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Volcanoes: eruptive style and associated landforms

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Title: Volcanoes: eruptive style and associated landforms


1
Volcanoes eruptive style and associated landforms
2
Viscosity
  • Resistance to flow

Which test tube contains the fluid with high
viscosity? Left? Right?
3
Viscosity
  • Which eruption was produced by high viscosity
    lava? What are the clues?

Eruption A
Eruption B
4
Why does one type of lava have a higher viscosity
than the other?
5
Why does one type of lava have a higher viscosity
than the other?
  • Tectonic setting
  • Source of lava
  • Composition

Basalt asthenosphere and oceanic crust
Andesite sediments, water, oceanic crust and
continental crust
Lower percentages of silicon and oxygen
Intermediate composition
6
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8
The Silicon Tetrahedron
  • Acts as a thickening agent
  • Building block to all rock forming minerals
  • Higher percentage higher viscosity

Rhyolite gt 65
Andesite 55-65
Basalt lt 55
9
Rhyolite is the lava type with the highest
percentages of silicon and oxygen
  • Most violent eruptions

10
Hot spot under continental crust
Notice the direction of plate movement
11
Andesite
  • Intermediate composition lava

12
Landforms associated with viscous lava
Andesitic lava produces stratovolcanoes
Rhyolitic or dacitic lava produces plugs.
13
Mt. Rainier
14
Mt. St. Helens before the 1980 eruption
Bulge plug that is pushed out by magma within
the conduit.
15
Mt. St. Helens after the eruption
Plug dome
16
Mt. St. Helens dome plug
The plug is nearly the height of the Washington
Monument and the width of four football fields.
17
Plug dome andesitic to rhyolitic in composition
18
Lassen Peak
  • Lassen Peak is a plug dome volcanic landform
  • Built from felsic lava
  • One of the largest on Earth
  • Carved by glaciers during the Ice Age

19
Crater Lake volcanic caldera
20
  • Caldera formation and subsequent plug
  • Volcanic eruption
  • Large volume of material extruded
  • Magma chamber empties
  • Volcano collapses into the empty magma chamber

21
Yellowstone hot spot under continental crust
  • Three large eruptions in the last 2 million, 1.3
    million and 600,000 years ago

Calderas formed when felsic lava produced
enormous eruptions.
22
Yellowstone caldera formation
23
Long Valley Caldera
  • An enormous eruption 760,000 years ago, forming a
    caldera

24
Landforms associated with low viscosity lavas
Basaltic lava flows produce shield volcanoes and
lava plains or flood basalts.
25
Shield volcano Mauna Loa is 9 miles high Built
over a long period of time Associated with
basaltic lava
26
Modoc Plateau, northeastern California (extension)
  • Medicine Lake volcanic field
  • Mt. Shasta is in the background
  • Tectonic setting?

27
Basaltic lava flows from fissures Layer upon
layer of lava flows Covers continental crust
Columbia River Basalts
14-16 million years old
28
What happened in Iceland?
  • Eyjafjallajokull's eruption creates an ash cloud
    that closed Europes airports for weeks
  • Shield volcano eruption under a layer of ice

29
Size comparison
30
Cinder cones found in most setting
Hawaii
  • Short lived events
  • made of cinders
  • generally about 1000 feet high

Mojave Desert
31
Composition,Viscosity and Eruptive Style
Composition
Basalt
Andesite
Rhyolite
Fluid
Pasty
Viscosity
Eruptive Style
Violent
Quiet
Cool
Temperature
Hot
32
The three Vs
Viscosity
Strombolian
Icelandic
Volatiles
Volume
Plinian
33
Volcanic material
  • Pyroclastic debris
  • Lava flow
  • Pieces of older rock and magma
  • Ash size to bombs
  • Smooth or chuncky

34
Volcanic Explosivity Index
  • Volume of material
  • How high the eruption column reached
  • How long the main eruption occurred
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