Transcript First lecture - 5 January, 2015

GE151j:
Introduction to
Volcanoes &
Volcanology
Bardarbunga eruptive flow, Iceland, 2 September, 2014
http://mashable.com/2014/09/11/iceland-bardabunga-volcano-eruption-photos/
We meet: M-T-W-Th @ 9:00-11:30
Robert E. Nelson ("Dr. Bob")
Office: Mudd 215
Phone: ext. 5804
e-mail: [email protected]
web page:
http://www.colby.edu/geology/ge151/index.html
Text
Please observe:
1 Regular class: 9:00-9:50 a.m.,
MWF, = 150 minutes per week
THIS class = 9:00-11:30 MTWTh,
= 150 minutes per week.
Take-home message:
Missing ONE DAY of this
class is comparable to missing an
entire WEEK during the regular
semester!
Printed syllabus will show topics we're covering, and
when, as well as readings.
Course grading will be based on:
- 1 homework assignment - geography (25
points)
- Classroom engagement will be key
- 1 hour exam ("midterm") on 15th (100 points)
(and yes, spelling and neatness counts!)
- 1 joint project on a volcano - 2-person teams
(more on this project later)(50 points)
- a technical* critique of a Hollywood volcano
movie (25 points)
*I.e., WHAT IS WRONG with the movie from a technical
perspective, based on what you've learned?
WARNINGS!
*
I will deduct ONE POINT on ANY written
work for each and every time I see
"volcanoe" or "techtonic!" (although
volcanoes IS the correct plural form)
* There will likely be at least a few days when,
due to the lengths of videos, we may run a tad
late in class. This WILL particularly be true
on days when projects will be presented.
* Cell phones are to be turned OFF and put
away during class at all times.
Course Goals: (1) To come to understand volcanoes, how they
work, why they are where they are, what you can
expect from them, and why.
E.g., Why are the volcanoes of Hawai'i and the Galápagos so
different from those of the Pacific Northwest or most
other places in the world?
Fernandina, Galápagos
Mt. Rainier, Washington
(2) To gain sufficient background in at least some basic geologic
principles, to help you gain an understanding of and
appreciation for the physical processes active today in
forming the landscape around you.
"To a person uninstructed in natural history, his
country or seaside stroll is a walk through a
gallery filled with wonderful works of art, ninetenths of which have their faces to the wall."
- T. H. Huxley
Three common misconceptions to dispel:
Myth #1: Volcanoes are the source for the magmas (molten rock).
They are the PRODUCT of the eruptions. The magma
originates much more deeply in the Earth, in the mantle.
And it does NOT originate in the molten outer core - which is
mostly iron, with some nickel!
The high volcanoes of the Andes, for example, are a product of
thousands of volcanic eruptions occurring in the same place,
building up a mountain on top of a thick wedge of folded,
mashed and mangled continental margin.
The view to the south down the length of the Andes, from 15,000 feet (4500 m) elevation.
Atacazo is a volcano atop this pile. Photo taken from Pichincha, another volcano.
Distance to coast: ~ 100 miles (160 km)
(comparable to the distance from here to NH border on I-95)
Myth #2. Lava flows are terrifyingly dangerous aspects of a volcanic
eruption. They are in fact the LEAST dangerous phase of any
eruption, because they're predictable! (That's why people live to
tell about them!)
Note these actively advancing flows in Hawai'i (left) and on Etna in
Italy (right). You don't need to look hard to know these are HOT!
Myth #3: Volcanoes are permanent fixtures on the landscape. Like
living things, they come into existence, are active for a time
(usually measured in thousands to millions of years), and then
die - becoming extinct - and gradually erode away.
Parícutin, in Mexico, came to
life in a cornfield in 1943.
Navidad, in Chile, erupted from
a flat valley bottom on
December 25th, 1988.
Eldfell was a new volcano that grew
rapidly in Iceland in 1973.
Eldfell in 1997.
Where ARE the volcanoes?
80% of the active volcanoes in the world lie on the
Pacific Ocean rim, the "Pacific Ring of Fire"
Other active volcanoes are scattered in Africa,
Iceland, the Mediterranean, the eastern Caribbean
and Indonesia.
