Download Plate Tectonics and Magma Movement

PlateTectonicsandMagmaMovement
You’vebeenhiredbyateamofscientiststodetermineifthecrustalplatesactuallymoveovertime.They’ve
sentyouatableofdatathatincludestheinformationabouttheHawaiianIslandsandsomeotherislands
thatarenearby.Thescientistshavetoldyouapproximatelyhowfarthevolcanicislandsareawayfrom
Hawaii’sKilaueaandapproximatelyhowoldthebasaltrocksontheislandsare.Theyneedyoutoanswer
thequestionsbelowinordertohelpthemdetermineifthecrustismovingandhowfastitismoving.They
wouldalsolikeyoutopredicthowfarawayfromKilaueaanothervolcanowillformifthecrustcontinuesto
move.
1. Firstgraphthedataonthegraphpaper.Thescientiststhinkthatitmightbeeasiesttolabelthe
islandsusingthenumbersthattheyprovided.(Rememberwhenyousetupyourgraphthatspeed
isequaltothedistancethatsomethingtravelsoverthetimethatittakestogothatdistance.)
2. Basedonthelocationoftheislandsasshownonyourgraph,doestheanomalyresponsiblefor
creatingtheHawaiianIslandChainappeartobemoving?(Includetheevidenceforyourideaand
explainwhattheevidencemeans.)
3. Ifthethingresponsiblefortheislandsismoving,canyoucalculatehowfastitisgoing?(Calculate
itsaveragespeed.)
4. In200,000years(0.2millionyears)willtherebeanotherisland?Iftherewillbeone,wherewillit
belocatedrelativetoKilauea?(Thisneedstoincludedistanceanddirection.)
HawaiianIslandsHotspotData
Volcano
number
Volcanoname
Age(Millions
ofYears
1
Kilauea
0.2
distance
from
Kilauea
(km)
0
3
MaunaKea
0.375
54
5
Kohala
0.43
100
6
EastMaui
0.75
182
7
Kahoolawe
1.03
185
8
WestMaui
1.32
221
9
Lanai
1.28
226
10
EastMolokai
1.76
256
11
WestMolokai
1.9
280
12
Koolau
2.6
339
13
Waianae
3.7
374
14
Kauai
5.1
519
15
Niihau
4.89
565
15a
Kaula
4
600
17
Nihoa
7.2
780
20
unnamed1
9.6
913
23
Necker
10.3
1058
26
LaPerouse
12
1209
27
BrooksBank
13
1256
30
Gardner
12.3
1435
36
Laysan
19.9
1818
37
Northampton
26.6
1841
50
Pearl&Hermes
20.6
2291
52
Midway
27.7
2432
57
unnamed2
28
2600
63
unnamed3
27.4
2825
65
Colahan
38.6
3128
65a
Abbott
38.7
3280
67
Daikakuji
42.4
3493
69
Yuryaku
43.4
3520
72
Kimmei
39.9
3668
74
Koko
48.1
3758
81
Ojin
55.2
4102
83
Jingu
55.4
4175
86
Nintoku
56.2
4452
90
Suiko1
59.6
4794
91
Suiko2
64.7
4860
HawaiianIslandsandHotSpots
KristaLindemann,April18,2001
Introduction
Whenyouthinkofislands,especiallyHawaii,thefirstthoughtthatcrossesone’smindiswarm
weather,sunnybeaches,andcoconuts.Buthaveyoueverwonderedhowislandssuchasthe
Hawaiianchainislandswereformed?Itisanamazingconceptthatapieceoflandislocatedoutin
themiddleofalargeocean.
HawaiianIslandFormation
Whendiscussingtheformationofislands,especiallytheHawaiianIslands,thetheoryofplate
tectonicsmustbereviewed.Theearthisbrokeninto12majorplates50-100kilometersthick,
whichmovehorizontally.Theseplatesfloatandslidealongtheearth’smantle,whichexplainswhy
mostoftheworld’svolcaniceruptionsandearthquakesoccurhere.
