Volcanism

Question 1

What is a volcano?

Answer 1

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

Question 2

What are the different styles of volcanism?

Answer 2

• Plate tectonic setting
• Type of magma
• Gas content

Question 3

What area has majority of all volcanoes?

Answer 3

Ring of fire

Question 4

Is there a direct link between volcanoes and plate tectonics?

Answer 4

Yes

Question 5

what is being erupted from volcanoes?

Answer 5

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

Question 6

explain the 2 Basalt rocks composition

Answer 6

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

Question 7

explain the difficulty of increasing silica content?

Answer 7

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

Question 8

explain relation between magma viscosity and volcanoes?

Answer 8

The volcano type is partially dependant on the magma viscosity

Question 9

Explain magma and gas content details

Answer 9

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

Question 10

explain viscosity characteristics related to gas content

Answer 10

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

Question 11

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

Answer 11

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

Question 12

What are the two types of eruptive styles?

Answer 12

Effusive and Explosive eruptions

Question 13

Explain “Effusive” Eruptive Style

Answer 13

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

Question 14

Explain “Explosive” eruptive style

Answer 14

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

Question 15

explain “Red” in Effusive style

Answer 15

Red produces lava flows and is peaceful

Question 16

Explain “Grey” in Explosive explosions

Answer 16

Blows up

Question 17

explain the Effusive volcanoes characteristics

Answer 17

• Basaltic
• Magma
• Shield Volcanoes

Question 18

Explain Eruptive volcanoes characteristics

Answer 18

• Andesitic (to rhyolitic)
• Magma
• Stratovolcano
• Subduction zones

Question 19

What are the main 2 types of volcanoes

Answer 19

• Shield volcano
• Stratovolcano

Question 20

Explain characteristics of Shield Volcano

Answer 20

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

Question 21

Explain characteristics of Stratovolcano (composite)

Answer 21

• Cone shaped
• Intermediate viscosity and silica content
• Andesite rock

Question 22

What is Laze

Question 23

What is vog

Answer 23

Volcanic smog
- SO2 and other chemicals

Question 24

What is Laze?

Answer 24

Lava haze
- forms when lava contacts seawater

Question 25

What gases are present in magma?

Answer 25

- Water vapour, CO2, SO2, H2S - released during eruptions or by fumaroles

Question 26

What are stratovolcanoes associated with?

Answer 26

- With convergent plate boundaries

Question 27

what are stratovolcanoes danger level?

Answer 27

High to very high

Question 28

What is a Caldera?

Answer 28

- Collapse of a volcano's magma chamber (huge over 100 km in diameter)

Question 29

What is a crater?

Answer 29

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

Question 30

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

Answer 30

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

Question 31

Explain Pyroclastic Flows?

Answer 31

- 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

Question 32

Explain what a Lateral Blast is?

Answer 32

- Explosions of gas and ash from the side of the volcano

Question 33

What is a Lahar?

Answer 33

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

Question 34

What is VEI?

Answer 34

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

Question 35

Explain Mount Merapi

Answer 35

- Active Stratovolcano in Indonesia - eruptions regular - small eruptions every 2-3 years - Large eruptions every 10-15 years

Question 36

Explain the series of alerts in Mount Merapi for volcanoes

Answer 36

- 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