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Geo1111 > Lecture 10: Volcanic Eruptions > Flashcards

Lecture 10: Volcanic Eruptions Flashcards

1
Q

Volcano

A

A mountain constructed by the eruption of molten rock from Earth’s interior and are a direct consequence of plate tectonics and mantle convection

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2
Q

Tallest mountain on earth

A

Mauna Kea

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3
Q

What do eruptions provide?

A

Provide highly productive solid to feed a civilization

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4
Q

What are the products of volcanic eruptions?

A

Volcanic gases
Pyroclastic debris
Lava flows

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5
Q

What is volcanic gas?

A

Expelled vapour and aerosols

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6
Q

What is pyroclastic debris?

A

Fragments blown out of a volcano

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7
Q

What is lava flow?

A

Flowing molten rock with various viscosities

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8
Q

What affects the viscosity of lava?

A

Due to its composition specifically its silica content
Temperature
Gas content

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9
Q

Runny lava (name, viscosity)

A

Basaltic lava (low viscosity)

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10
Q

Thick lave (name, viscosity)

A

Rhyolite lava, high viscosity

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11
Q

Lava in between thick and thin (name?)

A

Andesite lava

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12
Q

Basaltic lava

A

Runny-low viscosity, low silica, very hot, long flow distances, rapid speed

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13
Q

Rhyolite lava

A

Thick-high viscosity, has highest SiO2 content, it rarely flows and plugs the vent creating a lava dome

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14
Q

Andesitic lava

A

A viscous lava, that flows slower and has a higher silicon oxide content than a basalt. They lava hovers around the vent and its outer crust will fracture into rubble after cooled

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15
Q

Lava tubes

A

Conduits for basaltic lava, where overtime flow is entirely contained within the tube. Lava tubes are often miles long. Tubes prevent cooling, facilitating flow for miles. After volcanic episodes, lava tubes become caves that can transmit water.

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16
Q

Hawaiian word for describing basalt with a glassy, ropy, twisty texture.

A

Pahoehoe

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17
Q

Pahoehoe

A

A basalt with glassy, rope, twisty texture skin which forms when a hot basalt forms a skin.

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18
Q

Hawaiian word describing basalt that solidifies with a jagged, sharp, angular texture.

A

A’a’

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19
Q

A’a’

A

A basalt that solidifies with a jagged, sharp, angular texture that forms when hot flowing basalt cools and thickens. With flow the lava crumbles into sharp, jagged shards and fragments that solidify into hard solid rock.

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20
Q

Columnar jointing

A

Solidified flows that contract with vertical fractures that have cross sections that are hexagonal

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21
Q

Where is columnar jointing most common?

A

Basalt and other igneous rocks

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22
Q

Pillow basalt

A

Blobs of basalt that cooled rapidly by quenching in water.

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23
Q

Pillow basalt are a common feature of the

A

Mid ocean ridge

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24
Q

Mound of pillow basalt

A

A repeating process of lava pressure rupturing a pillow basalt

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25
Q

QUESTION:

Basaltic vs andesitic vs rhyolitic

A

SiO2 content, viscosity, pyroclastic debris, difficulty of gas escape:
basaltic

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26
Q

Rhyolitic lava flows

A

It has the highest SiO2, and is the most viscous. Their lava rarely flows

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27
Q

Lava domes/ volcanic domes

A

Bulbous mass of congealed lava which are associated with explosive eruptions of gas-poor magma

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28
Q

Explosive eruptions

A

Occur mostly in rhyolitic and andesitic magmas due to high gas content, they end up creating huge volumes of debris including volcanic ash

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29
Q

Pyroclastic flow

A

An avalanche made of hot ash, gas, & debris that develops from volcanic eruptions where the ash cloud/column/dome collapses and races down at very high deadly speeds

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30
Q

Volcaniclastic deposits

A

Large quantities of fragments for volcanic eruption

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31
Q

Materials of volcaniclastic deposits

A

Pyroclastic debris, preexisting rock, landslide debris, and lahars

32
Q

Lava fountains

A

Formed from baslatic eruptions that spew lots of released gases, ejecting clots and drops of molten magma.

33
Q

Pyroclastic materials size range

A

From small to large

34
Q

Tephra

A

Describes deposits of pyroclastic debris of any size

35
Q

Tuff

A

Lithified ash

36
Q

What type of volcaniclastic deposit accumulates like snow

A

Air-fall tuff

37
Q

Ignimbrite

A

Tuff that is deposited while still hold and welds together

38
Q

Categories describing volcaniclastic deposits

A

Pyroclastic: material accumulated from clouds of debris that hasn’t moved since deposition
Volcani-sedimentary: material moved after deposition
Fragmented lava: material from broken lava flows

39
Q

Volcanic debris flow

A

Flow of wetted debris, where the volcano is covered with ice/snow/rain

40
Q

Lahars

A

A flow of water-rich volcanic debris carrying ash and large blocks: destructive and deadly

