Evidence for plate motions
Measurement of plate motions
Makeup of the crustal plates
Plate boundaries

Environmental Geolo...
Your news items: ripped from the headlines

Thanks
Shedavia!

VERY large planet
VERY strange configuration
Tectonics is the study of large-scale movement and deformation of the earth’s
outer layers
A small number of rigid pieces ...
Magnetic stripes occur in ocean plates
As new crust is formed, magnetic field
occasionally reverses and changes cooling
ro...
Different boundaries
show up on the
earth‟s surface
Midocean ridges:
Divergent plates

Coastal mountains:
Convergent plate...
Plate Boundaries

Divergent Plate Boundary
Lithospheric plates move apart;
form oceanic ridges
Rising magma forms oceanic
...
Plate Boundaries

Convergent Plate Boundary
Lithospheric plates move
together
Heavy plate subducts
Mountains, quakes, volc...
Relative plate motions
Direction and speed vary a lot over the world
Longer arrow = faster rate

5cm.yr = ~1 mile
per 3200...
Faults: earthquake sites
Earthquake process
Earthquake hazards

Environmental Geology

jbartlett@national.edu
Faults are planes where rocks can
slip past each other
Three different types are based on
three different motions
Friction...





Energy releases from a dynamic earth occur
along faults
Earth’s crust moves very slowly
over time enough stress bu...





Energy is released during an earthquake
As the waves of energy are transmitted through the rock, this
energy with ...




Measured by a seismograph
Richter magnitude scale most common
Richter scale is logarithmic
• An earthquake of magni...









Shaking is the most obvious and violent effect, but is highly variable and
depends on initial conditions at...
Magnitude 7.7 , 15 km deep
Strike slip fault
~300,000 people involved
Like much of geology, prediction is
difficult on human scales
Models generate probabilities but
not predictions
Current fo...







Predicting ground shaking and movement along the fault – the
obvious hazards
Considering both structures and ...
Associated with boundaries
Variety of compositions
Variety of styles
Volcanic hazards

Environmental Geology

jbartlett@na...
Associated with
divergent or
convergent plate
boundaries
Different locations
mean different
composition & type
of volcanoe...




Mafic magmas
produce dark, dense ,
liquid lavas
• Relatively calm,
low drama events
• Ocean crust

Felsic magmas
pro...
Magma composition mafic  felsic affects
the lava properties
Silica is very stiff, tends to stick and then
explode
Contin...






Lava, not the principal hazard! Actually not life-threatening generally
Airborne/pyroclastic flows, way more da...
Ash cloud goes up and up into
stratosphere
Can circle for years or decades, blocking
sunlight
With enough blockage, global...
Very large eruptions have happened geologically recently
Results:
Global „volcanic winter‟ ~10 years
Enhanced cooling ~100...



Far from plate boundaries or magma
plumes
We are “near” one major risk:
Yellowstone, site of major potential
supervol...
Ch 03 - 05
Upcoming SlideShare
Loading in …5
×

Ch 03 - 05

259 views

Published on

Published in: Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
259
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
7
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Ch 03 - 05

