Geology

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.

True

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

False

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

False

The volcanic Explosivity Index (VEI) ranges from 0 to 10

False

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

False

During the summer of 1783, the greatest lava eruption of historic times poured forth at _____________ , accompanied by the release of an enormous volume of gases that enshrouded much of northern Europe in a "dry fog" or blue haze rich in SO2 ( one of the visible components of todays urban smog).

Iceland

The most peaceful eruptions are

Icelandic type eruptions

In 1883, Edvard Munch created his famous painting the scream after witnessing a blood a red sky over Oslo, Norway, caused by the eruption of

Krakatau volcano, Indonesia

____________ 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 from protective caps.

Stratovolcanoes

The volcanic explosivity (VEI) measures size of volcanic eruptions on a scale of 0 to 8. Between 1500 and 1981, one VEI 7 eruption occurred. This was

Tambora, in 1815

many of the deaths at Mount St. Helens on May 18, 1980 were related to

The effects of lateral blast

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

True

At a depth of 20 miles, basaltic rock melts at around 1400°C but this same rock will melt at only 1250°C at the earths surface.

True

Several geologic phenomena are being studied as signs of an impending volcanic eruption. These include seismic waves, ___________ , and the release of gases.

grounded information

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

90%

In 1883, this volcano exploded and the resulting tsunami killed 36,000 people on Java and Sumatra.

Krakatau

Magma compositions are independent of the amount of crustal rock melted and incorporated into the rising magma.

False

No magmas contain dissolved gasses

False

Nuee ardente ( French for glowing cloud) is another term used to describe lava flow

False

The largest number of hot spots lie beneath the Juan de Fuca Plate.

False

Silicon and oxygen link up to form all the silicon-oxygen

Tetrahedron

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

The subduction of Mediterranean sea floor beneath Europe.

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

True

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

True

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

True

In 1973 the town of Vestmannaeyjar on the island of Heimaey ( off the coast of Iceland), was devastated by pyroclastic flows which completely filled and closed the towns harbor.

True

In Icelandic type eruptions, low viscosity, low volatile content lava erupts peacefully.

True

In the last 2 million years, three catastrophic eruptions have occurred at Yellowstone at about 2 million, 1.3 million, and 600,000 years ago.

True

Largest lava dome known is Mount Lassen, California.

True

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.

True

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

True

Most magma is generated by decreasing the pressure on hot rock.

True

Over 80 percent of Earth's magma extruded through volcanism occurs at oceanic spreading centers.

True

Oxygen and silicon are so abundant in the earths crust that their percentages dwarf those of all other elements.

True

Pyroclastic flows can travel across bodies of water.

True

The eruption of Nevado del Ruiz in Columbia in 1985 dropped hot pyroclastic debris onto glaciers, resulting in Lahars.

True

The most abundant dissolved gas in Magma is water

True

The most dangerous volcanoes tend to be in the same general plate tectonic settings as the largest earthquakes in the world.

True

The plate tectonic process responsible for volcanoes in the pacific northwest region of north America is identical to the cause of the regions great earthquakes subduction of the Juan de Fuca plate.

True

The three V's of volcanology are

viscosity, volatiles, and volume

The dominant volcanic gas (Commonly 90% or more of total gas) is

water vapor (H2O)

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

Basaltic eruptions begin from circular fractures surrounding the bulge.

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

Southwestward

Some of earth's most beautiful mountains are _________, including Mount Kilimanjaro in Tanzania, Mount Shasta in California, Mount Rainier in Washington, and Mount Fuji in Japan.

Stratovolcanoes

In the united states, there was a great concern in the early 1980's when earthquakes were frequent, including harmonic tremor, and four magnitude 6 earthquakes caused damage near this volcanic center.

Long Valley caldera in California

The presence of water___________ the melting point of rock.

Lowers

On may 8, 1902 a massive eruption of this volcano killed 30,000 people In the town of St. Pierre. The volcano was

Mont pelee, Martinique

Crater lake, Oregon, fills the caldera of _________ which collapsed about 7600 years ago.