HowdoesthetheoryofplatetectonicsrelatetoformationoftheHawaiianIslands?Itdoesn’treally,
andthatistheamazingconceptbehindthesesHawaiianIslands.95percentoftheworld’sknown
volcanoesoccurclosetotheseplatemargins,butwhatabouttheremaining5percentofvolcanoes
thataren’toccurringattheplateboundary?HawaiianvolcanoesoccurwellwithinthePacificPlate,
closeto4,000kilometersfromthenearestplateboundary.Howthencouldthischainofislands
forminthemiddleofaplateawayfromitsboundariesifthecenterofvolcanicactivityoccursat
plateboundaries?
Thiswasamajorpuzzleinrelationtoplatetectonics.ACanadianscientist,J.TuzoWilson,
developedthisanswer.Wilson,whowasoneoftheco-authorsoftheplatetectonictheory,
suggestedinthe1960’sthattheconvectionintheunderlyingmantleproducedwhatwenowknow
ashotspots,andthattheislandsarosefrommagmapokingthroughtheseafloorastheplate
movedoverthehotspot.WilsonlookedtotheHawaiianIslandChainasdramaticproofofplate
movement.StretchingbothtothewestandnorthofHawaii,thereisastringofsmallerislandsand
submergedvolcanoesabout3,700mileslong.Eachoftheseislandsorseamounts(avolcanic
mountainfoundbelowsealevel)issaidtohaveformedinthelocationofHawaiipresently.Adding
toWilson’stheory,JasonMorganfurtheredtheideaofthehotspot.Morgansuggestedalarge
amountofexcessenergywaswellingupfromdeepwithintheplanet.Manyscientistsquestioned
Morgan’stheory,statingtheHawaiianchainofislandshasabendinit.Morganclaimedthereason
forthebendwasbecausethehotspotisstationary,concludingthatthePacificPlatechanged
directionaroundtheageoftheislandsatthebend.
Insimpleterms,hotspotsappeartobeplumesofmoltenmaterialthatwellupfromafixedposition
deepwithintheearthastheplatesmoveabovethem.Butit’snotthatsimple.Earthquakesplaya
majorroleinthehotspotformation.Thelocationofearthquakesatdepthindicatestheprocess
throughwhichmoltenrockswellupward.Theforcecomesfromlightermoltenrocksurroundedby
densecrystallinerocks.This,inreturn,changesthetemperatureandpressure,breakingthehard
surroundingrock,whichcausesearthquakes.
Themagmacomesfromalayer30-37milesbelowtheplate.Themagmathenrisestotheshallow
chamberpassingthroughthemantleandthecrustandfinallyreachingthesurface.Asthemagma
reachesthesurface,itcoolsquicklyandformspillowlava.Thispillowlavarestsonthecontact
edgesofthevolcanogrowingquicklyasmagma.Withtime,thesedevelopingvolcanoes-sea
mounts-becomecomplexuntilfinallybreakingthesurfaceoftheoceanandbecomeanisland.
WilsonthenexplainedtheHawaiianvolcanicchainofislands.Heproposedthattherewasan
upwellingofhotplasticrockoriginatingdeepbeneaththeplate.Thisplumerisesbyveryslow
convectionandcausessomemeltingbecauseofdecompressionasthehotrockrisesintothe
mantle.Thisplumeanditshotspotstayinonelocationwhiletheplateslidesoverthismagma.A
volcanothendevelopsoverthehotspotsandthendriftsawaywiththemovingplate.Thisprocess
isrepeatedcontinuouslyaslongastheplatesremaininmotionandthehotspotremainsactive.
Sohowdoweexplainthecontinuousthermalplumeataconstantspot?Theheatsourcecomes
fromthemantleoreventhecore.Thisindicatesthatthemagmausedinhotspotscomesfroma
deepersourcethanvolcanoesatplateboundaries.Infact,theHawaiianhotspothasbeenactivefor
80millionyears.Ifthetheoryofhotspotsholdstrue,theislandfurthestawayfromthehotspot
shouldbetheoldestandtheislandclosesttothehotspotshouldbetheyoungest.Also,theagingof
volcanoesawayfromthehotspotshouldmatchtherateofplatemovement.TheHawaiianIsland
chainindicatesthattheplatemoved10cmperyear.Thehotspottheoryalsoexplainedwhythe
HawaiianIslandsonlyhaveactivevolcanoesatthesoutheastendofthechain.Thehotspot
explanationsuggeststhatanotherislandwillsoonform.Thenextto-beisland,whichisinthe
works,istheLoihiseamount.
