Volcanoes Flashcards
On Exam 2
What are volcanoes? Where do most of them form?
A structure formed when magma becomes lava and erupts onto the surface
Form mainly along plate boundaries (strongest on convergent)
What are the two types of magma? What differentiates them and how does it affect volcanic eruptions?
Mafic: erupts at higher temperatures, more iron and magnesium, more water = lower viscosity, mellow eruptions, aka effusive
Felsic: erupts at lower temperatures, more silica, less water = higher viscosity, more explosive, more gas
What are the types of volcanic gases? What is this controlled by
Water Vapor, Carbon Dioxide, Sulfur Dioxide
Proportion of gas that erupts from a volcano is determined by magma composition
What is magma composition largely controlled by?
The location in which it formed, controlled largely by plate tectonics (is it a hotspot? subducting plate? collision?)
Ex: mantel = (ultra)mafic, oceanic = mafic, continental = felsic
What does Bowen’s Reaction Series have to do with this?
Magma composition will indicate formation temperature, which will influence what temp the volcano explodes at
What are some characteristics of Mafic Eruptions specifically?
Pahoehoe, Aa, Lava Fountains, and Pillow Lava
Pahoehoe (pa-hoy-hoy)
A basalt with a glassy, ropy texture that forms when the surface of the lava cools, creating a hot skin, and congeals into ribbons/ridges
Aa (ah-ah)
A volcanic rock with a jagged, blocky texture that forms when the molten interior continues to flow and breaks up the cooled surface
This shit HURTS to step on (hence the name ah ah)
Lava Fountain
A jet of lava being sprayed into the air, but they don’t go very far because they aren’t very gaseous (they’re mafic)
Pillow Lava
Bulbous features that form when mafic lava erupts into water and rapidly cools
What are some characteristics of Felsic and Intermediate Eruptions?
Aerosols, Pyroclastic Material, Pyroclastic Flow, Lahars, Rocks with Vesicles
Aerosols
A mixture of gas and particles that is ejected by a volcano and suspended into the atmosphere, potentially traveling for a long time or distance
Pyroclastic Material
Particles violently blown out of the volcano, which are classified based on size (bomb, lapilli, and ash)
Pyroclastic Flow and Lahars
A ground-hugging avalanche of hot volcanic ash that can move very fast and mix with water to create Lahars (volcanic mudslides)
Vesicles
Holes preserved in volcanic rocks caused by the escape of gases from the lava
More common in felsic rocks because they have more gas
What are some characteristic features of a volcanic in general?
The magma chamber, fissures, vents, craters, calderas, distinctive shape and profiles (determined by the magma composition)
Magma Chamber
An open cavity of highly fractured rock that may contain a large quantity of magma
Craters vs Calderas
Craters: bowl-shaped depression atop a volcano
Caldera: deep depression caused by the collapse of the volcano in on itself as the magma chamber empties
What are some distinctive volcanic profiles (i.e. what types of volcanoes are there)?
How does magma composition influence this?
Shield, Cinder cones, and Stratovolcanoes
Mafic lava = more flow = travels farther before cooling = wide
Felsic lava = more explosive = vertical building
Shield Volcanoes
Gentle sloping sides and a large diameter (caused by the flow of mafic lava)
Long duration of activity, but are non-explosive
Cinder Cones
Tall, steep-sided with a small diameter (caused by explosive felsic lava that mainly shoots/builds upwards)
Eruptions contain lots of pyroclastic material
Stratovolcanoes
AKA Composite Volcanoes
Tall and steep slopes that are built of alternating layers of lava, pyroclastic material, and debris
Are long-lived and explosive (the most dangerous)
In what way might a volcano benefit society?
They lead to fertile soil
What are the biggest dangers of volcanoes (what about them kills the most people)?
Pyroclastic Flow and Lahars are the most dangerous parts of the explosion itself (not the lava)
Many people also die from the aftermath (such as downed power lines and fires)
Why might people not evacuate?
Lack the ability (disabled, nowhere to go, can’t afford it, can’t leave work, language barriers)
Don’t want to leave behind possessions or pets
Don’t believe the threat is real (due to past false alarms and mistrust in the scientific community)
What are some ways that we try to protect people from volcanoes?
Danger assessment maps, volcano insurance, evacuation, diverting flows with water or explosives
What are the warning signs that a volcano might erupt?
Earthquake activity (due to magma moving around in the ground), heat flow, changes in shape, increases in gas emissions or changes in the gas mixture
What is recurrence interval? How does it classify volcanoes?
Average time between eruptions
- Active: recently erupted or likely to erupt
- Dormant: hasn’t erupted in a long time, but still could
- Extinct: the magma chamber is empty and will no longer erupt
How can volcanoes affect climate in the short-run? What about the long-run?
Short run: ash and aerosols high in the atmosphere can block sunlight and cause atmospheric cooling
Long run: the release of greenhouse gases will lead to warming
How do greenhouse gases work?
They hold sunlight within them and transfer it to other molecules
The more molecules of gas there are, the less room there is for the heat to escape, leading to a buildup within the system
