Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

_1_1_4 > VO L1: Why Volcanoes have Different Characteristics > Flashcards

VO L1: Why Volcanoes have Different Characteristics Flashcards

1
Q

How is magma formed?

A

Melting pre-existing rock in Earth’s interior.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is magma made of?

A

melt, crystals of minerals, gas bubbles. Magma is less dense than the crust.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why does magma rise toward surface of Earth?

A

It is less dense than the crust.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

For magma to rise to the crust, it must be…?

A

1) Less dense than the crust
2) Runny enough to flow (i.e. low viscosity)
3) Hot enough to stay liquid.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is lava?

A

Magma that has erupted and cools to form solid rock.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Top five elements of Earth’s crust?

A

Oxygen, silicon, aluminum, iron, calcium. All formed by magma rising to the Earth’s surface.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How much of Earth’s crust is comprised of oxygen?

A

45.2% by weight

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How much of Earth’s crust is comprised of silicon?

A

27.2% by weight

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Compare the SiO_2 (silicate) between continental and oceanic crusts.

A

The average continental crust is higher in silicate than oceanic crust. Influences the locations of explosive volcanoes on Earth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are minerals? Describe how they’re formed.

A

A mineral is a naturally occurring element or compound that has an ordered internal structure, a characteristic chemical composition, crystal form, and physical properties. Formed when magma cools and crystallizes, when the chemical components bond together.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the most common mineral that crystallize out of magma? Why?

A

Silicate. Because Si and O are the most common elements in Earth’s crust and upper mantle.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Name some common silicate minerals in volcanic rocks.

A

Feldspar, quartz, micas, hornblende, pyroxene, olivine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Main building block of all silicate minerals?

A

(SiO_4)^-4

A silicon atom linked to four oxygen atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What determines the size of the crystals that form in a solidified magma?

A

Depends on how long it takes the magma to cool.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What are intrusive rocks?

A

Formed by magma that cool slowly underground, in crustal magma chambers. The minerals crystallize in an interlocking texture of grains big enough for eye to see. May take 100s-1000s of years to grow crystals that large.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are extrusive rocks?

A

Formed by magma that extrudes at Earth’s surface- this magma cools quickly, commonly solidifying over days to weeks. Erupted magmas= lavas; they have small sized crystals, too small to be seen by eye. They form extrusive rocks, extrusive/ fine-grained in texture.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How long to form crystals that form intrusive rocks? What about for extrusive rocks? Other differences between intrusive/extrusive?

A

Intrusive: hundreds to thousands of years.

Extrusive: days to weeks.

Another difference is crystal size. Intrusive: can see with naked eye; big.
Extrusive: cannot see with naked eye; small.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What determines the array of eruptive products created when magma erupts at Earth’s surface?

A

the chemical composition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What causes lava flows?

A

Lava flows result when magma that is relatively low in gas content (less than a few %) erupts effusively at Earth’s surface.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is a pahoehoe? (pronounce: pah-hoy-hoy)

Why is it called that?

A

The ropy-textured of the surface of a lava flow.

Hawaiian term. These flows commonly occur on Hawaii.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is ‘a’a? (pronounce: ah-ah)

A

A lava flow with a rubble-y flow top consisting of broken fragment of lava.

It’s a Hawaiian term, meaning “painful surface to walk on”

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Describe volcanic glass. How is it formed?

A

This glass is called obsidian if massive, or pumice if it contains many bubbles (vesicles). Volcanic glass is formed when magma erupts and cools so quickly that crystallization doesn’t occur. Magma solidifies into glass, a supercooled liquid. Glass is not crystalline, but volcanic glass may contain some microscopic crystals of common minerals.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is obsidian? What is pumice? What are vesicles?

A

Both are volcanic glass
Obsidian: massive
Pumice: contains manny bubbles
Vesicles: the bubbles in pumice, formed from gas that escape from the magma during eruption

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is pyroclastic material?

A

means “fire piece” or hot fragment. Refers to fragments of all sizes that are erupted explosively out of a volcano. They range from fine material (ash, <2mm diameter) to lapilli (2-64mm) to larger blocks and bombs (> 64mm). Many pieces of pumice are pumice lapilli.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Which volcanic glass can float?

