Volcanism By Hans Ulrich Schmincke

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VolcanismBy Hans Ulrich Schmincke
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VolcanismBy Hans Ulrich Schmincke
Presented By Mahmuda Afrin Badhan Mount Holyoke
College 11
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A VOLCANO is not made on purpose to frighten
superstitious people into fits of piety and
devotion, nor to overwhelm devoted cities with
destruction a volcano should be considered as a
spiracle to the subterranean furnace, in order to
prevent the unnecessary elevation of land, and
fatal effects of earthquakes and we may rest
assured, that they, in general, wisely answer the
end of their intention, without being in
themselves an end, for which nature had exerted
such amazing power and excellent contrivance. -
James Hutton, Theory of the Earth, Codicote, 1795
The motivation to study volcanoes comes from
wanting to know what happens beneath volcanoes
and why they erupt the way they do --- as well as
the processes leading to it and how they behave
afterwards.
Details of recent eruptions are available at
www.volcano.si.edu/gvp. (The Global Volcanism
Network of the Smithsonian Institution and the US
Geological Survey)
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Early Perception of Volcanoes and Volcanic
Activities.
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• Myths about demons and gods in the interior of
  the Earth Fire from hell.
• Beneficial properties of volcanic eruptions
  Prometheus provided the basis for human existence
  by presenting the fire he had stolen from
  Hephaestus from the interior of the Earth.
• Scientific theories included the idea of heat
  panned by winds beneath volcanic valves and
  sulfur or some organic substance causing the
  fire.
• Mt. Shasta in N California believed to be home
  of exotic communities and bizarre creatures.
• Neptunists thought basalt columns were crystal-
• lized out of water at low temperature.
• In 1765, Nicolas Desmarest, a French geologist,
• made findings in Auvergne (France)
• that lead him to conclude they were formed by
• solidification of lava on the Earths surface.
• Volcanoes were commonly thought of as super-
• ficial features which formed not so long ago.
• Then Plutonists placed the roots of volcanoes
• much deeper in the Earth, which proved to be

http//giantcrystals.strahlen.org/europe/basalt1.j
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The First Text
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• Volcanology became a subdiscipline of Earth
  Science in the first quarter of the 19th century
  --- Leopold von Buch, Alexander von Humboldt and
  Poulett Scrope wrote first textbook on
  volcanology.

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ngHazards/B6ManagingHazards-Tectonics/B6ManagingHa
zards-Volcano/volcano_7big_montserrat_eruption.jpg

• Why do volcanoes exist and erupt?
• So that volcanologists have something to do.
• Prove that the Earth is alive and is in good
  health.
• Prove that our planet is very hot and dynamic
  inside.
• Feed materials to the Earths surface and
  atmosphere
• (which was generated by the degassing of
  volcanoes in the first place).
• Shows the flux of matter and energy from the
• Earths interior to the surface.

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http//www.nysm.nysed.gov/services/starks/images/v
olcano.jpg

• How do Volcanoes work?
• The Volcano-Magma System is divided into four
  zones for simplicity purposes.
• Root zones magma generated by partial melting
  of pre-existing older rocks.
• Processes in the root zones explain why a volcano
  forms at a particular place on the Earth and not
  somewhere else at any given time, the
  characteristic magma composition, the way it
  erupts, i.e. quietly, gushy, highly explosive.
• The intensity of the eruption depends on
• Composition
• Viscosity of the magma and rise speed
• Interaction with external water
• Expansion and bursting of bubbles formed when the
  magma saturates with volatile compounds.

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• Also
• All volcanoes emit gases, sometimes tens of
  thousands of tons without erupting explosively.
  For example, The Merapi volcano is a lava dome
  oozing out slowly over time and it appears to
  have lost most of its volatility by the time the
  magma reaches the surface.
• On the other hand, some volcanoes have ejecta
  rising as high as 40 km
• into the atmosphere and gases that rise even
  higher.

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The Global Framework of Volcanism

• Volcanic eruptions created our first crust 4.6
  billion years ago.
• The crust then modified over time due to erosion,
  covering by sediments, mountain-building and
  transformed through metamorphism.
• Crust formation occurs on a day by day scale.

