctic Québec):

Evidence of past and present slope processes

SamuelVeilleux^a,b,∗,NajatBhiry^a,b,ArmelleDecaulne^c

aDépartementdegéographie,UniversitéLaval,Québec,Canada

bCentred’étudesnordiques,UniversitéLaval,Québec,Canada

cCNRS,LaboratoireLETG,UniversitédeNantes,LabExDRIIHM,France

a r t i c l e i n f o

Articlehistory:

Received6June2019

Receivedinrevisedform14October2019 Accepted14October2019

Availableonline18October2019

Keywords:

Morphometry Slopedynamics Snowavalanches Periglacial Nunavik

a b s t r a c t

Topographic,granulometric,morphometric,petrographicandvegetationsurveyswereconductedonthe slopesofTasiapikValley,nearUmiujaq(Nunavik),todocumentmasswastingprocessesandtheirgeo- morphologicalimpact.Talusslopes,widespreadatthefootofthesteeprockwallsofTasiapikValley,are animportantlandscapefeatureinthearea.Thelithologyoftheslopedepositsattesttheirlocalorigin, namelytheresultofrockfallscomingfromtheadjacentwall.Locally,poorvegetationcoveringtheclasts exhibitsrecentlyfallendebris;elsewhere,denseshrubcoverhascolonizedtheslopesdemonstrating thelowactivitynowadays.On-goingperiglacialprocesseshaveledtoextensivedismantlingoftherock- face,enablingfordebrissupply.Followingthelastdeglaciation,paraglacialprocesseshavepotentially favouredslopeinstabilities.Theuseofautomaticcamerasduringthewinter2017–2018resultedinthe observationofmanysnow-avalancheevents;howeverfewrockfalleventshavebeenobserved.Spring snowavalancheshavecarriedrockdebristothetalusatthefootoftheslope;snowalsoenableddebris redistributionontheslopes.

1. Introduction

Northern landscapes have undergone many changes since theirdeglaciation.Inparticular,paraglacialconditions(e.g.glacio- isostaticreboundandrockfacedismantlement)inducedtalusslope formationbysupplyingdebristhroughthepressurereleaseonrock fracturesandfreeze-thawprocesses(BallantyneandBenn,1994;

MatsuokaandSakai,1999;Ballantyne,2002;Matsuoka,2008).

Nunavikispartofthelow-ArcticregionofeasternCanadaandits landscapeconsistsoflowhills,basinsandplateaus.Thefewstud- iesthathavebeenconductedinthisvastregionhavedemonstrated theoccurrenceofslopeprocessesonslopeslessthan100mhigh (Belzile,1984;BéginandFilion,1985;St-Cyr,1986;Marionetal., 1995;GermainandMartin,2012;Germain,2016).Recentstudies (Decaulneetal.,2018;Bhiryetal.,2019)conductedatWiyâshâkimî LakeinTursujuqNationalPark(Nunavik)showedthattalusslope formationstartedafterdeglaciationatabout4600BP,andthatslope processesarestillactivetoday. SomeofthevillagesinNunavik (Salluit,Kangiqsujuaqand Kangiqsualujjuaq) arelocatedwithin

∗ Correspondingauthorat:2405,ruedelaTerrasse,UniversitéLavalQuébec, QuébecG1V0A6,Canada.

E-mailaddress:[email protected](S.Veilleux).

glacialvalleyswithprominentslopes,whileothervillages(Umi- ujaq)aresituatednearhighcuestarelief(∼230m).Accordingly, itiscrucialtodocumentslopedynamicsandtoevaluateassoci- atedrisksonthelocalpopulation,visitorsandinfrastructures.For instance,inKangiqsualujjuaq(northeasternNunavik),adreadful snowavalanchehitthegymnasiumofSatuumavikschoolduring the1999NewYear’sEvecelebrations,causingthedeathof9people andinjuring25(Bérubé,2000;LiedandDomaas,2000;Germain, 2016).However, noextensive researchhasbeen conducted on slopeprocessesintheUmiujaqarea(includingsnowavalanches, landslideandrockfalls),theirtriggeringfactors,theiroccurrence and theirrunout distance.Generalconditionsare conducivefor bedrockdismantlingand masswasting,even withlimitedslope heights, butadditional knowledgeaboutslope processesis still required.

