Chapter 2 plate tectonics and physical hazards
This presentation is the property of its rightful owner.
Sponsored Links
1 / 35

Chapter 2 - Plate Tectonics and Physical Hazards PowerPoint PPT Presentation


  • 60 Views
  • Uploaded on
  • Presentation posted in: General

Chapter 2 - Plate Tectonics and Physical Hazards. The Big Picture. Pieces of Earth’s surface Move around Grind sideways Collide Sink into Earth’s hot interior Collisions create mountain ranges, cause tsunami Less directly, mountain ranges affect weather and climate.

Download Presentation

Chapter 2 - Plate Tectonics and Physical Hazards

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Chapter 2 plate tectonics and physical hazards

Chapter 2 - Plate Tectonics and Physical Hazards


The big picture

The Big Picture

  • Pieces of Earth’s surface

    • Move around

    • Grind sideways

    • Collide

    • Sink into Earth’s hot interior

  • Collisions create mountain ranges, cause tsunami

    • Less directly, mountain ranges affect weather and climate


Development of the theory

Development of the Theory

  • Continents drifted through oceanic crust  continental drift

  • Fit across Atlantic is best using edges of continental shelves

  • Mountain ranges, rocks, fossils and glacial erosion patterns match across Atlantic

  • Glaciers existed in areas now warm and tropical

  • Unsure of the mechanism causing the drift

Continents of Africa and South America fit together like puzzle pieces

Alfred Wegener (1912) proposed supercontinent Pangaea

The Origins of Continents and Oceans (1915)


Development of the theory1

Development of the Theory


Development of the theory2

Development of the Theory

Wegener’s continental drift hypothesis was rejected because its mechanism (continents plowing through ocean floors) was deemed not to be physically possible

More information about topography, appearance, age of ocean floor led to understanding of separation of continents

Late 1940s through the 1960s: discovery of mid-oceanic ridges and the science of paleomagnetism


Development of the theory3

Development of the Theory

  • Harry Hess (1960): ocean floors act as conveyor belts carrying continents in process of seafloor spreading

    • New oceanic crust wells up at mid-oceanic ridges

    • Oceanic crust spreads away from ridges

    • Oceanic crust sinks into deep oceanic trenches at continents’ edges

    • Spreading rate calculated to be 2.5 cm/year

    • Whole Atlantic Ocean floor created in about 180 million years


Development of the theory4

Development of the Theory


Development of the theory5

Development of the Theory

  • Confirmation of seafloor spreading in mid-1960s

    • Alternating polarity of Earth’s magnetic field is recorded in basaltic rocks of ocean floors

    • Vine and Matthews (early 1960s) found striped alternating magnetic pattern, parallel to mid-oceanic ridge, representing bands of rocks formed at ridge in past periods of Earth’s switching magnetic field polarity

      • Came to be known as the Vine-Matthews hypothesis

    • Rocks at ridges found to be young (< 1 million years old); rocks at trenches much older


Development of the theory6

Development of the Theory


Development of the theory7

Development of the Theory


Development of the theory8

Development of the Theory

  • Seafloor spreading and other evidence supports theory of plate tectonics (describes movement of Earth’s plates)

    • Landmasses formed Pangaea 225 million years ago

    • Pangaea breakup moved continents into current positions


Development of the theory9

Development of the Theory


Development of the theory10

Development of the Theory

  • Development of theory of plate tectonics as example of scientific method

    • Logical analysis of data to solve problems

    • Scientists make observations, develop tentative explanations (hypotheses)

    • Hypothesis must be testable

    • Tests and observations lead to acceptance, revision or rejection of hypothesis

    • If hypothesis continues to be supported by evidence over long time, it becomes a theory

    • Wegener’s continental drift hypothesis was modified to become theory of plate tectonics


Earth structure

Earth Structure

  • Layers of Earth based on rock composition: core, mantle, crust

  • Layers of Earth based on rock rigidity or strength:

    • Lithosphere is stiff, rigid outer rind of Earth, which makes up plates from 60 km (oceanic) to 200 km (continental) thick, including crust and denser underlying mantle

    • Asthenosphere is inner, hotter, more easily deformed layer


Earth structure1

Earth Structure


Earth structure2

Earth Structure

  • Continental crust

    • Silica-rich

    • Low density 2.7 g/cm3

    • 30-50 km thick

    • Stands higher than denser oceanic crust

  • Oceanic crust

    • Iron-, magnesium-rich, silica-poor

    • Higher density 3.0 g/cm3

    • 7 km thick

    • Floats lower than continental crust, on top of denser mantle


Earth structure do density lab here

Earth Structure (Do Density Lab here!)

