Transcript Volcanoes: eruptive style and associated landforms

Volcanoes: eruptive style and
associated landforms
Viscosity
• Resistance to flow
Which test tube contains the fluid with high viscosity?
Left? Right?
Viscosity
• Which eruption was produced by high
viscosity lava? What are the clues?
Eruption A
Eruption B
Why does one type of lava have a
higher viscosity than the other?
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
Intermediate composition
Lower percentages of
silicon and oxygen
The Silicon Tetrahedron
• Acts as a thickening agent
• Building block to all rock forming minerals
• Higher percentage = higher viscosity
Rhyolite > 65%
Andesite = 55-65 %
Basalt < 55%
Rhyolite is the lava type with the
highest percentages of silicon and
oxygen
• Most violent
eruptions
Hot spot under continental crust
Notice the direction of
plate movement
Andesite
• Intermediate
composition lava
Landforms associated with viscous
lava
Andesitic lava produces
stratovolcanoes
Rhyolitic or dacitic lava produces plugs.
Mt. Rainier
Mt. St. Helens: before the 1980
eruption
Bulge: plug
that is pushed
out by magma
within the
conduit.
Mt. St. Helens:
after the
eruption
Plug dome
Mt. St.
Helens:
dome plug
The plug is nearly the
height of the Washington
Monument and the width
of four football fields.
Plug dome: andesitic to rhyolitic in
composition
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
Crater Lake: volcanic caldera
Caldera formation and
subsequent plug
1.Volcanic eruption
2. Large volume of
material extruded
3. Magma chamber
empties
4. Volcano collapses
into the empty
magma chamber
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.
Yellowstone caldera formation
Long Valley
Caldera
• An enormous eruption 760,000 years ago,
forming a caldera
Landforms associated with low
viscosity lavas
Basaltic lava flows
produce shield
volcanoes and lava
plains or flood basalts.
Shield volcano
Mauna Loa is 9 miles high
Built over a long period of time
Associated with basaltic lava
Modoc Plateau, northeastern
California (extension)
• Medicine Lake
volcanic field
• Mt. Shasta is in the
background
– Tectonic setting?
Basaltic lava flows from
fissures
Columbia River Basalts
Layer upon layer of lava
flows
Covers continental crust
14-16 million years old
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
Size comparison
Cinder cones: found in most
setting
Hawaii
•Short lived
events
•made of cinders
•generally about
1000 feet high
Mojave Desert
Composition,Viscosity and Eruptive Style
Composition
Basalt
Fluid
Quiet
Hot
Andesite
Viscosity
Eruptive Style
Temperature
Rhyolite
Pasty
Violent
Cool
The three Vs
Viscosity
Strombolian
Icelandic
Volatiles
Volume
Plinian
Volcanic material
Pyroclastic debris
• Pieces of older rock and
magma
• Ash size to bombs
Lava flow
• Smooth or chuncky
Volcanic Explosivity Index
• Volume of material
• How high the eruption column reached
• How long the main eruption occurred