Themainobjectiveofthestudyistodocumentlandformsorgan- isationbuiltbygravitationalprocessesinTasiapikValleyandtheir contributiontotalusdevelopmentbasedongeomorphologicalsur- veys.Thisstudydiscussesslope evolution duringtheHolocene, fromthe retreatof the LaurentideIce Sheetin theareato the present-day,highlightingthepotentialriskatthevalleybottom.

(3)

Fig.1. LocationofTasiapikValleywithintheUmiujaqarea(A);regionalgeologyandquaternarysedimentsinTasiapikValley(B);distributionofthetalusslopesand investigatedslopes(C).Sourcesofbackgroundimages:MRNF(A,B),UMIorthomosaic(2010)(C).

1.1. Regionalsetting

TasiapikValley(56^◦33N,76^◦28W)islocated5kmeastofthe InuitvillageofUmiujaq,ontheeastcoastofHudsonBayinNunavik, Québec(Fig.1a).Itisapproximately4.5kmlongand1.5kmwide, followinganorthwest-southeastorientation.Atthesoutheastern endofthevalleyliesTasiujaqLake(formerlynamedGuillaume- DelisleLakeorRichmondGulf),a 691km² brackishwaterbody connectedwiththeHudson Bayby anarrowcataclinalchannel calledLeGoulet(ARK,2007).ThelakeispartofTursujuqNational Park,createdin2013.

The regional geologyis characterized by a Paleoproterozoic volcano-sedimentarysequencelyingunconformablyonthePre- cambrian shield (Fig. 1b). The volcano-sedimentary sequence includes limestone, quartz arenite, dolomite and sandstone strata(QingaalukFormation) underlyinga thick (∼15m) basalt layer (Nastapoka Group) dipping westward (Stockwell et al.,

1979; Chandlerand Schwarz, 1980; Chandler,1988; Eatonand Derbyshire,2010).This asymmetricalmonoclinal relief(cuesta) consistsofagentlewesternslopeandasteepeasternslopeand extendsover650kmalongtheeastcoastofHudsonBay(Dionne, 1976;GuimontandLaverdière,1980).TasiapikValleyliesatthe frontslopeof the cuestaonits southwestern side,whereas the northeasternsideconsistsofa residualbutte calledUmiujaaluk Hill.

QuaternarydepositsontheeastcoastofHudsonBayarethe resultofasuccessionofsedimentaryenvironmentsfollowingthe retreatoftheLaurentideIceSheetatabout8200cal.BP(Hillaire- Marcel,1976;AllardandSéguin,1985;Lavoieetal.,2012)(Fig.1b).

Lowlandsbelow271ma.s.l,thealtitudinallimitofthepostglacial TyrrellSeainTasiujaqLakearea(Fraseretal.,2005;Lavoieetal., 2012),arecoveredbydeep-waterandshallow-watermarinesed- iments, andlittoral deposits(raised beaches) thatwereformed duringstagesofrapidglacio-isostaticuplift(Hillaire-Marcel,1976).

(4)

Aglaciomarinefancomplexliesintheupstreampartofthevalley.

Itconsistsofﬂuvioglacialmaterialthatwasdepositedduringastill- standoftheicemarginaround8000cal.BP(LajeunesseandAllard, 2003b).

Thestudyareahasa coldsubarcticclimateandit islocated inthediscontinuouspermafrostzone(Allardand Lemay,2012).

Meanannualairtemperaturerecordedbetween2013and2017 variesbetween-5.6and-4.2^◦C,withmaximaof23^◦Candminima of−36^◦C (Fortier,2017).Meanannualprecipitationis approxi- mately500mm,with40%fallingassnow(Ménardetal.,1998).

TheUmiujaqareaislocatedattheedgeoftheshrubandforest tundrazones;lowshrubs,ericaceousplantsandlichenscoverthe upstreampartofTasiapikValley,whiledenseforestcoveroccupies thedownstreampart(Payette,1983).Shrubcoverhasexpanded signiﬁcantly(shrubiﬁcation)duringthe20^thcentury(Ménardetal., 1998;Provencher-Noletetal.,2014;Pelletieretal.,2018).

