Geology test 2

Created by clricha3 

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Which of the following best describes the bedrock in the Sierra Nevada Mountains in California? *

granite; batholiths

_______ is a major dissolved volatile constituent in both magmas and volcanic gases. *


The ______ ocean basin is rimmed by the most subduction zones. *


A ________ is an intrusive, igneous rock body that is tabular and concordant. *


_______ are usually the most abundant gases emitted during the basaltic volcanism. *

water and carbon dioxide

______ large, fairly steep-sided cones composed of lavas and pyroclastic layers *


_____ small basaltic cones built during one, short, eruptive episode *

cinder cones

_______ the big volcanoes of Hawaii *

shield volcanoes

Which statement during the May 1890 eruption of Mt. St. Helens is false? *

during the eruptive period the mountain peak was substantially built up by new lava flows

_____ tend to increase the explosive potential of a magma body beneath a volcano *

high viscosity and dissolved gas

What type of basaltic lava flow has a fairly smooth, unfragmented, ropy surface? *


______ destroyed the city of St. Pierre, Martinique in 1902 *

a nuee ardent

Which kind of eruptive activity is most likely to be highly explosive *

eruptions of big, continental margin, composite cones, or stratovolcanoes

Which kind of volcanism is typical of mid-oceanic ridge systems? *

submarine; basaltic lava flows

_____ magma is the most abundant type of magma erupted at oceanic spreading centers. *


Which of the following best describes the big Hawaiian volcanoes? *

are situated in the interior of the Pacific Plate above a hot spot deep in the mantle

Why do magmas rise toward the Earth's surface? *

magmas contain dissolved fluids such as water; most are less dense than the adjacent solid rock

_____ massive, gently sloping volcanoes built of successive, basaltic lava flows *

shield volcanoes

Why would a plume of solid silicate rock rising slowly from deep in the mantle begin melting as it neared the base of the lithosphere? *

temperatures remain high as lowered pressures decrease melting temperatures

Ash and lapilli are different sized pyroclastic particles *


The viscosities of magmas increase with increasing percentages of silica *


A ______ is a tabular, discordant igneous rock body. *


What two factors speed up rates of chemical reaction and weathering in rocks and soils? *

warm temperatures; very moist

The red, brown, and yellow soil-coloring minerals found is soils of Mississippi, Alabama and Georgia originated by what process? *

precipitation of iron oxides during the chemical weathering process

Which of the following best describes the "Dust Bowl" *

areas of severe wind erosion on the Great Plains, 1930's

Which one of the following is an important, mechanical weathering process for enlarging fractures and extending them deeper into large boulders and bedrock? *

frost wedging

Which of the following best describes sets of fractures in relatively fresh bedrock, such as granite, that are roughly parallel to the land surface and can resemble a Blooming Onion? *

sheeting (exfoliation) fractures

Which of the following statements concerning mechanical weathering is not true? *

involves a major change in the mineral composition of the weathered material

Which of the statements best describes erosion process? *

the process by which weathered rock and mineral particles are removed from one area and transported elsewhere

Which term best describes those processes that move weathered rock materials and soils downslope? *

mass wasting

Assume that water filling a crack in a rock undergoes cycles of freezing and melting. Which of the following statements is true? *

water expands as it freezes, causing the crack walls to be pushed apart

In which area would weathering by frost wedging probably be most effective? *

in moist; temperate climates

Abundant moisture and warm temperatures result in high rates of chemical weathering *


Sheeting is mainly a process of mechanical weathering *


Quartz is quite resistant to weathering and is an important component of sands in riverbeds and on beaches


Feldspars commonly decompose during weathering to clay minerals, silica, and soluble constituents *


Like most liquids, water decreases in volume when it freezes *


_____ weathering involves only a reduction in the sizes of bedrock, regolith, and mineral particles? *


In 1980, ______ was the first Cascade Range volcano to erupt since Mt. Lassen, California. *

Mt. St. Helens

Which type of basaltic lava flow has its surface covered with sharp-edged, angular blocks and rubble? *


What portion of an angular, fracture-bounded granitic block shows the highest rate of weathering?

the edges and corners

Most magmas are dominantly molten rock (a liquid called "melt"). What are the other two, smaller percentage components of most magmas?

solid and gas

Extrusive igneous rocks are _________, whereas intrusive igneous rocks are _________.

considered "volcanic" rocks because they form from lava extruded at the surface; considered "plutonic" rocks because they form from magma beneath the surface

Which type of magma is most likely to quench into a natural glass?

highly fluid, cools quickly

Crystallization of magma occurs when ________.

the magma cools causing ions to come closer together, the first ions being Si and O to form Si-O tetrahedra

Rocks that solidify from lava flows are typically finer grained than those that crystallize intrusively. Why?

The extrusive magma cools quickly so the mineral grains do not have time to grow any larger.

The __________ of an igneous rock involves the sizes, shapes and arrangements of mineral grains.


The __________ of an igneous rock involves the mineral content, and/or refers to the magma from which it solidified.


