Todays Plan

1
Todays Plan

• Finish Volcanic Hazards Workshop
• Learn about links between Plate Tectonics and
  volcanoes

2
Announcements

• Free Geology 101 tutoring _at_ Tutoring Center (OM
  387)
• By appointment (x3855), or drop in
• T 10-12
• W 11-12, 2-3
• Th 10-12, 630-830 pm (BH 201)
• F 11-12

3
Announcements

• Rock and Gem show this weekend
• Bloedel-Donovan Park, 2214 Electric
• Saturday Sunday 10-5
• Free!

4
Turn on the International Volcanic Hazards
Training Video now.
5
Your Answers Magma Viscosity

• What (A) increases or (B) decreases the viscosity
  of a magma? (This is important because more
  viscous magmas erupt more violently)

6
Question X

• Which of the following volcanic hazards affects
  many, but kills few?
• Pyroclastic Ash Fall
• Lahar (mudflow)
• Pyroclastic Ash Flow (nuée ardente)
• Tsunami

7
Question X

• Which of the following volcanic hazards affects
  many, but kills few?
• Pyroclastic Ash Fall
• Lahar (mudflow)
• Pyroclastic Ash Flow (nuée ardente)
• Tsunami

8
Question Y

• Which of the following is the main volcanic
  hazard for Bellingham?
• Pyroclastic Ash Fall
• Lahar (mudflow)
• Volcanic landslide
• Tsunami

9
Question Y

• Which of the following is the main volcanic
  hazard for Bellingham?
• Pyroclastic Ash Fall
• Lahar (mudflow)
• Volcanic landslide
• Tsunami

10
Question Z

• Which of the following is the least important
  volcanic hazard for Bellingham?
• Pyroclastic Ash Fall
• Lahar (mudflow)
• Lava flows
• Pyroclastic Ash Flow (nuée ardente)

11
Question Z

• Which of the following is the least important
  volcanic hazard for Bellingham?
• Pyroclastic Ash Fall
• Lahar (mudflow)
• Lava flows
• Pyroclastic Ash Flow (nuée ardente)

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Volcanoes, Rocks Plate Tectonics

• What causes a volcano?
• Why do they appear near the ocean?
• What type of rocks are formed in different
  locations?

13
Conceptual leaps from minerals to rocks to plates

• Minerals make up rocks
• Rocks can be
• Interlocking minerals crystallized from magma
  (igneous)
• Particles cemented together (sedimentary)
• Minerals re-crystallized from pre-existing rocks
  (metamorphic)

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Connecting Rocks to Plates

• Peridotite - mantle
• Most Iron (Fe) and Magnesium (Mg)
• Basalt (gabbro) - oceanic crust
• Less Fe and Mg (derived directly from mantle)
• Rhyolite (granite) - continental crust
• Least Fe and Mg (but most Silicon!)

16
Convergent Plate Boundaries
17
Convergent Plate Boundaries

• Continental Volcanic Arc
• e.g., WA
• Volcanic Island Arc
• e.g., Japan

18
Divergent Plate Boundaries

• Most are at mid-ocean ridges
• Mantle melts as pressure is reduced
• Melt is basaltic in composition
• Cooling basalt forms new oceanic crust

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Mid-ocean ridges

• Form pillow lava or pillow basalt as magma
  erupts into seawater.

20
Mid-ocean ridges

• Unusual circumstances can put a piece of the
  ocean crust on land, where we can observe pillow
  basalt.

21
Intraplate Volcanism

• Head of hot mantle collects at core-mantle
  boundary
• When it reaches the base of the crust it makes a
  huge amount of basalt (flood basalts)
• As plate moves over plume, a trail of volcanism
  forms

22
Intraplate Volcanism

• Head of hot mantle collects at core-mantle
  boundary
• When it reaches the base of the crust it makes a
  huge amount of basalt (flood basalts)
• As plate moves over plume, a trail of volcanism
  forms

23
Intraplate Volcanism

• Head of hot mantle collects at core-mantle
  boundary
• When it reaches the base of the crust it makes a
  huge amount of basalt (flood basalts)
• As plate moves over plume, a trail of volcanism
  forms

24
Intraplate Volcanism - Ocean

• forms basaltic volcanoes (Hawaii)

25
Intraplate Volcanism - Continent

• forms flood basalts, then more silica-rich
  volcanoes (calderas)
• Columbia River Basalts Yellowstone

26
WarmUp Question making magmas

• Q Geologists explain the occurence of magmatism
  (that is, intrusions below the earth's surface
  and volcanoes above it) by several different
  processes according to the tectonic setting. Each
  involves melting the mantle. Match up the
  tectonic setting with the most closely associated
  melting process.

