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LT3:Icandescribewhatmayhappenwhenplateboundariesmeet(e.g.,earthquakes,
tsunami,faults,mountainbuilding),withexamplesfromthePacificNorthwest.
Part1:ContinentalCrustvsOceanCrustBuoyancyDemo
TennisBall
SoccerBall
RelativeThickness
RelativeDensity
RelativeThickness
RelativeDensity
6.7 cm
0.367g/cm
22 cm
0.077g/cm
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Observations
Observations
TypeofCrust
TypeofCrust
Oceanic
Continental
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Part2:PlateTectonicsPhET
Intheearly1960s,thetheoryofplatetectonicsemergedandstartedarevolutionintheEarthSciences.Thesubsequent
verificationandrefinementofthetheoryhasledscientiststorecognizethat,directlyorindirectly,platetectonicsinfluence
nearlyallgeologicprocesses.
ThetheoryofplatetectonicsstatesthattheEarth’soutermostlayerisbrokenintoadozenorsoplatesthataremoving
relativetooneanotherontopofahotterlayer.
Settings
● Clickonthe“PlateMotion”Tab
● Checkthe“ShowLabels”box
● Checkthe“ShowSeawater”box
Example1.Drag2oldoceaniccrustsontothescreen.DragtheplateinthedirectionoftheREDarrow.
Diagram/Sketch
Directionof
PlateMovement
ç
è
BoundaryType
Divergent
Whatistheeffect/outcomeofthisplatemovement?
The ocean basin grows / gets bigger in size.
Example2.Drag2newoceaniccrustsontothescreen.DragtheplateinthedirectionoftheREDarrow.
Diagram/Sketch
Directionof
PlateMovement
ç
è
BoundaryType
Divergent
Whatistheeffect/outcomeofthisplatemovement?
The ocean basin grows / gets bigger in size.
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Example3.Drag2continentalcrustsontothescreen.DragtheplateinthedirectionoftheREDarrow.
Diagram/Sketch
Directionof
PlateMovement
ç
è
BoundaryType
Divergent
Whatistheeffect/outcomeofthisplatemovement?
The land/continent thins out and a new ocean forms
along the boundary. Over time the continents are
pushed further and further apart.
Example4.Drag1oldoceaniccrustand1newoceaniccrustontothescreen.DragtheplateinthedirectionoftheGREENarrow.
Diagram/Sketch
Directionof
PlateMovement
è
ç
BoundaryType
Convergent Subduction
Whatistheeffect/outcomeofthisplatemovement?
The old ocean crust gets pushed under the newer
ocean crust forming a trench and a volcanic island arc
on the younger ocean crust.
Example5.Drag1oldoceaniccrustand1continentalcrustontothescreen.DragtheplateinthedirectionoftheGREENarrow.
Diagram/Sketch
Directionof
PlateMovement
è
ç
BoundaryType
Convergent Subduction
Whatistheeffect/outcomeofthisplatemovement?
The ocean crust gets pushed under the continental
crust forming a trench and a volcanic arc on the
continent.
Example6.Drag2continentalcrustsontothescreen.DragtheplateinthedirectionoftheGREENarrow.
Diagram/Sketch
Directionof
PlateMovement
è
ç
BoundaryType
Convergent - Collision
Whatistheeffect/outcomeofthisplatemovement?
The continents collide and smash into each other. The
result is the thickening of the crust both above and
below the surface forming a mountain range.
Example7.Drag2crustsontothescreen.DragtheplateinthedirectionoftheBLUEarrow.
Diagram/Sketch
Directionof
PlateMovement
é
ê
BoundaryType
Transform
Whatistheeffect/outcomeofthisplatemovement?
The plates slide past each other. No crust is created or
destroyed.
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Part3:PlateBoundariesLab
ThetheoryofplatetectonicsstatesthatthecrustoftheEarthiscomposedof7majorplatesandnumeroussmallerplates.These
platesmoveonthetopofthehotplasticuppermantleknownastheasthenosphere.Thistheoryalsosaysthatmostofthese
platesareinmotion,creatingavarietyofinteractionsattheplateboundaries.Attheplateboundaries,platesmayconverge
(collide),diverge(separate),orslidepasteachotherinalateralmotion.Inaddition,someplatesmayappeartobeinactivity.
DivergentBoundary
1. Whathappenedtothefrostingbetweenthecrackers?
The frosting was pushed up between the crackers as they were pressed down and apart from each other.
2. Whatdothegrahamcrackersrepresent?
The lithosphere
3. Whatdoesthefrostingrepresent?
The asthenosphere
4. NameaspecificlocationontheEarthwherethiskindofboundaryactivitytakesplace.
The Mid Atlantic Ridge (between North America and Europe, as well as South America and Africa).
5. Whattypeoffeatureisproducedbythismovement?
A mid ocean ridge
6. Whatistheprocesscalledthatcreatesnewoceanfloorfromdivergingplates?
Seafloor Spreading
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ConvergentPlateBoundaries(ContinentalandOceanic)
1.Whathappenswhenatectonicplategetssubducted?
The subducting (sinking) plate is recycled.
2.NameaspecificlocationontheEarthwherethiskindofboundaryactivitytakesplace.