41
Q

Hyaloclastite

A

Shatters of lava quenched in water

42
Q

Gas expulsion occurs when

A

The pressure drops and magma rises

43
Q

Gas bubbles are called

A

Vesicles

44
Q

What controls eruption violence

A

The way in which gas escapes, difficult=violent

45
Q

Features of volcanic architecture

A

Magma chamber, fissures/vents, craters, calderas

46
Q

What are some distinctive profiles of volcanic architecture, largest to smallest

A

Shield volcanoes
stratovolcanoes
Cinder volcanoes

47
Q

Magma chambers

A

An open cavity or area of highly fractured rock that contains a lots of magma and is located in upper crust and ,may rise through a conduit to reach surface of volcano

48
Q

Magma that cools in magma chambers turn into

A

Intrusive rock

49
Q

Fissures

A

Magma that erupts along a linear tear

50
Q

What type of eruption displays a “curtain of fire”?

A

Fissure eruptions

51
Q

Fissures evolve to become

A

discrete vents that erupt from craters

52
Q

Crater

A

A bowl shaped depression at the top of a volcano that erupt from pipe-shaped conduits where lava will pile up around the vent

53
Q

Summit eruptions are located within

A

The summit crater

54
Q

What type of eruption/vent occurs at the side of a volcano?

A

Flank eruptions from flank vents

55
Q

Caldera

A

A large volcanic depression (much larger than craters) which form when magma chambers empty causing the volcano to collapse into an evacuated space.

56
Q

Shield volcanoes

A

Broad, slightly domed shaped that are formed by lateral flow of basaltic lava

57
Q

Cinder cones

A

Cone shaped pile of ejected lapilli-sized fragments with deep crater

58
Q

Stratovolcanoes

A

Also called composite volcanoes, cone shaped volcano with steep slopes of alternating felsic lava, tephra, and debris, eruptions are from layered pyroclastic eruptions and very viscous lava flows

59
Q

What type of volcano is the most violent?

A

Stratovolcano

60
Q

What type of volcano produces a nuee ardente?

A

Stratovolcano

61
Q

Eruption styles

A

Effusive eruptions: lava flows that are mostly basaltic can create lava fountains/rivers
Explosive eruptions: lava explodes upward is mainly rhyolitic/andesitic and create pyroclastic flows covering landscape with tephra
Strombolian eruptions: shoot out magma, lapilli and blocks at regular intervals

62
Q

What factors determine the violence or explosiveness of a volcanic eruption?**

A
  • composition of magma (high sulfur=high viscosity)
  • temperature of magma (low temp=high viscosity)
  • dissolved gases in the magma (low gas (low gas=high viscosity)
63
Q

What are the types of magma rock controls the nature of an eruption?

A

Igneous rocks:
Felsic(granitic/rhyolitic) are high in sulfur/viscosity
Mafic(basaltic): are low in sulfur/viscosity

64
Q

Why does magma rise to surface

A

Because magma is less dense than surrounding rock

65
Q

Viscosity and gas escape

A

The less viscous = easier escape of gas bubbles

66
Q

Vulcanian eruption

A

A moderate-sized explosive eruption

67
Q

Plinian eruption

A

An enormous explosion of volcanic material that ejects huge quantities of material into the atmosphere

68
Q

Eruption styles:

A

Hawaiian: low-viscosity; fire fountain discharge 1 km high; little pyroclastic material; non-explosive
Strombolian: blasts of lava, including bombs and tephra, create low elevation columns and pyroclastic flows; mildly explosive
Vulcanian: sustained explosions of highly viscous magma; columns reach several km high and collapse to produce pyroclastic flows; very explosive
Pelean: result from collapse of lava dome producing nueé ardente; violently explosive
Plinian: sustained ejection of magma resulting in eruption column up to 45 km high; ash cloud can circle the Earth in days; violently explosive
Phreatic: results when magma mixes with shallow groundwater, which flashes to steam and explosively erupts; no new magma reaches surface

69
Q

Largest eruption in modern day

A

Mt. Pinatubo in philippines

70
Q

Largest eruption documented in all history

A

Toba in indonesia

71
Q

What is a dominant control on volcanism?

A

Tectonic plate motion

72
Q

Volcanic settings are:

A
  • Mid-ocean ridges: spreading axes
  • Convergent boundaries: subduction zones
  • Continental rifts: incipient ocean basins
  • Oceanic hot spots
  • Continental hot spots and flood basalts
73
Q

Which flow is more deadly?

A

Pyroclastic flow not lava flow

74
Q

What is the best defense against volcanic hazards?

A

Understanding volcanic behaviou

75
Q

Effect on ashfall in modern day

A

Kills plants and crops
collapsing roof from heavy tephra
Abrasion of engine from gritty tephra
Tephra can become deadly lahar in flood water

76
Q

Volcanic blast

A

Rare hazard since most are vertical not sideways

77
Q

Landslide in volcanic eruptions

A

Large masses of material are deopsited quickly near a vent

Geo1111 (8 decks)

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