A

pumice. has low density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

How do pyroclasts erupt?

A

Pyroclasts can erupt as ballistic fragments (bombs or blocks), flows (pyroclastic flows), or fall deposits (air fall deposits).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Most common volcanic gas? What others?

A

Steam (H2O). Others: carbon dioxide, sulfur dioxide, hydrogen sulfide, hydrogen chloride.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What gives volcanic gas a rotten egg smell?

A

hydrogen sulfide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What volcanic gas accumulates in low areas?

A

Carbon dioxide, because it is denser than air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What happens if you inhale CO2 in much higher than usual concentrations?

A

It can produce a sour taste in the mouth and a stinging sensation in the nose and throat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What leads to the most explosive volcanic eruptions?

A

HIGH gas content and HIGH viscosity.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Range that gas content can vary in magma?

A

1 to 10%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Primary gases in magma?

A

H2O and CO2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Describe how magma erupts.

A

As magmas rise towards Earth’s surface, dissolved gases, which are compressed at depth, expand and try to escape the magma. Gas bubbles are formed, grow larger, and eventually explode. Magmas with higher gas contents have more explosive eruptions, and thus are more hazardous.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

The more easily magma flows, the more likely it is that gas bubbles in it will _____ and the magma will erupt _____ rather than explosively.

A

dissipate; effusively

36
Q

What influences viscosity?

A

1) Chemical composition: the more SiO2, higher the viscosity. Because Si-O bond is strong.
2) Temperature: as magma cools, more Si-O bonds form, magma is said to polymerize. This makes the magma stickier and thicker as it cools (aka more viscous).

37
Q

Relationship between m value (log of viscosity), viscosity and explosivity of volcanic eruption?

A

The higher the m value, the more viscous the lava and the more explosive the volcanic eruption.

38
Q

What is viscosity proportional to?

A

The weight percent of silicate (SiO2) in a magma.

Also proportional to 1/T of a magma where T= temperature

39
Q

What are mafic magmas?

A

Those with lowest silicate (SiO2) content. They exist at high temperatures, lowest viscosity, have low gas contents, and tend to erupt effusively (non-explosively). They form dark colored mafic rocks called basalts.

40
Q

What are felsic magmas?

A

Form at lower temperatures, have high viscosity, low gas contents, tend to erupt explosively. They form lighter-colored felsic rocks called rhyolites. Felsic magmas also tend to have higher gas contents than mafic magmas, and it is this combination of high viscosity and high gas content that leads to explosive eruptions.

41
Q

What are rhyolites?

A

Formed by felsic magmas. Lighter-colored felsic rocks.

42
Q

What kind of magma creates explosive eruptions?

A

felsic magma

43
Q

What kind of rocks does mafic magma form?

A

basalts (dark colored mafic rocks)

44
Q

Describe the sequence of events leading to an explosive eruption.

A

a. High silica magma forms in the crust by melting of pre-existing rock. Gas is dissolved in this magma due to the high pressure underground.
b. The magma rises towards Earth’s surface because it is less dense than the surrounding solid rock.
c. As the magma rises, the dissolved gas expands and forms bubbles in the magma. This process is called vesiculation.
d. Because the magma is also cooling at it rises, its viscosity is increasing (Si-O bonds are forming). The gas bubbles are trapped in the viscous magma and gas pressure builds within the bubbles as they get closer to the surface.
e. When the percentage of the bubbles in the magma is about 75%, they are close enough that they touch. The walls between adjacent bubbles are so thin that the gas pressure overcomes the viscosity of the magma.

f. BOOM! An explosive eruption takes place, and fragments of magma are erupted as pyroclasts.
If the magma was mafic (low in silica content), the included gas bubbles would be able to escape from the rising magma and pop easily upon eruption, resulting in less explosive eruptions.

45
Q

What is a volcano?

A

Mass of material that forms at Earth’s surface in responsive to one or more eruptions of magma. Most volcanoes form hills or mountains. (note: not all mountains/hills are volcanoes)

46
Q

What is a crater?

A

A steep-walled bowl-shaped depression surrounding the volcanic vent from which new material erupted. Found within each volcano.