Plate tectonics:
What makes
almost all of it
happen.
PLATE TECTONICS and
CONTINENTAL DRIFT
This has REVOLUTIONIZED the Earth Sciences much the way
Darwin and Natural Selection did to biology in the 19th century.
BASIC PREMISE:
The Earth's surface is comprised of 7 major,
and about 20 minor, plates that behave as
relatively brittle slabs, moving slowly
across a more plastic, deformable
underlayer, and creating much activity
where they are in contact with one
another, whether pulling apart, sliding
past, or coming towards each other.
The relatively brittle slabs, ca. 100 km thick, are
called LITHOSPHERE, and comprise the upper
part of the Earth's MANTLE as well as all the
overlying CRUST.
The lithosphere slabs are moved by slow (cm/yr)
flow within the relatively plastic
AESTHENOSPHERE in the upper mantle.
Evidence?
A. Not only do continental margins fit
together well (as first noticed in the
16th century) ...
... but (B) the geology matches pretty
well across those fits, too!
C. Fossils of Glossopteris (a plant) and Lystrosaurus (an animal) are found throughout
the Southern Hemisphere continents, though modern floras and faunas are
completely different. The Glossopteris fossils above, for example, are from
Australia (left) and South Africa (right).
Again: it is CRITICAL that modern biotas in these areas DIFFER!
Examples of the differences in
modern biota on different continents. For example, the Great
Apes are only found in the Old World, monkeys with
prehensile tails and cacti in the New. Eucalyptus is native
only to Australia. And hippos are naturally only found in the
Old World, mainly in Africa today.
D. Glacial evidence: Patterns of glaciation in the Southern Hemisphere around 245280 million years ago (Carboniferous-Permian) makes NO logical sense unless the
continents were in fact connected together.
E. Paleomagnetic evidence and dating of the sea floor rocks indicates new crust is
being formed at the mid-oceanic rise and ridge system (MORRS), and is moving
outwards from this area. Radiometric dating of these rocks shows they get
progressively older the farther away one is from the ridge. We have now even
observed active volcanism along the crest of this mountain system in several
locations.
Plate tectonics are driven by CONVECTION in the
mantle, produced by heat from radioactive decay.
.. and there's increasing evidence that at least in some areas, it's
even far more complicated than THIS!
If we look at the ocean floor, we see:
This mountain range is what is called the
Mid-Oceanic Rise and Ridge System (MORRS)
If we look closely at the MORRS, we see this topography:
Magma upwells to produce
volcanism along this ridge.
Volcanism is widespread
on the Mid-Oceanic Rise
and
Ridge
System
(MORRS), which runs
throughout the world's
ocean system.
In Iceland,
the rifting is
slowly
tearing the
island in
half.
Site of the Laki eruption of 1783-85.
NOTE that if the Earth's crust is being created
anew at the rise and ridge system, one of two
things must be happening:
Either:
A. The Earth is getting progressively
larger over time, or
B. The crust is being destroyed at about
the same rate it is being created.
The process of oceanic crust destruction is going on off the
western coast of almost ALL of the Americas, from British
Columbia to the southern tip of Chile, on all other margins of
the Pacific, as well as other places in the world:
Imbabura
Cotopaxi
Tungurahua
Imbabura, Cotopaxi and
Tungurahua are just three
of many volcanoes in
Ecuador that have been
produced by this process.
The same process is going on off the North American coast in
Oregon and Washington State:
(Andesite, Dacite)
Mt. Hood, Mt. Bachelor, and Mt.
Shasta of the Cascade Range are
also products of the same
process.
Mt. Rainier
Mt. Hood
Mt. Shasta
Mt. Bachelor
Oceanic lithosphere can also be subducted beneath other
oceanic lithosphere - creating an island arc system.
TYPICAL Island-arc systems include….
The Kuril Islands
The Aleutian Islands
The Japanese
archipelago
The Marianas
Islands
The Philippine
Islands
The Sumatra-Java Arc
The
Lesser
Antilles
This is WHY 80% of the active volcanoes in
the world lie on the "Pacific Ring of Fire"
This volcanic ring is created by subduction of oceanic
crust on almost all margins of the Pacific basin.
Time for a break ...
and a short video ...