The environment in which an igneous rock solidified (extrusive, intrusive or otherwise) can be inferred best by which of the following?

the rock's texture

The most important factor affecting the texture of an igneous rock is ________.

rate of cooling

Which of the following best describes an aphanitic texture?

the rock is crystalline, but mineral grains are too small to be seen with the unaided eye.

Volcanic glass and coarse-grained igneous rocks differ by which of the following?

The glass is formed mostly when lava cools in contact with water whereas phaneritic rocks cool deep beneath the surface.

In a porphyritic texture, what is represented by the rock's "groundmass"?

the lava after it erupted from a crystallizing magma chamber

Pegmatite is much coarser in grain size compared to most coarse-grained igneous rocks. What is a likely reason for this phaneritic texture?

The magma was rich in volatiles (like water) which aided in fast crystallization of large, but few numbers of crystals.

Which of the following is the likely cause of a vesicular texture?

Each vesicle was filled by a gas bubble when the lava was still mainly liquid.

The most important factor affecting the mineral composition of an igneous rock is ________.

chemical composition of the magma or lava

Which are definitions of "mafic" and "felsic"?

Mafic is a magma/rock that is rich in Fe and Mg, whereas felsic refers to that which is rich in feldspar and silica (quartz)

What type of composition would result in a magma if equal amounts of basaltic and granitic magma were mixed?


What type of composition would result in a magma if basaltic and granitic composition magma were mixed completely at a 1 to 3 ratio?


What composition magma is beneath the Mt. St. Helens volcano, and why?

felsic - very sticky magma makes for explosive eruptions

Which one of the following rock types contains the greatest amount of quartz?


Which of the following rocks is likely to have the most quartz within it and why?

intrusive rock that formed from cooling of relatively high silica magma

__________ composition lava is erupted at ocean ridges, whereas ____________ composition lava is erupted on continents.

basaltic, rhyolitic

Which of the following is characteristic of pegmatites?

consist of very coarse grained crystals of potassium feldspar, muscovite and quartz

Which one of the following rocks is the primary constituent of the upper layers of the oceanic crust?


According to Bowen's reaction series for cooling magma (above), which mineral(s) is/are likely to form a phenocryst in porphyritic basalt?

both olivine and pyroxene

According to Bowen's reaction series, which is the proper sequence of ferromagnesian silicate minerals crystallizing from a cooling magma?

Olivine - pyroxene - amphibole - biotite

According to Bowen's reaction series, which of the following minerals has the highest crystallization temperature?


Which one of the following rock types is most likely to contain calcium-rich feldspar?


On a global basis, most of the world's magma is generated in which part of the Earth?

the upper mantle

What is "magmatic differentiation"?

The process by which the same magma may produce different composition igneous rocks.

A single magma may generate several mineralogically different igneous rocks.


Magma is _________.

completely or partially molten material, which on cooling solidifies to form an igneous rock

What is meant by "extrusive" and "intrusive"?

Igneous rocks that cooled at the surface (volcanic) and interior to the surface (plutonic) of the Earth, respectively.

What is the most common extrusive igneous rock?


A slowly cooled magma will most likely result in a rock with which one of the following textures?


Intrusive igneous rocks differ from extrusive rocks primarily in their...**

crystal sizes

A _____ texture refers to rocks composed mainly of mineral and volcanic fragments. **


Technically, the process where by ions arrange themselves into orderly patterns during the cooling of a liquid is called **


Igneous rocks are named on the basis of what two characteristics? **

texture and mineral composition

Detrital sedimentary rocks have clastic textures **


Some limestones are of biochemical origin **


Graded bedding maybe identified in sediment as... **

layers with coarser sediments on the bottom and finer sediments at the top

What is the most common, chemical, sedimentary rock? **


What is the general name for microcrystalline quartz in sedimentary rocks? **


Chalk, coquina, and ancient coral reefs are primarily composed of microcrystalline quartz? **


Boulder conglomerates suggest deposition by strong winds in a desert **


Detrital sedimentary rocks are classified according to clastic particle size; chemical sedimentary rocks are named according to the most abundant minerals. **


_____ is composed mainly of lithified, organic debris that accumulated in ancient, heavily forested swamps? **


Clastic particles in a sedimentary breccia are rounded and are about the same size as fine-grained sand **


The chemical sedimentary rock, conglomerate, is composed of gravel-size, rounded, calcite oolites **


The most abundant mineral in detrital sediment rocks? **


Ferromagnesian minerals (like olivine and pyroxene) that crystalize at high temperatures in Bowen's reaction series are generally much less susceptible to chemical weathering than quartz **


What term describes the layer of partly decayed plant matter at the top of the soil profile in most forested areas? **


Like most other liquids, water decreases in volume when it freezes. **


Half dome in Yosemite National Park, California, and stone mountain in Georgia, are shaped mainly by what mechanical weathering process? **


Calcite, a major component of some monumental and building stones slowly dissolves in weakly acidic waters. **


Chemical weathering in bedrock below the land surface often begins along joints and sheeting fractures. **


Feldspars commonly decompose during weathering to clay minerals silica and soluble constituents **


Which form of chemical weathering specifically affects the iron contained in ferromagnesian rock-forming, silicate minerals? **


Quartz is quite resistant to weathering and is an important component of sands in riverbeds and on beaches. **


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