GHC Ch 6: Volcanism

Question 1

We locate volcanoes in the context of what?

Answer 1

plate tectonics

Question 2

What four factors determine whether eruptions are peaceful or explosive?

Answer 2

chemical composition, viscosity, gas content, and volume

Question 3

What are the 3 V’s of volcanology

Answer 3

Volatiles, Viscosity, and Volume

Question 4

90% of volcanism is associated with how many plate boundaries?

Answer 4

Two

Question 5

80% of volcanoes are at what kind of plate boundary?

Answer 5

spreading centers

Question 6

About 10% of volcanoes are at what plate boundary? And the rest of the 10%?

Answer 6

at subduction zones. above hot spots

Question 7

No volcanism associated with which to types of faults?

Answer 7

transform faults and continent-continent collisions

Question 8

Oceanic volcanoes are peaceful or explosive?

Answer 8

peaceful

Question 9

Subduction-zone volcanoes are peaceful or explosive?

Answer 9

explosive

Question 10

Which of the 92 elements are by far most abundant naturally occurring element of Earth’s crust?

Answer 10

Oxygen and silicon

Question 11

Oxygen and silicon typically join up as what?

Answer 11

SiO4 tetrahedron

Question 12

Minerals form in magma by what process?

Answer 12

crystallization

Question 13

Order of crystallization of different minerals in magma is known from what?

Answer 13

observation and experiment

Question 14

Elements combine to form…?

Answer 14

minerals

Question 15

Minerals combine to form…?

Answer 15

rocks

Question 16

Different compositions of magma result in different (…) rocks?

Answer 16

ingeneous

Question 17

If magma cools slowly and solidifies beneath surface, what type of rock results?

Answer 17

plutonic rocks

Question 18

If magma erupts and cools quickly at surface, what type of rock results?

Answer 18

volcanic rocks

Question 19

What is viscosity?

Answer 19

internal resistance to flow

Question 20

Water is high or low viscosity? Honey?

Answer 20

Low, high

Question 21

Viscosity determined by what three factors?

Answer 21

temperature, more silicon and oxygen tetrahedra, amount of crystals

Question 22

More silicon and oxygen tetrahedra results in higher or lower viscosity?

Answer 22

higher

Question 23

Solubility increases as pressure (…) and temperature (…)

Answer 23

increases, decreases

Question 24

What is the most abundant dissolved gas in magma?

Answer 24

Water

Question 25

As magma rises, pressure (...), water becomes (...)

Answer 25

decreases, gas bubbles

Question 26

Lower water content results in more or less peaceful eruptions.

Answer 26

more peacefull

Question 27

Rhyolitic magma has higher (...) and (...)

Answer 27

water content and viscosity

Question 28

In rhyolitic magma, many (...) form and can not escape through thick magma, so explode and result in violent, dangerous eruptions

Answer 28

steam bubbles

Question 29

At spreading centers, Plates pull apart so asthenosphere (...) and (...) under low pressure.

Answer 29

rises, melts

Question 30

At spreading centers, eruptions are peaceful or violent?

Answer 30

peaceful

Question 31

Subduction zones have violent eruptions because...?

Answer 31

Magma is generated by partial melting of mantle above the subducting plate with water in it, and melts overlying crust to produce magmas of variable composition

Question 32

Three things will cause rock to melt:

Answer 32

Lowering pressure Raising temperature Increasing water content

Question 33

What is the most common way to melt rock?

Answer 33

decompression melting: lowering pressure

Question 34

Magma at depth is under too much pressure for (...) to form

Answer 34

gas bubbles

Question 35

Eventually gas bubble volume may overwhelm magma,(...) that explode out as a (...)

Answer 35

fragmenting it into pieces, gas jet

Question 36

Concentration of water in magma largely determines (...) eruption.

Answer 36

peaceful or explosive

Question 37

Rhyolitic magma usually erupts violently because of high (...) and high (...).

Answer 37

water content, viscosity

Question 38

Low-water content, low-viscosity magma leads to...?

Answer 38

lava flows

Question 39

High-water content, high-viscosity magma leads to...?

Answer 39

pyroclastic debris

Question 40

What were some non-explosive eruptions?

Answer 40

Pahoehoe, Aa

Question 41

What are pyroclastic debris?

Answer 41

broken up fragments of magma and rock from violent gaseous explosions, classified by size

Question 42

Viscosity controls what about magma?

Answer 42

whether magma flows easily or piles up

Question 43

Volatile abundance controls whether magma...?

Answer 43

may ooze out harmlessly or explode

Question 44

Greater volume of magma leads to...?

Answer 44

more intense eruption

Question 45

Three V's of Shield Volcanoes? What does a shield volcano look like?

Answer 45

Low Viscosity, Low Volatiles, Large Volume. Great width compared to height.

Question 46

What is the Volcanic Explosivity Index?

Answer 46

Provides a means of evaluating eruptions according to volume of material erupted, height of eruption column and duration of major eruptive blast. Scale from 0 to 8.

Question 47

Three V's of Flood Basalts?

Answer 47

Low Viscosity, Low Volatiles, Very Large Volume

Question 48

Some flood basalts coincide with mass...?

Answer 48

extinctions

Question 49

Three V's of Stratovolcanoes? What does a Stratovolcano look like? What are they composed of?

Answer 49

High Viscosity, High Volatiles, Large Volume. Steep-sided, symmetrical volcanic peaks. alternating layers of pyroclastic debris and andesitic to rhyolitic lava flows.

Question 50

Plinian-type Eruptions? Water content and viscosity?

Answer 50

Gas-powered vertical columns of pyroclastic debris up to 50 km into the atmosphere. High water content and high viscosity.

Question 51

Vesuvius, 79 CE

Answer 51

Most of 4,000 people who remained in Pompeii killed by thick layers of hot pumice or pyroclastic flows

Question 52

Three V's of Calderas? What does a Calderas look like?

Answer 52

High Viscosity, High Volatiles, Very Large Volume. Large volcanic depressions formed by inward roof collapse into partially emptied magma reservoirs

Question 53

Where do Calderas occur?

Answer 53

Occur where large volumes of basaltic magma intrude to shallow depths and melt surrounding continental rock, to form high-viscosity, high-volatiles magma

Question 54

Yellowstone National Park has had how many recent catastrophic (ultra-Plinian) eruptions?

Answer 54

3

Question 55

The 3 mechanisms by which rocks melt? Which is most common?

Answer 55

Heating, Pressure decrease , Addition of water. Pressure decrease

Question 56

where volcanism is focused?

Answer 56

At the subduction zone

Question 57

What are the three types of magma?

Answer 57

Basaltic, Andesitic, and Rhyolitic

Question 58

Describe the anatomy of an eruption.

Answer 58

Magma rises from areas of high pressure to low pressure. Gas comes out of solution. Bubbles form. Bubbles overwhelm magma. Gas jet is created leading to a buoyant plume.