©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 11
Lesson #4
How did the Oceans get to be the way they are?
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 22
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 33
Origin of the oceans
• We weren’t there when the earth was formed so this is all theory– Theory:
guess, test, evaluate, repeat– Fact: observable
• Origin theories are pretty good– Fit the observations– Predict what you’ll find in new places– But expect them to change as new facts are observed
http://www.astro.psu.edu/~bmiller/astro11/pics/earth_from_space.jpghttp://www.astro.psu.edu/~bmiller/astro11/pics/earth_from_space.jpg
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 44
Faith vs. Science• Different sets of rules:
• Science: must be testable, subject to the “scientific method”– Question: theory, hypothesis– Test– Evaluate– Repeat, repeat, repeat…
• No theory ever becomes fact
• Faith: must be un-testable
• Problems happen when you mix these up
www.britanica.com
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 55
The Origin of the Earth
• This is the best theory we have– works very well– but expect it to change as
we learn more
• The universe is very large– nearest star is 27 million,
billion miles away– 4.5 light years (light travels
at 186,000 miles / second)
• How do we measure distance in space?– triangulation– light intensity
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 66
A Light-Year is a Measure of Distance
• A light-year is equal to– The distance light travels in one year
– exactly 9,460,730,472,580.8 kilometers– about 5,878,630,000,000 miles– Based on a year of 365.25 days; 86,400
seconds a day; 31,557,600 seconds a year– A speed of light of 299,792,458 meters per
second• 670,616,629 miles per hour
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 77
The Origin of Earth• The universe was formed roughly 15 billion years ago• The solar system formed roughly 5 billion years ago• formed from a nebula, which is a revolving mass of particles• some collected into stars (such as our sun)• others collected into planets (such as the earth) which continued to
revolve around it
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 88
The Origin of the Earth
• The planets formed as the particles condensed• conditions on each planet are determined by:
– distance from the sun
– amount of mass
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 99
Earth’s Structure
• Like other planets, the earth was formed through this process
• As it cooled, the heavier elements (iron, nickel) settled to the bottom (center) and the lighter elements (aluminum, silicon) floated to the top
• this resulted in the creation of concentric shells – Each with a distinct chemical composition– Layered on the basis of density
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1010
The Origin of the Oceans
• As the earth continued to cool, water and gases were given off– these accumulated in the
oceans and atmosphere respectively
– originally all of the water was in gaseous state due to the hot earth
– this processes took a long time and continues today
• The composition of the original ocean and atmosphere was determined by this process
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1111
The Origin of the Oceans
• Important Events in the Earth’s History• Each event paved the way for the next• Man is a relative newcomer
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1212
Earth’s Structure (Cont.)
• The earth’s interior is made up of several layers.
• The physical characteristics of each layer are determined by:– The chemical composition of the rocks– Temperature– Pressure
• These layers are can be defined two ways:– By acoustic velocity
• Crust, Mantle, Core
– By physical characteristics (rigidity, viscosity)• lithosphere, asthenosphere, mesosphere
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1313
Earth’s Structure (Cont.)(according to velocity)
• The crust is the outermost layer.– Relatively thin– Low density
material: aluminum, silicon, oxygen
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1414
Geologic Differences Between Continents and Ocean Basins (Cont.)
• Continental crust consists of granite– Igneous origin, solidified from molten material.
– Light in color.
– Mostly oxygen, silicon, aluminum.
• Oceanic crust consists of basalt– Volcanic origin, solidified from
material erupted onto Earth’s surface.
– Dark in color.
– Rich in oxygen, silicon, magnesium and iron.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1515
Geologic Differences Between Continents and Ocean Basins (Cont.)
