Igneous Rocks and Volcanoes
How much material was removed from the volcano?
2.8 cubic kilometers of a rock.
What is the range of shield volcano height?
300 to 10,000 meters.
What is the range of dome complex height?
500 to 2,000 meters.
What is the difference between a dike and a sill?
A dike intrudes across sedimentary layers, and a sill intrudes between sedimentary layers.
What is required to generate an igneous rock with a fine-grained texture?
A fine-grained texture is the product of rapid cooling and crystallization of lava.
Which of the following objects has a size similar to that of a lapilli?
A marble (15 mm).
Which of these most directly triggered the main eruption?
A massive landslide.
In addition to viscosity, which of the following parameters has an influence on whether a volcanic eruption will be effusive or violent?
Amount of gas in the magma.
What are composite volcanoes made of?
Basalt flows, pyroclastic deposits.
What are shield volcanoes generally made of?
Basalt flows.
Which of the following types of lava will most likely lead to a volcanic eruption of an effusive nature?
Basaltic.
What is a magma chamber called after the conduit has solidified and been exposed by erosion?
Batholith.
Which of the following terms is best described as a massive pluton/
Batholith.
Batholiths are known to form the cores of mountain ranges such as the Sierra Nevada. What is the implication of this observation?
Because batholiths form deep within Earth, the occurrence of one at the surface implies that it has since been uplifted and/or the rocks above have been removed.
What type of volcano is Mount St. Helen?
Composite.
What is the term for a tabular igneous pluton that occurs in an orientation that is discordant with the bedding surfaces of adjacent sedimentary rocks?
Dike.
What type of magma erupts out of dome complexes?
Felsic magma.
While working in the field, you find a dike cutting across some sedimentary rocks. What grain size would you expect to find in this pluton?
Fine-grained.
How are igneous rocks formed?
Formed by the cooling and crystallization of molten rock.
You have found a mafic rock with a phaneritic texture. What is a potential rock name?
Gabbro
Igneous rocks of felsic composition have _________ and _________ relative to mafic igneous rocks.
Greater silica; lower melting temperature.
Which of the following environments would produce igneous rocks?
Hot spots, divergent boundaries, and convergent boundaries.
Intrusive and extrusive igneous rocks are classified based on what character?
How quickly the molten rock cools and crystallizes, and where this occurs with respect to Earth's surface.
If previous eruptions has left Mount St. Helen with a different shape, what differences might have influenced the timing of the eruption?
If the northern slopes has been less steep initially (same height). The eruption would likely have happened later. If the volcano had been significantly shorter initially (same steepness), the eruption would likely have happened sooner.
A phaneritic texture is characteristic of a(n) ________________ igneous rock that cooled _________.
Intrusive; below the surface.
What is one way a glassy texture forms?
Lava cools rapidly.
Which of the following volcanic materials flows out of a volcanic vent?
Lava.
Which of the following is true about mafic igneous rocks?
Mafic igneous rocks are rich in Fe, Mg, and Ca.
What lies underneath volcanic features at Earth's surface?
Magma chambers and volcanic conduits.
Volcanic ash is best described as which of the following?
Microscopic pieces of rock ejected by a volcano.
In general, how often do most cinder cones erupt?
Most cinder cones erupt once.
Why did this last earthquake trigger a massive landslide?
Moving magma had over-steepened the mountain slopes.
Name two minerals that are unlikely to coexist in the same igneous rock.
Muscovite and pyroxene.
Which of the following textures describes an igneous rock with anomalously large crystals?
Pegmatitic.
Which of the following textures indicates two stages of cooling and crystallization?
Porphyritic.
Cinder cones are made of _________.
Pyroclastic deposits.
What minerals make up rhyolite?
Quartz, K-feldspar, and plagioclase feldspars, with relatively fewer biotite and amphiboles.
A hot spot that occurs in oceanic crust is likely to produce which of the following types of eruptions?
Quiet and effusive.
Which of the following types of magma has the highest viscosity?
Rhyolitic.
What information do geologists use to classify volcanoes?
Shape and type of deposits.
What type of volcanoes are the highest?
Shield volcanoes.
Which of the following are types of volcanoes?
Shield, Cinder, and Composite volcano.
What is the term for a tabular igneous pluton that occurs in an orientation that is concordant with the bedding surfaces of adjacent sedimentary rocks?
Sill.
What does it mean if an igneous rock has an aphanitic texture?
The igneous rock exhibits mineral crystals too small to see with the naked eye.
Why are shield volcanoes wider than composite volcanoes?
The lava that flows out of shield volcanoes is more fluid than the lava that flows out of composite volcanoes.
What does an igneous rock with a pyroclastic texture tell a geologist?
The rock was likely formed by a violent volcanic eruption.
Which igneous composition contains mostly olivine crystals with minor amounts of pyroxene?
Ultramafic.
Which of the following describes a texture containing bubble-shaped cavities?
Vesicular.
The subduction of oceanic crust under continental crust predominantly produces which of the following types of volcanic eruption?
Violent and explosive.
What is a volcanic conduit called after the conduit has solidified and been exposed by erosion?
Volcanic neck.
Why are volcanic rocks often exposed at Earth's surface as hills, ridges, and mountains surrounded by areas of lower elevation?
Volcanic rocks are often more resistant to erosion than surrounding rock.
Igneous rocks are mainly composed of ________ minerals.
silicate.