TheSWsideofTasiapikValleyhasanear-verticalrockwall.Itis approximately50mhighintheupstreampartofthevalley,butit increasesto230mnearTasiujaqLakeinthedownstreampart.Slope depositslieatthebaseoftheescarpment,connectingtherockwall tothevalleyﬂoor,buthave alsoaccumulatedonbasalticrocky outcropsintheuppermostpartoftherockwall(Fig.1c).TheNEside featuresastep-liketopography,withslopedepositseitherlocated atthebaseoftheslopeorperchedonbasalticandsedimentary rockyoutcrops.AgravelroadconnectingUmiujaqtoTasiujaqLake followsthecuestafrontslopeontheSWside.

1.2. Methods

Forthis study,18 talusslopeswereinvestigated,ontheSW and NE sides of Tasiapik Valley (Fig. 1c). Data were collected overfourfieldcampaignsduringthesummersof2016(August), 2017(August)and2018(JuneandAugust).Severalslopedeposits wereidentifiedbysatelliteimagerypriortoinitiatingfieldwork.

TwosetsoforthophotosfromQuébec’sMinistèredesRessources naturellesetdelaFaune(MRNF)wereused,onedatingfrom2004 (scale1/10,000,25cmresolution)andtheotherfrom2010(scale 1/10,000,15cmresolution).

Topographic surveys were conducted along 18 longitudinal transectsusingaLeicaDGPS(DifferentialGlobalPositioningSys- tem).Waypointswererecordedfromtheapexoftheslopedeposits totheirbase,perpendiculartotherockface.Datawereprocessed inArcGISandExceltoproducetopographicproﬁles,revealingthe microtopographicfeaturessuchasinﬂectionandtextureinaccu- ratedetails.Theestimationofthestageofevolutioniscarriedout fromtheHo/Hiratio,whereHocorrespondstotheheightofthe talusslopeandHitothetotalheightoftheslopeincludingtherock- wall(Francou,1988;Sellier,1992).Theratiogivesanoverviewof theexhaustionoftheremainingrockwall(debrissource)incon- comitancewiththetalusslopeformationonalongertimescale, namelysincethelastdeglaciation.Forexample,aratioapproach- ing1indicatesanadvancedslopedevelopmentstageduetothe lowheightoftheresidualwallcomparedtotheheightofthetalus slope.

Topographicdataandsatelliteimagerywereusedtomeasure rockfall runout distances (horizontaltravel distance) calculated fromthesourceareatothefarthestslopedebris.Inaddition,the reachangle,calculatedfromthesource-areatothefarthestslope debris,andtheshadowangle,calculatedfromtheapexofthetalus tothefarthestslopedebris,weredocumentedtoprovideinforma- tionabouttheextentofslopeprocessesinthearea.

On12ofthe18longitudinaltransects,granulometricandpetro- graphicsurveyswereconductedbysampling25randomlyselected rockfragmentsatintervalsof10–15malongthetransects.Debris weremeasuredalongthreeaxes:length(a-axis),width(b-axis)and thickness(c-axis).MeasurementswerecompiledinExcelandthen

analyzedtoproducedescriptivestatistics.Morphometricindices werealsocalculatedfromthesemeasures(Pérez,1989,Hétuand Gray,2000).Theﬂatteningindex(Fi)iscalculatedasfollows:

F_i=a+b

2c (1)

whereacorrespondstothelength,btothewidthandctothethick- nessofthefragment(Cailleux,1947).AhighFivalueindicatesthat thedebrishasaﬂattershape.Theelongationindex(Li)iscalculated asfollows:

L_i=a

b (2)

whereaandbcorrespondtothelengthandwidthofthefragment (Schneiderhöhn,1954).AhighLivalueindicatesthatthedebris tendstobeelongated.Finally,thesphericityindex(Si)iscalculated asfollows:

Si=_bc

a²

¹₃

(3) wherea,bandccorrespondtothelength,widthandthicknessof thefragment(Krumbein,1941).AvalueSiapproaching1indicates thatthedebrishasamoremassiveshape,sphericalinthecaseofa roundedfragmentandcubicforanangularfragment.Theseindices documentthefallingbehaviorofclasts,sincesphericaldebrisare pronetorolling,whileelongatedﬂatdebrisaremorelikelytoslide.

