Including...
Very impressive events
Potential for great destruction
And construction!
What a deal - both earth processes in one event
"The book" discusses the intermittent activity of individual volcanoes
Be careful here!
Human time scales are not up to the task of understanding the timing of geological events
Named after Vulcan - Roman God of Fire and Metalworking
Also Mr. Spock's home planet
More than 500 "active" volcanoes identified
DIGRESS TO: active vs. dormant vs. extinct
Many cultures associated volcanoes with gods
Hawaiian - Pele
Greek - Hephaestus (the ugly son of Hera)
Europe in the middle ages - lots of crazy ideas (no surprise here)
Gateway to hell
Prisons of the damned
Noises associated with volcanoes were the "screams of tormented souls"
Proposed by the R.C. church, which incinerated thousands for worshiping "false" deities
Very specific pattern (Merrill; fig. 15-3, pg. 391)
Usually associated with plate boundaries
DIGRESS TO: Pacific Ring of Fire
Also: Spreading centers are extremely active
Generally based upon the composition of the magma
DIGRESS TO: magma vs. lava
REVIEW: Magma compositions
Composition definitely related to regional tectonic setting
Plate boundaries
REVIEW: Plate Margins
These compositional differences lead to different types of volcanoes
Each quite different from the others
Eruptive characteristics
Shape of the resulting pile of debris
Regional tectonic setting
Tensional environments
Newly differentiated basaltic magma (blood of the earth)
Spreading centers
Also occur at Hot Spots - mantle plumes (Merrill; fig. 15-4, pg. 392)
Also referred to as "blowtorches"
Characteristics of mafic lavas and rocks
General description
Dark colored
Silica/Oxygen: 45% to 52%
High in iron, magnesium, calcium
Low in (or don't have) potassium, aluminum, sodium
Low volatile content
High temperature (>1000°C.)
Low viscosity - flow easily
Mineralogy
Olivine
Pyroxene
Plagioclase
Igneous rock formation
Basalt: extrusive, aphanitic
Diabase: medium texture
Gabbro: intrusive, phaneritic
Scoria: frothy
Various volcanic breccias
Wide range of clast sizes
Glassy rims commonly associated with submarine eruptions
These often shatter and break off
Eruptive characteristics
Relatively non-explosive
Due to high temperature, low silica, low volatiles
Flow like water in many cases
Put on your running shoes
DIGRESS TO: Pahoehoe vs. aa lavas
Flows cool and lose gas as they move away from the vent
Eruptions relatively quiet, but spectacular
Fissure eruptions
Extensional environment indeed!
Can cover immense areas
Columbia River Basalt
Fountains - of all sizes
Some incredible displays on Hawaii
Lava falls: Hawaii
Lava tubes: Lava Beds Nat. Monument
Lava lakes: Halemaumau, Mauna Loa
Pillow basalt: indicator of submarine eruption
Columnar jointing: indicator of subaerial eruption
Vesicular basalt (church rocks)
Cinder cones
Basalt flows commonly erupt from vents at the base of the cone
Morphology of mafic volcanoes
Shield volcanos - fluid lava
Examples of mafic volcanoes - describe each
Iceland: spreading center
Island of Hawaii: mantle plume
An incredible amount of rock has been produced!
