Volcanism is the study of volcanoes, their eruption processes, and their impacts. Early theories about volcanoes involved myths and ideas about supernatural causes of eruptions. In the 18th century, scientists like Hutton recognized volcanoes as surface expressions of subsurface geological processes. The emergence of plate tectonic theory in the mid-20th century helped explain the relationship between volcanism and plate boundaries. Magmas form by partial melting in the mantle and rise toward the surface due to their lower density. Composition and volatile content influence eruption styles. Modern monitoring uses tools like seismic, gas, deformation, and thermal sensors to observe and forecast eruptions. Major eruptions have advanced understanding of dynamics like pyrocl

1. Volcanism
By Hans Ulrich Schmincke
Presented By
Mahmuda Afrin Badhan
Mount Holyoke College ‘11
Volcanism
By Hans Ulrich Schmincke
http://www.fukubonsai.com/images3/VolcanoFlowAug2002.jpg

2. 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)
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
http://www.photopumpkin.com/wp-content/uploads/volcanoes-1.jpg

3. • 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 Earth’s 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
right.
Early Perception of Volcanoes and Volcanic Activities.
http://www.bhargavaz.net/rashi/volcano.jpg

4. The First Text…
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.
http://www.bicolbusinessdirectory.com/mayon-volcano-2006-eruption/mayon-volcano01.jpg

5. 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 Earth’s surface and atmosphere
(which was generated by the degassing of volcanoes in the first place).
• Shows the flux of matter and energy from the
Earth’s interior to the surface.
http://www.stacey.peak-media.co.uk/Year10/B6ManagingHazards/B6ManagingHazards-Tectonics/B6ManagingHazards-Volcano/volcano_7big_montserrat_eruption.jpg

6. 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.
http://www.nysm.nysed.gov/services/starks/images/volcano.jpg

7. 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
it’s 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.

8. 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.

9. Plate Tectonics
• 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.
http://lh3.google.com/_aomLKq12Qmc/RyX7UTZQCpI/AAAAAAAAAeg/0juTvBrpUtE/s800/CIMG1670.JPG

10. Magma
What is magma?
• Silicon is the main constituent of most minerals and rocks in the
Earth’s 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).
http://shisa.ukzn.ac.za/pictures/Magma.jpg

11. 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 Earth’s
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.
http://ems.anu.edu.au/projs/pictures/Kavachi.jpg

12. 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. It’s composition
depends on that of the source rock and degree of melt. The magmas
that rise to the Earth’s surface are usually not primary.
• Basalt magmas are generated in the Earth’s 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.

13. • 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 <1% by volume, CO2 is the main
gas phase.
• At ratio H20/C02 >1, 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.

14. 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,
http://volcanoes.usgs.gov/Imgs/Jpg/Monitoring/Gas/dds24-Gas0004_large.jpg

15. • 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/glossary.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
http://www.montserratreporter.org/Volcano%20Dome%20Jan2199.jpg

16. • 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.
http://www.wvdhsem.gov/WV_Disaster_Library/Library/Volcano/Mt%20St%20Helens_files/image055.jpg

17. 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
I. Products of previous volcanic eruptions.
II. Modern theoretical insight into transport mechanisms.
III. Energy involved in the eruption and transport mechanisms.
IV. Forecasting likely energies released.
V. 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.

18. Man and Volcanoes: The Benefits
We’ve benefited more from volcanoes than
we’ve suffered because volcanic eruptions
have produced:
• geothermal energy;
• ore deposits;
• volcanic soils;
• volcanic raw materials and their…
http://www.inhabitat.com/images/steamystuff2.jpg

19. Beauty!
http://www.smh.com.au/ffximage/2006/03/01/maunaloa_wideweb__430x322,2.jpg

20. Works Cited
• Alexander von Humboldt picture:
• http://en.wikipedia.org/wiki/Image:Alexander_von_Humboldt-
selfportrait.jpg
• Christian Leopold von Buch picture:
• http://portrait.kaar.at/Deutschsprachige%20Teil%203/images/leopold
_von_buch.jpg
• George Julius Poulett Scrope picture:
• http://www.eumed.net/cursecon/dic/dent/s/SCROPE.gif
• Other images (volcanoes, lava, etc.)
• http://emd.wa.gov/hazards/images/Volcano2.jpg
• http://www.son.washington.edu/safety/images/volcano.jpg
• http://www.destinbradwell.com/images/HawaiiVolc102sm.jpg
• http://www.earthmountainview.com/volcano_cleveland_plume.jpg
• http://asapblogs.typepad.com/news/images/2007/06/20/7bd693a649
a38f47f1bd69e9a838a5ed9a7.jpg
• http://newsfromrussia.com/img/idb/photo/1-977.jpg
• Schimincke, Hans-Ulrich. Volcanism. Springer; 1st ed. 2004. Corr.
2nd printing edition, 2005.