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Your Answers making magmas

• mid-ocean ridge magmatism (divergent plate
  boundaries)
• 74 said Bmantle convection leads to
  decompression melting

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Your Answers making magmas

• subduction zone magmatism (convergent plate
  boundaries)
• 75 said Awater (and other volatile components)
  from slab reduces the melting temp.of the
  overriding mantle

29
Your Answers making magmas

• hot spot magmatism (intra-plate magmatism)
• 87 said Cplume from core-mantle boundary leads
  to decompression melting

30
A Cooperative Quiz
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A Cooperative Quiz

• If convection in the mantle causes solid mantle
  to rise, then
• The mantle rock will erupt on the seafloor
• The mantle rock will melt (at least partially)
  producing basaltic magma
• The molten mantle will crystallize
• The subducting slab will rise

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A Cooperative Quiz

• If subduction releases water into the solid
  overlying mantle (see pic),
• The slab will melt
• The mantle rock will melt (at least partially)
  producing basaltic magma
• The molten mantle will crystallize
• The subducting slab will rise

35
A Cooperative Quiz

• Which of the following tectonic settings is
  likely to produce explosive volcanism?
• Hot spot under continental crust
• Hot spot under ocean crust
• Oceanic spreading ridge (divergent)
• Oceanic-continental plate convergence

36
Your Answers Dipping slabs

• QIf a subduction zone dips (sinks) toward the
  north, which side of the trench should you find
  the volcanic arc?
• Responses
• north side of the trench 68
• south side of the trench 16
• west side of the trench 4
• east side of the trench 4
• cannot determine 8

37
Your Answers Missing eruptions?

• Explain this

distribution of known historic volcanic eruptions
according to tectonic setting
volumetric production of lava/tephra according to
tectonic setting.
38
Your Answers Missing eruptions?

• Due to the fact that subduction and rift are
  similar it does show a correlation. They describe
  the convergence from the oceanic crust to the
  continental crust, subduction, and represent the
  place where this action is taking place, rift.

39
Your Answers Missing eruptions?

• Explain this

distribution of known historic volcanic eruptions
according to tectonic setting
volumetric production of lava/tephra according to
tectonic setting.
40
Your Answers Missing eruptions?

• It's said that the more often a volcano erupts,
  the less dangerous it is. So, this makes perfect
  sense. Volcanoes as a result of a rift happen
  least often, and emit the most volume of lava!

41
Your Answers Missing eruptions?

• Explain this

distribution of known historic volcanic eruptions
according to tectonic setting
volumetric production of lava/tephra according to
tectonic setting.
42
Your Answers Missing eruptions?

• I honestly have no idea. I am terrible with
  reading pie charts and I do not fully understand
  the question. I would say that it is impossible
  to know all the activity that is occurring.
  Especially on the ocean floor. Does the right one
  mean that there is more activity, than effects
  from that activity and the left mean that there
  is more .........oh I give up. No reason for me
  to B.S. I have no idea. I'll figure it out in
  class.

43
Your Answers Missing eruptions?

• Explain this

distribution of known historic volcanic eruptions
according to tectonic setting
volumetric production of lava/tephra according to
tectonic setting.
44
Your Answers Missing eruptions?

• Although a large amount of lava is produced in
  the rift tectonic setting, it is the very fluid,
  basaltic magma, which usually doesn't produce
  violent eruptions. Also, these rifts often occur
  on the ocean floor and contribute to seafloor
  spreading instead of forming volcanoes.
  Subduction zones produce less lava, but they are
  also more likely to form volcanic island arcs,
  which eventually have explosive eruptions.

45
Your Answers Missing eruptions?

• Explain this

distribution of known historic volcanic eruptions
according to tectonic setting
volumetric production of lava/tephra according to
tectonic setting.