• The density of granite is– 2.7 to 2.8
g/cm3
• The density of basalt is– 2.9 g/cm3
Basalt Granite
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1616
Oceanic Crust vs. Continental Crust
• Continental crust is thicker than oceanic crust– Also more variable– Much thicker under mountains
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1717
Earth’s Structure (Cont.)(according to velocity)
• The mantle lies below the crust.– Relatively thicker– Higher density
material: magnesium, iron, silicon, oxygen
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1818
Earth’s Structure (Cont.)(according to velocity)
• The core is below the mantle.– Thickest of all
layers
– Very dense material: iron, nickel• Outer: molten• Inner core: solid
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1919
Earth’s Structure (Cont.)(according to velocity)
• These three layers are determined by the speed at which sound travels through them– Crust– Mantle– Core
• But for plate tectonics, we need to consider their physical properties
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 2020
Earth’s Structure According to Physical properties
• Lithosphere– Upper layer
– rigid
• Asthenosphere– Just below the
lithosphere
– “plastic”
• Mesosphere
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 2121
Earth’s Structure According to Physical properties
• The lithosphere consists of the crust and uppermost mantle.– Hard,
– Rigid,
– Brittle
Molten
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 2222
Earth’s Structure According to Physical properties
The asthenosphere is below the lithosphere.– A portion of the
mantle– Rocks are
semi-melted.– Behavior is
plastic.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 2323
Earth’s Structure According to Physical properties
The mesosphere consists of the lower mantle.– Higher pressure
causes mantle rocks to change structure.
– More solid than the asthenosphere.
– No plastic flow, but still some flow.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 2424
Earth’s Structure According to Physical properties
• We know all of this through indirect evidence:– mass of earth
– transmission of sound
– samples
• NO direct samples– too deep
– too hot
– too much pressure
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 2525
Lithosphere• The crust
“floats” on the mantle beneath it
• Like an iceberg, there is more below the surface than above
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 2626
Isostasy
• This demo shows the effect of height and density on how an object floats
• This applies to icebergs and to the crust
• Isostasy Demo
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 2727
Isostasy explains the distribution of Earth’s topography
•Continental crust is lighter than ocean crust, so• It floats higher than oceanic crust
•Continental crust is thicker than ocean crust, so • It stands higher than ocean crust.• It has deeper roots than ocean crust.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 2828
Plate Tectonics
• The plate Tectonic theory revolutionized geology.
• It explains:– earthquakes– distribution of volcanoes– character of the
seafloor– age of the seafloor– shape of the ocean
basins– just about everything
http://nzphoto.tripod.com/volcano/PacificPlate.gifhttp://nzphoto.tripod.com/volcano/PacificPlate.gif
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 2929
Plate Tectonics
• Plate tectonics theory is based on two types of data
• 1) Continental Drift– Data about the continents, their shape, and
what’s on them– All based on observations above sea level
• 2) Seafloor spreading– Data about the sea floor, its shape, and
what’s on it– All based on observations below sea level
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 3030
Continental Drift
• The theory was proposed in 1915 by Alfred Wegener (a meteorologist) to explain Earth’s history.
• The theory states that a single continent, Pangaea, existed more than 200 million years ago.
• It broke up and the continents drifted apart
http://vaidehipatil.wordpress.com/category/design-2/illustration/
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 3131
Evidence for Continental drift
• There are several lines of evidence for continental drift, including:
• (1) “map fit”– when you
reposition the continents on a globe the all fit together
– the fit is stunning!
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 3232
Continental drift (cont.)
• (2) Glacial scarring– Glaciers gouge the rocks
– Regions of glacial scour “match” on opposing continents
– Must have happened before breakup of original continent
Glacial striations
Glacial striations
Glacial pot holes
Glacial scarring
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 3333
Continental drift (cont.)
• (3) Geologic evidence (rock type).
– Age of rock.– Mineralogy.– Structure.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 3434
Continental drift (cont.)
• (4) Fossils– Identical fossils found on continents which are
now separate
– Must have been connected at some point in the distant past
– Can determine age of separation by dating fossils
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 3535
Continental Drift (cont.)
• But Wegener’s theory lacked a mechanism– What made the continents move?
• Most scientists scoffed at the theory
• It was not accepted
for more than 50 years!
http://www.ucmp.berkeley.edu/history/wegener.gifhttp://www.ucmp.berkeley.edu/history/wegener.gif
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 3636
Breakup of Pangaea
Drift 1 Drift 2
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 3737
Sea-Floor Spreading
• Sea-floor spreading explains how ocean basins form
• But it also provides the mechanism that Wegener was missing
• It is based upon various pieces of scientific evidence– Deep sea soundings showing the existence and structure
of midocean ridge systems– Magnetometer readings of ridge systems– Pattern of earthquakes– Distribution of volcanoes– Chemistry of the rocks– Lots of other evidence
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 3838
Sea-Floor Spreading (Cont.)
• The midocean ridge was discovered in the mid-20th century from soundings of the deep sea-floor.