Petrographicsurveysprovidelithological dataforthemeasured fragments.Theirorigin,eitherlocal(associatedwiththelocalslope development)orexogenous(generallyfromglacialtransportand deposition),iscloselyrelatedtotheirlithology,thustheirgeneral shape,andtheirpositionontheslope.Theedgesofthedebriswere characterized,withaviewtodeterminingtheirorigin:anangu- larfragmenthasundergoneverylittleerosion,indicatingashort transportationdistance/localsource,whiledebristransportedby glaciersorreworkedintheTyrrellSeahasapronouncedrounded shape.

Vegetation cover was described at each sampling stationin ordertoassessrecentandcurrentprocessactivity.Hierarchicalval- ueswereattributedtoeachstationbasedonthetypeofvegetation andtheestimatedpercentageofcoverageonthedebris,providing relativeage-estimates:

1)Freshdebris:nolichenspeciesobservedontheclast;

2)Recentdebris:somelichenspeciesobservedontheclast;

3)Medium-ageddebris:severallichenspeciespartiallycoverthe clast;

4)Old-ageddebris:severalspeciesoflichensandmossespartially covertheclast;

5)Veryold-aged debris:several species of lichensand mosses totallycovertheclast;potentiallyalsocoveredwithlowshrubs.

Vegetation classificationvalues and Ho/Hiratiovalues were usedtoestimatethestageofslopedevelopment.Theadditionof thesetwovaluesgivesanoverviewoftheslopeevolutionfromboth shortterm(vegetation)andlongterm(Ho/Hi)perspectives.Values of1to5wereassignedtoeachlongitudinalprofileaccordingto theirHo/Hiratio,followingtheJenksnaturalbreaksclassification method(Jenks,1967);avalueapproaching1indicatesalowHo/Hi ratio,thusayoungerdevelopmentstage.Thevegetationvalues(i.e.

thelowest-freshest-valueperproﬁle,ranked1to5accordingto therelativeageestimatedescribedabove)wereaddedtoprovide anoveralldevelopmentscore.Inaddition,theageofshrubsatthe bottomoftalusalongtheSW-07,SW-08andSW-09proﬁleswas determinedusingdendrochronologyon11blacksprucesamples (Piceamariana).

Finally,inordertomonitorslopemovementsonashortertime scale,three ReconyxPC800 automatictime-lapsecameraswere

(5)

Fig.2.LocationofthecamerasalongtheSWsideofTasiapikValley.Frameviewofeachcameraisshownontheleft.Sourceofbackgroundimage:UMIorthomosaic(2010).

installedontheSWsideofthevalleyinAugust2017.Oneofthe cameras(TAS1)islocatedonthecuestaedge,abovetherockwall andtalusalongtheSW-07andSW-08proﬁles(Fig.2).Thelatteris coveredbyasecondcamera(TAS2)thatislocated300mawayfrom therockwall.Athirdcamera(TAS3)islocatedfurtherupstream nearthebaseofthetalusalongtheSW-06proﬁle.Approximately 14,000photosweretakenoveraone-yearperiodfromAugust2017 toAugust2018inthevalley.Photosweretakenduringdaytimeat one-hourintervalsuntilJune2018,thenat15or30minintervals (dependingonthelocation)untilAugust2018.