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Plate Tectonics
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AAAAAAeg/0juTvBrpUtE/s800/CIMG1670.JPG

• The volumes, heights and forms of volcanoes
  fundamentally depend on the physical and chemical
  properties of the magma.
• In other words, they depend on the processes in
  the root zones of the volcanoes whose dynamics is
  determined by their plate tectonic setting.
• Because of the motion due to plate tectonics, a
  single volcano does not tell much about its local
  origin.
• Morphology and architecture does not tell the
  type of tectonic setting e.g. caldera volcanoes
  (an irregular to subspherical collapse feature
  several km to tens of kilometers in diameter
  within a volcano formed by roof subsidence over
  an evacuated magma chamber) form in very
  different types of tectonic environments.
• Some volcanoes have forms governed by
  near-surface processes (e.g. interaction of magma
  and water) hence unsuitable to associate with any
  particular tectonic setting.
• Most volcanoes on Earth form either along
  convergent or divergent plate margins or in the
  continental or oceanic plate interiors.
• The magmas of volcanoes in each of these settings
  are characterized by specific chemical
  compositions.
• The volatile contents are well reflected in the
  mode of eruption.
• For example, volcanoes over subduction zones are
  highly explosive because there the water-rich
  sediments and oceanic crust are dehydrated at
  depth and the processes of magma formation are
  strongly governed by fluid release from the
  subducted slab.
• Magma composition and volcanic morphology show
  more complex characteristics in hybrid plate
  tectonic settings.

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Magma
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• What is magma?
• Silicon is the main constituent of most minerals
  and rocks in the Earths crust and mantle.
• Magma is molten matter of silicate composition.
• Most dominant volcanic rocks on Earth are
  basaltic lavas like those in the oceanic crust.
• They are 50 silicon dioxide (SiO2) by weight.
• For granites, this is 70-75 by weight.
• Carbonatite is an example of a non-silicate type
  of magma (which are unusual).

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http//ems.anu.edu.au/projs/pictures/Kavachi.jpg

• Where and how are magmas generated?
• Most magmas have basaltic composition and
  eruption temperatures of 1100 to 1250 degrees
  celcius, which is too high for them to have
  generated in the crust (where the temperature is
  about 500 degrees celcius).
• Magma is generated by partial melting of rocks in
  the Earths mantle or, in much smaller amounts,
  in the lower crust. Volcanoes are basically
  features on the surface where the magma can
  erupt.
• --------
• Why do magmas rise?
• They rise because of their lower density compared
  to the surrounding rocks.
• They also rise because of dynamic triggers, like
  the pressure due to rising mantle plumes.

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Also

• Magmas have varying degrees of differentiation
  during rise and cooling as well as variable
  degrees of contamination.
• There are three melting mechanisms addition of
  heat, decrease in pressure and addition of fluid
  phases to source rock.
• Primary magma is melt in equilibrium with source
  rock. Its composition depends on that of the
  source rock and degree of melt. The magmas that
  rise to the Earths surface are usually not
  primary.
• Basalt magmas are generated in the Earths mantle
  mostly by decompression.
• Granite magmas are formed mainly by partial
  melting of lower crust.
• The magmas that rise to the surface have
  differentiated and mixed to varying degrees.
• The most common but least understood magma
  chambers exist below mid-ocean ridges.
• The formation of many ore deposits is connected
  with differentiation of magmas.

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• Temperature, viscosity and gas content of magma
  can be determined by the chemical composition of
  a rock, analysis of its mineral components and
  glass inclusions in the mineral phases.
• The data framework allows us to predict the
  behavior of the magma.
• CO2 and H20 are the most important magmatic
  volatiles.
• In magmas with bubble content lt1 by volume, CO2
  is the main gas phase.
• At ratio H20/C02 gt1, H20 is the main phase
  contributing to internal pressure of a degassing
  magma.
• Gases such as SO2, H2S and the halogens, although
  found in magma, do not contribute much towards
  the triggering of explosive eruptions because of
  their low abundancy.
• The noble gases and N2 do not play a big role in
  the pressure build-up in a magma system because
  they occur in such small amounts.

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http//volcanoes.usgs.gov/Imgs/Jpg/Monitoring/Gas/
dds24-Gas0004_large.jpg

• How do Volcanologists work and why do they work
  on volcanoes?

• passion for working on volcanoes
• recruited by universities and research
  institutes
• motivated by I want to save the world (i.e.
  prevent disasters)
• strong interest in the most visible
  manifestation of visible earth
• Morphology of a volcano tells us a lot about the
  magma and processes
• involved in the particular eruption.
• Planetary volcanology has developed a lot from
  studies made from the
• active volcanism on Io, a moon of Venus, and also
  from Volcanic features
• on Mars and the Moon.
• Major revolutions in the understanding of how
  volcanoes work often come from large and
  well-studied eruptions, some producing greatly
  underestimated physical effects. For example,

