Transcript Midterm Exam Grade Spread 96.0 88.0 88.0 88.0 87.0 87.0 86.0 86.0 86.0 85.0 84.0 82.5 82.0 81.0 81.0 80.0 79.0 79.0 78.0 78.0 78.0 78.0 76.5 76.0 75.5 75.0 75.0 72.0 72.0 70.5 66.5 66.5 66.0 65.5 56.0 55.5 55.0 39.5 38.0 Please see me Monday, 26 January, 2015 Presentations Arenal, Costa Rica Sam Gomez Reventador, Ecuador Natalie Thompson Ubinas, Chile Christy Adler Corben Davis Megan Lasher Sarah Carrigan Ruapehu,

Midterm Exam Grade Spread
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88.0
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39.5
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Please
see me
Monday, 26 January, 2015 Presentations
Arenal, Costa Rica
Sam Gomez
Reventador, Ecuador
Natalie Thompson
Ubinas, Chile
Christy Adler
Corben Davis
Megan Lasher
Sarah Carrigan
Ruapehu, New Zealand
Gabe Harrington
Sean Fitzpatrick
Mt. Erebus, Antarctica
Kam Bounds
Ben Howard
Merapi, Indonesia
Matt Treveloni
Ryder Arsenault
Surtsey, Iceland
Patrick Deniger
Cameron Hillier
Tuesday, 27 January, 2015 Presentations
Stromboli, Italy
Carl Lipani
Jabari Hurdle-Price
Pico de Fogo,
Cape Verde Islands
Matt Epstein
Dan McDonald
Erta Ale, Ethiopia
Sarah Shoer
Anahita Valakche
Kilimanjaro, Tanzania Brian Levenson
Peg Schreiner
Mt. Cameroon, Cameroon McKayla Blanch Caroline Ferguson
Piton de la Fournaise,
Réunion Island
Syman Hossenbux
Clayton Chang
Taal, Luzon Island,
Philippines
Kadish Hagley
Changbaishan, China
Fuji, Japan
Emily Rosales
Navidad, Chile
Dylan Rothenberg
Ethan Zhang
Cecil Brooks
Signy Coakley
Vincent Lin
Caelin Price
EXPLOSIVE
ERUPTIONS
and Pyroclastic Flows
Part II
As you'll see in the Pinatubo video,
DATING
RADIOCARBON
of organic matter buried by volcanic deposits is
often the best way to determine age estimates for past
eruptions.
(Radiocarbon Dating, or 14C dating,
works only on organic matter,
and is useful on materials
generally up to around 40,000
years of age - hardly applicable
to rocks but very useful for any
organic matter that may be
associated with a geologic unit,
like a volcanic ash (at right). This
log is from a tree that was caught up in the
1912 pyroclastic flow of Novarupta, in Alaska.
THE MAIN REASON geologists would want to know about
when a volcano had erupted is because that can often be the
best indication of when it might erupt again.
Here's an hypothetical example:
14C
dating indicates that Mount Whunkatunka has erupted:
285 years ago (corroborated by historical records)
550 years ago
800 years ago
1050 years ago
1175 years ago
1350 years ago
and 1600 years ago
You have a chance to buy some beautiful lakeside property at the
foot of the mountain, for a bargain price. Do you think this
would be a wise investment on your part? Why or why not?
And how do you find OUT the eruptive history of this volcano??
How do you know it's a volcano in the first place??
Ceboruco, Mexico
1875
High Sierra Nevada – non-volcanic (apparent dome is a glacier)
Sutter Buttes, California
Seward Peninsula, Alaska – landslides in limestone
1.5 My ago
Here are the kickers:
(1) We only know the precise eruptive histories of a
relatively small handful of volcanoes!
(2) Figuring this out can take years of work. The
need is particularly great in those areas where
populations are great but economies are weak.
(3) FACT: Over 40% of the world's human population
lives within striking distance of volcanoes - on the
Pacific Ring of Fire in particular, but also
including the Mediterranean and Africa.
Even the big volcanoes are minor compared to THE
great eruptions of the past several million years.
These MAJOR CALDERA eruptions fortunately are rare events!
