Study of Volcanism and volcano

Volcanism
 Volcanism and Volcano
 Distribution of Volcanoes
 Kinds of Volcanoes
Types of Volcanic Hazards
 Preparing for Volcanic Emergencies

VolcanismVolcanism
• Volcanism is part of the process of bringing material from the deep interior ofVolcanism is part of the process of bringing material from the deep interior of
a planet and spilling it forth on the surface.a planet and spilling it forth on the surface. EruptionsEruptions also eject new moleculesalso eject new molecules
into the atmosphere. Volcanism is part of the process by which a planetinto the atmosphere. Volcanism is part of the process by which a planet
cools offcools off. Even though they are not volcanoes, geysers and hot springs are. Even though they are not volcanoes, geysers and hot springs are
also part of the volcanic process, involving water and hydrothermal activity.also part of the volcanic process, involving water and hydrothermal activity.
Some planetary bodies, like Jupiter's moon Europa, exhibit icy volcanism,Some planetary bodies, like Jupiter's moon Europa, exhibit icy volcanism,
which is another form of volcanism involving water.which is another form of volcanism involving water.
• There are several ways in which a volcanoThere are several ways in which a volcano formsforms, just as there are several, just as there are several
differentdifferent kindskinds of volcanoes.of volcanoes. On Earth, the most general cause of volcanismOn Earth, the most general cause of volcanism
is caused byis caused by subductionsubduction of the Earth's crust.of the Earth's crust.
•There are quite a few other planets which have volcanoes on the surface,There are quite a few other planets which have volcanoes on the surface,
includingincluding VenusVenus,, MarsMars, and Jupiter's moon, and Jupiter's moon IoIo. Other planets exhibit the results. Other planets exhibit the results
of volcanic activity. These include Mercury, the Earth'sof volcanic activity. These include Mercury, the Earth's MoonMoon, Jupiter's moon, Jupiter's moon
EuropaEuropa, and perhaps Neptune's moon, and perhaps Neptune's moon TritonTriton..

Volcanic Rocks and Associated LandformsVolcanic Rocks and Associated Landforms

This is an image of the eruption of Stromboli volcano.This is an image of the eruption of Stromboli volcano.

Low viscosity basaltic lava flowLow viscosity basaltic lava flow

Volcanism - VolcanoesVolcanism - Volcanoes
• A volcano is generally a conical shaped hill or mountain built by
accumulations of lava flows, tephra, and volcanic ash. About 95%
of active volcanoes occur at the plate subduction zones and at
the mid-oceanic ridges. The other 5% occur in areas associated
with lithospheric hot spots. These hot spots have no direct
relationships with areas of crustal creation or subduction zones. It is
believed that hot spots are caused by plumes of rising magma that
have their origin within the asthenosphere.
• Over the last 2 million years, volcanoes have been depositing lava,
tephra, and ash in particular areas of the globe. These areas occur at
hot spots, rift zones, and along plate boundaries where tectonic
subduction is taking place within the asthenosphere.
• The most prevalent kinds of volcanoes on the Earth's surface are the
kind which form the "Pacific Rim of Fire". Those are volcanoes which
form as a result of subduction of the nearby lithosphere.

Location of the Earth's major volcanoesLocation of the Earth's major volcanoes

KINDS OF VOLCANOESKINDS OF VOLCANOES
• Hot magma, rising from lower reaches of the Earth,
eventually, but not always, erupts onto the surface in
the form of lava. During the eruption of a volcano,
flowing lava and ash form a large cone. This cone is
what we know as a volcano.
• Among the different kinds of volcanoes are:
• composite volcanoes
• shield volcanoes
• cinder cones
• spatter cones

COMPOSITE VOLCANOCOMPOSITE VOLCANO
• The most majestic of the volcanoes are composite volcanoes,
also known as strato-volcanoes. Unlike the shield volcanoes
which are flat and broad, composite volcanoes are tall,
symmetrically shaped, with steep sides, sometimes rising
10,000 feet high. They are built of alternating layers of lava
flows, volcanic ash, cinders, blocks, and bombs.
• Famous composite volcanoes include Mount Fuji in Japan,
Mount Cotopaxi in Ecuador, Mount Shasta and Lassen in
California, Mount Hood in Oregon, Mount St. Helens and Mount
Rainier in Washington, Mt Pinatubo in the Philipenes, and Mt.
Etna in Italy.