Mount Mazama

On February 1943, a new volcano, a scoria cone, was born when an eruption rose up through a farm field near a village in mexico. This volcano is

Paricutin

_________ eruptions are the most violent types of explosive eruptions.

Plinian-type

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

Pompeii and Herculaneum

___________ in the Aegean sea underwent an explosive series of eruptions around 1628 B.C.E. that buried the Bronze age city of Akrotiri on Thera to depths of 70 meters.

Santorini

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.

True

A caldera collapse occurs

in the middle of the eruption

In August 1986, a gigantic volume of carbon dioxide gas belched forth from ___________ and swept down the adjacent valleys asphyxiating 1700 people.

Lake Nyos in Cameroon

Hawaiian volcanoes unlikely to erupt include

Diamond Head, and Oahu

A Scoria cone is likely to form if lava is low in gas content and high in viscosity

False

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.

False

Antarctica does not lie above any hot spots, partly explaining its massive volumes of ice.

False

At lake Nyos in 1986, a gas cloud wiped out all plant and animal life, as well as killed 1700 people.

False

At oceanic spreading centers, magmas are rhyolitic in composition

False

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

False

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

False

Hawaiian Volcanoes produce andesitic lava.

False

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

80%

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

Aa

During the 1990s, hundreds of trees were killed at Mammoth mountain, California, by the diffuse emission of _______ gas.

CO2

In August 1986, a gigantic volume of gas belched forth from lake Nyos in Cameroon and swept down the adjacent valleys asphyxiating 1700 people. The gas was

Carbon dioxide

This volcano erupted in 1883 in the sunda strait between Sumatra and java, exploding with a loudness heard 3000 miles away, then collapsing into its magma chamber, making a caldera and setting off tsunami that killed at least 36,000 people.

Mount Pele

A genuine success story of advance warning before a large eruption occurred in the Philippines in 1991 before the climactic eruption of

Mount Pinatubo

The two most active Cascade Range volcanoes over the past 4000 years are

Mount St. Helens and Mount Shasta

In 1985, this volcano produced a minor eruption that melted part of a glacier near its summit, sending a lahar down its slopes and killing at least 22,000 people.

Nevado Del Ruiz, Columbia

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

Pillow lava

Beneath continents, rising basaltic magmas are contaminated by sediments and continental crust rocks, altering mamga composition; the resultant andesitic to rhyolitic magmas have high contents of SiO2, relatively low temperatures, and high viscosity, which make it difficult for gasses to escape, causing explosive eruptions.

True

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 aa.

True

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

True

The jokulhaup that occurred in 1996 in Iceland

melted part of the ice cap, releasing a flood that at its peak flowed as the second largest river in the world.

Active volcanoes today in Oregon and Washington, including Mount St. Helens, result from

the subduction of the Juan de Fuca plate beneath North America

Hot spots occur only under oceanic plates.

False

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

False

Magma at spreading centers is low temperature, low viscosity, basaltic, with easy escape of gases, providing all the factors that promote the peaceful eruption of magma.

False

Pyroclastic flows cannot travel down all sides of a volcano simultaneously.

False

The radiocarbon process of documenting major eruptions dates for volcanoes in the past 50,000 years or so is the same as that used to work out dates of major prehistoric earthquakes.

True

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

True

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

True

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

True

When magma nears the surface, gases come out of solution and help cause volcanic eruption.

True

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

True

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

True

over 90 percent of volcanism is associated with the edges of tectonic plates, and most of the rest is caused by hot spots.

True

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

True

the pacific northwest of the united states (Washington and Oregon) has long term risk for both explosive

True

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

Vulcanian-type

A shield volcano has a great

Width compared to its height

Basaltic magmas have low contents of SiO2, low temperature, low viscosity, and allow easy escape of gasses, producing peaceful eruptions

False

Eruptions in Hawaii are always Peaceful

False