Volcanic Activity
What is a volcano?
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any hill, mound or sheet of igneous material made up of lava flows, pyroclastic roc
volcanism - manifestation at the surface by way of the release of a solid/liquid/gas
Earth
Average production of lava
o 2 km3 per year (land)
o 20 km3 per year (ocean floor)
Important to realize that not all volcanoes are similar to Hawaii!!
Two prerequisites need for volcanic activity:
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something to melt
source of heat
Lava flows are hot!
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the heat required to melt on kg of basalt = 1.9x106 Joules
by way of comparison, the total world energy production in 1998 was = 4.0x10 20 J
that could only melt about 2.1x1014 kg of basalt
what Kilauea produces on average in 5 hours!
General Styles of Volcanism
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extrusive
o effusive ==> lava flows
o explosive ==> pyroclastic deposits (tephra)
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intrusive
o intrusion ==> forcible entry of magma into or between rock formations or lay
Magma:
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molten material within the interior of a planet
cools and solidifies to form an igneous rock
components:
1. melt (liquid)
2. solids (crystals, lithics)
3. volatiles (gases)
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called lava when it is erupted on the surface
Formation
Most volcanoes are formed at destructive plate margins, where oceanic crust
sinks below the continental crust because oceanic crust is denser than its
continental counterpart. Friction will cause the oceanic crust to melt, and the
reduced density will force the newly formed magma to rise. As the magma
rises it pushes through the continental crust, erupting as volcanoes. For
example, Mount St. Helens is found inland from the margin between the
oceanic Juan de Fuca Plate and the continental North American Plate.
A volcano generally presents itself to the imagination as a mountain sending
forth from its summit great clouds of smoke with vast sheets of flame, and it is
not infrequently so described. The truth is that a volcano seldom emits either
smoke or flame. What is mistaken for smoke consists of vast volumes of fine
dust, mingled with steam and other vapours — chiefly sulphurous. What
appears to be flames is the glare from the erupting materials, glowing because
of their high temperature — this glare reflects off the clouds of dust and
steam, resembling fire.
Perhaps the most conspicuous part of a volcano is the crater, a basin, roughly
of a circular form, within which occurs a vent (or vents) from which magma
erupts as gases, lava, and ejecta. A crater can be of large dimensions, and
sometimes of vast depth. Very large features of this sort are termed calderas.
Some volcanoes consist of a crater alone, with scarcely any mountain at all;
but in the majority of cases the crater is situated on top of a mountain (the
volcano), which can tower to an enormous height. Volcanos that terminate in a
principal crater are usually of a conical form.
Volcanic cones are usually smaller features composed of loose ash and cinder,
with occasional masses of stone which have been tossed violently into the air
by the eruptive forces (and are thus called ejecta). Within the crater of a
volcano there may be numerous cones from which vapours are continually
issuing, with occasional volleys of ashes and stones. In some volcanoes these
cones form lower down the mountain, along rift zones.
Volcano types and structural components
One way of classifying volcanoes is by the type of material erupted, which
affects the shape of the volcano:
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Shield volcano: Hawaii and Iceland are examples of volcanoes which
extrude huge quantities of lava that gradually builds to form a wide
mountain. Their lava is generally very fluid and solidifies in long flows
as basalt. The largest lava shield on Earth, Mauna Loa, is 30,000 feet
high (it sits on the sea floor) and 75 miles in diameter. Olympus Mons
is a shield volcano on Mars, and the tallest mountain in the solar
system.
Smaller versions of the lava shield include the Lava Dome, Cone, and
Mound.
If the magma contains a lot (>65%) of silica the lava is called acidic
and is very viscous (not very fluid) and is pushed up in a blob which
will then solidify, Lassen Peak in California is an example. This type
of volcano has a tendency to explode because it easily plugs. Mt. Pelée
on the island of Martinique is another example.
If, on the other hand the magma contains relatively small (<52%)
amounts of silica, the lava is called basic, and it will be very fluid,
capable of flowing like water for long distances. A good example of
this is the Great ??s?hraun lava flow which was produced by an
eruptive fissure almost in the geographical center of Iceland roughly
8.000 years ago, and it flowed all the way down to the sea, a distance
of 130 kilometers, and covered an area of 800 sq.kms.
