GEOLOGICAL SIRMIONE A walk through time · Geological Sirmione. A walk through time 2 The history of Sirmione and Lake Garda is inevitably bound up with its geological formation over

GeologicalSirmione.Awalkthroughtime

1

GEOLOGICALSIRMIONEAwalkthroughtime


2

The history of Sirmione and LakeGarda is inevitably bound upwith its geologicalformationoverthemillennia.Itisfascinatingbecauseittakesyoubacktounknowneras, reconstructed through precise studies and meticulous research. You areespeciallytakenbacktoatimewhenthisstripoflandresistederosionfromnaturalelements and ended up being surrounded by water, giving rise to the beautifulpeninsulathattodayattractstouristsfromallovertheworld.Thankstothisremarkableinitiative,visitorscannowenjoySirmionefromadifferentperspective. They can continue to admire the Scaliger Castle, the remains of theGrottoes of Catullus and the splendid churches found in the old town; they willalways be delighted by the contrasting colours of the blue of the lake and theturquoisesky,whichturngoldenintheEastatdawnandintheWestatsunset.Butnowyoucanalso identifywhat liesbeneath the surface, fromthe towncentre totherockescarpmentattheextremetipofthepeninsula.ThereforeIwouldliketowarmlythankeveryonewhowasinvolvedinthisproject:theProLocovolunteers,whotirelesslychampionanyinitiativethataimstopromoteevery aspect of Sirmione, the teachers and students of Bagatta High School inDesenzano and the geologists Giovanni Fasser and Niccoló Crestana, whoenthusiasticallyagreedtotakeonsuchaspecialtask.NaturallywewouldalsoliketothankthevisitorstoSirmione,whowillreceiveacopyofthisbooklet.

TheDeputyMayorLuisaLavelli


3

Theaimofthisprojectwastowidenourknowledgeofthehistoryandevolutionofourterritoryfromadifferentperspective,soweenthusiasticallyjoinedtheoriginalprojectofgettingtoknowLakeGardafromageologicalpointofview.Theetymologicalmeaningoftheterm"geology"isverysimple:itisthesciencethatstudies the origin, history, morphology and constitution of the Earth. This maysound like an academic exercise, devoid of substance and disconnected fromeveryday life. In truth, it has never before been so important to understand theareas in which we live, not only to prevent the negative effects of possibleearthquakes, but also todefendourselves from increasingly frequent catastrophicevents,suchasflooding.Thelandonwhichweliveisalivingelement,capableofwelcomingusandfeedingus, which in turn requires respect and care. Geology helps us in this increasinglyimportantmissionandraisesawarenessofhowtobehaveresponsiblyregardingtheenvironment.We are therefore grateful to the ProLoco and the Municipal Administration ofSirmione and of course to Bagatta High School, for providing us with thisopportunity.

GeologistNiccolòCrestanaGeologistGiovanniFasser

Sirmione Pro Loco has been working for many years with the aim of promotingunderstanding and respect for the area in which we live. This is why we haveproducedthisinformationbookletaboutthegeologyofSirmioneaspartofawork-relatedlearningprojectwithBagattaHighSchoolinDesenzano.Everyoneinvolvedin this project deserves a heartfelt thank you. To everyone reading this booklet,whether locals or visitors, please continue to enjoy, love and respect the beautyaroundyou.

LuisellaBaccinelliPresidentofSirmioneProLoco


4

TheformationofLakeGarda

LakeGardaisthelargestoftheItalianlakes.Itwasformedbycomplexmodificationstotheearth'scrustthatoccurredmillionsofyearsagoandhasbeenthesubjectofin-depthstudiesbygeologists,especiallyinrecentyears.

Fromageologicalpointofview,wecanideallydivideLakeGardaintotwodifferentareas: Upper Garda and Lower Garda. A dividing line connects the two towns ofGardaandSalòandtracesanimaginaryborderthatcanbeeasilyseenbylookingatthelandscapeandmorphologyofthearea.

(lowercaption)

ImaginarylinethatdividesUpperandLowerGarda.


