Geol 5-
Pumice can only form from basalt lava.
False
two distinct mineral sizes
porphyritic (e.g., porphyritic basalt)
Plutons are:
Magma bodies within the deep crust.
Spreading center magmas are basaltic.
True
what is igneous rock
rock resulting from crystallized magma
What is the correct approximate composition of shield volcanoes?
10% pyroclastic deposits and 90% lava
A pyroclastic flow moving at top speed would be moving:
200 km/hr
How many people are currently at risk from volcanoes today?
500 million
How much time, roughly, may be needed to fully solidify a large accumulation of magma?
A million years
Igneous fractionation is responsible for the formation of A volcanic and island arcs B the continents C land masses at hot spots D the seafloors E All of the choices are correct.
All
Which of the following best describes igneous evolution?
All rocks evolved as a result of differentiation of early igneous rocks.
Volcanic arcs are typically composed of
Andesite
COMPOSITION: Intermediate SILICA CONTENT AND VISCOSITY: Intermediate: ~60% GAS CONTENT: 3%-4% EXPLOSIVITY POTENTIAL: Intermediate LAVA TEMPERATURE: Cooler: ~900°C-1000°C EXAMPLES OF VOLCANOES: Mount St. Helens, Mount Rainier
Andestic
COMPOSITION: Mafic SILICA CONTENT AND VISCOSITY: Least: ~50% (thin, runny) GAS CONTENT: 0.5%-2% EXPLOSIVITY POTENTIAL: Least LAVA TEMPERATURE: Hottest: 1100°C-1200°C EXAMPLES OF VOLCANOES: Mid-ocean ridges; plateau basalts like the Columbia Plateau; the Hawaiian Islands
Basaltic
predicts the order of minerals crystallizing from magma
Bowen's reaction series
TYPE: Central Vent Volcano SHAPE: Tall, with steep slopes; often irregular outline from past explosions and rugged dome areas MAGMA TYPE: Andesitic, silica-rich magma at subduction zone TECTONIC SETTING: Convergent boundary (usually) EXAMPLE: Mount Pinatubo, Mount St. Helens
Composite volcano or stratovolcano
Circular depressions created primarily by the explosive excavation of rock during eruptions
Craters
Dunite is a light apple green to yellowish green in color; therefore it is felsic.
False
Granite forms the bedrock of every ocean, covering millions of square kilometers.
False
High-silica magma tends to contain very little dissolved gas.
False
Minerals at the bottom of Bowen's series crystallize early in the cooling process, while the magma is still very hot.
False
Partial melting of the crust may lead to the formation of mafic to felsic magma.
False
Rhyolite, andesite, and basalt are all intrusive or plutonic rocks.
False
Spreading center volcanism very often produces violent eruptions.
False
The Cascade Range of the U.S. Pacific Northwest is an example of an island arc
False
The material in massive shield volcanoes is strong and is good at keeping the volcano structure together.
False
The term volcano refers to the vent (opening), but not the cone.
False
The wrathful Pele, goddess of volcanoes, is a famous story in what culture?
Hawaiian culture
The viscosity of magma increases when:
High silica content builds tetrahedral chains.
Why are hotspots characterized by both explosive and nonexplosive volcanism?
Hotspots may have different types of magma sources.
TYPE: Large-Scale Volcanic Terrains SHAPE: High plateau, massive volume (> 100,000 cubic meters); many layers of lava; no single distinct mountain MAGMA TYPE: Basaltic, low-silica TECTONIC SETTING: Variable setting; often midplate or continental margin EXAMPLE: Columbia Plateau, Washington
Large igneous province
formed at locations where massive quantities of basaltic lava pour from systems of long fissures (ground cracks) instead of from central vents.
Large igneous provinces (LIPs)
TYPE: Large-Scale Volcanic Terrains SHAPE: Broad slopes on long, linear ridge with central rift valley MAGMA TYPE: Basaltic, low-silica TECTONIC SETTING: Divergent boundary; spreading center along mid-ocean ridge EXAMPLE: Mid-Atlantic Ridge
Mid-ocean ridge
TYPE: Large-Scale Volcanic Terrains SHAPE: Low-relief system of vents, cones; occasional stratovolcano MAGMA TYPE: Basaltic, low-silica TECTONIC SETTING: Convergent boundary, or isolated midplate EXAMPLE: San Francisco Volcanic Field, Arizona
Monogenetic field
large volcanic explosions that push thick, dark columns of pyroclasts and gas high into the stratosphere.
Plinian eruption
TYPE: Central Vent Volcano SHAPE: Low-relief system of collapsed calderas and many small vents MAGMA TYPE: Rhyolitic, silica-rich magma (including melted crustal rock) TECTONIC SETTING: Convergent boundary or isolated midplate setting EXAMPLE: Yellowstone National Park
Rhyolite caldera complex
COMPOSITION: Felsic SILICA CONTENT AND VISCOSITY: Greatest: >70% (thick, stiff) GAS CONTENT: 4%-6% EXPLOSIVITY POTENTIAL: Greatest LAVA TEMPERATURE: Coolest: ~700°C-800°C EXAMPLES OF VOLCANOES: Yellowstone volcano
Rhyolitic
what lava has the highest gas content of the three main lava types.