Mauna Kea erupting.Mauna Kea erupting.

SHIELD VOLCANOESSHIELD VOLCANOES
• Shield volcanoes can grow to be very big. In fact, the oldest continental
regions of Earth may be the remains of ancient shield volcanoes.
• Unlike the composite volcanoes which are tall and thin, shield volcanoes are
tall and broad, with flat, rounded shapes. The Hawaiian volcanoes exemplify
the common type of shield volcano. They are built by countless outpourings
of lava that advance great distances from a central summit vent or group of
vents. The outpourings of lava are typically not accompanied by
pyroclastic material, which make the shield volcanoes relatively safe.
• Mauna Loa, the largest of the shield volcanoes, is 13,677 feet above sea
level, which means it rises over 28,000 feet above the deep ocean floor, and
would be the worlds tallest mountain if much of it were not underwater.
• Famous shield volcanoes include Mauna Loa, Kilauea, (two of the world's
most active volcanoes), and Olympus Mons of Mars.

CALDERACALDERA
• The most explosive type of volcano is the caldera. The cataclysmic
explosion of these volcanoes leaves a huge circular depression at the
Earth's surface. This depression is usually less than 40 kilometers in
diameter. These volcanoes form when "wet" granitic magma quickly
rises to the surface of the Earth. When it gets to within a few
kilometers of the surface the top of the magma cools to form a dome.
Beneath this dome the gaseous water in the magma creates extreme
pressures because of expansion. When the pressure becomes too
great the dome and magma are sent into the Earth's atmosphere in a
tremendous explosion. On the island of Krakatau, a caldera type
volcano exploded in 1883 ejecting 75 cubic kilometers of
material in the air and left a depression in the ground some 7
kilometers in diameter. A potentially very destructive caldera
covering an area of about 2000 square kilometers exists under
Yellowstone National Park in the United States

CINDER CONESCINDER CONES
• Cinder cones are simple volcanoes which have a bowl-shaped
crater at the summit and only grow to about a thousand feet,
the size of a hill. They usually are created of eruptions from a
single opening, unlike a strato-volcano or shield volcano which
can erupt from many different openings.
• They are usually made of piles of lava, not ash. During the
eruption, blobs ("cinders") of lava, blown into the air, break into
small fragments that fall around the opening to the volcano. The
pile forms an oval-shaped small volcano, as shown in the next
picture.
• Famous cinder cones include Paricutin in Mexico. Another well
known cinder cone is in the middle of Crater Lake.

Cinder cone volcano in the Mojave National Preserve, California

Spatter ConesSpatter Cones
• When erupting magma contains enough gas
to prevent the formation of lava flow, but not
enough to shatter into small fragments, the
lava is torn to fluid clots ranging in size from
1cm to 50 cm across called spatter.
• when the spatter falls back and welded
together around the vent forming a cone is
known as the spatter cone.

IMAGE OF Mt. COTOPAXI IN ECUADORIMAGE OF Mt. COTOPAXI IN ECUADOR

Mount St. Helens eruption on May 18, 1980Mount St. Helens eruption on May 18, 1980

• Volcanic Hazards
• Volcanic Gases
o Volcanic Gas and Climate Change
o Air Pollution
oSO2
Aerosols
• Lahars
• Pyroclastic Flows
• Volcanic Landslides
• Lava Flows
•T ephra
•Hazards Preparedness
Types Volcanic Hazards

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, ash, lahars, and
flooding.
Fortunately, volcanoes exhibit precursory unrest that if detected and
analyzed in time allows eruptions to be anticipated and communities at
risk to be forewarned with reliable information in sufficient time to
implement response plans and mitigation measures.
Types Volcanic Hazards