5

UpperGarda

TheupperGardaareacontainstheolderrocksformedinageologicalperiodabout200 million years ago, between the Triassic and the Pliocene eras. This area hasrocky outcrops such as Mount Baldo in the Verona area, the Tremosine-Tignaleplateau and the group of Spino-Pizzoccolo mountains on the Brescia side. Thepredominantrockformationisthe''Dolomite''whichconsistsofdolostone,adoublecarbonateofcalciumandmagnesiumCaMg(Co3)2.LakeGardaliesinthefoldsofthisrock that was fractured and deformed as a result of tectonic movements (withnumerous fault linesand fractures)due to thecollisionofplates in theprocessofAlpineorogenesis.

(lowercaption)

MountBaldoandUpperGardaseenfromSirmione.


6

The "Theory of plate tectonics" explains that the lithosphere is divided into 22plates, which are in constant movement and consequently cause seismic andvolcanic activity. The origin of mountain ranges is also closely linked to platemovement,as inthecaseoftheAlps,formedbythecollisionbetweentheAfricanandtheEurasianplates.

During the Triassic period these twoplatesbecame fragmentedand separatedbythe formationof the TethysOceanbasin and gave rise to high and low structuralzones (highor lowseabed)developinganenvironmentcharacterizedbyemergentareas, islands and coral reefs, alternating with areas of deeper basins, includingabyssalplains.SpecificallyLakeGardaislocatedbetweenadeepseaarea(Lombardyarea)andtheVenetoplatform.

(bluebox)

OROGENESIS:FromAncientGreekOROS (mountain)+GENESIS (origin); indicates theprocessbywhichanyhighgroundisformed.

(uppercaption)

ThedifferentfaultlinesoftheGardaarea.

(lowercaption)

ComputerreconstructionoftheTethysOcean.


7

ToexplainthefluvialoriginsofLakeGarda,clearlyvisibleintheUpperGardaarea,we must take a look at the "Messinian salinity crisis", dating back to about 6-7millionyearsagoandcausedbytherepeatedclosureoftheStraitofGibraltar,whichresulted in a partial desiccation of the Mediterranean Sea (what was left of theTethysOcean).Thepartialdesiccationoftheseanotonlyallowedthedepositionofevaporites (salt, gypsum, etc.), but also caused the coastlines to recede andincreasedtheerosivecapacityoftherivers intheAlpinewatersheds,forcingthemtodigdeepertoreachthelevelofthesea.Erosionhasthereforedeeplycarvedtherock,creatingtherivervalleysonwhichthegreatlakesofLombardynowsit.

(brownbox)

MESSINIANSALINITYCRISIS:GeologicaleventofthelastpartoftheMiocene(5MLNyearsago)duringwhichtheMediterraneanalmostcompletelyevaporatedduetotheclosureoftheStraitofGibraltar.

(lowercaption)

Exampleoftheerosivepowerofwater.


8

LowerGarda

TheSouthernendofLakeGarda,ontheotherhand,begantoform2millionyearsago, when the Garda valley began to undergo massive climate changes,characterizedbyperiodsofglaciationwithinterveningwarmerperiods.

These periods of climatic cooling coincidedwith the advance of enormous glaciertonguesthatoccupiedthevalleypreviouslyerodedbytherivers.

Recentgeologicalstudieshaveshownfivedistinctstagesofglaciation,inwhicheachstagetendstocanceloutthepreviousone,depositingnewsediment,causedbythemeltingoftheglacierthatdepositedpreviously.

• Stage I (known as Ciliverghe): the first glacier advancement is the mostimpressive and remains have been found in the area of Ciliverghe andCalvagese.Althoughitisnotpossibletoestablishthemovementoftheglacialfrontwithcertainty,itcanbeassumedthatitsadvancewasinfluencedbythemorphologyoftherockysubstratumandthencontainedtothenorth-westbytheslopesofthePrealpsandtothesouth-eastbythestructuraltectonicrisethatstillexistsbetweenGardaandthetipofSirmionepeninsula.

• Stage II (known asMount Faita):with the second advance of the glacier, itmovedslightlyeastwardsanditssedimentformedthehillsofGavardo.

