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Geo1111 > Lecture 10: Volcanic Eruptions > Flashcards

Lecture 10: Volcanic Eruptions Flashcards

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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
QUESTION: | Basaltic vs andesitic vs rhyolitic
SiO2 content, viscosity, pyroclastic debris, difficulty of gas escape: basaltic
26
Rhyolitic lava flows
It has the highest SiO2, and is the most viscous. Their lava rarely flows
27
Lava domes/ volcanic domes
Bulbous mass of congealed lava which are associated with explosive eruptions of gas-poor magma
28
Explosive eruptions
Occur mostly in rhyolitic and andesitic magmas due to high gas content, they end up creating huge volumes of debris including volcanic ash
29
Pyroclastic flow
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
30
Volcaniclastic deposits
Large quantities of fragments for volcanic eruption
31
Materials of volcaniclastic deposits
Pyroclastic debris, preexisting rock, landslide debris, and lahars
32
Lava fountains
Formed from baslatic eruptions that spew lots of released gases, ejecting clots and drops of molten magma.
33
Pyroclastic materials size range
From small to large
34
Tephra
Describes deposits of pyroclastic debris of any size
35
Tuff
Lithified ash
36
What type of volcaniclastic deposit accumulates like snow
Air-fall tuff
37
Ignimbrite
Tuff that is deposited while still hold and welds together
38
Categories describing volcaniclastic deposits
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
Volcanic debris flow
Flow of wetted debris, where the volcano is covered with ice/snow/rain
40
Lahars
A flow of water-rich volcanic debris carrying ash and large blocks: destructive and deadly
41
Hyaloclastite
Shatters of lava quenched in water
42
Gas expulsion occurs when
The pressure drops and magma rises
43
Gas bubbles are called
Vesicles
44
What controls eruption violence
The way in which gas escapes, difficult=violent
45
Features of volcanic architecture
Magma chamber, fissures/vents, craters, calderas
46
What are some distinctive profiles of volcanic architecture, largest to smallest
Shield volcanoes stratovolcanoes Cinder volcanoes
47
Magma chambers
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
Magma that cools in magma chambers turn into
Intrusive rock
49
Fissures
Magma that erupts along a linear tear
50
What type of eruption displays a “curtain of fire”?
Fissure eruptions
51
Fissures evolve to become
discrete vents that erupt from craters
52
Crater
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
Summit eruptions are located within
The summit crater
54
What type of eruption/vent occurs at the side of a volcano?
Flank eruptions from flank vents
55
Caldera
A large volcanic depression (much larger than craters) which form when magma chambers empty causing the volcano to collapse into an evacuated space.
56
Shield volcanoes
Broad, slightly domed shaped that are formed by lateral flow of basaltic lava
57
Cinder cones
Cone shaped pile of ejected lapilli-sized fragments with deep crater
58
Stratovolcanoes
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
What type of volcano is the most violent?
Stratovolcano
60
What type of volcano produces a nuee ardente?
Stratovolcano
61
Eruption styles
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
What factors determine the violence or explosiveness of a volcanic eruption?**
- 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
What are the types of magma rock controls the nature of an eruption?
Igneous rocks: Felsic(granitic/rhyolitic) are high in sulfur/viscosity Mafic(basaltic): are low in sulfur/viscosity
64
Why does magma rise to surface
Because magma is less dense than surrounding rock
65
Viscosity and gas escape
The less viscous = easier escape of gas bubbles
66
Vulcanian eruption
A moderate-sized explosive eruption
67
Plinian eruption
An enormous explosion of volcanic material that ejects huge quantities of material into the atmosphere
68
Eruption styles:
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
Largest eruption in modern day
Mt. Pinatubo in philippines
70
Largest eruption documented in all history
Toba in indonesia
71
What is a dominant control on volcanism?
Tectonic plate motion
72
Volcanic settings are:
* Mid-ocean ridges: spreading axes * Convergent boundaries: subduction zones * Continental rifts: incipient ocean basins * Oceanic hot spots * Continental hot spots and flood basalts
73
Which flow is more deadly?
Pyroclastic flow not lava flow
74
What is the best defense against volcanic hazards?
Understanding volcanic behaviou
75
Effect on ashfall in modern day
Kills plants and crops collapsing roof from heavy tephra Abrasion of engine from gritty tephra Tephra can become deadly lahar in flood water
76
Volcanic blast
Rare hazard since most are vertical not sideways
77
Landslide in volcanic eruptions
Large masses of material are deopsited quickly near a vent

Geo1111 (8 decks)

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