Rhyolitic
TYPE: Central Vent Volcano SHAPE: Large volume, gentle, low-angle slopes MAGMA TYPE: Basaltic, low-silica TECTONIC SETTING: Midplate setting or convergent boundary EXAMPLE: Mauna Loa Volcano, Hawaii
Shield Volcano
massive, low angle volcanoes with a distinct summit crater. They are fed by low-silica, low-gas basaltic magma from the upper mantle.
Shield volcanos
Which of the following gases produces acid rain and air pollution downwind from a volcano?
Sulfur dioxide
Decompression melting occurs approximately in between:
The lithosphere and the asthenosphere
Which of the following is true about the minerals that form early in the cooling process?
These minerals have the highest melting temperatures, are mostly dark in color, and are relatively enriched in iron and magnesium.
All other rocks have evolved from the mafic/ultramafic igneous parent rocks formed over 4 billion years ago.
True
Bowen's reaction series describes the process through which magma's chemical state becomes rich with silica as iron, magnesium, and calcium are lost during the early stages of crystallization.
True
Crustal rifting, volcanic eruptions, and mantle convection are all processes that allow decompression melting to take place under the crust because these processes decrease pressure on the rocks.
True
Gabbro is a mafic rock.
True
Generally, granite is relatively enriched in silicon and oxygen but depleted in iron and magnesium.
True
Geologists use both color trends and texture to identify and name igneous rocks.
True
Granite and basalt are two common igneous rocks composed of silicate minerals.
True
Granite and gabbro are both examples of phaneritic igneous rocks.
True
Hydrated minerals are minerals that contain large volumes of water.
True
Igneous rocks that cool beneath the surface for thousands of years develop large crystals and a coarse texture.
True
Long-quiet volcanoes have been known to release gases that can wipe out communities.
True
Marine sediment actually contains large volumes of seawater within its pores and vesicles.
True
Olivine, pyroxene, and calcium-rich plagioclase feldspar are all minerals that are stable in a solid state at high temperatures.
True
The buoyant plume of gas and ash formed by a Plinian eruption column can collapse around its outer edges and produce a pyroclastic flow.
True
The minerals produced when a body of magma is still very hot are quite different from those formed when it is cooler.
True
The process of differentiation is also referred to by geologists as fractionation, meaning that chemically distinct fractions of the parent magma are formed.
True
The rate of cooling exerts an important control on crystal size.
True
What are the three products of volcanism?
Volcanic gas, lava, and pyroclastic debris.
Lava flows from large igneous provinces are often visible in the walls of eroded river valleys. They measure:
a kilometer or more in total thickness.
______ is typically composed of low-silica basalt
a lava dome
Which of the following igneous rocks is the fine-grained volcanic equivalent of diorite?
andesite
Minerals too small to see
aphanitic
Tephra typically includes
ash (with particles less than 2.5 millimeters across), larger pyroclastic fragments called lapilli (particles 2.5 to 63 millimeters across), blocks (more than 63 millimeters across)
Where does fractionation mainly occur?
at divergent and convergent plate boundaries
What kind of igneous rock is formed when magma rises through fissures in the crust to the surface?
basalt
great magma chambers that form large intrusive structures that may extend over hundreds of kilometers and are often associated with diorite and gabbro
batholith
The melted rock or magma that occurs in the upper mantle as a result of decompression melting generally accumulates at what depths?
below 60 km to 100 km
vents on the sea floor that form as hot mineral -rich water rushes from the hot rock at mid-ocean ridges and mixes with surrounding cold ocean water
black smokers
a cone-shaped mass of material made by volcanic eruption
cinder cone
The main cause of caldera collapse is:
collapse of the roof of a magma chamber as magma erupts
Any rock that was older than and intruded by an igneous body.
country rock
Magma differentiation can include one or more, or any combination of, the following four processes:
crystal settling, magma migration, magma assimilation, and magma mixing
magma that is cooling undergoes
crystallization
Melting due to a drop in confining pressure that occurs as rock rises
decompression melting
Most melting in the mantle is a result of:
decompression melting
the line between the magma and rock field that contains little water.
dry melting curve
gushing; excessively demonstrative
effusive
a massive, high-velocity, billowing pillar of gas, molten rock, and solid particles that is blasted into the air with tremendous force
eruption column
lava and other volcanic products that have been forced onto Earth's surface
extrusive igneous rock
Describes magma or igneous rock that is rich in feldspars and silica and that is generally light in color (a contraction of feldspar and silica). High in silicon and oxygen
felsic
flow of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds of meters
flood basalt
What fraction of Earth is composed of igneous rock?
four-fifths
the process of differentiation where chemically distinct fractions of the parent magma are formed
fractionation
What kind of intrusive igneous rock is formed from magma that rises beneath a spreading center?
gabbro
no obvious minerals visible
glassy (e.g., obsidian)
Geysers on the seafloor, created where tectonic plates move apart, spewing hot and mineral-rich water into cold ocean depths.