Magma contains dissolved gases that are released into the atmosphere during
eruptions. Gases are also released from magma that either remains below ground (for
example, as an intrusion) or is rising toward the surface. In such cases, gases may
escape continuously into the atmosphere from the soil, volcanic vents, fumaroles, (a
volcano, through which hot sulfurous gases emerge) and hydrothermal systems.
At high pressures deep beneath the earth's surface, volcanic gases are dissolved in
molten rock. But as magma rises toward the surface where the pressure is lower, gases
held in the melt begin to form tiny bubbles. The increasing volume taken up by gas
bubbles makes the magma less dense than the surrounding rock, which may allow the
magma to continue its upward journey. Closer to the surface, the bubbles increase in
number and size so that the gas volume may exceed the melt volume in the magma,
creating a magma foam. The rapidly expanding gas bubbles of the foam can lead to
explosive eruptions in which the melt is fragmented into pieces of volcanic rock, known
as tephra.
Together with the tephra and entrained air, volcanic gases can rise tens of kilometers
into Earth's atmosphere during large explosive eruptions. Once airborne, the prevailing
winds may blow the eruption cloud hundreds to thousands of kilometers from a volcano.
The gases spread from an erupting vent primarily as acid aerosols (tiny acid droplets),
compounds attached to tephra particles, and microscopic salt particles.
Volcanic Gases and Their Effects

The most abundant gas typically released into the atmosphere from volcanic systems is
water vapor (H2O), followed by carbon dioxide (CO2) and sulfur dioxide (SO2).
Volcanoes also release smaller amounts of others gases, including hydrogen
sulfide (H2S), hydrogen (H2), carbon monoxide (CO), hydrogen chloride (HCL),
hydrogen fluoride (HF), and helium (He).
Sulfur dioxide (SO2)
The effects of SO2 on people and the environment vary widely depending on (1) the
amount of gas a volcano emits into the atmosphere; (2) whether the gas is injected into
the troposphere or stratosphere; and (3) the regional or global wind and weather pattern
that disperses the gas. Sulfur dioxide (SO2) is a colorless gas with a pungent odor that
irritates skin and the tissues and mucous membranes of the eyes, nose, and throat.
Sulfur dioxide chiefly affects upper respiratory tract and bronchi. The World Health
Organization recommends a concentration of no greater than 0.5 ppm over 24 hours for
maximum exposure. A concentration of 6-12 ppm can cause immediate irritation of the
nose and throat; 20 ppm can cause eye irritation; 10,000 ppm will irritate moist skin
within minutes.
Sulfur dioxide gas reacts chemically with sunlight, oxygen, dust particles, and water to
form volcanic smog known as vog.
Measurements from recent eruptions such as Mount St. Helens, Washington (1980), El
Chichon, Mexico (1982), and Mount Pinatubo, Philippines (1991), clearly show the
importance of sulfur aerosols in modifying climate, warming the stratosphere, and
cooling the troposphere. Research has also shown that the liquid drops of sulfuric acid
Volcanic Gases and Their Effects

Hydrogen sulfide (H2S)
Hydrogen sulfide (H2S) is a colorless, flammable gas with a strong offensive odor. It is
sometimes referred to as sewer gas. At low concentrations it can irritate the eyes and
acts as a depressant; at high concentrations it can cause irritation of the upper
respiratory tract and, during long exposure, pulmonary edema. A 30-minute exposure to
500 ppm results in headache, dizziness, excitement, staggering gait, and diarrhea,
followed sometimes by bronchitis or bronchopneumonia.
Carbon dioxide (CO2)
Volcanoes release more than 130 million tonnes of CO2 into the atmosphere every year.
This colorless, odorless gas usually does not pose a direct hazard to life because it
typically becomes diluted to low concentrations very quickly whether it is released
continuously from the ground or during episodic eruptions. But in certain circumstances,
CO2 may become concentrated at levels lethal to people and animals. Carbon dioxide
gas is heavier than air and the gas can flow into in low-lying areas; breathing air with
more than 30% CO2 can quickly induce unconsciousness and cause death. In volcanic
or other areas where CO2 emissions occur, it is important to avoid small depressions and
low areas that might be CO2 traps. The boundary between air and lethal gas can be
extremely sharp; even a single step upslope may be adequate to escape death.
Secondary Gas Emissions
Another type of gas release occurs when lava flows reach the ocean. Extreme heat from
molten lava boils and vaporizes seawater, leading to a series of chemical reactions. The
boiling and reactions produce a large white plume, locally known as lava haze or laze,