47
Q

_____, in Washington is an ice-clad volcano in the North Cascades. The volume of snow and ice on this mountain is greater than that of all the other Cascades volcanoes (except _____, also in Washington) combined.

A

Mount Baker; Mt. Rainier

48
Q

Describe mafic lavas flowing.

A

Mafic lavas are very fluid (low viscosity) and can travel long distances from a vent. They may flow downhill at speeds of up to 30 km/hr, and travel tens to over one hundred kilometers from their vent.

49
Q

Describe the shield volcano.

A

One common mafic volcanic landform is the shield volcano. It is tens of kilometers high and may be over 100 km across. Early observers thought that the shape of this type of volcano, which is much larger in diameter than it is high, reminded them of the shape of a Viking’s shield, hence the name. Repeated eruption of basaltic lava flows forms most of a shield volcano, although small eruptive centers called cinder cones are present on the flanks.

50
Q

Give examples of shield volcanoes.

A

The large volcanoes in Hawaii such as Mauna Loa, Mauna Kea, and Kilauea, are all examples of shield volcanoes.

51
Q

What is the world’s largest active volcano? What is its type? How tall is it?

A

Mauna Loa is the world’s largest active volcano; it rises 28,000 feet above the sea floor. It is a shield volcano.

52
Q

What is a cinder cone?

A

Conical hill formed from the accumulation of pyroclastic material (cinders are 4-32 mm in size) around a volcanic vent. The cones are commonly 10’s to 100’s of meters high and 100’s of meters across. One or more lava flows may issue from the vent after the cone forms. In general, cinder cones are composed of mafic magma, although andesitic cinder cones are do exist.

53
Q

When _______ magma erupts explosively, it can produce ash columns that penetrate to higher than 40 km into the atmosphere. Ash is the finest grained pyroclastic material, and if it gets into the stratosphere, it can travel around the world in upper level winds. When the winds die, ash falls out of the atmosphere due to gravity and it forms layers that blanket the landscape. This type of eruption occurred at Mt. St. Helens, in Washington State, on May 18, 1980; it was only one component of the most recent volcanic eruption to affect western North America outside of Alaska. Air-fall ash eruptions typically take place at composite volcanoes and calderas.

A

intermediate to felsic

54
Q

How high are the ash columns produced by intermediate to felsic magma?

A

40 km

55
Q

Where do air-fall ash eruptions typically take place?

A

at composite (strato-) volcanoes and calderas

56
Q

What is a stratovolcano/ composite volcano?

A

An intermediate to felsic volcanic landform. Composed of alternating layers of lava flows and pyroclastic layers, along with volcanic domes (see below) and tabular intrusions known as dykes and sills.

These volcanoes are tall, conical, and have steep slopes. Can be several km high and over 10 km across.

57
Q

How do composite volcanoes get their name?

A

They erupt magmas of a full range of silica contents.

58
Q

The mafic and some intermediate eruptions tend to form ___, whereas magmas with higher silica contents commonly erupt explosively as pyroclastic material, either in the form of _____(3).

A

flows; ;bombs, flows, or falls

59
Q

What are dykes and sills?

A

Tabular intrusions. Dykes: igneous rocks that intrude vertically
Sills: cut horizontally/along the land

60
Q

What is a lava dome?

A

An intermediate to felsic landform. A pile of viscous lava that forms over a vent. Has a mushroom-like shape, because lava is viscous and doesn’t travel far from the vent. Domes may stand alone, or be erupted in the center or on the flank of an existing volcano.

61
Q

What forms the mushroom like shape of the lava dome?

A

Lava doesn’t travel far from the vent. High viscosity.

62
Q

What’s a caldera?

A

A felsic volcanic landform (most of the time). They’re very large depressions in Earth’s crust, caused by voluminous eruption of explosive, felsic pyroclastic material. Typically 10’s to 100+ km across and km’s deep. They form because so much magma is erupted that the existing crust founders into the void left by the evacuated magma chamber.

63
Q

Difference between crater and caldera?

A

A crater is a depression on top of a volcanic vent, and it typically is only 10’s to 100’s of meters across, although craters on some of the Hawaiian shield volcanoes are kilometers across. A crater normally does not form because a block of crust is downdropped. Rather, it forms by default as piles of erupted material surround a volcanic vent.

