Geology Exam 1.1
What factors affect the melting of rocks?
1. Pressure 2. Volatiles 3. Heat
Which rock needs a microscope to see individual mineral grains?
Aphanitic
________ magma is the most abundant type of erupted at oceanic spreading centers.
Basaltic
the volcanoes of southwestern alaska and the aleutian islands
Composite/Stratovolcano
Which kind of eruptive activity is most likely to be highly explosive?
Eruptions of big, continental margin, composite cones or stratovolcanoes.
Bowen's reaction series predicts the sizes of the different mineral grains that grow from crystallizing magmas.
False
The last minerals to crystallize on Bowen's Reaction Series result in
Felsic
________ tend to increase the explosive potential of a magma body beneath a volcano.
High viscosity and dissolved gas
Why do magmas rise toward Earth's surface?
Magmas are mainly liquid and contain dissolved fluids such as water; most are less dense than the adjacent solid rock.
In a porphyritic rock, which mineral grains are the last to crystallize?
Matrix or groundmass
In 1980, ________ was the first Cascade Range volcano to erupt since Mt. Lassen, California, in 1915-16.
Mt. St. Helens
what mineral crystallizes first?
Olivine
The ________ ocean basin is rimmed by the most subduction zones.
Pacific
Which type of basaltic lava flow has a fairly smooth, unfragmented, ropy surface?
Pahoehoe
What is characterized by very coarse mineral grains?
Pegmatite
What are mineral grans that are of equal size and coarse enough to be seen w/out a microscope?
Phaneritic
What texture represents a single, long period of cooling and crsytallization?
Phaneritic
What rock has two or more, distinctly different sized populations of mineral grains?
Porphyritic
What volcanic rock is extremely vesicular?
Pumice
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.
Why are lava flows typically finer grained than intrusive igneous rocks?
The extrusive magma cools quickly so the mineral grains do not have time to grow
What is a good description of an aphanitic texture?
The rock is crystalline; mineral grains are too small to be visible without a magnifying lens or microscope
The Icelandic volcanoes are related to plate tectonics because ________.
They lie on a spreading center where two plates are moving apart
Basalt is the aphanitic or fine-grained equivalent of gabbro.
True
Glassy igneous rocks form when magma cools too fast for mineral grains to grow.
True
In an igneous rock with a phaneritic texture, the mineral grains are visible to the unaided eye
True
Olivine is an important mineral in peridotites and other ultramafic rocks
True
The viscosities of magmas increase with increasing percentages of silica.
True
________ is a major dissolved volatile constituent in both magmas and volcanic gases?
Water
Which type of basaltic lava flow has its surface covered with sharp-edged, angular blocks and rubble?
aa
Mount St. Helens is ________.
an explosive stratovolcano
Which of the following statements best describes the big Hawaiian volcanoes?
are situated in the interior of a large, pacific plate above a hot spot deep in. the mantle
Volcanic bombs originate ________.
as erupted magma blobs that partly congeal before falling to the ground
A ________ is the largest, perpendicular body of intrusive, igneous rock.
batholith
small basaltic cones built during one, short, eruptive episode
cinder cones
large, fairly steep-sided cones composed of lavas and pyroclastic layers
composite/stratovolcano
Basaltic lavas are generally hotter and more viscous than andesite lavas
false
In general, cinder cones are much larger than shield volcanoes.
false
The eruptions of the Hawaiian volcanoes may be described as explosive in comparision to the 1980 Mount St. Helens eruption
false
The recent (geologically) volcanic activity in Yellowstone National Park is ________.
related to intraplate, hot spot volcanism
Which one of the following best describes volcanism in the Cascade Range, northwestern United States?
related to plate subduction
Which one of the following shows the correct order (left to right) of decreasing magma viscosity?
rhyolite, andesite, basalt
A ________ volcano is a very large, gently sloping mound composed mainly of basaltic lava flows.
shield
massive, gently sloping volcanoes built of successive, basaltic lava flows
shield volcanoes
the big volcanoes of Hawaii
shield volcanoes
Which region has the greatest concentration of currently active volcanoes?
the circum-pacific area
Which of the following best describes Shiprock, a famous volcanic feature in New Mexico?
the eroded remains of a volcanic neck and radiating dikes
Which of the following is associated with deep mantle hot spots?
the volcanoes of Hawaii and the Quaternary activity in Yellowstone National Park
Basalt is the most common magma erupted along oceanic rift systems.
true
A ________ is a near surface, intrusive, igneous rock body that results from melt pooling between horizontal layers.
volcanic neck