Lahar is an Indonesian term that describes a hot or cold mixture of water and rock
fragments flowing down the slopes of a volcano and (or) river valleys. When moving, a
lahar looks like a mass of wet concrete that carries rock debris ranging in size from clay
to boulders more than 10 m in diameter. Lahars vary in size and speed. Small lahars
less than a few meters wide and several centimeters deep may flow a few meters per
second. Large lahars hundreds of meters wide and tens of meters deep can flow several
tens of meters per second--much too fast for people to outrun.
As a lahar rushes downstream from a volcano, its size, speed, and the amount of water
and rock debris it carries constantly change. By eroding rock debris and incorporating
additional water, lahars can easily grow to more than 10 times their initial size. But as a
lahar moves farther away from a volcano, it will eventually begin to lose its heavy load of
sediment and decrease in size.
Eruptions may trigger one or more lahars directly by quickly melting snow and ice on a
volcano or ejecting water from a crater lake. More often, lahars are formed by intense
rainfall during or after an eruption--rainwater can easily erode loose volcanic rock and
soil on hillsides and in river valleys. Some of the largest lahars begin as landslides of
saturated and hydrothermally altered rock on the flank of a volcano or adjacent
hillslopes.
Lahars almost always occur on or near stratovolcanoes because these volcanoes tend
to erupt explosively and their tall, steep cones are either snow covered, topped with a
crater lake, constructed of weakly consolidated rock debris that is easily eroded, or
internally weakened by hot hydrothermal fluids. Lahars are also common from the snow-
and ice-covered shield volcanoes in Iceland.
Lahars

Lahars Grow in Size Through Erosion
Lahars
Deadly Lahars from Nevado del Ruiz,
Colombia

Hundreds of lahars sweeping down from
nearby Unzen Volcano in Japan buried,
crushed, or carried away more than a
thousand homes like this one along the
Mizunashi River. Between August 1992 and
July 1993, lahars triggered by heavy rains
damaged about 1,300 houses. Each period
of heavy rain required the sudden
evacuation of several thousand residents
along two rivers heading on the volcano. The
deposits from these lahars consisted chiefly
of lava fragments derived from partial
collapses of the summit lava dome located 5
to 8 km upstream.
Lahars can bury valleys and communities with debris
Photograph by T. Pierson on February 3,
1995

Pyroclastic Flows and Their Effects
Pyroclastic flows are high-density mixtures of hot, dry rock fragments and hot gases that
move away from the vent that erupted them at high speeds. They may result from the
explosive eruption of molten or solid rock fragments, or both. They may also result from
the nonexplosive eruption of lava when parts of dome or a thick lava flow collapses down
a steep slope. Most pyroclastic flows consist of two parts: a basal flow of coarse
fragments that moves along the ground, and a turbulent cloud of ash that rises above
the basal flow. Ash may fall from this cloud over a wide area downwind from the
pyroclastic flow.