• It forms a continuous mountain range girdling the earth– ~60,000 km long– ~3 to 4 km high
• Geologically active– Volcanism, – Earthquakes – Faulting
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 3939
Sea-Floor Spreading
• Although ridge systems resemble mountain chains, they are formed in different ways.– Mountain chains
form by
compression
– Ridge systems
form by tension
ForceForce
ForceForce
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 4040
Sea-Floor Spreading• the crust is pulling apart at the ridge crest (tension)
• a valley forms where this happens
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 4141
Sea-Floor Spreading (Cont.)
• When a ridge comes on land, it rifts (tears) apart the continent!
Rifts
Red Sea
Sinai
Mediterranean Sea
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 4242
Sea-Floor Spreading• The ridge is visible where it goes
ashore as “mirrored” mountains.
• It looks just like this under water
ForceForce
Normal faults
Scarp
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 4343
Sea-Floor Spreading (Cont.)
• As the sea floor spreads.– It gets older (doesn’t everything?).– It cools and thickens.– It accumulates sediment.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 4444
Global Plate Tectonics
• Plate Tectonics = Sea Floor Spreading + Continental drift
• These two concepts came from separate sets of observations
• The Plate Tectonic theory:– Combined these ideas.– Answered almost all of our questions.– Provided incredible predictive POWER!http://www.enchantedlearning.com/egifs/Earthsplates.GIFhttp://www.enchantedlearning.com/egifs/Earthsplates.GIF
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 4545
Global Plate Tectonics (Cont.)
• Surface divided into 12 major plates.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 4646
Global Plate Tectonics (Cont.)
• These plates move!
• As they do, they collide with each other– Some portions are destroyed by subduction– Some are crushed into mountains
• The collisions
create
earthquakeshttp://images.google.com/imgres?http://images.google.com/imgres?imgurl=http://vulcan.wr.usgs.gov/Imgs/imgurl=http://vulcan.wr.usgs.gov/Imgs/Gif/PlateTectonics/Maps/Gif/PlateTectonics/Maps/map_plate_tectonics_world_bw.gif&imgrefmap_plate_tectonics_world_bw.gif&imgrefurl=http://vulcan.wr.usgs.gov/Glossary/url=http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/Maps/PlateTectonics/Maps/map_plate_tectonics_world.html&h=540&map_plate_tectonics_world.html&h=540&w=859&sz=23&hl=en&start=1&tbnid=15vw=859&sz=23&hl=en&start=1&tbnid=15vAfuTbbcud9M:&tbnh=91&tbnw=145&preAfuTbbcud9M:&tbnh=91&tbnw=145&prev=/images%3Fq%3Dplate%2Btectonicsv=/images%3Fq%3Dplate%2Btectonics%26hl%3Den%26hl%3Den
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 4747
Global Plate Tectonics (Cont.)
• Plates are slabs of lithosphere
• Lithosphere = rigid– Crust and uppermost mantle
– “floats” on the asthosphere (remember isostacy?)
• Asthenosphere = plastic, flows
Limited motion
Mesosphere
Plastic flow
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 4848
Global Plate Tectonics (Cont.)
• Nearly all seismic and volcanic activity is associated with plate boundaries.
• Plate boundaries and seismic activity:– Co-occur.
– Exist on continuous lines.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 4949
• There are 3 ways that plates can interact:– Separate
– Converge
– Slide past
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 5050
Global Plate Tectonics (Cont.)
• Three flavors of plate boundaries:– Midocean ridges
• Plates move apart• “spreading centers”• Addition of new crust to trailing
plate edge
– Subduction zones• Plates collide• Destruction of old crust
– Transform faults• Plates move past one another• Crust is neither created or
destroyed
Let’s take a look at these in some detail:Let’s take a look at these in some detail:
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 5151
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 5252
1) Midocean Ridges• Volcanism and
faulting
• Hydrothermal circulation
CopperZinc
Leadetc.
Basalt pillows, fresh from an eruptionin the rift valley.
Faultat axial fissure caused
by extensional force in therift valley.
Normal faults
Rift valley of a midocean ridge.
Hydrothermal vent
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 5353
2) Subduction Zones• Subduction zones are regions where lithosphere with
oceanic crust is being destroyed– Subducted lithosphere melts into the mantle.
– Earthquakes from the surface to 660 km.
– Magma rises to the surface and erupt at volcanoes.