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• Eruption of Mt. Pelee (Martinique, 1902) Nuees
  Ardentes - A French term applied to a highly
  heated mass of gas-charged ash which is expelled
  with explosive force and moves at hurricane speed
  down the mountainside.
• (Definition from http//volcano.und.edu/vwdocs/gl
  ossary.html)
• Eruption of Taal Volcano (Philippines, 1965)
  magma-water contact, base surges.
• Eruption of Mt. St. Helens (Washington, USA, 18
  May 1860) lasted six years sector collapse,
  lateral blasts, eruption forecast.
• Eruption of El Chichon (Mexico, 1982) sulphuric
  acid aerosols, climate impact.
• Eruption of Pinatubo (Philippines, 19 June 1991)
  another milestone in eruption prediction and
  effective mitigation and understanding volcanic
  climate forcing.
• Montserrat (Lesser Antilles, 1995 present)
  mechanisms of dome growth, pyroclastic density
  currents.
• Mt. Usu (Japan, March 31 August 2000)
  Phreatic eruptions and major ground deformation)
• Miyakejima (Japan, July-August, 2000) lateral
  magma withdrawal, caldera collapse and ensuing
  phreatomagmatic eruption

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/Volcano/Mt20St20Helens_files/image055.jpg

• The Kilauea volcano on the island of Hawaii is
  know to exhibit more activity than any other
  volcano on Earth.
• Its study has lead into more new insights into
  the architecture and dynamics of active
  volcanoes, flow and crystallization of lava and
  gas evolution than any other volcano.
• Modern analytic instruments used to study
  volcanoes include mass spectrometers, electron
  microprobe, broad-band seismometers, remote
  sensing, GPS, high resolution aerial laser
  scanning and computer power.
• Newer methods are the use of ion-probe, single
  crystal dating, and analytic probing into
  crystals to determine trace element, isotopic
  composition, and focused study of gas and fluid
  intrusion. They also help us look into the
  origins of magma and their evolution prior to
  eruption.
• Observations that help us to detect, quantify and
  predict processes and eruptions include tracking
  of airborne ash clouds, deformational evolution
  of volcanic edifices by radar, infrared radiation
  of higher temperature areas on active volcanoes,
  quantitative detection of gas emissions
  especially S02 (using total ozone mapping
  spectrometer), mapping aerosol clouds resulting
  from major Plinian eruptions, and mapping the
  surface of volcanoes with spatial resolution of
  better than 10m.
• Volcanoes are best studied in interdisciplinary
  fields, although this has proven to be very
  difficult.

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The Impact of Volcanic Activity on the
Environment and on Society.

• Media tends to only report volcanic activity when
  people or buildings have been harmed, usually
  because of the social and political problems
  arising and need of evacuation.
• People are being informed fully of the potential
  natural hazards in advance where applicable so
  that they can prepare themselves for a possible
  crisis. This is quite a revolution because
  traditionally the responsible authorities
  retained such info in order to prevent panic
  amongst the population.
• One major task of hazard-focused work is
  assembling hazard maps which is particularly
  analysis and mapping of
• Products of previous volcanic eruptions.
• Modern theoretical insight into transport
  mechanisms.
• Energy involved in the eruption and transport
  mechanisms.
• Forecasting likely energies released.
• Pathways based on analysis of older deposits.
• Public education has helped increase awareness of
  the importance of advanced preparation for such a
  crisis.
• Most people are reluctant to evacuate unless
  given strict orders or convinced by widespread
  gossips.
• Volcanologists are often consulted about the
  impact on climate from eruptions. We have the
  global warming and greenhouse effect issues but
  are climatic changes also caused by volcanic
  eruptions? Scientists study the volcanic forcing
  of climate to get the answers.

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Man and Volcanoes The Benefits
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• Weve benefited more from volcanoes than
• weve suffered because volcanic eruptions
• have produced
• geothermal energy
• ore deposits
• volcanic soils
• volcanic raw materials and their

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Beauty!
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• Works Cited
• Alexander von Humboldt picture
• http//en.wikipedia.org/wiki/ImageAlexander_von_H
  umboldt-selfportrait.jpg
• Christian Leopold von Buch picture
• http//portrait.kaar.at/Deutschsprachige20Teil20
  3/images/leopold_von_buch.jpg
• George Julius Poulett Scrope picture
• http//www.eumed.net/cursecon/dic/dent/s/SCROPE.gi
  f
• Other images (volcanoes, lava, etc.)
• http//emd.wa.gov/hazards/images/Volcano2.jpg
• http//www.son.washington.edu/safety/images/volcan
  o.jpg
• http//www.destinbradwell.com/images/HawaiiVolc102
  sm.jpg
• http//www.earthmountainview.com/volcano_cleveland
  _plume.jpg
• http//asapblogs.typepad.com/news/images/2007/06/2
  0/7bd693a649a38f47f1bd69e9a838a5ed9a7.jpg
• http//newsfromrussia.com/img/idb/photo/1-977.jpg
• Schimincke, Hans-Ulrich. Volcanism. Springer 1st
  ed. 2004. Corr. 2nd printing edition, 2005.