• Stage III (known as Carpenedolo): after the glacier melted it depositedmorainetoformthehillsofMedoleandthehillofVillaCortineinSirmione.


9

• Stage IV (known as Sedena): the fourth glaciation left little effect on theterritory; it consisted mainly of the alignment of the hills to the west ofLonato and the higher ground around Bardolino. During this extremelyimportantstagetheglaciercovered,forthefirsttime,thestructuraltectonicupliftcausedbythe“PuntaSanVigilio-Sirmione-Rivoltella”faultline.

• Stage V (known as Solferino): the last glaciation created ridges ofmorainichillswithverysteepslopesintheLowerWestGardaarea.Intheeast,ontheotherhand,thesedimentscreatedhillsof loweraltitudeandgentlerslopes.Finally, in the South, themoraine left by the end of the glacier formed theamphitheatreoftheGardamorainichillsasweknowthemtoday.

(uppercaption)

The5glaciationstages


10

It is interesting to note that in the Sirmione area the deposits are made up ofshallowsedimentsandgroundmorainecharacterizedbysilty-claydeposits.

A study of the different phases makes it clear that the five glacial tonguesunderwent a progressive eastward rotation. This shift is due to the tectonicmovementofthefaultsthatcausedthehillridgesinthewestandforcedtheglaciertorotateeastwards.

(uppercaption)

OntheleftThefiveglaciationstagesshowingtherotationtowardstheEast.

(lowercaption)

Garda:showingthedifferentdepthsofwaterduetoitsgeologicalorigins.


11

(uppercaption)

TheGrottoesofCatulluspromontory


12

GEOLOGICALSIRMIONE

Alongwalkthroughmillionsofyears

6-GrottediCatullo=GrottoesofCatullus

5-FonteBojola=TheBojolaSpring

4-LidodelleBionde=LidodelleBiondebeach

3-CollinaCortine=Cortinehill

2-PasseggiatadelleMuse=PasseggiatadelleMusewalk

1-CastelloScaligero=ScaligerCastle


13

IfyouwanttoviewSirmionefromageologicalpointofview,entertheoldtownpasttheScaligerCastle,thenturnrightalongthecastlemoatandturnleftintoVia Dante, continuing behind the church of Santa Maria della Neve. This iswhereyourjourneythroughtimebegins.

1- BELVEDERE“SPIAGGIADELLEMUSE”BEACHFromthisvantagepointyoucanadmireLakeGardainitsentirety.Itisinterestingto observe the differentmorphology of the lake and you easily distinguish thenorthern end of the lake and the southern end, divided by a hypothetical linefromGardatoSalò.Tothenorth-eastyoucanseetheimmensityofMountBaldoand to the north-west Mount Pizzoccolo and the rock formations of the westcoast.Theconstituent rock isDolomite.Thismorphology,dominatedbyasteepcoastlineoverhanging the lake, is causedby the fluvial genesisof the lake itself(partialdesiccationof theMediterraneanSea,strong increase in rivererosion intheAlpinevalleyfurrows)subsequentlyshapedbyglaciers,whosedepositshaveproduced the hills of the Benaco moraine amphitheatre, with gentler slopes(Bardolino-Lazise-Peschiera)tothesoutheast.

2- BEGINNINGOFTHE“PASSEGGIATADELLEMUSE”WALKWalkingbesidethelakeonthePasseggiatadelleMuse,toyourleftyoucansee the Cortine promontory formed by the so-called "SirmioneConglomerate". These are non-stratified conglomerates, withpredominantly calcareous pebbles, recently dated by isotopicmethods totheLowerPleistocene.Wecanobservethattheconglomerateisformedbyroundedpebbles(duetotheirlongjourney),cementedintotherockbythepressureoftheglacialmassespresentduringtheQuaternary.Thepebbleshavedifferentconsistenciesaccordingtotheirage.ThisrockformationcanbeseenalongalmostnearlyallofthePasseggiatadellaMusewalkuptothepierofHotelVillaCortine,wherethereisasharpchange.


