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Geography 1060 > Lecture 10: Volcanism and the Chemistry of Magma > Flashcards

Lecture 10: Volcanism and the Chemistry of Magma Flashcards

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1
Q

Volcanology

A

Study of the origin and ascent of magma through the planet’s mantle and crust and its eruption at the surface

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2
Q

Extinct

A

A volcano that has not erupted during the last several thousand years and is not expected to erupt again; for example, Kilimanjaro, Tanzania

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3
Q

Dormant

A

Volcanoes that have erupted during the last several thousand years but have been quiet in historical times; for example, Mount Meager, British Columbia

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4
Q

Active

A

A volcano is active if it is currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions, or if it has erupted in historic time. It’s important to note that the span of recorded history differs from region to region; in the Mediterranean, recorded history reaches back more than 3,000 years but in Hawai`i, little more than 200 years.

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5
Q

Stratovolcano

A

Volcanoes constructed of alternating layers of pyroclastic debris and lava flows; also called composite volcanoes
Med/high viscosity, med/high volatiles, large volume, great slow angle
Andesite

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6
Q

Shield volcano

A

Very wide volcanoes built of low-viscosity lava
Hawaiian
Low viscosity, low volatiles, large volume, low slope angle
Basalt

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7
Q

Somma volcano

A

Volcanic caldera that has been partially filled by a new central cone

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8
Q

Caldera

A 
A large (over two kilometres in diameter), basin-shaped volcanic depression, roughly circular in map view, that forms by a piston-like collapse of rock into a partially evacuated magma chamber
Rhyolite
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9
Q

Cinder cone

A

Most common types of volcanic cones
Form after violent eruptions blow lava fragments into the air, which then solidify and fall as cinders around the volcanic vent

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10
Q

Viscosity

A

Resistance to gradual deformation by shear stress or tensile stress – Internal Friction

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11
Q

What affects magma viscosity? (3)

A
  1. Gas escape
  2. Water content
  3. Silica content
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12
Q

Most common molecules in magma (3)

A

O-2, Si+4, SiO2

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13
Q

Second most common molecules in magma (2)

A

Al+3, Al2O3

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14
Q

Third most common molecules in magma (4)

A

Fe+2/+3, CaO, FeO, Fe2O3

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15
Q

Affect on magma: Left side of period table

A

Weaker bonds, therefore weaker magma viscosity

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16
Q

Bond energy and breakage

A

Higher bond energy, harder to break

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17
Q

Andesite

A

52-66% silica

Lava domes and stratovolcanoes

18
Q

Basalt

A

45-62% silica

Shield volcanoes

19
Q

Dacite

A

> 63% silica
Caldera
Viscous: explosive

20
Q

Rhyolite

A

> 66% silica

Caldera

21
Q

Mafic

A

Basalt
45-52% silicon dioxide
Higher temperature, earlier crystals

22
Q

Intermediate

A

Andesite

52-66% silicon dioxide

23
Q

Felsic

A

Rhyolite
>66% silicon dioxide
Lower temperature, latest crystals
Quartz

24
Q

Mid-ocean ridge volcanism

A

80% of the volcanism on Earth
Eruption on ridges at great depth
Takes time to build up to surface
Important hydrothermal activity

25
Q

Icelandic eruption

A 
Gentle eruption, non exposive
Low silica content
Low viscosity
Low gas content
Basaltic lava
Volcanic plateau and small shield volcanoes
26
Q

Hawaiian eruption

A 
Gentle eruption, non explosive
Low silica content
Low viscosity
Low gas content
Basaltic lava
Large shield volcanoes
27
Q

Strombolian eruption

A 
Gentle eruption, low explosive
Low silica content
Low viscosity
Low gas content
Basal to andesitic lava
Pyroclastic fragments
Scoria cones
28
Q

Vulcanian eruption

A 
Gentle eruption, moderate explosive
Low silica content
Low viscosity
Low gas content
Basalt to andesitic to rhyolite
Pyroclastic fragments
Scoria cones and stratovolcanoes
29
Q

Vesuvian eruption

A 
Explosive eruption
High silica content
High viscosity
High gas content
Adesitic lava
Pyroclastic fragments
30
Q

Kratatoan

A 
Explosive eruption
High silica content
High viscosity
High gas content
Adesitic lava
Pyroclastic fragments
31
Q

Pelean

A 
Explosive eruption
High silica content
High viscosity
High gas content
Rhyolitic lava
Pyroclastic fragments
32
Q

Plinian

A 
Explosive eruption, high explosivity
High silica content
High viscosity
High gas content
Andesite to rhyolitic lava
Pyroclastic fragments
Stratovolcanoes
33
Q

Volcanic eruptions in order of eruption force (8)

IHSVVKPP

A 
Icelandic
Hawaiian
Strombolian
Vulcanian
Vesuvian
Kratatoan
Pelean
Plinian
34
Q

Direct volcano hazards

A 
Lava
Pyroclastic flow
Nuee Ardentes
Pyroclastic surge
Ash fall 
Acid rain
Bombs
Lahar
Debris avalanche
Shock wave
Lateral blast
Gases
35
Q

Indirect volcano hazards

A

Change in groundwater
Lack of vegetation
Lack of solid ground

36
Q

Yellowstone

A 
Resurgent Caldera
Eruptions
2.1 Myr ago, 1.3 Myr ago, 0.64 Myr ago  (when is the next one?)
Lava Creek Tuff
640,000 years ago
1000 km3 of ash
37
Q

Can we predict when a volcano will erupt?

A 
Eruption recurrence history
Infrared photos of cone temp.
Temperature of steam
Bulges and slope movement
Seismic activity
38
Q

Long Valley California

A 
760,000 yr ago
400 km3 magma erupted
Pyroclastic flows covered > 1500km2
“Bishop Tuff”
Long Valley Caldera collapsed 2 km
Modern magma chamber: 10 km diameter, 8 km deep
600, 200 years ago
Associated with Mount St. Helens, 1980
39
Q

Risk of incorrect prediction?

A 
Mammoth Lakes is affluent resort town
20,000 residents during ski season
May 1982 USGS issued vol. haz. warning
House prices fell 40%, major economic impact
‘Cry wolf’ syndrome
40
Q

Mt. Pinatubo

A

1 Million people
Magma rose from 32 km in 500 yrs
June 7, 1991 small initial eruption, June 12 millions of m3 erupted, June 15 more than 5 km3 erupted
Ash cloud to 35 km in air, 480 km across
Blocked sunlight, filled valleys, lahars
300 people died
$1.5M monitoring saved 20,000 lives and >$500M evacuated property

41
Q

Canada’s volcano hazard

A

There are more than 200 potentially active volcanoes in Canada, 49 of which have erupted in the past 10,000 years

42
Q

Latest Canadian eruption

A

Iskut-Unuk River Cones in 1904

Geography 1060 (25 decks)

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