Pacific Ring of Fire (pretty much any boundary around the Pacific plate – a few exceptions)
3.Whatfeaturesareformedonthecontinentalongthisboundary?
Volcanoes and Earthquakes
4.Whatfeatureisformedintheoceanalongthesubductionzone?
Deep ocean trenches
ConvergentPlateBoundaries(ContinentalandContinental)
1. Whathappenstothewetendsofthegrahamcrackers?
They get all smashed/bent/crumpled up.
2. Inwhatwaydothewetcrackersactmoreliketherealcrustalplatesthanthedrycrackers?
They can bend rather than just break.
3. Whatfeaturedotheresultingendsofthewetcrackersrepresent?
Mountains
4. NameaspecificlocationontheEarthwherethistypeofboundaryactivitytakesplace.
Himalayan Mountains (between the Eurasian and Indian plates).
TransformBoundaries
1. Whyisthismovementoftendescribedas“horizontal”sliding?
The plates are just moving past each other with no vertical (up/down) movement.
2. NameaspecificlocationontheEarthwherethistypeofboundaryactivitytakesplace.
The San Andreas fault (between the North American and Pacific plates through California).
3. Nothinghappensatthebeginning,butasthepressureisincreased,thecrackersfinallybreak.Whatdowecall
thebreakingandvibratingoftheEarth’scrust?
An earthquake
ConclusionQuestions
GiveanexampleofhowplatemovementdirectlyaffectstheconstructionofEarth’ssurface.
Spreading leads to the creation of new crust (divergent boundaries)
GiveanexampleofhowplatemovementdirectlyaffectsthedestructionofEarth’ssurface.
Subduction of old ocean crust causes it to melt down and be recycled into new oceanic crust (convergent boundaries)
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Part4:NormalvsReverseFaults
NormalFaults
ReverseFaults
Diagram
Diagram
DirectionofForce
DirectionofForce
ç
è
è
ç
BoundaryType/s
BoundaryTypes
Divergent
Convergent
Part5:Megaquakes
“TheNextMegaquake”wasproducedbytheBBCin2005.IntheshadowoftheDec.262004Sumatraquakeand
tsunami(BoxingDayintheUK),ittellsthestoryofthe1700Cascadiaeventanddescribesthedynamicsofthe
Cascadiasubductionzoneandthepotentialforadevastatingevent.
Answerthefollowingquestions(beneatandcomplete):
1. WhydidgeologistsdismisstheriskofamegaquakeinCascadia?
The Cascadia subduction zone has been virtually silent meaning there was hardly any seismic activity. It wasn’t
creating any earthquakes.
2. WhydidBrianAtwaterstarttolookforevidenceofthemegaquake?
He thought that the native legends could be a warning that the PNW was at risk for giant earthquakes.
3. WhatevidencedidBrianAtwaterfind?Whattypeofdepositdidthetsunamileave?
He found evidence of a spruce forest under layers of salt marsh with a layer of sand.
4. WhatdidtherecordsthatDr.Satakefoundtellhim?Whatisanorphantsunami?
The Japanese records at four separate locations showed the arrival of a tsunami that was not paired with an
earthquake. An orphan tsunamis is a tsunamis that has no known earthquake that could have caused the wave.
5. Whatwasthe“ghostforest?”Whattypesofevidencedidthe“ghostforest”provide?
The ghost forest was a grove of very large trees along the Washington coast that all died hundreds of years ago but
are still standing today. By examining the tree rings it was discovered that ALL of the trees died at the same time
during the early part of 1700.
6. Whatdetermineshowlargeanearthquakewillbe?
The amount of energy released during the earthquake. The bigger the earthquake the more energy is released.
7. Whowouldbeespeciallyatriskfromthetsunami?HowdoesSeattlecompare?
Anyone along low-lying areas on the coasts and beaches of the PNW would be at risk. Seattle would be spared as it
is located inland.
8. Comparedtomostearthquakes,whatspecialcharacteristicswouldaM9quakehave?
A M9 earthquake would have shaking that lasts for a very long time (up to five minutes).
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9. BrianAtwaterdeterminedtherecordofthe4previousCascadiaquakes.Whatweretheirdates?
600 BC, 400 AD, 700 AD, 1700 AD
10. DescribethehypothesizedfaultruptureofaCascadiaevent.Howlongwouldtherupturetake?
The rupture would likely start at one end and rupture like a zipper down the Cascadia Subduction Zone. Intense
shaking from the earthquake would last nearly five minutes.
11. Thefirstearthquakewavewouldfeellike:____”thelongestfewminutesofpeople’slives”___
12. Whatrisksarepresentforbuildingsfarinland?
Unsecured furniture, falling debris, shattering glass, collapse of un-reinforced masonry (brick) buildings, potential
total collapse of high-rise buildings, liquefaction
13. HowdoesthescaleofaCascadiaeventcompareto“typical”earthquakes?
It will be an event on a large regional scale (whole PNW) not like the localized earthquakes that we are used to.
SelfReflection:ColortheSmileyFacethatshowshowwellyoufeelyouunderstandLT#3
WhatHaveILearnedaboutLT#3:
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