(~ once every 100,000 years worldwide) Some notable ones would include:
Toba
70,000 years ago
Yellowstone
600,000 years ago
Long Valley, CA*
780,000 years ago
Ngorongoro Caldera, Tanzania (?) ~1,000,000 years ago
Valles Caldera, NM
1,100,000 years ago
Yellowstone
1,200,000 years ago
Valles Caldera, NM
1,400,000 years ago
Yellowstone
2,200,000 years ago
Cerro Galan, Argentina
2,200,000 years ago
* In 1980-82, hundreds of earthquakes per day recorded movement
of magma deep beneath Long Valley, but activity since then has
been relatively quiet most of the time.
Note that the calderas produced in these enormous explosive events
are commonly TENS OF KM across! The ashes that are produced
also become important stratigraphic markers in the geology.
See http://www.extremescience.com/zoom/index.php/volcanoes/24-caldera-volcano
VEI =
Volcano
Explosivity
Index
VEI 8 =
"Supervolcano"
eruption 
Yellowstone Caldera
2.5 million years ago
(~ 6000 km3)
Ngorongoro Caldera,
Tanzania
Mono Lake
Mono Craters
Mammoth
Mountain
Ski Resort
Long Valley Caldera, eastern Sierra Nevada, California
How do these come about? Here's one scenario, worked out for
the Long Valley Caldera, applicable to Yellowstone and probably
the others as well.
We'll start with a
relatively calm landscape
(ignoring the possibility
of previous eruptions to
help simplify matters!).
Mafic magma,
commonly from a
mantle plume,
begins to rise
beneath the area,
melting the highersilica rocks ahead of
it to produce a
secondary magma
of felsic
composition.
As this plume rises,
because the mafic
magma is much hotter,
it melts an increasing
amount of the highersilica rocks ahead of it.
(Remember that the
higher the silica
content, the lower the
melting temperature.)
The overlying crustal
rocks also probably
have significant water
in them, which also
will lower their melting
temperatures.
A large plume of felsic
magma is generated
ahead of the rising
mafic plume, which
slows as it is starting to
crystallize itself from
the lower
temperatures. (It's
been losing a
tremendous amount of
heat in melting all of
the surrounding rocks,
and also has a much
higher crystallization
temperature.)
Stress created by the
rising magma creates
both earthquakes and
fractures in the
Earth's surface, from
which volcanic gasses
start to escape. Air
samples taken from
soils in Long Valley
ca. 1996, in an area
where all the trees
had died, showed
CO2 levels of
approximately 90%.
Normal air is <0.03%
carbon dioxide.
Not uncommonly, the
magmas never make
it to the surface, but
instead crystallize
underground in a
layered pluton.
Gases may continue
escaping for
thousands of years,
and hot spring
activity is also
common if water is
available.
The more extreme result
is a catastrophic
eruption that opens a
hole in the Earth up to
5000 km2 in size, in an
eruption that begins
small, by "unzipping"
as multiple vents erupt
simultaneously. The
overall area may then
remain an area of
tectonic, thermal and
renewed volcanic
activity for centuries or
even millennia.
Mammoth Mountain ski area
At left, a specimen of Bishop
Tuff erupted from Long Valley
Caldera some 760,000 years ago.
In places, this unit is over 60 m
(200 feet) thick.
Exposures of the Galan Ignimbrite in northern Argentina
The Yellowstone
Caldera is also
something worth
considering. The
park itself is about
the size of the state
of Rhode Island.
By some estimates,
this caldera may
have yielded the
largest explosive
eruption in Earth
history in many
millions of years.
The mountains in the distance are the far rim of the Yellowstone
Caldera. The opposite rim is almost an equal distance BEHIND
this point of view. Yellowstone Lake lies in the foreground.
The Yellowstone Hot Spot
MAY be the same as that
which was responsible for
the Columbia flood basalts.
Yellowstone
experienced
over 1000
earthquakes
early in
2010, but ...
fortunately,
nothing
happened!
The "breathing caldera" analogy ....
The Pearlette Ash (as it's
called) from Yellowstone is
still quite thick in central
Kansas! (Kansas Geological
Survey photos)
Tomorrow:
SUPERVOLCANO!