GLG110 Geologic Disasters and the Environment

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GLG110 Geologic Disasters and the Environment
Today Chapter 6 Volcanoes
Instructor Professor Ramon Arrowsmith Email
ramon.arrowsmith_at_asu.edu Office PSF-640
480-965-3541
TA Tom Foltz Email Thomas.foltz_at_asu.edu Office
PSH-574
Course Website http//glg110.asu.edu
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Disaster of the day
0740 September 18 The eruption is much the same
this morning as it was yesterday morning. The
Wilipea bench is rather active, lava pouring
into the water from several points on the leading
edge of the bench northeast of its seawardmost
tip. Both fingers of the Wilipea lobe have
breakouts, but none is near the visitor area.
During the past 24 hours, the main, eastern part
of the feeding flow has advanced 20 m or so along
the old 1995 surface above the new northeastern
Wilipea bench.

• Kilauea ongoing eruptions

Lava falling into water off southeast-facing
front of Wilipea delta (bench).
http//hvo.wr.usgs.gov/kilauea/update/

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Tumulus (mounds) pushed up as lava flow inflated.
Lava covered this part of the road on September
12-13, but tumulus has mainly grown by inflation
in past two days. Tumulus is elongate parallel to
roadway, perhaps influenced by road cuts. 0630.
http//hvo.wr.usgs.gov/kilauea/update/
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Oblique view of the Big Island of Hawaii
classic shield
http//www.nps.gov/carto/silvretta/bryce_dem/hawai
i.html
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Kilauea and volcano plumbing
Keller, 2002
http//volcanoes.usgs.gov/About/What/Monitor/Defor
mation/TiltKilauea.html
Intrusion of magma from below pressurizes magma
chamber and inflates volcano. Eruption then
releases the pressure and the volcano deflates.
We know this from monitoring ground motion
(tilts).
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Global volcanoes and the ring of fire most of
the 550 active volcanoes on earth are located
along the margins of adjacent plates
http//www.geology.sdsu.edu/how_volcanoes_work/Thu
mblinks/plates_page.html
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Idealized diagram showing plate tectonic
processes and their relation to plate tectonic
activity
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Igneous Rocks

• Formed from the cooling and consolidation of lava
  or magma
• plutonic (intrusive) cooled below the
  surface
• volcanic (extrusive) cooled on the surface

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Magma Vs. Lava

• What is the difference?
• Magma molten rock beneath Earths surface
• Lava magma that has traveled to the surface

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Classification of Igneous Rocks

• We classify igneous rocks using two major
  properties
• Texture
• Extrusive or intrusive
• Chemical Composition
• Relative amounts of Si, O, Mg, Fe, K, Al, Na, Ca

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Igneous Textures

• Glassy no minerals present
• Crystalline rocks made of mineral grains
• a) Coarse grained
• b) Fine grained
• c) Mixture of coarse and fine
• Vesicular with bubble holes
• Pyroclastic fragmental texture

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Xl Size and Cooling Rate
crystal size
cooling rate
Slow cooling
larger crystals
Fast cooling
small or no crystals
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Igneous Textures

• fast cooling magma/lava
• forms at or near surface
• sometimes holes present
• cant see individual crystals

• forms far
• below surface
• slow cooling
• intergrown
• crystals

Fine-grained
Coarse-grained

• very rapid
• cooling
• ions unable to
• unite in orderly
• crystalline
• structure

• magma cooled slowly for a while before erupting
• minerals crystallized at different temperatures
  and/or rates

Glassy
Mixture of coarse and fine
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Igneous Compositions

• Mainly silicate minerals
• Determined by composition of magma from which it
  crystallized
• Magma primarily comprised of 8 elements
• Si, O, Al, Ca, Na, K, Mg, Fe

Most abundant
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What Makes a Magma?
Usually a silicate melt (liquid) at high
temperatures (650 to 1200C). Mixture of all the
elements that make up minerals plus volatile
components H2O, CO2, Cl, F, S These components
form gases and will boil off when pressure is
released.
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From Magma to Igneous Rock

• Magma
• cools
• solidifies
• forms silicate minerals

Two major silicate mineral groups end members
FELSIC silicates (LIGHT color)
MAFIC silicates (DARK color)
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Viscosity

• Viscosity Resistance to flow
• Factors
• Compositionhigher SiO2 -gt higher
  viscositylower volatiles -gt higher viscosity
• Temperature lower temperature -gt higher
  viscosity

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Intrusive/extrusive Igneous Rocks

• Granite and rhyolite
• Chiefly composed of quartz and feldspar.

