Eruption
andErosion
SciencetellsusadifferentstoryoftheIguazúFalls.Thefallsstartedtoformabout130millionyearsagowhenthesupercontinentGondwanabrokeapart.SouthAmericaseparatedfromAfrica.ThistriggeredoneofthelargestvolcaniceventsinEarth’s history.
Atthetime,theareawheretheIguazúFallsislocatedwasagiantdesert.LavapouredfromvolcanoesandotheropeningsinEarth’scrust.Itcoveredthedesert.Thenthelavacooledandhardened.Itbuiltupaplateaumadeofthree,massiveflatlayersofbasalt rock.
![](/nationalgeographic/adventurer_march_2021/the_wonders_of_the_falls_3/1044974/Step_1.400_0_1.png)
Waterfallsareformedasariverflowsfromhardrocktosoft rock.
![](/nationalgeographic/adventurer_march_2021/the_wonders_of_the_falls_3/1044982/Step_2.400_0_1.png)
Therivererodesthesoftrockatafasterrate.Itformsastepinthe river bed.
![](/nationalgeographic/adventurer_march_2021/the_wonders_of_the_falls_3/1044983/Step_3.320_0_1.png)
Thehardrockthatisleftcreatesahardledge.Theriverfallsoverthe ledge.
![](/nationalgeographic/adventurer_march_2021/the_wonders_of_the_falls_3/1044973/NGX0321_EE_20A.480_0_1.jpg)
TheIguazúRiveremptiesintotheParanáRiverwherethebordersofBrazil,Argentina,andParaguaymeet.ThisareaisknownastheTriple Frontier.
ButEarth’splateskeptmoving.Thelayerswereliftedintoahighplateau.Faults,orcracks,appearedinthem.Waterstartedtorundownthefaultsanderoded,orworeaway,theland.ThemightyParanáriverbedformed.Muchlater,theIguazúRiverappearedandstartedtofeedinto it.
Thefallsstartedtoformatthesitewherethesetworiversmeet.Buttoday,theyareabout23kilometers(14miles)upstream.Erosion,onceagain,getsthecredit.AswaterfellintotheParanáRiverfromtheIguazú’splateau,it weatheredawaythelayersofrockonthebottom.Theupperlayershadnothingtosupportthem,so
they crumbled.
Today,thelayersofIguazúFallslooklikeagiantstaircase.Andalong,narrowcanyonwithscoresofrockyislandsleadsthewaytotheParanáRiver.Erosioncontinues,andthecanyongetsabout3millimeters
(0.1inches)longereach year.
Brazil
Argentina
Paraná
Iguazú
Paraguay
IntotheRainforest
Asamazingasthewaterfallsare,thewaterisjustpartofthebeautythatsurroundsIguazúFalls.TheyexistinthesubtropicalAtlanticForest,oneofthemostbiodiverseecosystemsinSouthAmerica.Itishometomorethan2,000plantspecies,
68mammals,422birds,morethan
40reptiles,18amphibians,and250typesofbutterflies.Manyoftheplantsandanimalsthatliveherearen’tfoundanywhereelseinthe world.
![](/nationalgeographic/adventurer_march_2021/the_wonders_of_the_falls_3/1044979/toukan.320_0_1.png)
![](/nationalgeographic/adventurer_march_2021/the_wonders_of_the_falls_3/1044978/monkey.320_0_1.png)
blackcapuchin monkey
toucan
![](/nationalgeographic/adventurer_march_2021/the_wonders_of_the_falls_3/1044976/NGX0321_EE_21A.640_0_1.jpg)
Bewareofthecoatis!Theycaneasilybiteyourhandwhentheytrytograbyour food.
AsIwalkedthroughtherainforest,Isawtallpalmtreesandeventallerlaurelsandrosewoods.Papayafruithungfromsmalltreesundertheumbrellasofhuge leaves.
Flashesofblueflutteredthroughtheair.Youreyehadtobequicktospotthesebluemorphobutterflies.Ialsocaughtaglimpseofatoucaninflight.Isawcapybarassunningthemselvesontheriverbank.Ialsogotagoodviewofayoungcaimanrestinginshallowwater.Raccoon-likecoatisseemedtobeeverywhere!Ikeptaneyeoutfortapirs,monkeys,giantanteaters,orjaguars.Thoseanimalslivehere, too.