Volcanic cones result from eruptions that throw out mostly small
pieces of rock that build up around the vent. These can be relatively
short-lived eruptions that produce a cone-shaped hill perhaps 100 to
1000 feet high.
Stratovolcanoes or composite volcanoes such as Mt. Fuji in Japan,
Vesuvius in Italy, Mount Erebus in Antarctica, and Mount Rainier in
the northwestern United States are tall conical mountains composed of
both lava and rocks.
Supervolcanoes are a class of volcanoes that have a large caldera and
can potentially produce devastation on a continental scale and cause
major global weather pattern changes. Potential candidates include
Yellowstone National Park and Lake Toba, but are very hard to define
given that there is no minimum requirement to be categorized as a
supervolcano.
Volcanoes are usually situated either at the boundaries between tectonic plates
or over hot spots. Volcanoes may be either dormant (having no activity) or
active (near constant expulsion and occasional eruptions), and change state
unpredictably.
Volcanoes on land often take the form of flat cones, as the expulsions build up
over the years, or in short-lived cinder cones. Under water, volcanoes often
form rather steep pillars and in due time break the ocean surface in new
islands.
Types of Volcanic Eruptions
During an episode of activity, a volcano commonly displays a distinctive
pattern of behavior. Some mild eruptions merely discharge steam and other
gases, whereas other eruptions quietly extrude quantities of lava. The most
spectacular eruptions consist of violent explosions that blast great clouds of
gas-laden debris into the atmosphere.
The type of volcanic eruption Is often labeled with the name of a well-known
volcano where characteristic behavior is similar--hence the use of such terms
as "Strombolian," "Vulcanian," "Vesuvian," "Pelean," "Hawaiian," and others.
Some volcanoes may exhibit only one characteristic type of eruption during an
interval of activity--others may display an entire sequence of types.
In a Strombolian-type eruption observed during the 1965 activity of Irazú
Volcano in Costa Rica, huge clots of molten lava burst from the summit crater
to form luminous arcs through the sky. Collecting on the flanks of the cone,
lava clots combined to stream down the slopes in fiery rivulets.
n contrast, the eruptive activity of Parícutin Volcano in 1947 demonstrated a
"Vulcanian"-type eruption, in which a dense cloud of ash-laden gas explodes
from the crater and rises high above the peak. Steaming ash forms a whitish
cloud near the upper level of the cone.
In a "Vesuvian" eruption, as typified by the eruption of Mount Vesuvius in
Italy in A.D. 79, great quantities of ash-laden gas are violently discharged to
form cauliflower-shaped cloud high above the volcano.
In a "Peléan" or "Nuée Ardente (glowing cloud) eruption, such as occurred on
the Mayon Volcano in the Philippines in 1968, a large quantity of gas, dust,
ash, and incandescent lava fragments are blown out of a central crater, fall
back, and form tongue-like, glowing avalanches that move downslope at
velocities as great as 100 miles per hour. Such eruptive activity can cause
great destruction and loss of life if it occurs in populated areas, as
demonstrated by the devastation of St. Pierre during the 1902 eruption of
Mont Pelée on Martinique, Lesser Antilles.
H
" awaiian" eruptions may occur along fissures or fractures that serve as
linear vents, such as during the eruption of Mauna Loa Volcano in Hawaii in
1950; or they may occur at a central vent such as during the 1959 eruption in
Kilauea Iki Crater of Kilauea Volcano, Hawaii. In fissure-type eruptions,
molten, incandescent lava spurts from a fissure on the volcano's rift zone and
feeds lava streams that flow downslope. In central-vent eruptions, a fountain
of fiery lava spurts to a height of several hundred feet or more. Such lava may
collect in old pit craters to form lava lakes, or form cones, or feed radiating
flows.
P
" hreatic" (or steam-blast) eruptions are driven by explosive expanding
steam resulting from cold ground or surface water coming into contact with
hot rock or magma. The distinguishing feature of phreatic explosions is that
they only blast out fragments of preexisting solid rock from the volcanic
conduit; no new magma is erupted. Phreatic activity is generally weak, but can
be quite violent in some cases, such as the 1965 eruption of Taal Volcano,
Philippines, and the 1975-76 activity at La Soufrière, Guadeloupe (Lesser
Antilles).
