Download Volcanoes, Lavas, Minerals

Volcanoes, Lavas, Minerals
Allan Treiman
LPI
Heat Within, 2009
Plan of Talk

Breaking the Tyranny of Three
– Three types of volcanoes
– Three types of lavas

Volcanoes explained simply
– Lava Properties
– Eruption Style
– Eruption Environments
Lava Properties in terms of Atoms
 Igneous Rocks and Minerals

Three Types of
Volcanoes ?
Shield
 Composite /
Stratovolcano
 Cinder Cone

At real scale.

Like comparing a brick to a
brick building
So Many More
Kinds of Volcanoes
Caldera Complex ‘SuperVolcano’
 Lava Plateau
 Dome
 Single Flow
 Tuff Ring
 And …

What Controls the Shape of a
Volcano?

Properties of lava
– Viscosity (runny or stiff)
– Dissolved Gas - Explosive or Effusive
– % Solid grains in lava
Volume and Rate of each eruption
 Number of individual eruptions
 Environment around eruption

What is Lava?
What is lava?
– Molten material at a planet’s surface
– Solidifies at surface conditions

Many sorts of ‘lava’
–
–
–
–

Most common is silicate - abundant SiO44Molten sulfur, carbonate, iron oxide
Mud is not lava, really (but “mud volcanos”)
Water is not lava on Earth (but is elsewhere)
What is magma?
– More general - not necessarily erupts
Andesite
South Sister
SiO 2
TiO2
Al 2 O3
Fe2 O3
FeO
MnO
MgO
CaO
Na2 O
K2 O
P2O5
H2 O
63.0
1.15
16.24
2.87
2.94
0.08
1.52
4.04
4.86
2.00
0.28
0.68
Sum
99.9
Silicate lavas molecular!



Si - O bonds much stronger than others
Silica tetrahedra, SiO44-, polymerize
In lava, single silica tetrahedra flow
past each other easily, like cous-cous


In lava, large silicate polymers
tangle together, like spaghetti,
and flow poorly
More Silica (SiO2) = bigger,
more connected polymers

Low Silica (SiO2 < 52%) is basalt
– Runny as motor oil, or corn syrup

Intermediate Silica
– Andesite: 52 - 63% SiO2
– Dacite: 63 - 68 % SiO2
– Stiffer than taffy

High Silica, > 68 % SiO2
gives 3-D polymers
– Rhyolite/Granite - flows
like window glass
Andesite
South Sister
SiO 2
TiO2
Al 2 O3
Fe2 O3
FeO
MnO
MgO
CaO
Na2 O
K2 O
P2O5
H2 O
63.0
1.15
16.24
2.87
2.94
0.08
1.52
4.04
4.86
2.00
0.28
0.68
Sum
99.9
Why does Vapor
Matter?

Force for explosive eruptions
– Water & CO2 vapor bubbles out
as magma nears surface
– No vapor, no explosion!
Stiff water-rich magma makes
foam (pumice) & shards of
glassy ash - huge eruptions
 Pumice + ash and water vapor
can flow together as a ‘slurry’
= an ash flow

Volcanic Ash!
Ash flow =
pyroclastic flow
Video at
http://www.geo.mtu.edu/volcanoes/west.indies/soufriere/govt/images/051296/
Caldera Complex
“Super-Volcanos”
Yellowstone




Valles Grandes, NM
Caldera is 22 km across
Rhyolite ash flows & domes
Slope outside caldera ~2°
Crystals in Lava
Solid crystals make lava more viscous
 What kinds of crystals?

– Olivine (Mg,Fe)2SiO4 - olive green, glassy
– Pyroxene (Ca,Mg,Fe)SiO3 - black/green, breaks
on flat surfaces (cleavage)
– Feldspar - plagioclase (Ca,Na)(Al,Si)Si2O8 clear-white-greenish, glassy, breaks on flat
surfaces.
– Quartz - SiO2 - clear, glassy, curved fractures.

Stop to look at minerals & rocks …
Single Eruption or Flow




Paricutin Cinder Cone - 1.4
km3 lava (typical)
Columbia River, Grande
Ronde - to 750 km long,
2000 km3 lava
Yellowstone - Lava Creek
Tuff (like at Valles Caldera) ~1000 km3 ash
How much is a cubic
kilometer?
Many Eruptions
Mauna Loa Shield ~75,000 km3 lava
 Columbia River Basalts
~170,000 km3 lava
 Olympus Mons (Mars) ~500,000 km3 lava
 Ontong-Java Plateau ?6,000,000 km3 lava

Environment of
Eruption

Into Air
– Typical

Into Water
– Maar Crater
– Tuff Ring
– Pillow Lava

Into Ice
– Tuya Buttes

Into Vacuum ?
The End.