Columbia River / Modoc Plateau basalt
Continental fissure eruptions
Parícutin: cinder cone
Regional tectonic setting
Compressional environments
Subduction zones
Re-melting of mafic crust, continental debris, and organic sediments
Characteristics of intermediate lavas and rocks
General description
Medium colored
Silica/Oxygen: 53% to 65%
Varying amounts of all the major rock-forming elements
Medium volatile content
Medium temperature
Mineralogy
Plagioclase
Amphibole
Muscovite/Biotite
Quartz
Igneous rock formation
Andesite: extrusive, aphanitic
Diorite: intrusive, phaneritic
Various volcanic breccias
Eruptive characteristics: (KaBoom)
Eruptions relatively explosive, VERY impressive
Mt. St. Helens is a SMALL example
Explosiveness due to high volatile content
Like shaking up a can of carbonated soda
Also due to "stickiness" of magma (high silica content)
Results in the formation of "pyroclastic" material
Pyro = fire; clast = small piece of broken rock
All different sizes can be formed
Get blown out by the force of the blast
Pyroclastic flows - nuée ardente
You CANNOT outrun one of these
Associated features
Volcanic gasses
Carbon dioxide: dense and will smother life when concentrated on surface
Sulfur dioxide: combines with water to make sulfuric acid
Tephra and ash deposits
Ashfalls: Just like snow, but don't melt in the spring
Will develop into good soil, with time (the earth's time frame)
Lahars
These types of volcanoes often form high mountain peaks
Collect snow and ice
Melt when an eruption occurs
Major flooding downhill
Can pick up massive amounts of pyroclastic (and other) debris
Houses, mobile homes, cows, slow cats
Whatever is loose and in the way
Extensive damage and loss of life
Morphology of intermediate volcanoes
Composite cones (stratovolcanoes)
Layered pyroclastics and flows
KaBoom then ooze; KaBoom then ooze; KaBoom then ooze
Examples of intermediate volcanoes
Mt. St. Helens
Mt. Pinatubo
Potential risk
Very great risk
From initial blast, pyroclastic flows, lahars, ashfalls
Several major urban areas in potential risk zones
The western flank of the Cascade Range
Mt. Shasta and the I-5 corridor
the Puget Sound in general
Portland, Oregon
Lucked out big time when St. Helens blew to the northeast!
DESCRIBE: difference in lahar distance related to a southern blast
What about Mt. Hood?
A west-directed blast would be a real problem
Regional tectonic setting
Intra-plate hot spots
Tough to get granitic magma close enough to the surface to erupt
Eruptions are (fortunately) very infrequent (by the human time scale)
Origins VERY uncertain
Characteristics of felsic lavas and rocks
General description
Light colored
Silica/Oxygen: >65%
High in potassium, aluminum, sodium
Low in (or don't have) iron, magnesium, calcium
High volatile content
Low temperature (600°C. - 900°C.)
High viscosity
Mineralogy
Potash Feldspar
Quartz
Muscovite/Biotite
Amphibole
Igneous rock formation
Rhyolite: extrusive, aphanitic
Granite: intrusive, phaneritic
Pumice: frothy
Obsidian: glassy
Various volcanic breccias
Eruptive characteristics: (KaBoom)^2
Eruptions very explosive, MOST impressive
Explosiveness again due to very high volatile and silica content
DIGRESS TO: Most felsic magmas cool as intrusive igneous rocks
Obsidian and pumice: volcanic glass
Very quick cooling
No time for crystallization
Morphology of felsic volcanoes
Lava domes: very sticky
Caldera: very explosive
Examples of felsic volcanoes
Yellowstone National Park
Long Valley Caldera, California
Newberry Crater obsidian flows
Potential Risk
Ask the folks in Bishop, Lone Pine, or Wyoming how safe they feel
(chorus)
Now, I don't know
I don't know
I don't know where I'm a-gonna go
When the volcano blows
Let me say now
I don't know
I don't know
I don't know where I'm a-gonna go
When the volcano blows
Ground she's movin' under me
Tidal waves out on the sea
Sulfur smoke up in the sky
Pretty soon we learn to fly
Let me hear you now
chorus (1)
Now my girl quickly said to me
Mon, you better watch your feet
Lava come down soft and hot
You better love-a me now or love-a me not
Let me say now
chorus (1)
No time to count what I'm worth
Cuz I just left the planet Earth
Where I go I hope there's rum
Not to worry, man soon come
chorus (2)
But I don't want to land in New York City
Don't want to land in Mexico
Don't want to land on no Three Mile Island
Don't want to see my skin aglow
Don't want to land in Comanche Sky Park
Or in Nashville Tennessee
Don't want to land in no San Juan Airport
Or the Yukon Territory
Don't want to land no San Diego
Don't want to land in no Buzzard's Bay
Don't want to land on no Ayatollah
I got nothing more to say
chorus (2)