Upload
others
View
0
Download
0
Embed Size (px)
Citation preview
Phenomenon:FrostWedgingThissimpledemonstrationcanbeusedasaphenomenonatthebeginningofaunitonphysical(mechanical)weatheringofrocks.ThiseasydemonstrationcanbeusedtoactivatestudentthinkingabouthowphysicalprocessesmaychangerocksattheEarth’ssurface.Frostwedgingisaphysicalprocesswhererockscanbebrokenintosmallerpiecesandiscausedbyrepeatedcyclesoffreezingandthawing.Waterhastheuniquepropertyofexpanding(~9%)whenitfreezes.Theexpansionoficeiswhyicefloatsinliquidwater.AttheEarth’ssurface,liquidwaterworksitswayintocracksinrock,anduponfreezing,expandsandenlargestheseopenings.Aftermanyfreeze-thawcycles,therockisbrokenintoangularfragmentsasseeninthetopfigure.Frostwedgingisanespeciallyefficientprocessinmountainousregionswherethereisalargeseasonaland/ordailychangeintemperature.Inthisclassroomactivity,plasterofParisisamodelforrockandasmallwaterballoonisamodelforwaterwithinafractureinarock.MixwaterandplasterofParis(accordingtothelabeldirections)andhalffilla12oz.plasticcupwiththeplaster.Putasmallwaterballoon(~1inchdiameter)inthecenterofthecupandfilltherestofthecupwithplaster.Makesurethattheplastercompletelyencapsulatesthewaterballoonandthatitisnotexposedtothesideofthecup.Aftertheplastersets,removeitfromthecup.Asanexperimentalcontrol,itisusefultoprepareanothercupofplasterwithoutawaterballoon.
Aftertheplasterhasdried(oneormoredays),putbothpiecesofplasterintoafreezer.Asthewaterballoonfreezes,itexpandsandcrackstheplaster.Inthefigure,thepieceofplasterontheleftdoesnotcontainawaterballoonanddidnotfracturewhenputinthefreezer.Ontheright,theplastercontainsawaterballoonthatfracturedwhenitwasfrozen.Usingacontrolinthisactivity,demonstratesthattheplasterfracturesbecauseoftheexpansionofthewaterballoonwheniffreezesandnotjustbecausetheplasterwasputinthefreezer.
hays.outcrop.org/images/weathering/press4e/figure-07-12.jpg