  1. 1. Evidence for plate motions Measurement of plate motions Makeup of the crustal plates Plate boundaries Environmental Geology jbartlett@national.edu
  2. 2. Your news items: ripped from the headlines Thanks Shedavia! VERY large planet VERY strange configuration
  3. 3. Tectonics is the study of large-scale movement and deformation of the earth’s outer layers A small number of rigid pieces = plates form ocean basins & continents These move on top of flowing earth materials beneath Plate tectonics studies the interaction of crust plates over a weak or partly molten layer in the earth’s upper mantle
  4. 4. Magnetic stripes occur in ocean plates As new crust is formed, magnetic field occasionally reverses and changes cooling rocks These stripes are great evidence for new crust formation pushing ocean crust out from the center – thus called “divergent” boundaries
  5. 5. Different boundaries show up on the earth‟s surface Midocean ridges: Divergent plates Coastal mountains: Convergent plates In between: Transform boundaries
  6. 6. Plate Boundaries Divergent Plate Boundary Lithospheric plates move apart; form oceanic ridges Rising magma forms oceanic ridges and new oceanic crust Forces plates apart Convergent Plate Boundary Lithospheric plates move together Heavy plate subducts Mountains, quakes, volcanoes Transform Boundaries – short segments of a ridge Transform faults offset ridge, move „sideways‟ San Andreas Fault –
  7. 7. Plate Boundaries Convergent Plate Boundary Lithospheric plates move together Heavy plate subducts Mountains, quakes, volcanoes Divergent Plate Boundary Lithospheric plates move apart; form oceanic ridges Rising magma forms oceanic ridges and new oceanic crust Forces plates apart Transform Boundaries – short segments of a ridge Transform faults offset ridge, move „sideways‟ San Andreas Fault –
  8. 8. Relative plate motions Direction and speed vary a lot over the world Longer arrow = faster rate 5cm.yr = ~1 mile per 32000 years
  9. 9. Faults: earthquake sites Earthquake process Earthquake hazards Environmental Geology jbartlett@national.edu
  10. 10. Faults are planes where rocks can slip past each other Three different types are based on three different motions Friction between rocks against slipping generates elastic deformation and builds up energy before failure When the stress exceeds the friction (or rupture strength of the rock), a sudden movement occurs to release the stress Normal fault
  11. 11.    Energy releases from a dynamic earth occur along faults Earth’s crust moves very slowly over time enough stress builds up and a brittle release occurs – an earthquake Stress is suddenly released and transferred Actual site of the first movement along a fault is the focus (or hypocenter) Actual point on the earth’s surface directly above the focus is the epicenter
  12. 12.    Energy is released during an earthquake As the waves of energy are transmitted through the rock, this energy with be felt by people at the surface Magnitude – the amount of ground motion related to an earthquake Intensity – effect on humans, and their structures, caused by the energy released by an earthquake
  13. 13.    Measured by a seismograph Richter magnitude scale most common Richter scale is logarithmic • An earthquake of magnitude 4 causes 10 times more ground movement as one of magnitude 3 • The energy released by an earthquake of magnitude 4 releases about 30 times more energy than an earthquake of magnitude 3
  14. 14.       Shaking is the most obvious and violent effect, but is highly variable and depends on initial conditions at location Large magnitudes may have small or large human impact Tsunamis are seismic sea waves. When an undersea or near-shore earthquake occurs, sudden movement of the sea floor may set up waves traveling away from that spot, hitting shore with devastating effect Fire is caused by broken gas lines and infrastructure Power outages, water disruption are major impacts Famine and disease have been major historical impacts
  15. 15. Magnitude 7.7 , 15 km deep Strike slip fault ~300,000 people involved
  16. 16. Like much of geology, prediction is difficult on human scales Models generate probabilities but not predictions Current focus looks at indicators like „seismic gaps‟ Active hazard areas can go sometime soon – like in the next 100, 1000 or 10,000 years!
  17. 17.       Predicting ground shaking and movement along the fault – the obvious hazards Considering both structures and bedrocks Designing “earthquake-resistant” buildings Knowing the characteristics of the earthquakes in a particular region The best building codes are typically applied only to new construction Liquefaction and Landslides can be a serious secondary earthquake hazard in hilly areas
  18. 18. Associated with boundaries Variety of compositions Variety of styles Volcanic hazards Environmental Geology jbartlett@national.edu
  19. 19. Associated with divergent or convergent plate boundaries Different locations mean different composition & type of volcanoes Iron rich mantle stuff Subducted melting stuff
  20. 20.   Mafic magmas produce dark, dense , liquid lavas • Relatively calm, low drama events • Ocean crust Felsic magmas produce light colored, sticky lavas • Stiffness causes violent eruptions • Very dangerous • Continental crust Composition  Depth Felsic Intermediate low iron light toned Mafic high iron dark toned Volcanic: Surface, fine grained Rhyolite Andesite Basalt Plutonic: Deep, coarse grained Granite Diorite Gabbro Make up continental crust Make up ocean crust
  21. 21. Magma composition mafic  felsic affects the lava properties Silica is very stiff, tends to stick and then explode Continental environments tend to have water and volatiles melted along with magma Explosive versus calm eruptions
  22. 22.      Lava, not the principal hazard! Actually not life-threatening generally Airborne/pyroclastic flows, way more dangerous than lava flows Ash falls from eruptions can be much more devastating than lava Gas, steam and poisons can also spew from volcanoes Lahars, a volcanic ash and water mudflow Pulaweh, Indonesia
  23. 23. Ash cloud goes up and up into stratosphere Can circle for years or decades, blocking sunlight With enough blockage, global temperature can be altered with huge economic effects
  24. 24. Very large eruptions have happened geologically recently Results: Global „volcanic winter‟ ~10 years Enhanced cooling ~1000 years Effect on humans… dramatic 6 supervolcanoes of >1000 km3 In the recent past {toba} Historic eruption: Mt Tambora, 1815, ~160 km3 Result: „year without summer‟
  25. 25.   Far from plate boundaries or magma plumes We are “near” one major risk: Yellowstone, site of major potential supervolcano BBC: 12/10/13 Large Yellowstone magma chamber may be 3 times larger than estimated before, so these maps may underestimate effect US Geologic Survey: “Thick ash deposits would bury vast areas of the United States… injection of huge volumes of volcanic gases into the atmosphere could drastically affect global climate. Fortunately, the Yellowstone volcanic system shows no signs that it is headed toward such an eruption in the near future”

×