14

3- VILLACORTINEPIERThisiswherethegeologyofSirmionechanges.Behindthebaryoucanseeanother type of rock, which is part of a formation called the ScagliaLombarda,madeupofsedimentarylimestoneandmarl,withveryevidentstratification planes, predominantly pink, red and gray in alternation. Thesametypeofrockcanalsobeseenonthelakebottom.ThepresenceofthisformationisduetotheSanVigilio-Sirmione-Rivoltellafaultthatisfoundindepthatthispoint.Thecompressivetectonicmovementofthisfaultcausedtheaforementioned rock formation,whichwashundredsofmetresdeep,topushtothesurface.Thisrockformation(ScagliaRossa)datesbacktotheCretaceousperiod,inotherwordsabout80millionyearsago!

4- LIDODELLEBIONDEPIERAsyoucontinuetoLidodelleBiondebeach,atthepier,tothenorth,youcanseetheGrottoesofCatulluspromontory,madeupentirelyof“ScagliaRossa”marlandlimestone.Lookingattherockinfrontofyou,youcanseehow the rock layers run inaW-NWdirection,with inclinationsof6° and10°, in a NE-SW direction. This trend remains constant throughout therocky escarpment, as we shall see later. The Bojola spring can also befound in this area, at about 200metres from the lake shore, in a placewhere the thermalwater reaches the aforementioned fault and finds itswaytothesurface.Nearthebeachthereisoneofthewellsdugtoexploitthehotspring.


15

5- PIAZZALEORTIMANARAPiazzaleOrtiManaraisoutsidetheentrancetotheGrottoesofCatullus:fromthispanoramicpositionyoucanobserveonceagainthedifferentmorphologyofUpperandLowerGarda.Southof theGulfofSalò the landscape isgentler,mostlyhilly,with the exception of the Rocca di Manerba, which is an older formation. Theorigin of the Rocca is attributable to compressive tectonicmovements along thenumerousfaultspresentinthatarea.ThehillssouthoftheRocca,whichdistinguishthe south-west coast of the lake, are instead of glacial origin and formed bymoraine deposits,mainly silty-clay, depositedwhen the glaciers retreated in thevariousphasesthatshapedthelowerendofthelake.TotherightoftheRoccadiManerbayoucanseethelargestofGarda’sislands:theIsoladelGarda,alsoknownasIsolaBorghese.

6- THEWALKBACKINTOTOWNWhilereturningtothetowncentre,alongviaCatullo,youcanonceagainseethelimestoneandcalcareousmarlof theCretaceous (ScagliaRossa)perioduntil youreachPiazzalePiatti.ContinuingalongviaPiana,the"Sirmioneconglomerate"canbeseenagainbehindhousesandhotels.TheareaofSirmionepeninsulathatdoesnot have any rock ismainly formed by gravel deposits of lake origin and glacialdeposits,mainlysilt-clay,linkedtothevariousglacialphasesoftheQuaternary.


16

ThegeologyofSirmione

AswehaveseenwhendiscussingtheoriginofLakeGarda,theterritoryofSirmioneconsists mainly of fine-grained deposits of a silt-clay nature, in other words, ofmaterialdepositedbytheglaciersthatformedthesouthernendofthelake.

The tip of the peninsula,which extends into the lake, is different.We can in factidentify the presence of outcropping rock: the promontory of the "Grottoes ofCatullus"formedbymarlandredlimestone,inflakes(Cretaceous=80millionyearsago) and the promontory of the Cortine hill, constituted by the "SirmioneConglomerate", composed of stratified conglomerates with mainly calcareouspebbles(EarlyPleistocene=about1millionyearsago).

Theoriginofthesetworockformations,belongingtodifferenteras,surfacingonlyat the tip of the peninsula, is due to a tectonic phenomenon. In fact this area isintersectedby the "PuntaSanVigilio - Sirmione -Rivoltella" reverse fault that cutthenorthernpartofthepeninsulaintwoandcausedtheriseoftherockysubstrate,whichshouldbedeeper.

Tosummarise,whatisunusualabouttheterritoryofSirmioneisthecoexistenceofvarious types of rocks attributable to epochs and geological phenomena that areextremely different from one another and that cannot be attributable to otherstructuresnearbyfromageographicalpointofview.

