Chap 5 Volcanoes

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Chap 5 - Volcanoes
Mt Pinatubo, Phillipines - 1991 explosive
eruption (silicic)
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Conical shape - typical
Soufriere Hills Volcano, Montserrat 1995 to now
predominantly effusive, some explosions Andesitic
composition (intermediate)
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Kileaeu, Hawaii 1983 to now - effusive eruption

basaltic composition
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Ruins of the Visitors Center After Lava Cooled
Source Photograph by J.D. Griggs, USGS Photo
Library, Denver, CO.
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Lava Tube
Skylight
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Mount Cameroon, W Africa Erupted 2 months in 2000
2002 Mildly explosive lava flows Basaltic
composition
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Overview

• Magma Sources and Types
• Kinds and Locations of Volcanic Activity
• Hazards Related to Volcanoes
• Issues in Predicting Volcanic Eruptions
• Present and Future Volcanic Hazards in the United
  States

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Magma Source

• Areas Where Magma Forms (need heat!)
• Upper mantle asthenosphere
• depths of 50 to 250 km
• High temps (800-1100º C), medium pressure
• Mantle rocks partially melt (in different ways)
• Divergent plate boundaries
• Hot spots e.g. Hawaii
• Above subduction zones e.g. Lesser Antilles

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Plate tectonics Asthenosphere is where melting
occurs
Asthenospheric wedge
Source http//www.geol.umd.edu/jmerck/gal04/GEOL
388/lectures/02.html
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Volcanology of Lesser Antilles Arc
11 main islands
Island of Saba-northernmost
Grenada-southernmost
All volcanism dominantly andesitic (60 SiO2),
with exception of Soufriere, St. Vincent
(basaltic andesite-58SiO2)
Andesites volcanoes generally involve
dome-building eruptions
Best example - Soufrière Hills volcano on
Montserrat erupting since July 1995 still
continues!
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Magma Types

• Composition
• Magmas gt Fe, Mg Low in SiO2 - mafic vs
• Magmas gt SiO2 lower in Fe Mg felsic aka
  silicic
• Dependent on tectonic setting
• (1) Ocean spreading ridges and hot spots
• Mafic rocks (e.g.basalt)
• (2) Continental rifts continental arcs felsic
  (e.g.rhyolite, andesite)
• (3) Subduction zones island arcs intermediate
  e.g. andesite

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Mafic Basalt
Ultramafic Peridotite
Source http//www.tmm.utexas.edu/npl/mineralogy/B
lowups/Olivine_in_peridotite_xenolith.htm
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Felsic-mafic andesite
Source http//www.otago.ac.nz/geology/features/ro
cks-minerals/rocks.html
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Felsic Rhyolite
Source http//resourcescommittee.house.gov/subcom
mittees/emr/usgsweb/photogallery/
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Magma properties

• Magma is composed of melt crystals
  dissolved gases such as H2O CO2 SO2
• Pressure builds up as magmas rises to surface
• Silicic more SiO2 more dissolved gas
  viscous explosive
• Mafic less SiO2 more fluid less dissolved
  gas gas escapes
• Rate of Ascent from Magma Chamber to Surface
  also IMPORTANT
• What kind of volcano is safest to live by?

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Mount St. Helens (western U.S.A.)

• May 1980 Initial avalanche
• Plinian eruption
• then dome growth for 6 years

Quiet for 18 years
Restarted dome building Oct 2004 to date
Source Photograph courtesy of USGS Photo
Library, Denver, CO.
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Mount St. Helens - pre 1980 eruption
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Mount St. Helens - post dome growth (1987)
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Mt Pinatubo, Phillipines - June 1991 explosive
eruption (silicic)
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Tracking the Path of Sulfuric-Acid Mist 20
million tons of SO2 in atmosphere! After 1
month, ash acid had circled the Earth
Source Image by G.J. Orme, Department of the
Army, Ft. Bragg, NC.
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Pinatubo Effects on Near-Surface Temperatures
Nuclear War?
Source Data from National Geophysical Data
Center.
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Issues in Predicting Volcanic Eruptions

• Classification of Volcanoes by Activity
• Active, dormant (sleeping) extinct
• Statistics
• Typical volcano erupts once in 220 years
• 20 erupt less than once in 1000 years

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Issues in Predicting Volcanic Eruptions

• Monitoring
• 300 to 500 active volcanoes on Earth
• Volcanic Precursors
• Seismic activity (earthquakes)
• Tilting, bulging, uplift of surface (indicates
  rising magma)
• Volcanic gases increases/decreases in SO2
  (measurable) H2O (not measurable) etc