Remnant of a
building in Francisco
Leon that was
destroyed by
pyroclastic flows and
surges during the
eruption of El
Chichon volcano in
southeastern Mexico
between March 29
and April 4, 1982.
Francisco Leon was
located about 5 km
SSE of the volcano.
The reinforcement
rods in the concrete
wall are bent in the
direction of flow (right
to left). Photograph by R.I. Tilling on June 1, 1982

Effects of Pyroclastic Flows
A pyroclastic flow will destroy nearly everything in its path. With rock fragments ranging
in size from ash to boulders traveling across the ground at speeds typically greater than
80 km per hour, pyroclastic flows knock down, shatter, bury or carry away nearly all
objects and structures in their way. The extreme temperatures of rocks and gas inside
pyroclastic flows, generally between 200°C and 700°C, can cause combustible material
to burn, especially petroleum products, wood, vegetation, and houses.
Pyroclastic flows vary considerably in size and speed, but even relatively small flows that
move less than 5 km from a volcano can destroy buildings, forests, and farmland. And
on the margins of pyroclastic flows, death and serious injury to people and animals may
result from burns and inhalation of hot ash and gases.
Pyroclastic flows generally follow valleys or other low-lying areas and, depending on the
volume of rock debris carried by the flow, they can deposit layers of loose rock
fragments to depths ranging from less than one meter to more than 200 m. Such loose
layers of ash and volcanic rock debris in valleys and on hillslopes can lead to lahars
indirectly by:
1. Damming or blocking tributary streams, which may cause water to form a lake behind
the blockage, overtop and erode the blockage, and mix with the rock fragments.
2. Increasing the rate of stream runoff and erosion during subsequent rainstorms. Hot
pyroclastic flows and surges can also directly generate lahars by eroding and mixing with
snow and ice on a volcano's flanks, thereby sending a sudden torrent of water surging
down adjacent valleys.

Volcano Landslides and their Effects
Landslides are large masses of rock and soil that fall, slide, or flow very rapidly under the
force of gravity. These mixtures of debris move in a wet or dry state, or both. Landslides
commonly originate as massive rockslides or avalanches which disintegrate during
movement into fragments ranging in size from small particles to enormous blocks
hundreds of meters across. If the moving rock debris is large enough and contains a
large content of water and fine material (typically, >3-5 percent of clay-sized particles),
the landslide may transform into a lahar and flow downvalley more than 100 km from a
volcano!
Landslides are common on volcanoes because their massive cones (1) typically rise
hundreds to thousands of meters above the surrounding terrain; and (2) are often
weakened by the very process that created them--the rise and eruption of molten rock.
Each time magma moves toward the surface, overlying rocks are shouldered aside as
the molten rock makes room for itself, often creating internal shear zones or
oversteepening one or more sides of the cone.
A large landslide often buries valleys with tens to hundreds of meters of rock debris,
forming a chaotic landscape marked by dozens of small hills and closed depressions. If
the deposit is thick enough, it may dam tributary streams to form lakes in the subsequent
days to months; the lakes may eventually drain catastrophically and generate lahars and
floods downstream.
Landslides also generate some of the largest and most deadly lahars, either by
transforming directly into a lahar or, after it stops moving, from dewatering of the deposit.

his house is partially buried in a lahar
deposit that was formed by the dewatering
of a large volcano landslide from Mount
St. Helens, Washington. Early on the
morning of May 18, 1980, the landslide
swept into the upper North Fork Toutle
River valley and came to rest within about
22 km of the volcano. The landslide
deposit, however, was saturated with
water, and contained snow and ice blocks
from the volcano's former glaciers. As
soon as the landslide stopped moving,
water percolated to the top of the deposit
and poured across its irregular surface,
forming many lahars that merged as they
rushed down the valley. The peak flow
swept from the deposit about 5 hours after
the landslide was emplaced! generate lahars that travel far downstream
Photograph by L. Topinka in 1981.
Effect of Volcanic landslides

Fluid basalt lava flow,
Mauna Loa, Hawai`i
Lava flows are streams of molten rock that
pour or ooze from an erupting vent. Lava is
erupted during either nonexplosive activity or
explosive lava fountains. Lava flows destroy
everything in their path, but most move slowly
enough that people can move out of the way.
The speed at which lava moves across the
ground depends on several factors, including
(1) type of lava erupted and its viscosity; (2)
steepness of the ground over which it travels;
(3) whether the lava flows as a broad sheet,
through a confined channel, or down a lava
tube; and (4) rate of lava production at the
vent.
Lava Flows and their Effects
Fluid basalt lava flow, Mauna Loa,
Hawai`i