  • Elevation difference between continental and oceanic crust explained by isostacy

    • Floating solid object displaces liquid of same mass

    • Crust (continental or oceanic) floats atop mantle (denser mantle slowly flows away to accommodate crust)


Earth structure3

Earth Structure


Earth structure4

Earth Structure

Boundary between crust and mantle identified as density difference: Mohorovicic Discontinuity (Moho)

Boundary between lithosphere and asthenosphere has been identified as zone of lower velocity for seismic (earthquake) waves traveling through mantle: low-velocity zone (LVZ)


Earth structure5

Earth Structure


Earth structure6

Earth Structure

  • Lithosphere is broken into about 12 large plates, most of which are combination of continental and oceanic areas, moving up to 11 cm/year

  • Plates move away from each other at divergent boundaries – usually mid-oceanic ridges

  • Plates move toward each other at convergent boundaries

    • Subduction zone: one plate dives under other, into mantle

    • Continent-continent collision: low density of continents prevents subduction, crumple up into each other instead

  • Plates slide past each other at transform boundaries


Earth structure7

Earth Structure

Lithosphere is broken into about 12 large plates, most of which are combination of continental and oceanic areas, moving up to 11 cm/year


Earth structure8

Earth Structure

Three types of boundaries, divergent, convergent and transform, found at western edge of North America


Hazards and plate boundaries

Hazards and Plate Boundaries

Most earthquake and volcanic activity occurs at plate boundaries

Subduction zones between oceanic and continental plates along Pacific coasts

Collisions between continents in mountain belts of southern Europe and Asia

Rapidly spreading divergent boundaries follow mid-oceanic ridges

Slowly spreading divergent boundaries pull apart continents (East African Rift zone)


Hazards and plate boundaries1

Hazards and Plate Boundaries


Divergent boundaries

Divergent Boundaries

  • Plates pull apart (by sinking of heavy lithosphere at trenches)

  • System of connected oceanic ridges through ocean basins

    • Only above sea level at Iceland

    • Fissures open every 200-300 years in Iceland’s central valley, erupting large basalt flows

  • Spreading centers are source of basalt that covers all ocean floors, 2/3 Earth’s surface

  • Little volcanic or earthquake hazard


Convergent boundaries

Convergent Boundaries

  • Subduction zones – where two plates meet, denser (oceanic) plate slides beneath other and sinks into mantle

  • Contact zone sticks then slips, in huge earthquakes

    • Sudden movement of ocean floor can generate tsunami

  • Line of volcanoes forms inland from subduction trench

    • After being subducted, water-rich serpentinite heats up and breaks down, releases water

    • Released water rises into mantle, causes partial melting

    • Basalt magma rises to surface to form volcano

    • If basalt magma rises through continental crust, mixes to form rhyolite magma


Convergent boundaries1

Convergent Boundaries


Collision of continents

Collision of Continents

  • Neither plate sinks (too light to penetrate mantle)

  • High mountains are pushed up

    • Accompanied by large earthquakes

    • Forms Himalayas, Tibetan plateau, Caucasus


Collision of continents1

Collision of Continents


Transform boundaries

Transform Boundaries

  • Plates slide past each other without pulling apart or colliding

  • Oceanic transform faults offset mid-oceanic ridges

    • Direction of offset does not indicate relative movement on transform fault

  • Transform faults on continents generate large earthquakes, near large population centers

    • North Anatolian fault in Turkey

    • San Andreas fault in California


Transform boundaries1

Transform Boundaries


Hotspot volcanoes

Hotspot Volcanoes

  • Volcano is surface expression of hotspot:

    • Column of hot, partially molten rock rising through mantle, burning through overlying moving plate, to form track of volcanoes, far from plate boundary

    • Hotspot volcanoes erupt at active end of chain of extinct volcanoes, which get progressively older farther from active end

    • Hawaiian-Emperor chain in Pacific, Yellowstone line of resurgent calderas

    • Columns of hot rock (plume) appear fixed in mantle

    • Hot rock melts near surface as pressure drops


Hotspot volcanoes1

Hotspot Volcanoes


Hotspot volcanoes2

Hotspot Volcanoes


  • Login