(bluebox)

REVERSEFAULT:afaultinwhichonepartispusheduphigherthantheother.Reversefaultscanleadtomovementswhereolderrocksoverlapmorerecentrocks.


17

(uppercaption)

TheSirmioneConglomerate.

(lowercaption)

TheSanVigilio–Sirmione–Rivoltellafault.


18

TheBOJOLAspring

Itisnotuncommontofindhotspringsalongdifferentkindsoftectonicfaultlines.Inthe case of Sirmione the "San Vigilio - Sirmione -Rivoltella" fault has allowed thethermal water to reach the surface as the Bojola spring, which flows about 200metresfromtheshore,atadepthof18metres,withatemperatureof70°Celsius.

This thermal water begins its journey in the area of the small Dolomites (MountBaldo and the Lessini mountains) where the meteoric waters infiltrate, due tocarsism,intotherockfracturesandcavitiesanddescendtoadepthofabout4km,flowingoverasolidwaterproofcrystallinebaserock.Duringitsjourney,thewaterisenriched with chemical components that give it a sulphurous-salsobromoiodiccharacter i.e. enriched with sulphur, in the form of hydrogen sulphide, sodium,bromineandiodine)and,duetothegeothermalgradient,itstemperatureincreases.Thepresenceofgas(watervapour)alsocreates

(lowercaption)

Bojolathermalwater.


19

anincreaseinpressure,whichcausesthewatertorisealongfracturesorfaultlines.Thefirstinformationabouttheexistenceofthespringdatesbackto1546,butitwasonly in 1891, thanks to more precise studies made by the science professor atBagatta high school, Don Angelo Piatti and the ingenuity of Giuseppe Piana, thatthey were able to channel the thermal water to the surface. Since then theexploitation of the spring has become an economic and tourist opportunity forSirmione.Todate, threewellshavebeendug toaccess thewater,allon the faultlinementionedabove.

(uppercaption)

ThetipofSirmionepeninsulawithitsgeologicalfeatures.MAP

Hotwatersource

KEY

Depositideltardopleistocene/olocene=LatePleistocene/Holocenedeposits

ConglomeratodiSirmione(SIR2)=Sirmioneconglomerate(SIR2)

ConglomeratodiSirmione(SIR1)=Sirmioneconglomerate(SIR1)

Calcarimarnosideltardocretaceo=LateCretaceousmarllimestone

Calcarimarnosideltardocretaceo=LateCretaceousmarllimestone

Piattaformadiabrasione=Abrasionplatform

Affioramenti=Outcrops

Faglie=Faultlines

Giacituradistrato=stratasequence


20

Seismicityoftheterritory

Earthquakes are phenomena caused by tectonicmovement along a fault line andthey generate energy transmitted through elastic waves that make the earthvibrate.Thepointoforiginofanearthquakeiscalleditshypocenterandislocatedonthefaultline;itssurfaceprojectionpointiscalledtheepicentre.

There are different types of plate boundary movements that can generateearthquakes:

• Convergent(twoplatesslidetowardeachotherandcollide).

• Divergent(twoplatesslideapartfromeachother),

• Transform(twoplatesslideorgrindpasteachother).

(upperimage)Scarpatadifaglia=Faultescarpment

EPICENTRO=EPICENTRE

IPOCENTRO=HYPOCENTRE

Faglia=Fault

(blueline)

Fagliatrascorrente=Transformfault

Faglianormale=Normalfault

Fagliainversa=Reversefault


21

The seismograph is an instrument that traces seismic waves in the form of aseismogram.The"magnitude"isdeterminedbythemaximumheightoftheseismicwave. However magnitude is not the only way of measuring the effects of anearthquake. Local seismic amplification phenomena are also crucial, linked to thecharacteristicsof the landonwhich thebuildingsare constructed: a clay soilwithlowconsistencyamplifiestheeffectsoftheseismicshock,whereasinthepresenceofarockysubstratetherearenosucheffects.Furthermore,coseismiceffectslinkedto an earthquake can cause serious damage to buildings located in areas at risk,suchasslopessubjecttolandslides.

