• In Action
How They Get Formed.
• There are hot spots that build the volcanoes up into the shape of the
type of volcano.
• Volcanoes form when hot material from below rises and leaks into
• The hot material, called magma, rising from lower ground, gathers in
a reservoir called the magma chamber. Eventually, but not always,
the magma erupts onto the surface and forms lava. Strong
earthquakes accompany rising lava, and the volcano may swell just
before an eruption, as shown in this animation.
• White arrows in the picture show the volcano getting bigger as the
lava rises inside. Scientist measure the swelling of a volcano before
• The different reasons why a volcano forms are
• when bubbles of material rise to the surface
• when the crust is forced to go down
Why They Erupt
• When rock inside the earth gets too hat the volcano will erupt.
Volcanoes are openings in the earth's crust. When the volcano
erupts, gas and rocks come out of the opening. The rock is very hot,
so it is molten, which means melted. Scientists call this melted rock
magma. Crystals and minerals are in the rock, but the crystals
dissolve because it is so hot. When the magma gets to the surface,
it is called lava. When the lava hardens, it is called *lava rock.
• There are pockets of magma underneath the
earth in some parts of the world. The magma presses against rock
the earth's crust. When the magma finds a spot in the crust where
there aren't very many rocks, it pushes to the surface.
• CRUST- the outermost layer of the earth
• MOLTEN- melted rock and minerals
• MAGMA- Melted rock and gas
LAVA-Magma when it reaches the surface
• LAVA ROCK- Hardened lava
How They Erupt
• The way volcanoes erupt usually takes a long time and this is how volcanoes
erupt. First a volcano makes something called magma from melted rock. The
magma goes through a circulation. It has to form at the bottom of the volcano and
then start its way up the main vent. The main vent is a hole that is in the volcano and
when the volcano is ready to erupt the lava is at the top of the main vent. The
magma goes up the main vent slowly while it is still getting hotter. When the magma
is about half way up the main vent it turns into lava. Lava is a very hot liquid which
burns the remaining rocks from the magma. The lava slowly continues up the main
vent. While going up the lava continues to get hotter and hotter. Ash and rocks are
collected and the lava is getting hotter and hotter while the lava is continuing its way
up the main vent. When the lava is at the top of the main vent the volcano
erupts. The lava blasts out of the volcano along with ash, rocks, and a cloud of dust
that is very thick. The ash and rock crumble to the ground, but the lava is either
moving down the volcano side very slowly or at a high speed. The lava burns down
almost everything in its way, and it sometimes leaves bits of things burning. The lava
from the volcano can cool fast, or sometimes the lava will slowly cool down from its
intense heat. Lava that cools slowly forms igneous rocks. There are many types of
igneous rocks. Volcanoes can damage themselves in the explosion. A volcano
literally blows its top off. One of the volcanoes that has blown its
How They Erupt
• top from an explosion is Mt. St. Helens. Mt. St. Helens has erupted
more than once.
Volcanoes can be under water or on land. Volcanoes that are under
water take a longer time than if they are on land because they are
under water the water slows down the magma and lava but if the
volcano is on land the lava and magma can move quicker up the
main vent. It just depends on the environment how fast the volcano
can make the magma the magma makes lava and the volcano
makes an explosion. If the volcano is under water the cooled lava
will probably make an island. The Hawaiian Islands is an example
of island made by a chain of volcanoes. Now go back to the front
page of our site and go to a different page on our site and of course
be prepared to learn more about volcanoes.
What Comes Out Of Them
Magma, lava, lava rock, and volcanic ash
comes out of a volcano.
MAGMA- Melted rock and gas
LAVA-Magma when it reaches the surface
LAVA ROCK- Hardened lava
VOLCANIC ASH- consists of tiny jagged
pieces of rock and glass.
• Volcanoligists have classified volcanoes
into groups based on the Shape of the
volcano, the materials they are built of,
and the way the volcano erupts.
• Geologists generally group volcanoes into
four main kinds--cinder cones, composite
volcanoes, shield volcanoes, and lava
Cinder cones are the simplest type of volcano. They are built from particles and blobs
of congealed lava ejected from a single vent. As the gas-charged lava is blown
violently into the air, it breaks into small fragments that solidify and fall as cinders
around the vent to form a circular or oval cone. Most cinder cones have a bowl-
shaped crater at the summit and rarely rise more than a thousand feet or so above
their surroundings. Cinder cones are numerous in western North America as well as
throughout other volcanic terrains of the world. In 1943 a cinder cone started growing
on a farm near the village of Parícutin in Mexico. Explosive eruptions caused by gas
rapidly expanding and escaping from molten lava formed cinders that fell back around
the vent, building up the cone to a height of 1,200 feet. The last explosive eruption
left a funnel-shaped crater at the top of the cone. After the excess gases had largely
dissipated, the molten rock quietly poured out on the surrounding surface of the cone
and moved downslope as lava flows. This order of events--eruption, formation of
cone and crater, lava flow--is a common sequence in the formation of cinder cones.
