Abigbouldersticksoutofthedriedmud.Thisrockistooheavytopickup.Yet,ithasmysteriouslymoved.Afewdaysago,itwas250meters(820feet)away.Atrailshowswhereitmovedacrossthe dirt.
Thisisn’ttheonlyrockonthemovehere.ManyoftherocksinthispartofDeathValleydon’tstayinoneplace.Theirtrailscrisscrossthecrackedmudofadried lake.
Someglideinstraightlines,thenstopandsettleintothedrymud.Somerocksmoveinpairs.Otherszigzagthiswayandthat,leavingajaggedtrail.Howdidtheymove?Noonehaseverseenit.It’sa mystery.
Bouldersmysteriouslyzigand zaginDeathValley,California, U.S.A.
North
America
Death
Valley
Amantakesaphotographofbouldersandtheir trails.
Searching
foraCause
Overtheyears,peoplehavecomeupwithwildwaystoexplainhowtherocksmove.Somepeoplesaytherocksaremagicalandmoveontheirown.Otherssayaliensfromspacearemovingthem.Stillothersthinkprankstersareplayingtricks,movingtherockswhennooneislooking.Scientistshavelookedforevidenceinnaturetofind answers.
Anearlytheorywasthatgravitymovestherocks.Thisforcecouldtugontherocksandpullthemdownhill.Eventhoughthisarealooksflat,itactuallyslopesa little.
So,scientistslookedforpatternsinwhichdirectiontherocksmoved.That’swhenthegravitytheoryfellapart.Mostoftherockshadmoveduphill.Gravitypullsthingsdown,not up.
Anothertheorywasthatwindspushedtherocks.Thewindsherearestrong.Thescientistsdidexperimentstotestthewindtheory.Oneevenusedthewindfromaplanepropellertotrytomovetherocks.Thetestsshowedthatwindsaren’tstrongenoughtomovethebiggest boulders.
Thisvideofollowsthetrailmadebyaheavy stone.
ColdClue
Finally,scientistsnoticedthattherocksseemtomoveonlyinthewinter.That’swhenthisareasometimesfloods.Athinlayerofwatersurroundsthe rocks.
Studyingthewaterledscientiststonewtheories.GeologistPaulaMessinaobservedathinlayerofslimybacteriagrowinginthewater.Theslimemakesthegroundreallyslippery,sotherockscanslideeasily.Evenasmallwindmaybeabletopushthe rocks.
AnExperiment
ThewatergavescientistRalphLorenzadifferentidea.Couldringsoficeformaroundtherocks?Sinceicefloatsonwater,theicemightlifteventhebiggestrocksalittle.Thenalightwindcouldpush them.
Lorenzdidanexperimenttoseeifhistheoryworked.Hetesteditonamodel,andtherockmoved!Itsbottomscrapedalongthesand,leavingatrail.So,itseemsthaticeandwindcouldhelptherocksmove.Socouldbacteriaandwind.Boththeoriesarepossible.Noone’severseentherocksmove,sothismysteryremains unsolved.
Scientist RalphLorenz standsnearafloodedareaofDeath Valley.