Samantha_Hernandez_Chapter-4
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Chapter 4 Igneous Processes and Volcanoes
1.
What is magma?
How does magma differ from lava?
What are the major components of
magma?
Magma is composed of molten rock and is stored in the Earth's crust.
Lava is magma that
reaches the surface of our planet through a volcano vent
. The most abundant elements
are oxygen and silicon, followed by aluminum, iron, calcium, sodium, magnesium, and
potassium
.
2. In what basic settings to intrusive and extrusive igneous rocks originate?
Intrusive rock originates beneath the surface while an extrusive rock originates at the surface.
3. Differentiate between felsic and mafic igneous rocks.
Mafic rocks are those that are high in dark-colored minerals composed mainly of magnesium
and iron. Felsic rocks, such as granite, are high in light-colored minerals, including
feldspar
and
quartz.
4. How does the rate of cooling influence crystal size?
What other factors influence the texture
of igneous rocks?
Slower cooling results in fewer, larger crystals, while more rapid cooling results in a solid mass of
small interwoven crystals. Other factors include
the origin of the rock's formation and how it
formed
.
5. Compare and contrast each of the following pairs of igneous rocks:
a. granite and diorite
-Granite is a course grained rock composed of quartz and feldspar. Granite is found in
abundance in the continental crust. Because of granites beauty it is used to make
tombstones, monuments and stone buildings.
-Diorite is a course grained rock that looks like granite. Unlike granite, diorite contains
little or no visible crystals and has a higher percentage of dark silicate minerals. Diorite is
composed of plagioclase, feldspar, and amphibole.
b. basalt and gabbro
-Basalt is a fine-grained rock composed of pyroxene and plagioclase felspar, with less
amounts of olivine and amphibole. Basalt is the most common extrusive igneous rock.
Upper layers of the ocean crust are composed of basalt.
-Gabbro is the intrusive equivalent of basalt. Gabbro tends to be dark green to black in
color similar to basalt. Gabbro is uncommon in the continental crust, but like basalt
makes up a portion of the oceanic crust.
c. andesite and rhyolite
-Andesite is a fine-grained medium-gray rock of volcanic origin. Andesite displays a
porphyritic texture, and the phenocrysts are often light rectangular crystals of
plagioclase feldspar. Andesite resembles rhyolite and requires a microscope to
differentiate.
-Rhyolite is the fine-grained equivalent to granite. Rhyolite is composed mostly of light-
colored silicates. Rhyolite is typically buff or pink toned, occasionally grey. Rhyolite
frequently contains glass fragments which means the rhyolite was cooled rapidly.
6. What is magmatic differentiation?
How might this process lead to the formation of several
different igneous rocks from a single magma?
Magmatic differentiation is the formation of a magma body having a mineralogy or chemical
composition that is different than the parent magma. Crystal setting is a cause of magmatic
differentiation and happens when earlier-formed minerals are denser than the liquid portion
and sink to the bottom of the magma chamber. Different igneous rocks form from a single
magma when foreign material is incorporated and changes the composition of the magma.
Melting of these new foreign materials into the magma is referred to as assimilation and
changes the overall chemical composition of the magma body.
7. Describe each of the four basic intrusive features (dikes, sills, laccoliths, and batholiths).
Dikes are discordant bodies that form when magma is forcibly injected into fractures and cut
across bedding surfaces into other structures in the host rock.
Sills are horizontal bodies that form when magma exploits weakness between sedimentary beds
of rock structure. Dikes and sills are typically shallow features, occurring where the country
rocks are sufficiently brittle.
Laccoliths occur when igneous rock is forcibly injected between sedimentary strata and arch the
beds above while leaving those below relatively flat.
Batholiths occur as mammoth linear structures several hundred kilometers long and up to 100
kilometers wide. Batholiths can cover a large area, but most are less than 10 kilometers thick.
8. List three factors that determine the nature of a volcanic eruption.
What role does each
play?
Three factors that determine the nature of a volcanic eruption include its composition,
temperature, and gases. Temperature strongly influences the mobility of lava, as lava cools it
begins to harden and eventually lava flow stops. A volcanoes composition is directly related to
viscosity. A magmas viscosity is related to its silica content, the more silica the greater its
viscosity. The gaseous components of magma are made mostly of dissolved water and affect the
mobility of magma. Gases also give magmas their explosive qualities.
9. Compare and contrast the three main types of volcanoes (consider size, composition, shape,
and eruptive style) and give an example of each type.
The three main types of volcanoes are shield, cinder cone, and composite cones. Cinder cone
volcanoes are large and deep sided with steep angles; they are built out of ejected lava that
hardens. Most cinder cone eruptions are from vents located by the base of the volcano. An
example of a cinder cone volcano is Cerro Negro located in Nicaragua. Shield volcanoes are
broad, and dome shaped with sloped sides, resembling a warrior shield. When a shield volcano
erupts the lava flows easily, unless water has gotten into the vent. An example of a shield
volcano is the Mauna Loa in Hawaii. A composite cone is rather large and a near symmetrical
cone shape. Composite cones are composed of layers of ash and cinders from formerly erupted
volcanoes. The eruption style of a composite cone is highly dangerous and vicious. An example
of a Composite cone is Mayon in the Philippines.
10. Are volcanoes in the Ring of Fire generally described as relatively quiet or violent?
Name a
volcano that would support your answer.
The volcanoes located in the ring of fire and are described as violent. The volcanoes in the ring
of fire mainly consist of composite cones, and their eruptions are considered highly dangerous.
The volcanoes in the ring of fire often contain water, which produces powerful explosions.
Krakatoa located in Indonesia and surrounded by water, blew up in the late 1800's killing over
10,000 people.
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