During 9 years of activity, Parícutin built a prominent cone, covered about 100 square
miles with ashes, and destroyed the town of San Juan. Geologists from many parts of
the world studied Parícutin during its lifetime and learned a great deal about
volcanism, its products, and the modification of a volcanic landform by erosion.
• Some of the Earth's grandest mountains are composite volcanoes. They are typically
steep-sided, symmetrical cones of large dimension built of alternating layers of lava
flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 8,000 feet
above their bases. Some of the most conspicuous and beautiful mountains in the
world are composite volcanoes, including Mount Fuji in Japan, Mount Cotopaxi in
Ecuador, Mount Shasta in California, Mount Hood in Oregon, and Mount St. Helens
and Mount Rainier in Washington. Most composite volcanoes have a crater at the
summit which contains a central vent or a clustered group of vents. Lavas either flow
through breaks in the crater wall or issue from fissures on the flanks of the cone.
Lava, solidified within the fissures, forms dikes that act as ribs which greatly
strengthen the cone. The essential feature of a composite volcano is a conduit
system through which magma from a reservoir deep in the Earth's crust rises to the
surface. The volcano is built up by the accumulation of material erupted through the
conduit and increases in size as lava, cinders, ash, etc., are added to its slopes.
When a composite volcano becomes dormant, erosion begins to destroy the cone. As
the cone is stripped away, the hardened magma filling the conduit (the volcanic plug)
and fissures (the dikes) becomes exposed, and it too is slowly reduced by erosion.
Finally, all that remains is the plug and dike complex projecting above the land
surface--a telltale remnant of the vanished volcano.
• The Evolution of a Composite Volcano
• A. Magma, rising upward through a conduit, erupts at the Earth's
surface to form a volcanic cone. Lava flows spread over the
• B. As volcanic activity continues, perhaps over spans of hundreds of
years, the cone is built to a great height and lava flows form an
extensive plateau around its base. During this period, streams
enlarge and deepend their valleys.
• C. When volcanic activity ceases, erosion starts to destroy the cone.
After thousands of years, the great cone is stripped away to expose
the hardened quot;volcanic plugquot; in the conduit. During this period of
inactivity, streams broaden their valleys and dissect the lava plateau
to form isolated lava-capped mesas.
• D. Continued erosion removes all traces of the cone and the land is
worn down to a surface of low relief. All that remains is a projecting
plug or quot;volcanic neck,quot; a small lava-capped mesa, and vestiges of
the once lofty volcano and its surrounding lava plateau.
• Shield volcanoes, the third type of volcano, are built almost entirely of fluid lava flows.
Flow after flow pours out in all directions from a central summit vent, or group of
vents, building a broad, gently sloping cone of flat, domical shape, with a profile much
like that of a warrior's shield. They are built up slowly by the accretion of thousands of
highly fluid lava flows called basalt lava that spread widely over great distances, and
then cool as thin, gently dipping sheets. Lavas also commonly erupt from vents along
fractures (rift zones) that develop on the flanks of the cone. Some of the largest
volcanoes in the world are shield volcanoes. In northern California and Oregon, many
shield volcanoes have diameters of 3 or 4 miles and heights of 1,500 to 2,000 feet.
The Hawaiian Islands are composed of linear chains of these volcanoes including
Kilauea and Mauna Loa on the island of Hawaii-- two of the world's most active
volcanoes. The floor of the ocean is more than 15,000 feet deep at the bases of the
islands. As Mauna Loa, the largest of the shield volcanoes (and also the world's
largest active volcano), projects 13,677 feet above sea level, its top is over 28,000
feet above the deep ocean floor. In some eruptions, basaltic lava pours out quietly
from long fissures instead of central vents and floods the surrounding countryside
with lava flow upon lava flow, forming broad plateaus. Lava plateaus of this type can
be seen in Iceland, southeastern Washington, eastern Oregon, and southern Idaho.
