Magmas and Volcanoes
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What are the three types of volcanoes?
- Shield volcanoes
- Tephra cones
What does a Shield volcano look like?
- Dome shaped
- Gentle slopes
What composition does a Shield volcano have?
What kind of flow does a shield volcano have?
What does a Stratovolcano look like?
What kind of flow does a Stratavolcano have?
Pyroclastic and Lava
What composition does a Stratovolcano have?
What does a Tephra cone look like?
- formed from pyroclastic debris around a vent
- magma is gas rich
What composition does a Tephra cone have?
What flow does a Tephra cone have?
What are craters?
Depressions near summit from which volcanic materials are ejected
What are Lava Domes?
Late-stage, very viscous lava extruded after most gas exsolved
What are calderas?
- Circular, steep walled basins >1km in diameter near summit
What is a Resurgent dome?
- Due to uplift of caldera
- also small tephra cones/lava flows
What are Diatremes?
Volcanic pipes filled with rubble of broken rock
Is all lava erupted from volcanoes?
What are Fissure Eruptions?
- Extrusion of basaltic lava along elongate fractures
What are Plateau basalts?
Wide, flat plains produced by lavas from fissure eruptions
What are Pillow basalts?
Pillow shaped masses of basalt formed by submarine eruptions
What are Ash Flows?
- Andesitic or Rhyolitic magma
- Less common than basalt
What causes Thermal Springs?
Ground water heated by hot rock in or near old magma bodies
What is a Geyser?
- Thermal spring that displays intermittent eruptions of water and steam
- Pressure builds and water reaches above boiling point
What are 5 Volcanic Hazards?
- Pyroclastic flows
- Burial and or suffocation from ash
What is Magma?
Molten Rock, together with any suspended mineral grains and dissolved gases, that forms by melting of rock in crust and mantle
What is a Volcano?
Vent from which magma and gases are erupted
What is Lava?
Magma that reaches earth's surface
What is Magma made out of?
- Si02 always predominant
- Characterized by high Temperatures
How hot is Magma?
1000 - 1200 degrees Celsius
What is Viscosity?
The thickness of lava
Higher temperature lava will have a ________ viscosity.
Low temperature lava will have a _______ viscosity.
Lava that is High in Si02 will have a ______ viscosity.
Lava that is Lower in Si02 will have a ______ viscosity.
What is Pahoehoe?
Smooth ropy-surfaced lava formed from very hot fluid lava
What is Aa?
Rubbly, rough-looking lava formed from cooler, very viscous lava
What does lower density cause in magma?
What are some examples of Nonexplosive volcanoes?
- Lava fountain
- Spatter cone
- Lava Tube
How does a Lava fountain form?
Forms when basaltic magma rises so rapidly that gas bubbles from solution
How does a spatter cone form?
Forms when bits of falling lava pile up beside the vent
What are Lava tubes?
Subsurface channels in Pahoehoe lava flows
What is a Vesicle?
- Gas bubble holes preserved in solidified rock
- produces rocks with vesicular texture
What are Amygdules?
Vesicles filled by secondary minerals
What type of Magma is explosive?
Viscous Andesitic and Rhyolitic with high dissolved gas content
What is Pumice?
Froth of innumerable glass walled bubbles
What is ash?
Tiny fragments of shattered solidified magma
What is a Eruption Column?
Mixture of hot gas and tephra rising rapidly into the air
What is Tephra fall?
Rain of debris particles as eruption cloud drifts with upper winds
What is a Pyroclastic flow?
- Denser than air
- mixture of hot gas and ash
- fast and lethal
What is Ignimbrite?
Solidified deposit resulting from pyroclastic flow
What is a Lateral Blast?
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