Natural Disasters Exam 2-Chapter 6 Volcanic Eruptions

T/F Most volcanism is associated with hot spots

False

T/F No magmas contain dissolved gasses

False

T/F Scoria cones form from repeated eruptions over the course of many decades

False

T/F The Volcanic Explosively Index (VEI) ranges from 1 to 100

False

T/F The higher the viscosity of magma, the more fluid is its behavior

False

A mantle hot spot has generated a long-lived plume beneath Yellowstone National Parkm and the North American continent is moving ______________ above it about 2 to 4 cm/yr.

Southwestward

_____________ are steep-sided, symmetrical volcanic peaks built of alternating layers of pyroclastic debris capped by high-viscosity andesitic to

Stratovolcanoes

Pyroclastic debris is ___________

a. chucks of magma and rocks blown into the air by gas in a volcanic eruption

A caldera collapse occurs ___________.

after the magma chamber is mostly empty

__________ melting occurs when a rock melts due to a lowering of pressure

E. Decompression

Over ________________ of volcanism is associated with edges of tectonic plates.

A. 90%

The most peaceful eruptions are ___________ eruptions.

A. Icelandic type

As minerals form in magma kept at a constant temperature, what happens to the viscosity of that magma?

A. It increases

Crater Lake, Oregon, fills the caldera of ____________ which collapsed about 7,600 years ago

A. Mt. Mazama

The most famous of all volcanoes probably is Vesuvius, and the most famous of its eruptions are those of 79 which buried the cities of ___________.

A. Pompeii and Herculaneum

Spreading centers have relatively peaceful eruptions of magma because the __________________.

A. Si02 poor magma is at high temperatures

In magma, _______________ is the most abundant dissolved gas.

A. Water vapor (H2O)

Slow flowing, more viscous basaltic lava commonly has a rough, blocky texture called ____________.

A. aa

What erupts in a geyser?

A. superheated water and steam

What is the cause of volcanism at Italy;s Vesuvius, Stromboli, Vulcano and Etna?

A. the subduction of Meduterranean seafloor beneath Europe

A shield volcano has a great ________________.

B,. Width compared to its height

Over ___________ of Earth's magma extruded through volcanism takes place at the oceanic spreading centers.

B. 90%

Which of following correctly lists the order in which the listed minerals form in a cooling magma from the first to the last to form?

B. Olivine, pyroxene, amphibole, biotite mica, and quartz

A well-informed conical volcano located above an active subduction zone that has not erupted in 12,000 years is _________________.

C. Dormant, but will likely erupt again at some point

Most rifting occurs at the spreading centers _________.

C. Located below sea level

__________________ eruptions are the most violent types of explosive eruptions

C. Plinian-type

Silicon and oxygen link up to form the silicon-oxygen

C. Tetrahedron

Hawaiian volcanoes unlikely to erupt include _____________.

D. Diamond Head Oahu

The number of active "hot spots" on Earth over the last 10 million years active is _____________.

D. More than 100

If basaltic lava reaches the sea or a lake, it cools rapidly into _________ lava.

D. pillow

T/F Although there are 92 naturally occurring elements, a mere eight make up more than 98 perfect of Earth's crust

True

T/F Basaltic magma has the lowest viscosity, so more of it reaches the surface.

True

T/F Decreasing the pressure on hot rock generates most magma

True

T/F Hot spots can be under the oceans, under the continents, in the center of plates, and at spreading centers

True

T/F If lava reaches the sea or a lake it cools rapidly into ellipsoidal masses called pillow lava

True

T/F If two magmas have the same composition, the hotter of the two magmas will have a lower viscosity

True

T/F Oxygen and silicon are so abundant in Earth's crust that their percentages dwarf those of all other elements

True

T/F The largest number of hot spots lies beneath Africa

True

T/F The most abundant dissolved gas in magmas is H2O

True

T/F The process of mineral formation in a cooling magma is called crystallization

True

T/F When it comes to volcanic hazards, the key problem is how easily the dissolved gases can escape from the magma

True

____________ eruptions are common first phased in the eruptions of volcanoes as they "clear their throats" before emitting larger eruptions

c. Vulcanian-type

The viscosity of magma is lowered by _____________.

d. All of these choices are correct

Rock may melt by ___________.

d. All of these choices are correct. a. Lowering the pressure on it B. raising its temperature c. increasing its water content

The presence of water __________ the melting point of rock.

B. lowers

The 3 V's of volcanology are ____________.

B. viscosity, volatiles, and volume

The formation of a giant continental caldera includes all but which of the following?

Basaltic eruptions begin forming circular fracutures surrounding the bulge.

T/F Antartica does not lie above any hot spots

False

T/F At oceanic spreading centers, magmas are rhyolitic in composition

False

T/F Hawaiian volcanoes produce andesitic lava

False

T/F Hot spots occur only under oceanic plates

False

T/F If the magma cools and solidifies below the surface, it crystallizes as volcanic rocks.

False

T/F Less than 20 percent of Earth's magma extruded through volcanism occurs at oceanic spreading centers.

False