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Unit 6: Earth Shaped from the Outside in. Cycle 18: Volcanism & earthquakes Cycle 19: Plate Tectonics Cycle 20: Weathering & Erosion. Connection to last unit….

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unit 6 earth shaped from the outside in

Unit 6: Earth Shaped from the Outside in

Cycle 18: Volcanism & earthquakes

Cycle 19: Plate Tectonics

Cycle 20: Weathering & Erosion

connection to last unit
Connection to last unit…
  • To deeply understand the processes that create rocks and minerals such as volcanism, weathering, pressue, etc. need more information about where in the world these things happen
connections beyond
Connections beyond…
  • Why learn it?
    • So inherently cool!
    • So dangerous, need to be prepared
    • So relevent, in the news eery day impacting people around the world
class opener
Class Opener
  • Do mapping activity
  • Are all the earthquakes and volcanoes evenly spaced randomly across earth’s surface?
  • Why do earthquakes and volcanoes occur where they do?
volcanoes volcanism
Volcanoes &Volcanism
  • Volcanoes=the cone structure volcanism=movement of magma out of the earth
  • Volcanism is caused by solid rock melting. Liquid rock is less dense and therefor rises
    • Review: kinetic molecular theory of matter
what 3 things cause rock to melt and rise
What 3 things cause rock to melt and rise?
  • Increasing temperature
  • Adding water
  • Decreasing pressure

Convergent Subduction Plate

Boundary Volcanism

Divergent Plate

Boundary Volcanism

  • Along plate boundaries & intra-plate areas
    • Ring of Fire
    • Mid-Ocean Ridge
    • Hot Spots
    • Volcanic Arcs


Volcanism (hotspots)


Convergent Subduction Volcanism

    • Plates are colliding with each other and subducting. lithosphere is being melted
    • Volcanism due to increased temps, water
  • Divergent Volcanism
    • Plates are ripping apart
    • Volcanism due to melting of asthenosphere due to less pressure from above
  • IntraplateHotspot Volcanism
    • In middle of plates
    • Hot spot in mantle
    • plume rises towards the surface due to density difference
volcanic structures
Volcanic Structures
  • As eruptive materials pile up at an opening a “volcano” forms
      • Shield
      • Composite
      • Cinder

Shield Volcano

Shield Volcanco

-Low angle slopes of 1-10

Largest volcano

-Hawaii, Iceland

-Generally on ocean floor

-”quiet” eruption

-made of basalt lava flows, no ash or pyroclastics

-basaltic magma, low gas trapping


Composite Cone/Stratovolcano

Steeper slopes 10-25, taller than cinder cones. Smaller in height and width than shield volcanoes

Cascades (Mt. St. Helens), Andes

Volcanoes on continents over ocean-land subduction zones

Alternating Explosive/quiet eruptions

Built up by alternating layers of lava and pyroclastics

Built over tens to hundreds of thousands of years

Andesitic (or Granitic) composition magma, gas rich


Cinder Cones

Smallest volcanic features have large craters with steep slopes of 30-40

Paricutin, Mexico

Generally forms on continents

Explosive eruptions

Built of pyroclastics (tephra/cinders) not lava flows.

Generally short lived eruptions - weeks to a few years until the magma is degassed, then it solidifies in the pipe and flows form from the base

Paricutin, Mexico, cinder cone soon after its birth in 1943 in a Mexican cornfield.

what determines the shape eruption type
What determines the shape, eruption type…
  • What determines what kind of volcano forms?
    • The eruptive materials (lava vs. pyroclastics)
  • What determines what kind of eruptive materials occur?
    • Type of eruption (explosive vs. quiet)
  • What determines what kind of eruption occurs?
    • The amount of pressure build up from trapped gas especially
  • What determines the gas content and composition of the magma?
    • What type of rocks are being melted, ocean floor, continental, both, asthenosphere, LOCATION
warning signs of impending eruption
Warning signs of impending eruption
  • Earthquakes increase in frequency and strength
  • Ash and gas increases
  • Bulging of volcano side
  • Pyroclastics: breathing, hit by it
  • Lahars/mudflows: concrete flood
  • Poisenous hot gases: can’t breath
  • Pyroclastic flows: instant incineration
  • 700km/hr (450mph)
earth s layers
Earth’s Layers
  • Formed during early precambrian when earth was liquid rock all over
  • 3 layers based on differences in composition
    • Crust, mantle, core
  • 5 layers based on differences in “stiffness/fluidity” of material
    • Lithosphere, asthenosphere, lower mantle, outer core, inner core
  • How do we know?
    • Earthquakes!
    • Seismic waves travel faster in denser materials.
    • S-waves only travel through solids (both rigid and plastic)
    • Inferences based on overall density calculations for earth, observations of surface materials, lava, and meteorites
what is an earthquake
What is an Earthquake?
  • Definition: sudden, strong shaking of the earth’s crust caused by release of energy
  • Usually happens along faults
Movement of rigid solid crust causes stress in rocks
  • Rocks bend/stretch/compress/distort their shape
  • Breaking point reached and rocks release energy and move along fault
  • Go back to original “unbent” shape
  • Can only occur in rigid solids of crust
body waves
P waves

Primary wave



Arrive first

Push-pull waves (compress/stretch rock, no shape change)

Move through solids, liquids and gases

S waves




Arrive Second

Up and down waves (change shape of rock)

Only move through solids

Body waves
locating the epicenter of an earthquake
Locating the epicenter of an earthquake
  • The farther the station is from the epicenter, the greater the time is between the arrival of primary and secondary waves
  • Need 3 stations
travel time graph
Travel Time Graph
  • How long does it take the S & P wave each to travel 1000 mi? 2000 mi?
  • How much sooner will the P wave arrive at a seisograph station 1000 mi away from the earthquake location? 2000mi?
  • What is the general relationship between difference in arrival time between P & S wave and distance?
  • This graph can help geologists identify distance to earthquake epicenter but not…
    • Direction!
earthquake dangers
Earthquake dangers
  • Falling objects
  • Collapsing buildings
  • Collapsing bridges, tunnels, etc.
  • Fires (caused by broken gas lines etc.)
  • Tsunamis near coast
  • Interuption in medical and other emergency services due to debris and road closures
safety precautions
Safety Precautions
  • Inside:
    • Drop, cover, hold on! Protect your head from falling objects, windows etc.
    • Don’t try to get outside during shaking
    • Be prepared for aftershocks
  • Preparing your home for EQ safety
    • Bolt bookcases etc. to wall
    • No heavy objects above bed
    • Know how to turn off gas & water
  • Caught at the coast:
    • Did the tide go out quickly? If you are seeing more of the bottom of the ocean than you should…
    • Get to higher ground!
earthquake frequency and cause
Earthquake frequency and cause
  • Earthquakes in New England?
  • What causes earthquakes
  • Most frequently at plate boundaries but can happen anywhere in plate, especially if there are faults already in rock