• Same chemical composition different cooling
  rates
• Melting point
• 800 C
• High viscosity
• High silica content
• 70-75

Granite Rhyolite
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Intrusive/extrusive Igneous Rocks

• Diorite and andesite the chief mineral is
  plagioclase

• Same chemical composition different cooling
  rates
• Melting point
• 1000 C
• Medium viscosity
• Intermediate silica content (60)

Diorite Andesite
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Intrusive/extrusive Igneous Rocks

• Gabbro-Peridotite and Basalt
• gt50 pyroxene and olivine

• Same chemical composition different cooling
  rates
• Melting point
• 1200 C
• Low viscosity
• Low silica content
• 45-50

Gabbro Basalt
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Types of volcanoes
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Stratovolcano example Mt Fuji, Japan
http//www.volcanoworld.org/vwdocs/volc_images/img
_fuji.html
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Dome example Venus domes and Mt. Lassen
http//www.volcanoworld.org/vwdocs/volc_images
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Cinder cone volcano Sunset Crater (AZ)

• 1,000 feet (300 m) high and 1 mile (1.6 km) in
  base diameter
• Began erupting in 1064-1065
• Hollywood wanted to blow it up in 1920s to
  simulate an eruption

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What comes out of a volcano?

• Lava
• Cinders
• Ash
• Gases

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Factors that influence eruptive styleVISCOSITY

• Lava composition
• more silica more viscous (silicate chains)
• Lava temperature
• hotter lava less viscous
• Amount of gas (volatiles) in lava
• More gas less viscous

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Factors that influence eruptive styleGAS CONTENT

• Gas can provide the force to violently hurl magma
  ash from volcano

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Factors that influence eruptive styleGAS
CONTENT VISCOSITY

• quantity of dissolved gases
• viscosity of magma
• how violent/gentle eruption is

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Examples of US Volcanic hazards

• Mt. Rainier, Washington Mudflows
• Long Valley California unrest
• Arizonas Sunset Crater eruption of 1066 AD

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Mt. Rainier and deposits of two mudflows (Osceola
is 5000 years old and Electron mudflowsmaller
and lighteris 500 years old)
Keller, 2002
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Mt. Rainier map showing potential volcanic hazards
http//www.ess.washington.edu/SEIS/PNSN/RAINIER/we
lcome.html
Keller, 2002
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Forecasting volcanic activity

• Seismic activity
• Thermal, magnetic, and hydrologic monitoring
• Topographic monitoring
• Gas emissions
• Geologic history
• ALERTS

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Long Valley Caldera
http//www.volcanoworld.org/vwdocs/volc_images/nor
th_america/california/long_valley.html
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Long Valley caldera
http//www.volcanoworld.org/vwdocs/volc_images/nor
th_america/california/long_valley.html
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Sunset Crater, AZ
Flagstaff
http//wrgis.wr.usgs.gov/docs/usgsnps/sunset/sucri
mgal.html
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The first evidence from the Southwest United
States of possible ritual behavior related to
volcanism
The eruption heavily affected the areas
inhabitants. Creation of new farmlands by the
cinder mulch, as well as increased precipitation
at that time, led to migration to the region
where cinder depths were optimal, while areas
with too much cinder depth became depopulated.
In the wall of a small masonry structure 6 km
west of Sunset Crater, a fresh basalt clast,
geochemically correlable with Sunset Crater,
contains casts of shucked ears of corn and husks.
A similar clast is on display at Sunset Crater
visitor center and collectors reputedly have
other samples. Corn casts occur on the surface
and deep into the rock. Our failed attempts to
produce a cast of Hopi corn in a Hawaiian lava
flow demonstrate that the Sunset Crater casts
were not made by a flow over-running corn, nor by
flicking lava onto corn. We suggest that
corn-impressed rocks record ritual offerings at
approachable hornitos. Ort, et al.,
http//gsa.confex.com/gsa/2001AM/finalprogram/abst
ract_23098.htm