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In part, the viscosity of magma is dependent

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Subject: Geology
Due on: 04/03/2017
Posted On: 04/03/2017 08:54 AM

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QUESTION 1

1. In part, the viscosity of magma is dependent on the amount of silica tetrahedrons in the melt. Why does a high amount of silica increase the magma’s viscosity?

A melt rich in silica electrically and mechanically exclude other ions. These excluded ions (notably iron and calcium) collect along the sides of magma’s passageway and constrict the magma’s flow.

Because all of the silica tetrahedrons have the same charge, they mutually repel each other. With a high number of silica tetrahedrons, the repulsive forces prevent the melt from being pushed together and flow.

The silica tetrahedrons are much larger than the other ions found in the magma melt. These large ions impede the movement of the melt.

Silica tetrahedrons tend to form bonds very easily. The bond formation creates more complex crystal structures which prevents the magma from flowing easily.

2.99 points

QUESTION 2

1. What influence does the temperature of a melt have on its viscosity?

Temperature has no affect on the viscosity.

The viscosity goes down as the temerature increases.

The viscosity goes up as the temperature goes up.

2.77 points

QUESTION 3

1. Which of the following is the dominant volatile emitted during a volcanic eruption?

carbon dioxide

sulfur dioxide

carbon monoxide

water (steam)

2.83 points

QUESTION 4

1. What role do volatiles, like carbon dioxide (and others), have in the style of volcanic eruption?

The higher the percentage of volatiles, the more explosive the eruption is likely to be.

The higher the percentage of volatiles, the lower the viscosity of the magma. This results in very quiet lava flows instead of explosions.

Once exposed to atmospheric oxygen the volatiles combust. This creates the explosions associated with most eruptions.

A high gas content means that there has been a great deal of magmatic separation of the molten mass. The resulting volcanic eruption then will be very quiet (non explosive).

2.77 points

QUESTION 5

1. On Earth, what is the reason that many shield cones are so large?

They have been situated over an active hot spot for hundreds of millions of years that has continued to feed the volcano.

They are created by very fluid lava flows that persist for many centuries.

The largest of the Earthly shield cones are found in the oceans. Without interference from terrestrial landforms (like mountains) these shield cones can continue to grow in size.

2.77 points

QUESTION 6

1. Where are the largest volcanoes in the Solar System?

Venus

Mars

Jupiter

Earth

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QUESTION 7

1. How do calderas form?

They are collapse features created when magma moves out away from an area. The resulting reduction in pressure causes a collapse of the rocks at the surface.

Most calderas are the result of a process called “degassing”. The rocks and molten material near the top of the volcano simply emit gasses. This reduces the pore pressures in the rock allowing the rocks to collapse to form the caldera.

They are the result of powerful explosions that blast huge holes along the surface of the volcano.

They are the result of rock melting near the volcano’s summit. The melted rock flows out onto the surface creating the large depression.

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QUESTION 8

1. The largest type of volcano

Shield cone

Domestic cone

Composite cone

Cinder cone

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QUESTION 9

1. The smallest type of volcano

Composite cone

Domestic cone

Strato cone

Cinder cone

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QUESTION 10

1. Most explosive

Composite cone

Cinder cone

Shield cone

Domestic cone

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QUESTION 11

1. Commonly, these volcanoes are one time eruptions

Shield cone

Composite cone

Cinder cone

Singular cone

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QUESTION 12

1. The Hawaiian Volcanoes are of this type

Polynesian cone

Cinder cone

Shield cone

Composite cone

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QUESTION 13

1. Mt St Helens is this type of volcano.

Cinder cone

Fissure cone

Shield cone

Composite cone

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QUESTION 14

1. Olympus Mons is this type of volcano

Shield cone

Singular cone

Crater cone

Composite cone

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QUESTION 15

1. The San Francisco Peaks of Arizona are this type of volcano

Composite cone

Shield cone

Domestic cone

Cinder cone

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QUESTION 16

1. Sunset Crater is a

Cinder cone

Rift cone

Domestic cone

Shield cone

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QUESTION 17

1. What is the difference between a caldera and a crater?

Calderas are found only at the summit of the volcano, craters can be found anywhere on the volcano.

Calderas are associated with very silica rich volcanoes while the crater is produced by more basaltic volcanoes.

Calderas are formed when lava flows into fissures along the flanks of an active volcano and craters are areas where lava flows outwards.

The only difference is size. calderas are generally larger that craters. Calderas are generally formed by collapse and most craters are produced by explosions.

2.77 points

QUESTION 18

1.

This image shows the dates (in millions of years) of the volcanic activity associated with what is known as the Yellowstone Hot Spot. Why do the dates get progressively older towards the west?

These volcanic eruptions are located along a continuously developing rift. The rift, called the Yellowstone Rift, is opening up from west to east and allows molten material to erupt as volcanoes as it does.

These eruptions are associated with a spreading center below the crust along the Rocky Mountains. The dates show how fast the spreading center is opening.

The North American Plate is slowly moving to the west and overriding the hot spot.

The Yellowstone Hot Spot is moving in a generally eastward direction.

2.77 points

QUESTION 19

1. Why is the Yellowstone Calder considered a threat?

An eruption would disrupt the Earth’s balance of atmospheric gases and reduce the ozone levels significantly.

An eruption of the caldera would produce prodigious amounts of ozone that would greatly influence the Earth’s climate.