hydrothermal vents
process in which igneous magma fractionally crystallizes and partially melts to produce myriad igneous products, which enter the rock cycle, and thus produce diversity throughout al rock families
igneous evolution
A type of rock that forms from the cooling of molten rock at or below the surface.
igneous rock
Which were the first rocks to be formed as Earth's surface cooled and crystallized billions of years ago?
igneous rock
Three main rock groups
igneous, sedimentary, metamorphic
Where is granite most commonly found?
in mountainous areas
between that of mafic rocks and felsic rocks—are composed of minerals that are somewhat abundant in iron, magnesium, calcium potassium, sodium, and oxygen.
intermediate
magma that has crystallized within the crust without being exposed to the cool temperatures of the atmosphere and shallow crust
intrusive igneous rock
Plate techtonics is important to igneous evolution because:
it provides for many igneous enviornments
Relatively small, mushroom-shaped pluton that forms when magma intrudes into parallel rock layers close to Earth's surface.
laccolith
a voluminous emplacement of predominantly mafic extrusive and intrusive igneous rock whose origins lie in processes other than "normal" seafloor spreading. They include continental flood basalts, ocean basin flood basalts, and aseismic ridges
large igneous provinces
what variety of volcano does not belong under the central vent volcano category?
large ingeous provinces
Large-colume volcanically derived crust with complex origin, typically not originating with "classic" central vent volcano.
large-scale volcanic terrains
Magma that reaches Earth's surface from a vent or fissure
lava
describes magma or igneous rock that is rich in magnesium and iron and that is generally dark in color. High in iron, magnesium, and calcium
mafic
As magma migrates into and through the crust, its composition changes. A single "parent" magma body can produce dozens of different types of igneous rocks
magma differentiation
What kind of valuable deposits crystallize out of the hot water coming from black smokers?
metallic sulfide
a collection of cinder cones and/or maar vents and the lava flows and pyroclastic deposits associated with them—a field—of vents and flows, sometimes numbering in the hundreds or thousands
monogenetic volcanic field
What is the name of the mineral that is a naturally formed volcanic glass?
obsidian
what are the eight common igneous rock-forming minerals in Bowen's reaction series:
orthoclase, quartz, plagioclase, muscovite, biotite, amphibole, pyroxene, and olivine
Occurs when some minerals melt while others remain solid.
partial melting
When two plates diverge and a spreading center is formed, hot rock from the asthenosphere flows up to fill the voids in the fractured lithosphere. At the beginning of this process, the mantle rock is solid and ultramafic. At this point what is the mantle rock probably composed of?
peridotite
minerals large enough to see with naked eye
phaneritic (e.g., granite)
explosions caused by rapid expansion of steam when magma comes in contact with groundwater
phreatomagmatic eruption
igneous rock that has solidified beneath the earth's surface
plutonic or intrusive
fused, glassy volcanic rock fragments and ash from explosive volcanic eruption
pyroclasitc or fragmental (e.g., tuff)
a high-speed avalanche of hot ash, rock fragments, and gas that can reach temperatures of up to 800°C and move at speeds of up to 200 to 250 kilometers/hour
pyroclastic flows
What volcano type is characterized by a low relief system of collapsed calderas and many small vents?
rhyolite caldera complex
What is the most explosive volcano type on Earth?
rhyolite caldera complexes
what are the seven most common igneous rocks:
rhyolite, granite, andesite, diorite, basalt, gabbro, and peridotite
Mauna Loa in Hawaii is an example of what kind of volcano?
shield volcano
What kind of volcano is andesite an important and frequent component of?
stratovolcano
Which type of volcano accounts for the great majority of Earth's volcanic and island arcs?
stratovolcanoes
Which type of volcano accounts for the largest proportion of Earth's individual volcanoes?
stratovolcanoes
Andesite is formed at: Basalt is formed at: Gabbro is formed at:
subduction zones hotspots spreading centers
_______ come out of volcanoes and are responsible for damage to Earth's ozone layer because they forms new molecules with ozone gas.
sulfur aerosols
airborne pyroclasts
tephra
What was the largest basalt eruption in recorded history?
the Laki fissure zone in 1783
When did N.L. Bowen and his colleagues develop Bowen's reaction series?
the early 1900's
Basalt eruptions are typically fissure eruptions.
true
solidified pyroclastic debris that has accumulated on the ground
tuff
Igneous rock composed mainly of iron and magnesium-rich minerals
ultramafic
The order of mineral crystallization in a cooling magma body of average composition is typically:
ultramafic, mafic, intermediate, felsic
Opening in the crust through which lava flows
vent
many holes or pits in rock surface caused by escaping gas
vesicular (e.g., vesicular basalt)
any landform that releases lava, gas, or ashes, or has done so in the past.
volcano
What is the official title of scientists who study volcanoes.
volcanologists
What often fills maars over time?
water
a solidified bed of ash and lapilli that's welded into a mass of glass shards
welded tuff
a rock fragment that is enclosed within melted magma.
xenolith