2. Results

2.1. Topographyofslopedeposits

TheSWproﬁlesshowasteeper slopegradient,witha mean angleof25.3^◦andamedianangleof26.3^◦,whiletheNEproﬁles haveameanangleof21.2^◦andamedianangleof17.5^◦(Table1;

Fig.3).Aslightordistinctconcavityofthetalusslopeisapparent onsixofthenineSWprofiles,whiletheSW-01andSW-06profiles arevirtuallylinear.TheSW-09profileshowsamorecomplexshape

(linearproximalpartandchaoticdistalpart).OntheNEside,there isnodistinctconcaveprofile,yetsevenofthenineprofilesshow eitheraslightlyconcaveoralinearshape,whiletheNE-04andNE- 07profilesrespectivelyshowacomplexandaconvexshape.Four profiles(SW-07,SW-08,SW-09andNE-09)exhibitastrongbasal concavity(Fig.3).

2.2. Relativedatingofslopes

ThemeanHo/HiindexontheSW (0.36)and NEsides(0.25) indicatesthattheremainingrockwallisgenerallyhigherthantalus slopes(index<0.5)(Table2).However,thestep-liketopography ontheNEside,comparedtothenear-verticalrockwallontheSW side,couldmeanthattheNEsidehasreachedamoreadvanced stageofdevelopment.Talusslopesnearthesouthernmarginof bothsides(alongtheSW-07,SW-08,SW-09andNE-09profiles) arelocatedunderhighverticalrockwallswithHo/Hiindexbelow 0.2,thusindicatingayoungerdevelopmentstage.TheSW-04and SW-05profilesindicateanolderstagethantheotherSWprofiles, withrespectiveindexvaluesof0.56and0.62.

(6)

Table1

Topographicparametersoftheinvestigatedslopes.

Proﬁles Slopeangle(^◦) Meanangle(^◦) Medianangle(^◦) Inﬂection

SW-01 18.4

25.3 26.3

linear

SW-02 28.1 slightlyconcave

SW-03 28.3 slightlyconcave

SW-04 19.3 concave

SW-05 24.9 concave

SW-06 27.1 linear

SW-07 26.3 concave

SW-08 30.0 concave

SW-09 25.2 complex

NE-01 14.2

21.2 17.5

linear

NE-02 12.3 slightlyconcave

NE-04 16.1 complex

NE-05 17.4 linear

NE-06 31.8 linear

NE-07 27.1 convex

NE-08 23.2 linear

Table2

CalculationofHo/Hiindex.

Proﬁles Talusbaseelev.(m) Talusapexelev.(m) Hovalue Rockwallelev.(m) Hivalue Ho/Hiindex

SW-01 171.3 187.6 16.3 222 50.7 0.321

SW-02 147.3 178.3 31.0 216 68.7 0.451

SW-03 146.3 176.8 30.5 208 31.7 0.494

SW-04 151.4 183.2 31.8 208 56.6 0.562

SW-05 148.0 187.9 39.9 212 64.0 0.623

SW-06 127.4 159.2 31.8 212 84.6 0.376

SW-07 46.5 82.0 35.5 214 167.5 0.212

SW-08 47.6 67.2 19.6 222 174.4 0.112

SW-09 49.6 75.9 26.3 272 222.4 0.118

NE-01 156.1 169.9 13.8 202 45.9 0.301

NE-02 157.2 167.3 10.1 252 94.8 0.107

NE-03 164.6 182.8 18.2 254 89.4 0.204

NE-04 163.0 184.3 21.3 270 107.0 0.199

NE-05 162.1 178.1 16.0 282 119.9 0.133

NE-06 225.6 260.8 35.2 282 54.4 0.624

NE-07 131.7 167.5 35.8 292 160.3 0.223

NE-08 134.6 184.0 49.4 302 167.4 0.295

NE-09 161.2 188.8 27.6 312 150.8 0.183

Examinationofthevegetationcoveringthesurficialdebrison theslopedepositsrevealedthepresenceandpositionoffewfresh deposits.MostofthedebrishadaclearvegetationcoverontheSW side(Fig.4).Intheapicalpartsofthetalusslopes,variouslichens and/ormossesareabundant,whilea discontinuousthinstripof herbaceousplantsandlowshrubsislocatedattheedgeoftherock- wallundisturbedbypresent-dayslopeactivity.Distalpartsalso featureabundantlichensandmossesonmostoftheclastsalong withthickmossescoveringtheslopedepositsandlowshrubs;this trendisespeciallyevidentontheSW-07andSW-09profiles.Asimi- lartrendwasobservedontheNEprofiles,asmostsamplingstations intheapicalpartofthetalusslopesshowmediumtoold-agesta- tus,whilesamplingstationsinthedistalpartsindicateolder-age status.However,debrisalongtheSW-08,NE-06andNE-09profiles appeartobemorerecent,withlittleoverallcoverageandthepres- enceoffewlichens.Somefreshdebriswerescatteredalongmost oftheprofiles(Table3).