– Ocean sediments are partially scraped off at the trench.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 5454
Global Plate Tectonics• Lithosphere with
ocean crust is destroyed at subduction zones.
– So, amount of seafloor built at spreading centers equals the amount recycled into the mantle in subduction zones.
http://whyfiles.org/031volcano/images/subduction.gifhttp://whyfiles.org/031volcano/images/subduction.gif
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 5555
Subduction
• Explosive volcanic activity.
• Ash falls.
• Lava flows.
• Pyroclastic flows.
• Mud flows.
• Gases.
Mt. St. Helens, May 18, 1980
Stromboli, Italy
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 5656
Global Plate Tectonics (Cont.)
• Subduction is ocurring under:– Japan– Western South America– Central America– Alaska– New Zealand– Caribbean– Northwest USA!
Mt. St. Helens
Mt. Ranier
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 5757
Global Plate Tectonics (Cont.)
• The Pacific Ocean is surrounded by a “Ring of Fire”– The Ring of Fire includes both volcanoes and earthquakes.
– All are subduction-related
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 5858
3) Transform Faults
• “Transform”= side by side motion
• Offset the ridge axis• Relative movement is
horizontal• Plates are moving in
opposite directions• This wreaks havoc!
Transform faults
Rift valley
Rift valley
Pla
te A
Pla
te B
Movement
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 5959
Plate Tectonics (cont.)
• On our West Coast:– Subduction motion has
been transformed into lateral motion in central and southern California.
– This causes the Pacific Plate to move past the North American Plate.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 6060
Plate Tectonics (cont.)
• This transform fault is the infamous San Andreas of California.
• The fault joins the Juan de Fuca Ridge and EPR.
• The strike-slip fault causes massive earthquakes.
San Andreas Fault
San Andreas,Corrizo Plain
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 6161
Transform faults• The same topography
you see near San Francisco exists in many, many places on the sea floor
http://www.oceanexplorer.noaa.gov/explorations/05lostcity/logs/july23/media/karson1atf_600.jpghttp://www.oceanexplorer.noaa.gov/explorations/05lostcity/logs/july23/media/karson1atf_600.jpg
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 6262
Plate Tectonics (cont.)
• These earthquakes:– Are certain to continue
– Vary in strength according to built-up stress
San Francisco, Marina District
Nimitz Freeway, Oakland
Farm field in Santa Cruz
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 6363
New Zealand Quake 2-22-2011
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 6464
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 6565
What causes the plates to move?
• Thermal convection– Produces slow moving currents in the
underlying asthenosphere which exerts drag on the lithospheric plates setting them in motion.
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 6666
Consequences of PT: Hot Spots• Deep sources of extra-hot magma
• rise up through mantle
• are cause of intra-plate volcanism YellowstoneYellowstone
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 6767
Consequences of PT: Hot Spots
• As plate passes over source of volcanism, a chain of islands is formed
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 6868
Island Chains• For
example, the Hawaiian Islands
• Note ages• Ancient
Hawaiians noticed this– referred to
it as Pele moving from island to island
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 6969
Hawaiian / Emperor Seamount Chain
• All produced by the same hot spot
• age progresses uniformly out the chain
• plate motion changed to produce the bend in the chain
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 7070
Hot Spot Traces
• The Hawaiian Islands are only one example
• each hot spot under the Pacific plate produces an island chain
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 7171
Consequences of PT: Atolls and Guyots
- Off-axis volcanism creates- Off-axis volcanism createsVolcanoesVolcanoes- as the plate settles, so do - as the plate settles, so do
the volcanoes the volcanoes
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 7272
Formation of an Atoll or Guyot
• Starts off with volcanic seamount
• as plate and seamount subside, coral grows upward
• if coral keeps up, an atoll is formed
• if not, a guyot• Coral requires
warm, clear water
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 7373
Atoll / Guyot Animation
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 7474
Atoll Structure
Diego Garcia, Chagos Islands, Indian Ocean
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 7575
Future – Headed to “Pangaea Ultima”????
©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 7676
Summary
• Features of Earth’s surface are determined by the interaction of lithospheric plates.
• Seismic activity is most intense at plate boundaries.
• Crustal material is created at ridges and destroyed at subduction zones.
• The movement of lithospheric plates disrupts continents and leads to the expansion or contraction of ocean basins.