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GEOL 106 > Volcanism > Flashcards

Volcanism Flashcards

1
Q

What is a volcano?

A

Opening in the earth’s crust through which lava, volcanic ash, and gases escape
- Rupture (vent, fissure) in crust

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2
Q

What are the different styles of volcanism?

A
  • Plate tectonic setting
  • Type of magma
  • Gas content
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3
Q

What area has majority of all volcanoes?

A

Ring of fire

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4
Q

Is there a direct link between volcanoes and plate tectonics?

A

Yes

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5
Q

what is being erupted from volcanoes?

A

rock types with differing silica (SiO2) content
- At mid-ocean ridges - Basalt
- Above hot spots - Basalt
- Subduction zones - Andesite
- Magma moving up through crust - Rhyolite

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6
Q

explain the 2 Basalt rocks composition

A
  • A’a: rubble-like texture, higher viscosity
  • Pahoehoe: smooth ropy texture, low viscosity
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7
Q

explain the difficulty of increasing silica content?

A

silica content above 50% make it tougher to flow
- Blocky has high viscosity

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8
Q

explain relation between magma viscosity and volcanoes?

A

The volcano type is partially dependant on the magma viscosity

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9
Q

Explain magma and gas content details

A
  • Explosivity related to gas content
  • greater gas content = more explosive
  • Rhylitic magma: more gas than basaltic magma
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10
Q

explain viscosity characteristics related to gas content

A
  • if viscosity is high - more difficult for gas to escape (pressure builds up - a bigger eruption)
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11
Q

Explain how low gas and high gas/ low silica and high silica content affects volcanism?

A
  • Low gas/low silica: runny lava, quiet eruption
  • Low gas, high silica: quiet eruption
  • High gas/low silica
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12
Q

What are the two types of eruptive styles?

A

Effusive and Explosive eruptions

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13
Q

Explain “Effusive” Eruptive Style

A
  • Produces lava flows
    - flows stream away from vents, lava lakes can form
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14
Q

Explain “Explosive” eruptive style

A
  • produces pyroclastic flows
    - caused by gas pressure in the more viscous magma
    - Erupts - pressure released explosively
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15
Q

explain “Red” in Effusive style

A

Red produces lava flows and is peaceful

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16
Q

Explain “Grey” in Explosive explosions

A

Blows up

17
Q

explain the Effusive volcanoes characteristics

A
  • Basaltic
  • Magma
  • Shield Volcanoes
18
Q

Explain Eruptive volcanoes characteristics

A
  • Andesitic (to rhyolitic)
  • Magma
  • Stratovolcano
  • Subduction zones
19
Q

What are the main 2 types of volcanoes

A
  • Shield volcano
  • Stratovolcano
20
Q

Explain characteristics of Shield Volcano

A
  • Low Silica content
  • Low viscosity
  • Basalt rock
  • Lava flows
  • Largest volcano type on Earth
  • Broad, dome shaped, sloping
  • Gasses: vog, laze
21
Q

Explain characteristics of Stratovolcano (composite)

A
  • Cone shaped
  • Intermediate viscosity and silica content
  • Andesite rock
22
Q

What is Laze

A
23
Q

What is vog

A

Volcanic smog
- SO2 and other chemicals

24
Q

What is Laze?

A

Lava haze
- forms when lava contacts seawater

25
Q

What gases are present in magma?

A
  • Water vapour, CO2, SO2, H2S
  • released during eruptions or by fumaroles
26
Q

What are stratovolcanoes associated with?

A
  • With convergent plate boundaries
27
Q

what are stratovolcanoes danger level?

A

High to very high

28
Q

What is a Caldera?

A
  • Collapse of a volcano’s magma chamber (huge over 100 km in diameter)
29
Q

What is a crater?

A

basin above volcano’s vent, created by outwards explosion (smaller in diameter (a few km))

30
Q

Within Pyroclastic hazards, how are blocks and bombs different in terms of fragments?

A
  • Block: pre-existing rocks shattered by eruptions
  • Bomb - lava cools as it travels through air, stream-lined
31
Q

Explain Pyroclastic Flows?

A
  • One of the most lethal parts of a volcanic eruption
  • Hot
  • Mixture of rock fragments, gas, and ash that travels away from volcanic vent or collapsing flow front
32
Q

Explain what a Lateral Blast is?

A
  • Explosions of gas and ash from the side of the volcano
33
Q

What is a Lahar?

A

Lahar: Mudflow composed of hot or cold pyroclastic material, water, mud and debris travelling downslope

34
Q

What is VEI?

A

Volcanic Explosivity index
- How explosive a Volcano is
- 0 to 8

35
Q

Explain Mount Merapi

A
  • Active Stratovolcano in Indonesia
  • eruptions regular
  • small eruptions every 2-3 years
  • Large eruptions every 10-15 years
36
Q

Explain the series of alerts in Mount Merapi for volcanoes

A
  • Level 1: the volcano is experiencing normal activity
  • Level 2: both visual and seismic data indicate an increase in activity
  • Activity is continuing to increase, there is a concern that an eruption will occur
  • Level 4: the eruption has initiated

GEOL 106 (9 decks)

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