The most powerful eruptions are called "plinian" and involve the explosive
ejection of relatively viscous lava. Large plinian eruptions--such as during 18
May 1980 at Mount St. Helens or, more recently, during 15 June 1991 at
Pinatubo in the Philippines--can send ash and volcanic gas tens of miles into
the air. The resulting ash fallout can affect large areas hundreds of miles
downwind. Fast-moving deadly pyroclastic flows ("nuées ardentes") are also
commonly associated with plinian eruptions.
Effects of Volcano Activity
Volcanic eruptions are one of Earth's most dramatic and violent agents of
change. Not only can powerful explosive eruptions drastically alter land and
water for tens of kilometers around a volcano, but tiny liquid droplets of
sulfuric acid erupted into the stratosphere can change our planet's climate
temporarily. Eruptions often force people living near volcanoes to abandon
their land and homes, sometimes forever. Those living farther away are likely
to avoid complete destruction, but their cities and towns, crops, industrial
plants, transportation systems, and electrical grids can still be damaged by
tephra, lahars, and flooding.
Volcanic activity since 1700 A.D. has killed more than 260,000 people,
destroyed entire cities and forests, and severely disrupted local economies for
months to years. Even with our improved ability to identify hazardous areas
and warn of impending eruptions, increasing numbers of people face certain
danger. Scientists have estimated that by the year 2000, the population at risk
from volcanoes is likely to increase to at least 500 million, which is
comparable to the entire world's population at the beginning of the seventeenth
century! Clearly, scientists face a formidable challenge in providing reliable
and timely warnings of eruptions to so many people at risk
Notable Volcanic Disasters
Since the year A.D. 1500, more than 300,000 people have died from volcanic
activity. Most people were killed by only a few eruptions. For example, the
huge explosive eruption of Tambora volcano in 1815 killed more than 90,000
people, primarily by starvation because the eruption destroyed crops and
farmland. In the 20th century, eruptions at Mont Pelée and Nevado del Ruiz
volcanoes killed more than 50,000 people. These examples demonstrate the
importance of knowing the type and location of hazards associated with
currently active and potentially active volcanoes. Plannng for these hazards
ahead of time can prevent future volcanic activity from becoming a disaster.
This table summarizes notable historical volcanic activity that resulted in at
least 300 fatalities. Accurate numbers of deaths are difficult to obtain, even
today, and the historic record often fails to provide reliable estimates. A
question mark follows those numbers when the exact causes of deaths are not
known. See Volcanoes of the World below for more information.
Primary Cause of Death
Volcano
Pyroclastic
Flow
Country
Year
Lahar
Kelut
Indonesia
1586
Vesuvius
Italy
1631
Raung
Indonesia
1638
Merapi
Indonesia
1672
3001
Awu
Indonesia
1711
~3,000
Oshima
Japan
1741
Makian
Indonesia
1760
Papadanyan
Indonesia
1772
Gamalama
Indonesia
1775
Lakagígar
(Laki)
Iceland
1783
Asama
Japan
1783
Unzen
Japan
1792
Mayon
Philippines
1814
1,200
Tambora
Indonesia
1815
12,000
Galunggung
Indonesia
1822
4,000
Nevado del
Colombia
1845
1,000
Tephra
Landslide
Tsunami
10,000
>4,000
>1,000
1,481
~2,000
2,960
1,300
466
~1,400
~15,000
Ruiz
Awu
Indonesia
1856
3,000
Cotopaxi
Ecuador
1877
>300
Krakatau
Indonesia
1883
Ritter
Papua
New
Guinea
1888
Awu
Indonesia
1892
1,5323
Soufrière
St. Vincent
1902
1,680
Mount
Pelée
Martinique
1902
29,000
Santa Maria
Guatemala
1902
~1,5004
Taal
Philippines
1911
1,3355
Kelut
Indonesia
1919
Merapi
Indonesia
1930
1,369
Rabaul
Caldera
Papua
New
Guinea
1937
507 6
Lamington
Papua
New
Guinea
1951
2,942
HibokHibok
Philippines
1951
>500
Agung
Indonesia
1963
>1,1487
El Chichón
Mexico
1982
>2,000
Nevado del
Ruiz
Colombia
1985
Lake Nyos
Cameroon
1986
Mount
Pinatubo
Philippines
19911996
Table notes
~5,000
~31,417
3,0002
5,110
>23,000
>5008
300
1. Merapi, 1672; one source gives total of 3,000 fatalities and another
gives total of 300
2. Ritter, 1888; landslide triggered a tsunamis that killed "hundreds" and
perhaps as many as 3,000 people
3. Awu, 1892; source descriptions suggest 25% of these fatalities may
have been caused by lahars
4. Santa María, 1902; one source suggests "hundreds" of fatalities were
caused by collapsed houses from the weight of tephra, and several
thousand more people died from malaria outbreak
5. Taal, 1911; perhaps 20% of these fatalities were caused by tsunamis
from explosive activity in the crater lake
6. Rabaul Caldera, 1937; sources suggest 50% caused by pyroclastic
flows, 40% caused by tephra, 5% caused by tsunamis, 5% caused by
exposure or starvation
7. Agung, 1963; perhaps more than 1,500 fatalities occurred, 14% caused
by tephra, 14% caused by lahars
8. Mount Pinatubo, 1991; post-eruption lahars have caused many more
deaths and destruction to farmland and communities than the Jun 15,
1991 eruption
Types of Volcanoes:
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Central Vent Volcanoes
1. Stratovolcano (Composite Cone):
 conical-shaped volcano
 lavas interbedded with pyroclastic deposits
 ex. Mt. St. Helens, Mt. Fuego, Guatemala
2. Shield:
 broad, gently sloping volcano
 generally composed of overlapping, interfingering basalt flows
 ex. Hawaii, Galapagos, Iceland
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Volcanic Plains
1. Flood Basalt
 extensive flat-lying sheets of lava
 typically erupted from linear fissures
 ex. Columbia Plateau, Deccan Trapps
2. Ash-Flow Plain:
 ex. Yellowstone, Ngorongoro
3. Basaltic Plains:
 ex. Snake River Plain
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Monogenetic Volcanic Features (one eruptive phase)
o Lava Flow (Hawaii, etc.)
o Lava Dome (Mt. St. Helens domes)
o Cinder Cone (Paricutin, MX)
o Spatter Cone (Hawaii)
o Tuff Ring (Diamond Head, Hawaii)
o Maar Crater (Pinacate, MX)
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Submarine Volcanism: shields, seamounts, lava flows
Methods used in predicting eruptions
Science has not yet been able to predict with absolute certainty when a
volcanic eruption will take place, but significant progress in judging when
one is probable has been made in recent time.
Volcanologists use the following to forecast eruptions.
Seismicity
Seismic activity (small earthquakes and tremors) always occurs as volcanoes
awaken and prepare to erupt. Some volcanoes normally have continuing
low-level seismic activity, but an increase can signify an eruption. The types
of earthquakes that occur and where they start and end are also key signs.
Volcanic seismicity has three major forms: short-period earthquakes, longperiod earthquakes, and harmonic tremor.
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Short-period earthquakes are like normal fault-related earthquakes.
They are related to the fracturing of brittle rock as the magma forces
its way upward. These short-period earthquakes signify the growth of
a magma body near the surface.
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Long-period earthquakes are believed to indicate increased gas
pressure in a volcano's "plumbing system." They are similar to the
clanging sometimes heard in your home's plumbing system. These
oscillations are the equivalent of acoustic vibrations in a chamber, in
the context of magma chambers within the volcanic dome.
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Harmonic tremor occurs when there is sustained movement of
magma below the surface.
Patterns of seismicity are complex and often difficult to interpret. However,
increasing activity is very worrisome, especially if long-period events become
dominant and episodes of harmonic tremor appear.
In December 2000 scientists at the National Centre for Prevention of
Disasters in Mexico City predicted an eruption witihin two days from
Popocat?etl, on the outskirts of Mexico city. Their prediction used reserarch
done by M. Chouet, a Swiss vulacanologist, into increasing long-period
oscillations as an indicator of an imminent eruption. The government
evacuated tens of thousands of people.
Forty eight hours later, bang on time, the volcano erupted spectacularly. It
was Popocat?etl's largest eruption for a thousand years and yet no one was
hurt.
