Geology chapter 4
What mafic volcanic rock is formed at seafloor spreading ridges?
Basalt
Magmas that contain 45 to 50% silica are called
mafic
Landslides may lead to volcanic eruptions when ______.
the removal of material allows gases to escape
Which of the following describe mafic magma?
Contains 45 to 50% silica Has a relatively high amount of iron and magnesium
What will a decrease in pressure do to a rock that is already nearly hot enough to melt?
It will cause the rock to start melting.
Which of the following describe stratovolcanoes?
They are also known as composite volcanoes. They are known to erupt explosively. They are made up of both pyroclastic and lava flow layers
Which of the following describe the volcanoes of the Cascade Range?
They are composite volcanoes. They are created through the process of subduction.
Which of the following describe lahars?
They are made of ash and water. They move quickly.
How did the residents of Heimaey in Iceland deter erupting lava from closing off their harbor?
They pumped seawater on it to cool and harden it.
Melting of the asthenosphere can occur due to a(n)
drop, decrease, lowering, or reduction
The ______ associated with active volcanic activity are often inconvenient for the nearby residents and business owners, as it can be difficult to predict how long the activity will last.
evacuation
The viscosity of magma is its resistance to flow and is controlled by the silica content. Which is more viscous: mafic or felsic magma?
felsic
Eruptions of lava from cracks in the earth's surface, as opposed to from single vents, are called
fissure
Carbon monoxide, carbon dioxide, fluorine, sulfur compounds, and water vapor are all
gases
While lava usually is not life threatening, it is
hot
scientists are still uncertain the reason for
hot spots
How will a large amount of volcanic ash and dust from a single large eruption affect global climate?
it will cause regional or global cooling for months up to a few years.
A rare success story in diverting a lava flow occurred in the early 1970s, when residents on the island of Heimaey in Iceland pumped ocean water to cool the lava in order to ______.
keep their fishing harbor open
A fast-moving volcanic mudflow created through the combination of ash and water is called a
lahar
The asthenosphere is described as being ultramafic, meaning that it is very rich in ferromagnesian minerals. When it melts, it usually forms ______ magma.
mafic
The partial melting of the ultramafic mantle creates magma that is
mafic
Explanations for hot spots include that they lie above regions in the mantle or in the outer core that are hotter due to a higher percentage of ______.
radioactive materials
Magma that is rich in silica is called ______.
felsic
How many of the world's 300 to 500 active volcanoes are actively monitored?
some of tthem
The volcanoes of the Aleutian Islands are ______ volcanoes that are ______ in composition.
strato-; andesitic
What type of volcano is composed of both pyroclastic and lava flow layers?
stratovolcano
Most magma originates in the upper mantle because the ______ is high enough and the ______ low enough to at least partially melt the rock there.
temperature; pressure
earthquakes, harmonic tremors, and changes in topography and gas emission
activity
Most of the world's active volcanoes are located ______.
along plate boundaries
What type of pyroclastic material causes the following problems: it can bury cities, it is slippery, it can cause roofs to collapse, it is bad for people's lungs, and it is damaging to engines and other mechanical equipment?
ash
Formed by either the collapse of a volcano into an emptied magma chamber or the enlargement of an existing crater, a ______ represents a very large volcanic eruption.
caldera
A very large volcanic crater is known as a(n
caldera
Magma composition is controlled by the type of
rock
Most magma originates in the ______.
upper mantle
Evacuations necessitated by impending volcanic eruptions have saved significant numbers of lives, yet they can be seen as inconvenient and disruptive because ______.
volcanoes don't always erupt in the time and fashion they are expected to
Choose all of the statements that correctly describe the relationship between plate setting, magma behavior, and hazards.
Each plate setting creates magma of a certain composition. The composition of the magma controls how the magma erupts. The way a magma erupts determines the type of hazards associated with it.
How is magma behavior related to plate setting and volcanic hazards?
Each tectonic setting produces a distinct type of magma which erupts in a way directed by its composition.
How is volcanic activity associated with landslides
Earthquakes associated with moving magma may cause landslides. Steep and/or coastal volcanoes may have materials that are weakened and fail suddenly. Landslides may allow volcanic gases to escape.
How does volcanic ash and dust cause cooling of the climate?
It blocks sunlight from reaching earth.
Choose all of the hazards associated with volcanic ash.
It causes mechanical failures. It can bury entire cities. It is dangerous to breathe since it is composed of microscopic glass.
Which of the following best describes the eruptive history of the Yellowstone caldera?
It has had three major explosive eruptions in recent geologic history.
Which of the following describe a pyroclastic flow?
It is a very dangerous volcanic hazard. It is also known as a nuée ardente.
What is the composition of the magma and rocks formed at seafloor spreading ridges?
Mafic
Many of the world's active volcanoes are located along the rim of the ______.
Pacific Ocean
What volcanic hazard is associated with the eruption of Krakatoa in 1883? This event is famous for blowing the island apart, creating a tsunami, and allegedly creating the loudest noise ever heard.
Phreatic explosion
Where does the majority of volcanic activity occur?
Seafloor spreading ridges
Which of the following commonly precede a volcanic eruption?
Seismic activity Changes in the volcano's shape Changes in gas emissions
what are the two primary controls on magma composition?
The extent of melting The parent material
Which of these volcanoes in the Cascades is the most recently active?
St. Helen
Of all the gases listed below that are emitted by volcanoes, which is the primary?
Water vapor
Fissure eruptions occur ______ and can result in massive outpourings of basalt.
on continents or on the seafloor
Water that is heated because it is near magma may cause a volcanic eruption called a(n
phreatic
explosion of Krakatoa in 1883 was so forceful that it blew the island apart.
phreatic
The largest on earth, __________ volcanoes are created from hundreds to thousands of runny basalt flows.
shield
What type of volcano is produced from fluid basalt flows that create a large, broad, gently sloping structure?
shield
Seafloor spreading ridges are the most volcanically active areas on earth's surface because ______.
they are so widespread
Lava is typically ______ or hotter.
850
What is the primary hazard of concern associated with the stratovolcanoes in the Aleutians?
Ash causing aviation hazards
When a volcano erupts due to the creation of large amount of steam, it is called a ______.
phreatic explosion
The entire town of St. Pierre, save for one person, died in a(n)
pyroclastic
What volcanic hazard killed nearly every person in the town of St. Pierre on the island of Martinique when Mont Pelée erupted in 1902?
pyroclastic