Chapter 6 Exam (Volcanic Eruptions:Plate Tectonics And Magma)

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

Over _________ of volcanism is associated with the edges of tectonic plates.

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

Spreading centers are an ideal location for volcanism because ______________.

Silicon and oxygen link up to form the silicon-oxygen ______________.

The typical trend in a rising plume of subduction-zone magma is to increase the ____________.

The viscosity of magma is lowered by __________.

In magma, __________ is the most abundant dissolved gas.

Rock may melt by _______________.

The presence of water ________ the melting point of rock.

Mineral growth in magmas at the surface with temperatures around 1,000 to 1,200°C occurs in the following way

Why does the magma from some volcanoes flow smoothly and relatively peacefully, while the magma from other volcanoes blasts forth violently and deals death over wide areas?

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

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

What erupts in a geyser?

The volcanic explosivity index (VEI) measures size of volcanic eruptions on a scale of 0 to 8. Between 1500 and 1980, one VEI 7 eruption occurred. This was ______________.

The three 'Vs' of volcanology are __________________.

A shield volcano has a great ___________.

Hawaiian volcanoes unlikely to erupt include _________________.

The most peaceful eruptions are __________ eruptions.

On 20 February 1943, a new volcano named __________, a scoria cone, was born when an eruption rose up through a farm field near a village in Mexico.

__________ are steep-sided, symmetrical volcanic peaks built of alternating layers of pyroclastic debris capped by high-viscosity andesitic to rhyolitic lava flows that solidify to form protective caps.

Some of Earth's most beautiful mountains are ________, including Mt. Kilimanjaro in Tanzania, Mt. Shasta in California, Mt. Rainier in Washington, and Mt. Fuji in Japan.

_________ eruptions are common first phases in the eruptions of volcanoes as they "clear their throats" before emitting larger eruptions.

__________ eruptions are the most violent types of explosive eruptions.

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

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

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

A caldera collapse occurs ________________.

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

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

This volcano erupted in 1883 in the Sunda Strait between Sumatra and Java, exploding with a loudness heard 3,000 miles away, then collapsing into its magma chamber, making a caldera and setting off a tsunami that killed at least 36,000 people.

____________ in the Aegean Sea underwent an explosive series of eruptions around 1628 bce that buried the Bronze Age city of Akrotiri on Thera to depths of 70 meters.

Most rifting occurs at spreading centers __________.

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

If all of the following rocks were to completely melt and reach the same final temperature, which would produce magma with highest viscosity?

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

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?

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

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

Pyroclastic debris is __________.

Water circulating at thousands of feet below the surface can be heated to temperatures far above 100°C (212°F) without boiling because the pressure of the overlying groundwater body is so great.

Decreasing the pressure on hot rock generates most magma.

Magma at great depth does not contain gas bubbles because the high pressure at depth keeps gas dissolved in solution.

Gas bubbles decrease in number and volume as magma keeps rising upward to lower pressures, helping to propel magma upward through fractures or pipes toward an eruption.

Although there are 92 naturally occurring elements, a mere eight make up more than 98 percent of Earth's crust.

Oxygen and silicon are so abundant in Earth's crust that their percentages dwarf those of all other elements.

The process of mineral formation in a cooling magma is called crystallization.

While there are many hundreds of different minerals, the overwhelming majority of Earth's crust is composed of just eight common rock-forming minerals.

No magmas contain dissolved gases.

The higher the viscosity of magma, the more fluid is its behavior.

The highest temperatures and highest SiO2 contents are in basaltic magma, giving it the lowest viscosity and easiest fluid flow.

The lowest temperatures and highest SiO2 contents occur in rhyolitic magma, material so viscous that it commonly does not flow.

Most volcanism is associated with hot spots.

About 80 percent of the magma reaching Earth's surface is basaltic, with only about 10 percent andesitic and 10 percent rhyolitic.

Less than 20 percent of Earth's magma extruded through volcanism occurs at oceanic spreading centers.

Basaltic magma has the lowest viscosity, so more of it reaches the surface; the more viscous rhyolitic magmas are so sluggish that they tend to be trapped deep below the surface where they cool, solidify, and grow into the larger mineral crystals of plutonic rocks.

At oceanic spreading centers, magmas are rhyolitic in composition.

Below the ocean basins, basaltic magmas have low contents of SiO2, low temperature, low viscosity, and allow easy escape of gases, producing peaceful eruptions.

Beneath continents, rising basaltic magmas are contaminated by sediments and continental-crust rocks, altering magma compositions; the resultant andesitic-to-rhyolitic magmas have high contents of SiO2, relatively low temperatures, and high viscosity.

The primary reason magma forms at subduction zones is that the subducting plate carries a cover of sediments, water, and hydrated minerals down with it, which lowers the temperature required for the adjacent overlying mantle lithospheric rock to melt.

The variations in the composition of magmas govern whether eruptions are peaceful or explosive.

Magma rising in a subduction zone tends to get more "contaminated" with high-silica minerals than does magma rising in a spreading ridge.

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

If the magma reaches the surface, it forms volcanic rocks, named for Vulcan, the Roman god of fire.

Highly fluid basaltic lava may cool with a smooth, ropy surface called pahoehoe, whereas lower temperature, slower flowing, more viscous basaltic lava commonly has a rough, blocky texture called.

Airborne pyroclasts have their finest grains settle down from the atmosphere first, closest to the volcano, followed by progressively coarser material at greater distances away.

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

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

At a depth of 32 km, basaltic rock melts at around 1,400°C but this same rock will melt at only 1,250°C at Earth's surface.

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

Antarctica does not lie above any hot spots.

The largest number of hot spots lies beneath Africa.

The three most recent catastrophic Yellowstone eruptions occurred at 2.06 million, 1.29 million, and 640,000 years ago.

The Volcanic Explosivity Index (VEI) ranges from 1 to 100.

If two magmas have the same composition, the hotter of the two magmas will have a lower viscosity.

When gas escapes quickly and violently from lava it may produce a frothy glass full of holes left by former gas bubbles; this porous material, known as pumice, contains so many holes it can float on water.

Because volcanologists are aware of the potential hazards, no volcanologist has ever been killed studying a volcano.

Transform faults have lots of associated volcanism because the strike-slip motions keep a "lid" on the hot asthenosphere below, allowing it to melt.

The most abundant dissolved gas in magmas is H20.

Scoria cones form from repeated eruptions over the course of many decades.

Eruptions in Hawaii are always peaceful.

Lava domes form when high-viscosity magma with low-volatile content cools quickly, forming a hardened dome a few meters to a kilometer or so in height.

Hot spots occur only under oceanic plates.

Hawaiian volcanoes produce andesitic lava.

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