It could erupt and cover much of the western US with volcanic dust and ash.

The threat is basically limited to the tourism of the area. An eruption could disrupt the groundwater structure and cause many of the popular thermal features to shut down or become erratic.

2.77 points

QUESTION 20

1. Mt St Helens had a very explosive eruption in 1980 that was followed by numerous smaller eruptions and the buildup of a basaltic dome in its vent. What was responsible for its initial violence and subsequent lesser eruptions?

A magma surge forced the initial violent eruption. That surge depleted the magma reservoir beneath the surface that resulted in weaker eruptions.

crystallization and cooling of the magma

differentiation of the magma body below

melting glacial ice mixed with the magma to produce the initial explosion, but also cooled the magma so later eruptions were limited

2.77 points

QUESTION 21

1. How did the second eruption (the ring eruption) of Mt Mazama create Crater Lake?

The ring eruption blasted the summit of the volcano leaving the depression now occupied by crater lake.

The ring eruption was created by the collapse of the summit to form the caldera that is now occupied by Crater Lake.

The ring eruption was a series of eruptions around the summit of Mt Mazama. The buildup of volcanic rocks from these eruptions created a central basin that is now the area of Crater Lake.

2.77 points

QUESTION 22

1. Why is Crater Lake one of the clearest lakes in the world?

The drainage is, for the most part, away from the lake. Streams flow down the outer flanks of the volcano instead of into the lake.

The water is the result of the cooling of the magma body. Water escapes the cooling magma and accumulates in the caldera. Although the lake is very clear, it is also very acidic.

The volcanic rocks around the lake consist of very durable volcanic glass and do not contribute sediment to make the lake muddy.

The lake received its water only from clean groundwater springs.

2.77 points

QUESTION 23

1. Aside from size, what is the main difference between shield and cinder cones?

The lava of the shield cones is much cooler than that of the cinder cones.

The only difference between the two types of volcanoes is the size.

The lava of the cinder cones is full of volatiles (gases)

The lava of the cinder cones has a great deal more silica.

2.77 points

QUESTION 24

1. Economically speaking, of what value are cinder cones?

They are a source of geothermal energy.

They often contain valuable minerals like peridot and sapphires.

They are a source of cinders for construction.

The cinders are used in the manufacture of glass.

2.77 points

QUESTION 25

1. Why is a pyroclastic flow so dangerous?

It is very hot.

It moves down the flank of the volcano very rapidly.

It contains no oxygen

All of the above.

2.77 points

QUESTION 26

1. What type of rock results from a pyroclastic flow.

granite and a little diorite

volcanic tuff or simply ash and cinders

any of these choices

obsidian and basalt

2.77 points

QUESTION 27

1. The Columbia River Basalt Flood is a huge accumulation of basalt that represents about 1 million years of eruptions. What was the source of this deluge of basalt?

A supervolcano in eastern Washington created the flows.

Most likely the basalt was erupted from a series of fissures situated over a mantle plume.

The flows were the result of an asteroid impact. The heat of the impact created an abundance of molten rock.

The basalt came from a very active downward plunge of the Juan de Fuca Plate off the west coast of North America.

2.77 points

QUESTION 28

1. An intrusion that cuts across existing rocks is called a

Sill

Dike

Laccolith

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QUESTION 29

1. An intrusion that is parallel to the rocks into which it intrudes is which of the following?

Sill

Batholith

Stock

Volcanic Pipe or Neck

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QUESTION 30

1. The biggest of the igneous intrusions.

Batholith

Sill

Stock

Dike

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QUESTION 31

1. This type of intrusion forms the cores of mountain ranges.

Sill

Batholith

Dike

Laccolith

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QUESTION 32

1. The central peak of Shiprock in New Mexico is a

Dike

Laccolith

Stock

Volcanic neck (or pipe)

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QUESTION 33

1. Mt Rushmore, South Dakota is a great exmaple of a

batholith

monolith

laccolith

pacholith

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QUESTION 34

1. How does columnar jointing form?

Crystallization forms the huge columns.

The alignment of platy minerals.

Cooling of the rock and the resulting contraction.

The release of volatiles from the lava or magma.

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QUESTION 35

1. How is a basaltic sill distinguished from a buried basaltic lava flow in the field? (In the "field" means out in nature.)

Lava flows consist of a more solid type of basalt while the sills may contain an abundance of gas pockets.

Sills are always horizontal while lava flows can form at many different angles.

Lava flows will not develop columnar jointing while sills will.

The sill will have a baked layer above and below it while the lava flow will bake only the layer below it.

2.77 points

QUESTION 36

1. What is the “problem with pegmatites” at Mt Rushmore, South Dakota?

The pegmatites are avenues for toxic volatiles associated with the parent magma body. As a result, they pose a risk to park visitors.

They are of economic importance because of the valuable minerals they contain. The mountain and its pegmatites are threatened by mining companies.

The problem is only cosmetic. Close-up views of the sculpted faces show the pegmatite veins and many visitors consider them unattractive.

The pegmatites are zones of weakness as they formed along cracks in the granite.

Tags dependent magma viscosity question points volcano eruption magma eruptions cones lake lava flows theyare flow shieldcone type rocks volatiles volcanoes crater rock created result cinder viscosity aociated sill summit cindercone basalt compositecone form

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