ByaddinguptheHo/Hiindexvaluesandthevegetationclas- sificationvalues,wecanestimatethedevelopmentalstageofthe slopes.AsshownonFig.5,theSW-08andNE-09profilesseemtobe attheyoungestdevelopmentalstageamongallthetalusslopes.The Ho/Hiindexandthevegetationclassificationvaluesareconsistent forsomeprofiles,showingaconcomitanceforbothparameters.

Forexample,thetalusslopealongNE-09proﬁlehasalowHo/Hi index(0.183)andthereisverypoorlichencover onthedebris.

However,thetwoparametersprovedtobecontradictoryforsome

talusslopes,particularlyfortheSW-09proﬁles,duetotheoverly highrockwall(increaseddebrissupplypotential)andthepresence ofwell-developedvegetation(limiteddebrissupplyonthetalus slope).Bothof theseﬁndings indicatethatthe debrissupply is sporadic.

2.3. Sourceandmorphometryofslopedeposits

Threeclassesofdebriswereidentiﬁedalongtheinvestigated proﬁles: 1) basalt, 2) sedimentary rocks (comprising dolomite, limestone,quartzareniteandsandstone),and3)graniticgneiss (Fig.6).

OntheSWside,sedimentaryrockdebriscomprised64.5%of thesampledclasts,whereasbasaltdebrisaccountedfor35.4%and gneissfor0.07%.Sedimentaryrockdebrisrepresentedalargerpro- portionontheNEside,accountingfor89.4%ofallclasts,whilebasalt andgneissaccountedfor6.4%and4.2%.Assumingthetopbasalt layeris∼15mthickthroughoutthevalley;thosevaluescoincide withthelargeproportionofsedimentaryrockstrataavailablefor debrissupplyontheexposedrockwall. Sedimentaryrockstrata accountfor90%(∼140m)oftherockwall(∼155m)abovetheSW- 07, SW-08andSW-09proﬁles. IntheupstreampartoftheSW side,sedimentaryrockstrataaccountfor57%(∼20m)oftherockwall(∼35m).OntheNEside,thetopbasaltlayerhasconsiderably recededonmostoftheinvestigatedslopes,revealingrockyout- cropscomposedofsedimentaryrockstrata.However,therockwall

(7)

Fig.3. Longitudinalcross-sectionoftheinvestigatedslopes.Sourceofbackgroundimage:UMIorthomosaic(2010).

abovetheNE-06proﬁleismainlycomposedofbasalt(68%oftotal height).

Bycomparingtherespectiveproportionsofeachlithologyat samplingstationsalongtheprofiles,many oftheslopedeposits showconsistentratiosofsedimentaryrocksand/orbasaltdebris fromtheapextothebaseoftheslope.OntheSWside,thepro- portionofbasaltdebrisvariesbetween80%and84%throughout thesamplingstationsontheSW-02profileandbetween14%and 26%ontheSW-07profile.OntheNEside,theproportionofsed- imentaryrockdebrisvariesbetween80%and88%ontheNE-02

profile,whiletheNE-08andNE-09profiles shownodifference assedimentaryrockdebriscompose100%ofthetalus.However, someoftheslopedepositsshowanincreasingproportionofbasalt materialtowardthefootofthetalus.Forexample,alongtheSW- 08profile,thebasaltdebrispercentageincreasesfrom17%atthe apexto37%atthebottomoftheslope;ontheSW-09profile,it increasessignificantlyfrom12%to100%.Finally,ontheNE-06pro- file,thebasaltdebrisareonlylocatedatthebottomofthetalus, whereasthesedimentaryrockdebriscomprisestheentireapical part.