(bluebox)

GEOGNOSTICSURVEY:Asurveybasedonanalysisoftheground,itsstrataanditsgeologicalcharacteristics.From"GEOGNOSIA",inancientGreekGEO(LAND)+GNOSIA(KNOWLEDGE).

ASeismicHazardMapcreatedbytheINGVestablishesthebasicseismicdangersofthe Italian territory through parameters that indicate expected seismic activity. Ithasbeenusedtosubdividethenationalterritoryintoseismiczonesbyestablishingdifferent levelsofdanger,decreasing from1 to4. Sirmioneandthe lowerendofLake Garda are classified in seismic zone 2, but more detailed studies (SeismicMicrozonation)of the town,basedongeognosticgroundsurveys andgeophysicalsurveys,havenotedtheheterogeneityoftheterrainandthedifferentareasbasedonthepossiblephenomenaoflocalseismicamplification.ForthisreasonSirmionehas been mapped by subdividing it into micro-zones that take into account thedifferent nature, and therefore the different response, of the ground to seismicwaves. The detailed analysis of the territory, through seismic microzonation,therefore provides the tools to draw up a Territorial Government Plan that takesintoaccounttheseismicrisk,

(upperimage)

SISMOGRAMMI=SEISMOGRAM

ROCCIA=ROCK

TERRENISOFFICI=SOFTGROUND

RILIEVOINROCCIA=ROCKYHIGHGROUND

ONDESISMICHE=SEISMICWAVES


22


23

Key

Terrenidicopertura=Groundcoverage

CLIc - Silty clay with faintly gravelly stretches ranging from consistent to veryconsistent,ofalakebednature

CLti-Siltyclaywithfairlygravellystretches,fromslightlyconsistenttoconsistent,oftill

GMfl - Silty and clayey gravel and sands frommoderately thick to thick, of glaciallakebednature

GMlc-Gravelwithpebblesandsilty-clayeysandsfrommoderatelythicktothick,ofalakebednature

MLlc - Sandy silt with fragments of rock, from scarcely tomoderately thick, of alakebednature

Substratogeologico=Geologicalsubstrate

LPS-Lapideostratificato=stratifiedrock

GR-Granularecementato=Cementedgranularground

Elementitettonicostrutturali=Structuraltectonicelements

Fagliainversapotenzialmenteattivaecapace(certa)=

Potentiallyactivereversefault(certain)

Fagliainversapotenzialmenteattivaecapace(incerta)

Potentiallyactivereversefault(uncertain)

Giacituradistrato=stratasequence

(lowercaption)

Mappadimicrozonazionedelterritorio=Microzonationmapoftheterritory


24

a fundamental tool for informedplanningof infrastructures andbuildings in strictcompliance with seismic regulations. This tool was also used to update themunicipalEmergencyandCivilProtectionPlan,againbasedonseismicrisk.


25

ProducedbyProLocoSirmione

Aspartofawork-relatedlearningproject

withBagattaHighSchoolinDesenzano(Years2018-2019)

ProjectleaderLUISELLABACCINELLI

Geologicalinstructionandrevisionoftextsby

GeologistNICCOLO’CRESTANA

GeologistGIOVANNIFASSER

Texts,ideationanddevelopmentofmaterialsby

ALINAANJUM–classIVAsocialscience

GIULIOBELLA–classIVAscience

SAMIHASSANE–classIVAscience

MARTINAMOSCHETTO–classIVAscience

TIAREELISABETHPRATI–classIVBlanguages

ANNASTERZA–classIVAclassicalstudies

TranslationbyLORETTASIGNORIandKENTHOMAS

Asincerethankyouto

PatriziaFacchinettiandRossellaBaccinelli

Photographsofthegeologicalwalk

(centresection)takenbythestudentsofBagatta,theotherswereavailableoninternet.

ThankyoualsotoHotelVillaCortinefortheirkindco-operation.

Documents

GEOLOGICAL SIRMIONE A walk through time · Geological Sirmione. A walk through time 2 The history of Sirmione and Lake Garda is inevitably bound up with its geological formation over