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Tilt Record of Kilauea, Hawaii (from tiltmeter on
flank of volcano)
Source Data from The Puu Oo Eruptions of
Kilauea Volcano, Volcanoes in Hawaii, U.S.
Geological Survey.
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Present and Future Volcanic Hazards in the United
States

• Hawaii
• Cascade Range
• The Aleutians
• Long Valley and Yellowstone Calderas

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Hazard Map of Kilauea
Source Map courtesy U.S. Geological
Survey/Hawaii Volcanoes Observatory.
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Lava Flowing Over New Road
Source Photograph courtesy of USGS Photo
Library, Denver, CO.
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Lava Flowing Over cliff
Source http//epsc.wustl.edu/rbuchwaldt/cenozoic
.html
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Aerial View of Invading Lava Flows
Source Photograph by J.D. Griggs, courtesy of
USGS Photo Library, Denver, CO.
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House Set Aflame by Lava
Source Photograph courtesy of USGS Photo
Library, Denver, CO.
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Hazard Zones on Montserrat -andesitic dome
volcano
Source Montserrat Volcano Observatory.
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Mudflows from Mt. Rainier major threat in the
future
Source Data from T.W. Sisson, USGS Open-File
Report 95-642.
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Satellite of Volcanic Peaks in SW Alaska
(Aleutian Island Arc)
Source Photograph courtesy of USGS Photo
Library, Denver, CO.
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Augustine Volcano Erupting
Source Photograph by M.E. Yount courtesy of
USGS Photo Library, Denver, CO.
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A close call in the Aleutians

• 1989 Redoubt volcano
• -KLM Jetliner flies through ash cloud at 37,000
  ft.
• - Lost power in all four engines
• - Fell 13,000 ft before restarting engines

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Ash Plume from Redoubt Volcano, Alaska (1989
eruption)
Source http//www2.nature.nps.gov/geology/hazards
/
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Map of Mammoth Lakes Area
Source After R.A. Bailey, U.S. Geological
Survey, 1983.
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Thermal Activity at Yellowstone
SourceCourtesy of Carla W. Montgomery.
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Track of N. America over Yellowstone Hot Spot
This is a supervolcano that erupts 600 000 yrs
and now overdue
Source Data and Base Map from U.S. Geological
Survey.
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Less voluminous basalt outpouring from plume tail
- linear volcanic chain
Initial vast outpouring of basalt lava-flood
basalts
Hot-Spot Volcanism
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Toxic gases CO2?
Cameroon, 1986
Source http//wps.prenhall.com/wps/media/objects/
476/488316/ch13.html
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Carbon Dioxide Cloud Over Lake Nyos, Cameroon
Source Photograph by M.L. Tuttle, USGS Photo
Library, Denver, CO.
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Animal Carcasses From Deadly Cloud 1700 people
died through suffocation (not poisoning)
Source Photograph by M.L. Tuttle, USGS Photo
Library, Denver, CO.
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Mount Etna, Sicily Most active volcano in Europe
Source http//www1.ncdc.noaa.gov/pub/data/images/
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Ash Cloud from Mount St. Helens (May 1980)
Source http//pubs.usgs.gov/fs/fs027-00/
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What is Volcanic Ash? Small jagged pieces of
rocks, minerals, and volcanic glass the size of
sand and silt (less than 1/12 inch or 2
millimeters in diameter) Though called "ash,"
volcanic ash is not the product of combustion,
like the soft fluffy material created by burning
wood, leaves, or paper. Volcanic ash is hard,
does not dissolve in water, is extremely abrasive
and mildly corrosive, and conducts electricity
when wet. Ash is v. dangerous to humans, it is
known to cause lung cancer following prolonged
exposure.
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Recent studies on Montserrat ash have shown that
particles lt 10?m settle on the lung and cause
lung cancer
Source http//pubs.usgs.gov/fs/fs027-00/
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Source http//pubs.usgs.gov/fs/fs027-00/
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VOLCANIC ASH - generally nasty stuff
! Conducts electricity Power outages are
common Can interrupt or prevent telephone and
radio communications Clog air filters, car
engines Collapse roofs Respiratory problems
Source http//pubs.usgs.gov/fs/fs027-00/
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Volcanoes in Space?
Olympus Mons The largest volcano in the solar
system
Source http//www.spacetoday.org/images/Mars/Mars
Express/OlympusMonsWide700x525.jpg
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Olympus Mons Caldera, Mars (depth 3 km
Source http//www.esa.int/externals/images/015-09
0204_1-0037_01-6v.jpg
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Olympus Mons Caldera walls
Source http//www.spaceref.com/news/viewsr.html?p
id11888