Gas Emissions
As magma nears the surface and its pressure decreases, gases escape. This
process is much like what happens when you open a bottle of soda and
carbon dioxide escapes. Sulfur dioxide is one of the main components of
volcanic gases, and increasing amounts of it herald the arrival of more and
more magma near the surface. For example, on May 13, 1991, 500 tons of
sulfur dioxide were released from Mount Pinatubo in the Philippines. On
May 28--just two weeks later--sulfur dioxide emissions had increased to
5,000 tons, ten times the earlier amount. Mount Pinatubo erupted on June
12, 1991. On several occasions, such as before the Mount Pinatubo
eruption, sulfur dioxide emissions have dropped to low levels prior to
eruptions. Most scientists believe that this drop in gas levels is caused by the
sealing of gas passages by hardened magma. Such an event leads to
increased pressure in the volcano's plumbing system and an increased
chance of an explosive eruption.
Ground Deformation
Swelling of the volcano signals that magma has accumulated near the
surface. Scientists monitoring an active volcano will often measure the tilt of
the slope and track changes in the rate of swelling. An increased rate of
swelling--especially if accompanied by an increase in sulfur dioxide
emissions and harmonic tremors--is a high probability sign of an impending
event.
Volcanic activity
There are many different kinds of volcanic activity and eruptions:
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phreatic (steam) eruptions
explosive eruption of high-silica lava (e.g., rhyolite)
effusive eruption of low-silica lava (e.g., basalt)
pyroclastic flows
lahars (debris flow)
carbon dioxide emission
All of these activities can pose a hazard to humans.
Volcanic activity is often accompanied by earthquakes, hot springs, fumaroles,
solfatare and geysers. Low-magnitude earthquakes often precede eruptions.
Surprisingly, there is no consensus among volcanologists on how to define an
"active" volcano. The lifespan of a volcano can vary from months to several
million years, making such a distinction sometimes meaningless when
compared to the lifespans of humans or even civilizations. For example, many
of Earth's volcanoes have erupted dozens of times in the past few thousand
years but are not currently showing signs of activity. Given the long lifespan
of such volcanoes, they are very active. By our lifespans, however, they are
not. Complicating the definition are volcanoes that become restless but do not
actually erupt. Are these volcanoes active?
Scientists usually consider a volcano active if it is currently erupting or
showing signs of unrest, such as unusual earthquake activity or significant
new gas emissions. Many scientists also consider a volcano active if it has
erupted in historic time. It is important to note that the span of recorded
history differs from region to region; in the Mediterranean, recorded history
reaches back more than 3,000 years but in the Pacific Northwest of the United
States, it reaches back less than 300 years, and in Hawaii, little more than 200
years.
Dormant volcanoes are those that are not currently active (as defined above),
but could become restless or erupt again.
Extinct volcanoes are those that scientists consider unlikely to erupt again.
Whether a volcano is truly extinct is often difficult to determine. For example,
since calderas have lifespans sometimes measured in millions of years, a
caldera that has not produced an eruption in tens of thousands of years is
likely to be considered dormant instead of extinct. Yellowstone caldera in
Yellowstone National Park is at least 2 million years old and hasn't erupted
for 70,000 years, yet scientists do not consider Yellowstone as extinct. In fact,
because the caldera has frequent earthquakes, a very active geothermal
system, and rapid rates of ground uplift, many scientists consider it to be a
very active volcano.
Famous volcanoes include
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Mauna Loa
Mauna Kea
Mount Erebus
Etna
Hekla
Krakatoa
Vesuvius
Mount Fuji
Mount St. Helens
References used :
Tilling, R.I., 1989, Volcanic hazards and their mitigation: Progress and
problems: Review of Geophysics, v. 27, no. 2, p. 237-269.
Simkin, T., and Siebert, L., 1995, Volcanoes of the World: Geoscience Press,
Inc., p. 165-176
http://ivis.eps.pitt.edu/courses/hazards/lectures/4.pdf
http://www.wacklepedia.com/v/vo/volcano.html
http://snrs.unl.edu/amet498/drake/effects.html
http://www.geo.mtu.edu/volcanoes/hazards/primer/