64
Q

How is a volcanic crater formed?

A

forms by default as piles of erupted material surround a volcanic vent

65
Q

Describe how a caldera is formed.

A

Formation and accumulation of a very large body of felsic magma in a near-surface magma chamber. This magma is buoyant and it domes the overlying crust, creating both radial and ring fractures.

Gas pressure in the felsic magma chamber increases to the point that explosive fragmentation occurs. Pyroclastic material erupts through fractures in the overlying crust in the form of pyroclastic flows, and produces a deposit known as an ash flow tuff sheet. This tuff sheet blankets the countryside for many kilometers out from the caldera, and some of the tuff sheet is deposited in the center of the caldera.

So much magma erupts that the roof of the caldera collapses back into the void left by the evacuated magma, producing a very large closed depression in the surface.

66
Q

What is the most explosive type of volcano?

A

Caldera-forming eruptions. Eruptions are infrequent in human lifetimes.

67
Q

Name some large, fairly young calderas in western North America.

A

Crater Lake was formed 6700 years ago by caldera-forming eruption that destroyed a composite cone known as Mt. Mazama. Other nearby big calderas: Yellowstone, Long Valley. Both formed calderas about 1 million years ago. Eruption is possible but probably not caldera-forming eruption

68
Q

When did Yellowstone and Long Valley calderas form?

A

1 million years ago

69
Q

Describe how Crater Lake formed.

A

(a) Mount Mazama volcano stood high just prior to its eruption. (b) In 5677 BCE, a gaseous eruption emptied a huge volume of viscous magma. (c) The gigantic eruption left a void inside the weakened mountain, and the unsupported material collapsed into the emptied magma chamber. (d) The waters of Crater Lake now fill the caldera, and a small new volcanic cone (Wizard Island) has built above lake level.
(bottom left) Schematic map of the Yellowstone hotspot area. The North American plate is moving southwest, thus the hot-spot magma plume erupts progressively farther northeast with time. Three giant calderas have erupted in the last 2 million years - at 2, 1.3, and 0.6 million years ago. Cross-hatched area was covered by hot, killing pyroclastic flows during the eruption of 600,000 years ago.

70
Q

The North American plate is moving _____, thus the hot-spot magma plume erupts progressively farther ______ with time.

A

southwest ; northeast

71
Q

How many giant calderas have erupted in the last 2 million years? When precisely?

A
  1. At 2, 1.3, and 0.6 million years ago.
72
Q

What kind of volcano is Mt Rainier, Washington?

A

composite cone/ stratovolcano. same magnitude height and width (a bit wider)

73
Q

What kind of volcano is Mauna Loa, Hawaii?

A

shield volcano. it is wider than tall

74
Q

What kind of volcano is Sunset Crater, Arizona?

A

cinder cone

75
Q

Size of volcano order?

A

A cinder cone is about 1 order of magnitude smaller than a stratovolcano, which is about 1 order of magnitude smaller than a shield volcano.

76
Q

Dimensions of cinder cone?

A

is about 4× as wide as it is high

77
Q

Dimensions of stratovolcano?

A

has the same magnitude height and width

78
Q

Dimensions of shield volcano?

A

has a great width compared to its height

79
Q

What kind of magma erupt quietly?

A

Mafic magmas with low silica (hence, low viscosity)

80
Q

Low viscosity, low volatiles, large volume = what volcano?

A

shield volcanoes

81
Q

medium/high viscosity, medium/high volatiles, large volume = what volcanic landform?

A

stratovolcanoes

82
Q

high viscosity, low volatiles, small volume = what volcanic landform?

A

lava domes

83
Q

high viscosity, high volatiles, very large volume = what volcanic landform?

A

calderas

84
Q

low viscosity, low volatiles, very large volume = what volcanic landform?

A

flood basalts

85
Q

low/medium viscosity, medium/high volatiles, small volume = what volcanic landform?

A

scoria/cinder cones

86
Q

Why do most felsic magmas erupt explosively?

A

High viscosity and high gas content

_1_1_4 (23 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions