GEL 130QR- Midterm Exam Guide - Comprehensive Notes for the exam ( 16 pages long!)

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Published on 13 Oct 2017
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GEL 130QR
MIDTERM EXAM
STUDY GUIDE
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IGNEOUS ROCKS AND INTRUSIVE ACTIVITY (Chapter4):
How are Igneous Rocks formed? – Igneous rocks form either deep beneath the earth’s
surface from magma or cool above the surface when lava cools
Contrast magma and lava. – Magma is underground and lava is aboveground
Explain how are igneous rocks classified? (according to their composition and texture)
oComposition – Granitic (felsic), Andesitic (Intermediate), Basaltic (Mafic), Ultramafic
oTexture - Glassy, Porphyritic (two different crystal sizes), Phaneritic (coarse-grained),
Vesicular (voids left from air bubbles), Pyroclastic (fragmental), and Aphanitic (fine-grained).
List the different igneous rock textures (aphanitic, phaneritic, porphyritic, vesicular,
and glassy) and explain their origins: Describe how the rate of magma cooling influences the
size of crystals (and texture) in igneous rocks.
oGlassy – molten rock is ejected into the atmosphere where it is cooled quickly to
become a solid
oPorphyritic – large mass of magma over millions of years, over this time the
large crystals can form
oPhaneritic – large masses of magma slowly crystallize at great depth
oVesicular – gas bubbles escape as lava solidifies
oPyroclastic – consolidation of individual rock fragments ejected during explosive
volcanic eruptions
oAphanitic – igneous rocks that form at the surface or as small intrusive masses
within the upper crust
Igneous rocks are composed mainly of which group of minerals? - Silicate minerals
Differentiate between felsic (granitic) and mafic (basaltic) igneous rocks – Felsic
igneous rocks are composed of light-colored felsic rocks that is 70% silica while Mafic
igneous rocks are composed of dark-colored with 45% dark silica material
Be able to work with the Igneous Rock classification chart (chart will be provided
during the exam)
Where and how does magma originate?
oMagma is generated by solid rock at subduction and convergent boundaries.
oDecompression Melting – melting that occurs as rock ascends due to a drop in
confining pressure
oAddition of Water – moist rocks are more malleable compared to other rocks,
sugar example
oTemperature Increase – melting crustal rocks, at subduction zone
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List and describe various kinds of intrusive igneous bodies: dike, sill, stock and batholith.
oDike – a tabular-shaped intrusive igneous rock feature that cuts through the
surrounding rock; through the rock, up and down
oSill – a tabular igneous body that has intruded parallel to the layering of
preexisting rock; parallel to the rock layers
oStock – a structure that results from the emplacement and crystallization of
magma beneath the Earth’s surface; small batholith, minor exposure
oBatholith – a large mass of igneous rock that formed when magma was emplaced
at depth, crystallized, and subsequently exposed by erosion
How the different types of magma and igneous rocks are related to Plate Tectonics? -
VOLCANOES AND VOLCANIC HAZARDS (Chapter 5):
List three factors that determine the nature of a volcanic eruption. What role does each
play?
oTemperature – the hotter it creates a more fluid lava, the cooler it is the higher the
viscosity
oComposition – the more silica in magma, the greater its viscossity
oDissolved Gases – loss of gases renders magma more viscous, gases give magma an
explosive aspect
Why is a volcano fed by highly viscous magma likely to be a greater threat to life
and property than a volcano supplied with very fluid magma?
oA volcano fed by highly viscous magma is likely to be a greater threat to life and
property than a volcano supplied with very fluid magma because highly viscous magma can
produce explosive eruptions with hot ash and gases
Compare and contrast the three main types of volcanoes: consider size, shape, and
eruptive style.
oShield Volcanos – a broad, gently sloping volcano built from fluid basaltic lavas
oCinder Cone Volcanos – a rather small volcano built primarily of ejected lava
fragments that consist mostly of pea-to-walnut-size lapilli
oComposite Volcanos – stratovolcano, a volcano composed of both lava flows and
pyroclastic material
Name a prominent volcano (example) for each of the three types of volcanoes.
oShield Volcano – Mauna Loa, Hawaii
oCinder Cone Volcano – Paricutin, Mexico
oComposite Volcano – Ring of Fire volcanos, Pacific Ocean
Lahar – a debris flow on the slopes of a volcano that results when unstable layers of
ash and debris become saturated and flow downslope, usually following stream channels
Plate Tectonics and volcanic activity
oVolcanos at Convergent – forms a volcanic arc, the two plates move towards
each other and the oceanic lithosphere sinks below the crust. As it sinks it gets
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Document Summary

Igneous rocks form either deep beneath the earth"s o o surface from magma or cool above the surface when lava cools. Magma is underground and lava is aboveground. Explain how are igneous rocks classified? (according to their composition and texture) Composition granitic (felsic), andesitic (intermediate), basaltic (mafic), ultramafic. Texture - glassy, porphyritic (two different crystal sizes), phaneritic (coarse-grained), Vesicular (voids left from air bubbles), pyroclastic (fragmental), and aphanitic (fine-grained). Differentiate between felsic (granitic) and mafic (basaltic) igneous rocks felsic igneous rocks are composed of light-colored felsic rocks that is 70% silica while mafic igneous rocks are composed of dark-colored with 45% dark silica material. Be able to work with the igneous rock classification chart (chart will be provided during the exam) List three factors that determine the nature of a volcanic eruption. Temperature the hotter it creates a more fluid lava, the cooler it is the higher the viscosity o o.

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