Volcanism Flashcards
What is a volcano?
Opening in the earth’s crust through which lava, volcanic ash, and gases escape
- Rupture (vent, fissure) in crust
What are the different styles of volcanism?
- Plate tectonic setting
- Type of magma
- Gas content
What area has majority of all volcanoes?
Ring of fire
Is there a direct link between volcanoes and plate tectonics?
Yes
what is being erupted from volcanoes?
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
explain the 2 Basalt rocks composition
- A’a: rubble-like texture, higher viscosity
- Pahoehoe: smooth ropy texture, low viscosity
explain the difficulty of increasing silica content?
silica content above 50% make it tougher to flow
- Blocky has high viscosity
explain relation between magma viscosity and volcanoes?
The volcano type is partially dependant on the magma viscosity
Explain magma and gas content details
- Explosivity related to gas content
- greater gas content = more explosive
- Rhylitic magma: more gas than basaltic magma
explain viscosity characteristics related to gas content
- if viscosity is high - more difficult for gas to escape (pressure builds up - a bigger eruption)
Explain how low gas and high gas/ low silica and high silica content affects volcanism?
- Low gas/low silica: runny lava, quiet eruption
- Low gas, high silica: quiet eruption
- High gas/low silica
What are the two types of eruptive styles?
Effusive and Explosive eruptions
Explain “Effusive” Eruptive Style
- Produces lava flows
- flows stream away from vents, lava lakes can form
Explain “Explosive” eruptive style
- produces pyroclastic flows
- caused by gas pressure in the more viscous magma
- Erupts - pressure released explosively
explain “Red” in Effusive style
Red produces lava flows and is peaceful
Explain “Grey” in Explosive explosions
Blows up
explain the Effusive volcanoes characteristics
- Basaltic
- Magma
- Shield Volcanoes
Explain Eruptive volcanoes characteristics
- Andesitic (to rhyolitic)
- Magma
- Stratovolcano
- Subduction zones
What are the main 2 types of volcanoes
- Shield volcano
- Stratovolcano
Explain characteristics of Shield Volcano
- Low Silica content
- Low viscosity
- Basalt rock
- Lava flows
- Largest volcano type on Earth
- Broad, dome shaped, sloping
- Gasses: vog, laze
Explain characteristics of Stratovolcano (composite)
- Cone shaped
- Intermediate viscosity and silica content
- Andesite rock
What is Laze
What is vog
Volcanic smog
- SO2 and other chemicals
What is Laze?
Lava haze
- forms when lava contacts seawater
What gases are present in magma?
- Water vapour, CO2, SO2, H2S
- released during eruptions or by fumaroles
What are stratovolcanoes associated with?
- With convergent plate boundaries
what are stratovolcanoes danger level?
High to very high
What is a Caldera?
- Collapse of a volcano’s magma chamber (huge over 100 km in diameter)
What is a crater?
basin above volcano’s vent, created by outwards explosion (smaller in diameter (a few km))
Within Pyroclastic hazards, how are blocks and bombs different in terms of fragments?
- Block: pre-existing rocks shattered by eruptions
- Bomb - lava cools as it travels through air, stream-lined
Explain Pyroclastic Flows?
- 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
Explain what a Lateral Blast is?
- Explosions of gas and ash from the side of the volcano
What is a Lahar?
Lahar: Mudflow composed of hot or cold pyroclastic material, water, mud and debris travelling downslope
What is VEI?
Volcanic Explosivity index
- How explosive a Volcano is
- 0 to 8
Explain Mount Merapi
- Active Stratovolcano in Indonesia
- eruptions regular
- small eruptions every 2-3 years
- Large eruptions every 10-15 years
Explain the series of alerts in Mount Merapi for volcanoes
- 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
