Different Types of Volcanoes and Volcanic Rocks
In Partnership with Dr. Nancy R. Riggs
By: Shawneya Jackson
Honors Science
December 16, 20
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Have you ever wondered what is inside a volcano, and what is produced by an eruption?
Volcanoes form a great variation of rock, which are classified into three main groups; igneous,
sedimentary, and metamorphic rocks. However,
igneous rocks are formed from the magma in the
Earth’s mantle. They sometimes have holes or bubbles,
and may appear glassy. Igneous rocks can be classified
as intrusive or extrusive. Intrusive igneous rocks are
course-grained because they cool slowly inside the
Earth. Extrusive igneous rocks are fine-grained because
they cool quickly on the Earth’s surface. Metamorphic
These are the three classifications
rocks are formed by different rocks that have had a change
of
rocks.
in temperature, pressure, or chemical reactions. Sedimentary rocks are also formed by other
rocks have been in an erosion.
Dr. Nancy R. Riggs studies volcanology and geochronology. She travels around the world
studying different types of volcanoes and what is inside them. Volcanology is the formation,
distribution, and classification of volcanoes. It deals with the structure and different components
that are ejected during an eruption. Some components that are erupted from the volcano are;
pyroclastic flaws, lava, dust, ash, and volcanic gases. A geochronologist also studies tiny crystals
that are taken out of volcanic rocks and sandstone, which helps figure how old they are.
Volcanoes are separated into four main groups; cinder cones, composite volcanoes, shield
volcanoes, and lava domes. A cinder cone volcano, also called a tephra cone volcano, is a “small
volume cone consisting predominantly of tephra that result from strombolian eruptions
(“Volcanic Landforms”).” Cinder cone volcanoes usually consist of basaltic or andesite
components. The slope of a cinder cone volcano is controlled by the angle of repose (angle of
stable slope for loose unconsolidated material) and is usually 25-35 degrees Fahrenheit. They
also have a bowl-shaped crater at the summit of the volcano. Usually, they do not rise 1,000 feet
above their surroundings. Cinder cone volcanoes are located western part of North America, and
are numerous throughout the volcanic terrains around the world. Composite volcanoes
(stratovolcanoes) are “steep-sided, symmetrical cones of large dimension built alternating layer
of lava flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 8,000 feet above
their bases (“Principal Types of Volcanoes”).”
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Composite volcanoes have a crater at the summit and have
long periods of time without being active. The main feature of
composite volcanoes is the conduit system, “through which
magma from a reservoir deep in the Earth’s crust rises to the
surface (“Volcanic Landforms”).” They are built from the
This is a diagram of the
accumulation of component that were erupted through the conduit components a composite
volcano has.
system which increases in size.
Shield volcanoes are built entirely out of fluid lava flows. The lava pours out in all directions and
creates s gentle sloped cone of a flat, domical shape like a warriors shield. They are made of thin
lava flows that built up over the central vent, and of basaltic magma that flows down the slopes
of a shield volcano. Shield volcanoes do not usually have a very circular or oval shape.
Lava domes are formed by relatively small bulbous masses of lava to viscous to flow any great
distance; consequently, on extrusion, the lava piles over and around its vent (“Principal Types of
Volcanoes”).” The dome then grows large by an expansion from the inside. When it expands the
outer surface cools and hardens. It then shatters, spilling loose fragments down the side. Lava
domes are also known as volcanic domes. The domes sometimes form “craggy knobs or spines
over the volcanic vent, whereas others form short, steep-sided lava flow known as “coules”
(“Principal Types of Volcanoes”).”
Volcanoes erupt because of density and pressure. Sine “magma is less dense than the rock that
surrounds it, they try to float to the surface (“Volcanic Materials Identification”).” If the magma
has water and dissolved gases, the gases and dissolved water will quickly expand into steam and
gas that causes it to erupt when magma reaches the surface.
There are seven effects that will cause a volcanic eruption, but three predominate effects which
are; the buoyancy of the magma, pressure from exsolved gases in the magma, and the injection
of a new set of magma in an already filled magma chamber. This is because, the rock in the
Earth melts, the mass stays the same, but the volume increases. Since magma is less dense, it
rises to the surface.
There are three different types of volcanic components: lava, rock fragments, and gas. Lava is
molten, which means melted to a liquid. There are different types of lava Aa, block, Pahoehoe,
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and pillow lava. Aa lava is a rough, jagged, and spiny. Block are fragments of lava or a larger
rock than 6 millimeters. Pahoehoe is fluid lava that is in a solidified form, which is smooth,
billowy, and has a rappy surface. Pillow lava is a type of fluid lava that has been erupted or
underwater. [Rock fragments are called tephra and they are formed by Aa.] Gas is made out of
steam, it has carbon dioxide, sulfur dioxide, nitrogen, and different gases.
Volcanoes maybe dangerous, but they are a part of nature. There are different types of volcanoes,
and you can tell them apart by how each of them look, or by the magma. Each volcano is made
of a type of magma, andesite, basaltic, and rhyolite. There are many ways to tell which rocks are
which, or the different types of volcanoes. Each volcano is different like every world with their
personalities.
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Works Cited
Coffey, Jerry. "Why Do Volcanoes Erupt?." Universe Today. Universe Today, 31 Oct 2010.
Web. 16 Dec 2013. <http://www.universetoday.com/77111/why-do-volcanoes-erupt/>.
"Principal Types of Volcanoes." USGS. John Watson, 1 Mar 2011. Web. 16 Dec 2013.
<http://pubs.usgs.gov/gip/volc/structures.html>.
"Types of Volcanic Rock." Science Learning Sparking Fresh Thinking. Science Learning Hub,
20 Apr 2010. Web. 16 Dec 2013. <http://www.sciencelearn.org.nz/Contexts/Volcanoes/ScienceIdeas-and-Concepts/Types-of-volcanic-rock>.
"Volcanic Landforms." . N.p., 13 Sep 2013. Web. 16 Dec 2013.
<http://www.tulane.edu/~sanelson/Natural_Disasters/volclandforms.htm>.
"Volcanic Materials Identification." Earth Science Lab. Richard Hardwood, 8 February 2011.
Web. 16 Dec 2013.
<http://facweb.bhc.edu/academics/science/harwoodr/GEOL101/Labs/VolcanicMaterials/>.
VOLCANIC ROCKS." . Oregon State edu. Web. 16 Dec 2013.
<http://volcano.oregonstate.edu/vwdocs/vwlessons/volcanic_rocks.html>.
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