Everything in the path of an advancing
lava flow will be knocked over,
surrounded, or buried by lava, or ignited
by the extremely hot temperature of lava.
When lava erupts beneath a glacier or
flows over snow and ice, meltwater from
the ice and snow can result in far-reaching
lahars. If lava enters a body of water or
water enters a lava tube, the water may
boil violently and cause an explosive
shower of molten spatter over a wide area.
Methane gas, produced as lava buries
vegetation, can migrate in subsurface
voids and explode when heated. Thick
viscous lava flows, especially those that
build a dome, can collapse to form fast-
moving pyroclastic flows.
Lava Flows and their Effects
Àà lava flow moves through an
intersection in the Royal Garderns
subdivision on the south flank of Kilauea
Volcano, Hawaiì.
Photograph by J.D. Griggs in 1984.

Tephra is a general term for fragments of
volcanic rock and lava regardless of size
that are blasted into the air by explosions
or carried upward by hot gases in eruption
columns or lava fountains. Such fragments
range in size from less than 2 mm (ash) to
more than 1 m in diameter. Large-sized
tephra typically falls back to the ground on
or close to the volcano and progressively
smaller fragments are carried away from
the vent by wind. Volcanic ash, the
smallest tephra fragments, can travel
hundreds to thousands of kilometers
downwind from a volcano.
Tephra and its effect

Mount St. Helens
Tephra: ash & pumice
Kilauea Tephra:
reticulite
Kilauea Tephra:
Pele's hair
Mount St. Helens
Tephra: block
Tephra consists of a wide range
of rock particles (size, shape,
density, and chemical
composition), including
combinations of pumice, glass
shards, crystals from different
types of minerals, and shattered
rocks of all types (igneous,
sedimentary, and metamorphic).
A great variety of terms are used
to describe the range of rock
fragments thrown into the air by
volcanoes. The terms classify
the fragments according to size,
shape, or the way in which they
form and travel.
Different sizes of Tephra

Ash usually covers a much larger area and
disrupts the lives of far more people than
the other more lethal types of volcano
hazards. Unfortunately, the size of ash
particles that fall to the ground and the
thickness of ashfall downwind from an
erupting volcano are difficult to predict in
advance. Not only is there a wide range in
the size of an eruption that might occur and
the amount of tephra injected into the
atmosphere, but the direction and strength
of the prevailing wind can vary widely.
Volcanic ash: how far will it fall downwind from an
erupting volcano?
Pumice and ash cover cars and airport
runways

Communication is key to saving lives
Recent advances in volcano monitoring, new and refined volcano-hazard
assessments, and better warning schemes have significantly improved
our capability to warn of volcano hazards and impending eruptions. Our
volcano information and warnings, however, no matter how timely or
precise, will reduce volcanic risk only if they are communicated effectively
to a wide audience, especially to people who live and work in potentially
hazardous areas and to emergency-management specialists.
Increasing public awareness of volcano hazards
In addition to carrying out specialized studies on volcanoes and hazards
posed by them, we participate in a wide variety of projects and activities
intended to increase awareness of volcano hazards and minimize future
consequences of volcano activity in the United States.
Preparing for Volcanic Emergencies

participates in volcano-emergency planning workshops and emergency-response
exercises
convenes international, regional, and local workshops focused on volcano-hazard
issues
prepares educational materials with partners, including exhibits, fact sheets, booklets,
video programs, and maps
collaborates with emergency-management specialists to develop effective warning
schemes,
meets with community leaders and residents wanting information about potentially
dangerous volcanoes in their area
works with the news media and media producers
leads educational field trips to active and potentially dangerous volcanoes for the public,
officials, local residents, educators, and students
helps educators and students with classroom presentations, teacher workshops, field
trips, an
The Volcano Hazards Program:

Study of Volcanism and volcano

Study of Volcanism and volcano

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