GHC Ch 6: Volcanism Flashcards Preview

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Flashcards in GHC Ch 6: Volcanism Deck (58):
1

We locate volcanoes in the context of what?

plate tectonics

2

What four factors determine whether eruptions are peaceful or explosive?

chemical composition, viscosity, gas content, and volume

3

What are the 3 V’s of volcanology

Volatiles, Viscosity, and Volume

4

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

Two

5

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

spreading centers

6

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

at subduction zones. above hot spots

7

No volcanism associated with which to types of faults?

transform faults and continent-continent collisions

8

Oceanic volcanoes are peaceful or explosive?

peaceful

9

Subduction-zone volcanoes are peaceful or explosive?

explosive

10

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

Oxygen and silicon

11

Oxygen and silicon typically join up as what?

SiO4 tetrahedron

12

Minerals form in magma by what process?

crystallization

13

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

observation and experiment

14

Elements combine to form...?

minerals

15

Minerals combine to form...?

rocks

16

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

ingeneous

17

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

plutonic rocks

18

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

volcanic rocks

19

What is viscosity?

internal resistance to flow

20

Water is high or low viscosity? Honey?

Low, high

21

Viscosity determined by what three factors?

temperature, more silicon and oxygen tetrahedra, amount of crystals

22

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

higher

23

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

increases, decreases

24

What is the most abundant dissolved gas in magma?

Water

25

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

decreases, gas bubbles

26

Lower water content results in more or less peaceful eruptions.

more peacefull

27

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

water content and viscosity

28

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

steam bubbles

29

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

rises, melts

30

At spreading centers, eruptions are peaceful or violent?

peaceful

31

Subduction zones have violent eruptions because...?

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

32

Three things will cause rock to melt:

Lowering pressure
Raising temperature
Increasing water content

33

What is the most common way to melt rock?

decompression melting: lowering pressure

34

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

gas bubbles

35

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

fragmenting it into pieces, gas jet

36

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

peaceful or explosive

37

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

water content, viscosity

38

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

lava flows

39

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

pyroclastic debris

40

What were some non-explosive eruptions?

Pahoehoe, Aa

41

What are pyroclastic debris?

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

42

Viscosity controls what about magma?

whether magma flows easily or piles up

43

Volatile abundance controls whether magma...?

may ooze out harmlessly or explode

44

Greater volume of magma leads to...?

more intense eruption

45

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

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

46

What is the Volcanic Explosivity Index?

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.

47

Three V's of Flood Basalts?

Low Viscosity, Low Volatiles, Very Large Volume

48

Some flood basalts coincide with mass...?

extinctions

49

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

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

50

Plinian-type Eruptions? Water content and viscosity?

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

51

Vesuvius, 79 CE

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

52

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

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

53

Where do Calderas occur?

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

54

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

3

55

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

Heating, Pressure decrease , Addition of water. Pressure decrease

56

where volcanism is focused?

At the subduction zone

57

What are the three types of magma?

Basaltic, Andesitic, and Rhyolitic

58

Describe the anatomy of an eruption.

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.