Mosthotspotvolcanoesareeffusive.Thisisconceptexplainshowtheislandsareformed.An
effusiveeruptionreferstothetypeoferuptionthatcharacterizesHawaii.Effusiveisatypeof
eruptioninwhichthegascontentinthemagmaislowandthemagmaislesscohesivecausingthe
gasestoboiloutlessviolently.
Conclusion
Newdiscoveriesaremadeeverydayanditbecomesmoreevidentthatthestudyofvolcanoes,plate
tectonicsandhotspotsareallverycloselyrelatedtotheformationoftheHawaiianIslands.Sothe
nexttimeyouthinkaboutHawaii,don’tjustconsiderthesun,sand,andbeaches.Thinkaboutthis
amazingcreationofislandformationthroughtheprocessofhotspotsandrealizejusthowcomplex
theworldreallyis.
Bibliography:
Ballard,R.(1983).ExploringOurLivingPlanet.WashingtonD.C:NationalGeographicSociety.
Decker,B.,Decker,R.(1991).MountainsofFire:TheNatureofVolcanoes.Cambridge:Cambridge
UniversityPress.
“HotSpots”:MantleThermalPlumes.May5,1999.U.S.GeologicalSurvey(USGS).
http://pubs.usgs.gov/publications/text/Hawaiian.htmlMarch7,2001
Miller,R.(1983).PlanetEarth:ContinentsinCollision.Alexandria:Time-LifeBooks.
Prager,E.(2000).FuriousEarth.NewYork:McGraw-Hill.
SummarizingOurReading–HawaiianIslandsandHotSpots
Directions:Formgroupsoftwo.OnepartnerwillreadthefirstparagraphoftheHawaiianIslands
andHotSpotsarticleoutloud.Whenthefirstpartnerisfinished,thesecondpartnerwill
summarizetheparagraphoutloud.Bothpartnerswilldeterminewhatthesummaryofthe
paragraphisandwriteitdowninthespaceprovided.Continueuntilallparagraphshavebeenread
andsummarized.
Paragraph1:
Paragraph2:
Paragraph3:
Paragraph4:
Paragraph5:
Paragraph6:
Paragraph7:
Paragraph8:
Paragraph9:
MainIdeaProtocol
Afteryouhavefinishedreading,summarizingandhighlighting,determinewhichofyourhighlights
ismostimportanttoyou.Paraphrasetheoneyoupickedandrecordyourparaphrasebelow.
(Thisisyourmainidea.)
Formagroupoffourpeople.Youwillbeusingthelastwordprotocoltoshareouteveryone’smain
ideas.Aftereveryonehasfinishedsharingandparaphrasing,discussinyourgroupswhatyour
groupmembersdeterminedistheoverallmainideafromthereading.Recordthegroup’smain
ideainthespacebelow.
MapComparison
ThescientistswereabletoconvinceNASAtotakesomeimagesoftheHawaiianIslandchainand
emailittoyou.Whilereviewingthetopographicaldatawiththeteam,thescientistsdiscoverthat
thereisanothervolcanoforminganislandoffofthecoastoftheBigIslandofHawaii.Theyalso
receiveddatasuggestingthattheanomalycausingtheislandchainhasnotchangeditslocation
overtimeandthatitliesbelowtheEarth’scrustintheEarth’smantle.Inordertomakesurethat
thisdataistrue,theysentittoyouforverification.
1. Writealistofinformationthatyounoticeaboutthemapandcomparethemaptoyour
graphonthepreviouspage.
2. ThescientistsnamedthenewvolcanoLoihiandsaythatitisapproximately60kmfrom
Kilauea.Isthisconsistentwithyourvolcanoprediction?
3. Ifthehotspotinthemantleisnotmoving,thenwhatismovingthatiscausingthevolcanoes
toappeartomovefromAlaska/RussiantowardCalifornia?
Morequestions…
4. IfthethingthatisactuallymovingisthePacificPlateoftheEarth’scrust,dothemapand
yourgrapheddataindicatethatthePacificPlateismovingataconstantspeed?
5. Drawarepresentationofwhatmighthappeninthenext20millionyearsonthePacific
Plate.