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Plate Tectonics. Continental Drift. Historical Landmass Locations. Fossil Evidence Supporting Plate Tectonics. Developing the Theory. (1) demonstration of the ruggedness and youth of the ocean floor; (2) confirmation of repeated reversals of the Earth magnetic field in the geologic past;

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Plate tectonics l.jpg

Plate Tectonics

Continental Drift




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Developing the Theory

  • (1) demonstration of the ruggedness and youth of the ocean floor;

  • (2) confirmation of repeated reversals of the Earth magnetic field in the geologic past;

  • (3) emergence of the seafloor-spreading hypothesis and associated recycling of oceanic crust; and

  • (4) precise documentation that the world's earthquake and volcanic activity is concentrated along oceanic trenches and submarine mountain ranges.


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Developing the Theory (continued)

  • (1) demonstration of the ruggedness and youth of the ocean floor.

  • (See next slide)






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Plate Motions

  • There are four types of plate boundaries:

  • Divergent boundaries -- where new crust is generated as the plates pull away from each other.

  • Convergent boundaries -- where crust is destroyed as one plate dives under another.

  • Transform boundaries -- where crust is neither produced nor destroyed as the plates slide horizontally past each other.

  • Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.




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Mid-Atlantic Ridge Example

Red triangles denote active volcanoes


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Aerial view of the area around Thingvellir, Iceland, showing a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Divergent Boundary – East Africa a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

Map of East Africa showing some of the historically active volcanoes(red triangles) and the Afar Triangle (shaded, center) -- a so-called triple junction (or triple point), where three plates are pulling away from one another


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Summit Crater of 'Erta 'Ale (Ethiopia) a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Oldoinyo Lengai, erupts in 1966 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Convergent Boundaries a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. Oceanic-continental convergence


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Convergent Boundaries a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. (example)


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Oceanic-oceanic convergence a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Continental-continental convergence a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Continental-continental convergence a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

The collision between the Indian and Eurasian plates has pushed up the Himalayas and the Tibetan Plateau


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Continental-continental convergence a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. Indian – Eurasian Plates


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The Himalayas: a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. Two Continents CollideThe 6,000-km-plus journey of the India landmass (Indian Plate) before its collision with Asia (Eurasian Plate) about 40 to 50 million years ago. India was once situated well south of the Equator, near the continent of Australia.


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Transform Boundaries a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

The Blanco, Mendocino, Murray, and Molokai fracture zones are some of the many fracture zones (transform faults) that scar the ocean floor and offset ridges (see text). The San Andreas is one of the few transform faults exposed on land.


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San Andreas fault a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

Aerial view of the San Andreas fault slicing through the Carrizo Plain in the Temblor Range east of the city of San Luis Obispo.


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Plate-boundary Zones a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Rates of Motion a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

  • The Arctic Ridge has the slowest rate (less than 2.5 cm/yr)

  • The East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile, has the fastest rate (more than 15 cm/yr).


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Hotspots: Mantle Thermal Plumes a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Prominent Thermal Hotspots a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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The Long Trail of the Hawaiian Hotspot a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

Map of part of the Pacific basin showing the volcanic trail of the Hawaiian hotspot-- 6,000-km-long Hawaiian Ridge-Emperor Seamounts chain.


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Plate Tectonics & People a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

  • Natural hazards

    • Earthquakes

    • Volcanic eruptions

    • Tsunamis

  • Natural resources

    • Fertile soils

    • Ore deposits

    • Fossil fuels

    • Geothermal energy


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Earthquakes a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

Aerial view, looking north toward San Francisco, of Crystal Springs Reservoir, which follows the San Andreas fault zone.


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Earthquakes a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. (continued)

Map of the San Andreas and a few of the other faults in California, segments of which display different behavior: locked or creeping


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Fault Creeping a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

Left:Creeping along the Calaveras fault has bent the retaining wall and offset the sidewalk along 5th Street in Hollister, California (about 75 km south-southeast of San Jose). Right:Close-up of the offset of the curb.


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Earthquakes & Volcanoes a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

  • Christopherson TextChapter 12 pp 375-end-of-chapter


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What Causes Earthquakes? a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Epicenter and Focus a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

  • Focus 

    • Location within the earth where fault rupture actually occurs 

  • Epicenter 

    • Location on the surface above the focus


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Types of Faults a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

Faults are classified on the basis of the kind of motion that occurs on them

  • Joints - no movement

  • Strike-slip - horizontal motion (wrench faults)


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Types of Faults a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

  • Joints - No Movement

  • Strike-Slip - Horizontal Motion (Wrench Faults)


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Joints - No Movement a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Left Lateral Strike Slip a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Right Lateral Strike Slip a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

San Andreas

21 feet in 1906


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Dip-Slip - Vertical Motion a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. Normal Fault (Extension)

Alaska, 1964 - up to 150 Ft


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Reverse or Thrust Fault (compression) a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Eastern North America Earthquakes 1534-1994 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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U.S. Earthquakes, 1973-2002 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Seismic Risk Level Maps for the U.S. a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. Probable ground acceleration in 50 years. Blue = small, red = large


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Seismic Risk Level Maps for the U.S. a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. Probability of Damage in 100 Years. Blue = Negligible, Green = Low, Red = High.


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M 7.9 Earthquake on November 3, 2002 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

  • The largest earthquake known to occur in the world this year struck central Alaska on Sunday, November 3. The epicenter of the Nov. 3 temblor was located approximately 75 miles south of Fairbanks and 176 miles north of Anchorage. It struck at 1:12 PM local time, causing countless landslides and road closures, but minimal structural damage and amazingly few injuries and no deaths.


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M 7.9 Earthquake on November 3, 2002 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.

  • Overall, the geologists found that measurable scarps indicate that the north side of the Denali fault moved to the east and vertically up relative to the south. Maximum offsets on the Denali fault were 22 feet at the Tok Highway cutoff, a road that goes from Tok to Glenallen and intersects with the Alaska Highway, and were 6.5 feet on the Totschunda fault.

  • This earthquake is one of the largest ever recorded on U.S. soil and the largest seismic event ever recorded on the Denali fault system.


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Denali Fault Earthquake a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Rock Avalanches Across Black Rapids Glacier a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Alaska Earthquake Pictures Taken by Local Resident a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Alaska Earthquake Pictures Taken by Local Resident a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Alaska Earthquake Pictures Taken by Local Resident a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Alaska Earthquake Pictures Taken by Local Resident a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Alaskan Pipeline a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Northway Road - 4th of November 2002 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Road Offset, Richardson Hwy a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Volcanoes a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Two expressions of volcanic activity. a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Volcanic fountaining in Hawaii. a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Kilauea landscape. a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Mt.Etna, Sicily – July 2001 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Mt.Etna, Sicily – July 2001 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Mt.Etna, Sicily – July 2001 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Mt.Etna, Sicily – July 2001 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Mt.Etna, Sicily July 2001 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Mt.Etna, Sicily – July 2001 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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Mt.Etna, Sicily – July 2001 a fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge.


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