Download Geology of the Cliffs

CliffsofMoherGeology
TherocksthatmakeuptheCliffsofMoherwereformedover300millionyearsagoduring
theUpperCarboniferousperiod.BandsofNamuriansandstone,siltstoneandshaleare
exposedinaspectacularfashionandhereonecanstudyanexampleofasedimentarybasin
normallyonlyvisibleunderthesea.
Atthattimealargelandmasswaslocatedtothesouthwestoftheancientmarinebasin.
Heavyrainfallonthelandcreatedgreatfloodsthatwashedsandandmudintoancient
riversthatflowednortheastwardstothesea.Thesand,siltandmudcarriedbytheselarge
riversweredumpedintotheseaatthemouthofgreatdelta(similartothemouthofthe
MississippiRiverasweknowittoday).Overthemillionsofyearsthatfollowed,the
sedimentswerecompactedintosolidrockandwerepushednorthwardsduetomovements
intheearth’splates.Itisthesesedimentaryrocklayersofsandstones,siltstone,mudstone
andshalethatmakeuptheCliffsofMohertoday.
Therocklayersarerichinfossilformationsandgeologistsconsidertheareaoneofthe
world’sforemostnaturallaboratoriesforthestudyofdeltaicdepositionthroughdeepwater
systems.EachrocklayerintheCliffsofMoherisarepresentationofaspecificeventinthe
lifeoftheancientdeltaasitmigratedintothesea.Individuallayersofrocksvaryfrom
centimetrestometresinthicknessbuttogethertheyformanaturalfeaturethatstandsover
200metresabovetheoceanthatthehighestpoint.Justasthepagesofabooktellusapart
ofabiggerstory,eachlayerofrocktellssomethingaboutthelocalenvironmentthatexisted
over300millionyearsagowhattheserockswereformed.
TherearetwotypesoftracefossilsintheCliffsofMoherflagstones.Thesquigglytrails,
calledscolicia,arefeedingtrailsleftbysomeunidentifiedmarinecreatureandare
commonlyreferredtoasworming.Itcouldhavebeenaworm,asnailoracrustacean.A
secondlessobvioustypeoftracefossilisthesmall,circularburrowmark.Theseburrowsare
preservedascastsofthefeeding(orescape)burrowleftbyanunidentifiedmarinecreature.
Otherflagstonesaremarkedwithfossilizedwaveripplemarks.Justliketheripplemarkswe
oftenseeonthebeachorinshallowseawater,theseripplemarksformedinthesandsand
siltsontheancientseafloor.Theattractivepatternsleftbythefossilshaveledtoademand
forMoherorLiscannorflagstoneandduringthe19thcenturyathrivingquarryingindustry
sprungupinthisarea.Thepavingthroughoutthevisitorcentreandonthecliffedge
viewingplatforms,wallsandpathwayshasbeendonewithlocalLiscannororMoherslate
flags.
TodaytheCliffsareundergoingcoastalerosion.Wavesconstantlycrashagainstthefootof
thecliffs,andthisincessantwaveactionerodesthecliffbase,causingsectionsoftheupper
clifffacetocollapseintotheseaundertheirownweight.Avarietyofcoastallandformscan
beseenbothfromthetopofthecliffsandfromoffshore.Seacavesareformedalongthe
footofthecliffsandovertimethesedevelopintoSeaStacksandSeaStumps.Wind,rain
andiceallcontributetotheerosionofthecliffface.
Thegreatseastack(Branaunmore)atthefootoftheCliffsofMoher,belowO’Brien’sTower
stands67metreshigh.Thiscolumnofrockwasoncepartofthecliffsbutcoastalerosion
slowlyremovedthelayersofrockjoiningittothemainland.Furtherwest,alongthecliffs,a
numberofseacaveshaveformedatthefootofthecliffs.Oneofthesefeaturedfamouslyin
the2009movie–HarryPotter&theHalfBloodPrince.Alargeseaarchcanalsobeseenat
Hag’sHeadbelowtheNapoleonicsignaltowerandmultiplesmallerseaarchescanbeseen
fromsealevel.
TheCliffsofMoherformpartoftheBurrenandCliffsofMoherGeoparkwhichwasawarded
membershipoftheUNESCOsupportedGlobalGeoparksNetworkin2011.