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Volcanoes: eruptive style and associated landforms

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Presentation on theme: "Volcanoes: eruptive style and associated landforms"— Presentation transcript:

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



8 The Silicon Tetrahedron
Acts as a thickening agent Building block to all rock forming minerals Higher percentage = higher viscosity Rhyolite > 65% Andesite = % Basalt < 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 Columbia River Basalts
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 Europe’s 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
Basalt Andesite Rhyolite Fluid Viscosity Pasty Eruptive Style Quiet Violent Temperature Cool 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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