Along the Snake River in Idaho, and the Columbia River in Washington and Oregon,
these lava flows are beautifully exposed and measure more than a mile in total
Volcanic or lava domes are formed by relatively small, bulbous masses of lava too
viscous to flow any great distance; consequently, on extrusion, the lava piles over
and around its vent. A dome grows largely by expansion from within. As it grows its
outer surface cools and hardens, then shatters, spilling loose fragments down its
sides. Some domes form craggy knobs or spines over the volcanic vent, whereas
others form short, steep-sided lava flows known as quot;coulees.quot; Volcanic domes
commonly occur within the craters or on the flanks of large composite volcanoes. The
nearly circular Novarupta Dome that formed during the 1912 eruption of Katmai
Volcano, Alaska, measures 800 feet across and 200 feet high. The internal structure
of this dome--defined by layering of lava fanning upward and outward from the
center--indicates that it grew largely by expansion from within. Mont Pelée in
Martinique, Lesser Antilles, and Lassen Peak and Mono domes in California are
examples of lava domes. An extremely destructive eruption accompanied the growth
of a dome at Mont Pelée in 1902. The coastal town of St. Pierre, about 4 miles
downslope to the south, was demolished and nearly 30,000 inhabitants were killed by
an incandescent, high-velocity ash flow and associated hot gases and volcanic dust.
Only two men survived; one because he was in a poorly ventilated, dungeon-like jail
cell and the other who somehow made his way safely through the burning city.
Does It Have To Be Hot Or Cold
• Hydrocarbon seeps on the Gulf of Mexico (GOM) seafloor are conventionally defined as quot;coldquot;, being
characterized by hydrocarbon-rich fluid emissions at ambient sea floor temperature, mineralization of gas
hydrates, precipitation of carbonates depleted in 13C, association with chemosynthetic fauna (mussel beds, tube
worms etc.) and dominance of microbial processes fueled by venting hydrocarbons within the sediments. Analyses
of carbonate phases, pore-fluids and biomarkers from cores (length~25cm) taken by ALVIN from an active mud
volcano on the northern Gulf of Mexico slope (GC-272, 27°41`25quot;; 91°32`28quot;) point towards a vent setting far
more complex than sites previously investigated. We argue that the mud volcano setting in GC-272 is
distinguished by episodes of cold methane venting when gas hydrates are forming in the sediment pore spaces
(visually confirmed) alternating with periodic hot venting of warm brines (formation fluids) advected on the sea
floor. We support our argument with the evidence that follows. Scalenohedral calcite crystals (1-2 mm in size)
scattered within the sediment exhibit unusually negative δ18O values (down to -6‰ PDB) and δ13C values
ranging from -2 ‰ to - 20‰ PDB. Temperature calculations based on the δ18O composition of the calcites and
coexisting pore fluids yield a fluid temperature of ~45°C which is far higher than the recorded bottom water
temperatures of ~8°C at a depth of 680 m. Pore fluid Na/Cl ratios (0.92-1.2) confirm the mixing of cold GOM
bottom waters (Na/Cl=0.82) with advecting hot brines (Na/Cl=~1.0) resulting in a brine fluid at 45°C. The δ13C of
the calcites is isotopically heavier by comparison with typical seep carbonates from the GOM suggesting a mixed
carbon source consisting of pore fluid DIC, brine DIC and bottom seawater DIC. Hence the scalenohedral calcites
are the product of hot venting episodes and are precipitated within the sediments from calcite-saturated pore-fluids
(SI= ~5). Biomarker assays of the organic matter indicate that anaerobic oxidation of methane coupled with
bacterial sulfate reduction (BSR/AMO) are the dominant processes within the sediments. Archaea derived
archaeol and sn-2- hydroxyarchaeol are found to be most abundant within the sediments and are extremely
depleted in 13C (upto -120‰ PDB). δ13C values of fatty acids are slightly enriched in 13C (< - 40‰ PDB),
suggesting their (partial) origin from bacteria involved in the turnover of methane. The most negative value (-89‰
PDB) is found for the cy-C17:0D11,12 (or cy-D17:0ω5,6), which is derived from sulfate reducing bacteria
performing anaerobic oxidation of methane. This vent site represents a potentially unique extreme environment for
microbial processes, exhibiting characteristics of both hot (hydrothermal) and cold vents. An improved
understanding of Green Canyon 272 mud volcano site on the northern GOM slope will contribute to better
assessment of microbial adaptation to natural variables like fluctuating temperatures and salinity.
Which State Has The Most
STATE NUMBER OFACTIVE VOLCANOES
New Mexico 3
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