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Questions and Answers
What do pillow lavas indicate about the lava flow?
What do pillow lavas indicate about the lava flow?
- It contains a high amount of gas.
- It has a low viscosity.
- It formed above the surface of a land mass.
- It formed below the surface of a water body. (correct)
The gaseous portion of most magmas typically makes up 10 to 15 percent of its total weight.
The gaseous portion of most magmas typically makes up 10 to 15 percent of its total weight.
False (B)
The particles produced during explosive volcanic eruptions are called ___ materials.
The particles produced during explosive volcanic eruptions are called ___ materials.
pyroclastic
Which of the following gases is a significant contributor to air pollution from volcanoes?
Which of the following gases is a significant contributor to air pollution from volcanoes?
What is the primary component of volcanic gases emitted from magma?
What is the primary component of volcanic gases emitted from magma?
Match the types of pyroclastic materials with their descriptions:
Match the types of pyroclastic materials with their descriptions:
What happens to gases in magma when the confining pressure is reduced?
What happens to gases in magma when the confining pressure is reduced?
The gas-rich viscous magma erupts explosively to produce volcanic ___ that can be hazardous.
The gas-rich viscous magma erupts explosively to produce volcanic ___ that can be hazardous.
What primarily causes explosive volcanic eruptions?
What primarily causes explosive volcanic eruptions?
Pahoehoe lava flows are typically cooler and less fluid than aa lava flows.
Pahoehoe lava flows are typically cooler and less fluid than aa lava flows.
The volcanic materials erupted can include lava, large volumes of gas, and _____ materials.
The volcanic materials erupted can include lava, large volumes of gas, and _____ materials.
What are the two main types of lava flows mentioned in the content?
What are the two main types of lava flows mentioned in the content?
Match the lava types to their characteristics:
Match the lava types to their characteristics:
What type of lava flow is characterized by surfaces of large blocks and rough edges?
What type of lava flow is characterized by surfaces of large blocks and rough edges?
Block lavas can travel longer distances compared to fluid basaltic magmas.
Block lavas can travel longer distances compared to fluid basaltic magmas.
What happens to gas bubbles in magma as it nears the Earth's surface?
What happens to gas bubbles in magma as it nears the Earth's surface?
Which type of lava is characterized by low viscosity and can flow great distances?
Which type of lava is characterized by low viscosity and can flow great distances?
Higher silica content in magma leads to lower viscosity.
Higher silica content in magma leads to lower viscosity.
What is the term for the resistance to flow in a fluid material?
What is the term for the resistance to flow in a fluid material?
Magma that produces rocks rich in silica, such as granite, is referred to as __________.
Magma that produces rocks rich in silica, such as granite, is referred to as __________.
Match the types of volcanic eruptions with their characteristics:
Match the types of volcanic eruptions with their characteristics:
Which of the following factors does NOT influence the viscosity of magma?
Which of the following factors does NOT influence the viscosity of magma?
Pyroclastic flows are usually harmless and pose little threat to surrounding areas.
Pyroclastic flows are usually harmless and pose little threat to surrounding areas.
Name the two primary gas types found in volcanic eruptions.
Name the two primary gas types found in volcanic eruptions.
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Study Notes
Lava Flow and Pillow Lavas
- Interior lava advances by breaking through hardened surface, creating repeated extrusion of molten basalt, similar to toothpaste.
- Resulting lava flows form pillow lavas, which are tube-like structures stacked atop each other.
- Pillow lavas indicate formation beneath a water body, aiding geologic history reconstruction.
Gases in Magma
- Magmas contain dissolved gases, or volatiles, held under confining pressure; upon pressure release, gases escape.
- Gaseous content typically comprises 1 to 6 percent of magma weight, predominantly as water vapor.
- Volcanic gas emissions can exceed thousands of tons daily. Important gases include sulfur dioxide (SO2), which contributes to atmospheric pollution and can form toxic compounds.
Pyroclastic Materials
- Eruptions eject pulverized rock, lava, and glass known as pyroclastic materials or tephra.
- Particle sizes vary, including ash (less than 2 mm) to large fragments weighing several tons.
- Ash and dust arise from explosive eruptions of gas-rich, viscous magma, producing fine glassy fragments and welded tuff upon settling.
Types of Lava Flows
- More than 90 percent of Earth's lava is basaltic, with andesitic and rhyolitic lavas making up the remainder.
- The aa flow consists of rough, jagged surfaces with sharp edges, while pahoehoe flows are smooth and resemble twisted ropes.
- Pahoehoe flows are hotter and more fluid than aa, and conversion from pahoehoe to aa can occur, but not vice versa.
Block and Pillow Lavas
- Block lavas arise from viscous andesitic and rhyolitic magmas, characterized by short, prominent flows comprising massive, detached blocks.
- Pillow lavas often form on ocean floors, with outer skin quickly freezing into basaltic glass.
Nature of Volcanic Eruptions
- Volcanic eruptions can be explosive or non-explosive, influenced by factors such as temperature, composition, and gas content.
Viscosity in Magma
- Viscosity measures resistance to flow; higher viscosity leads to greater resistance.
- Temperature strongly affects lava mobility; increased temperature decreases viscosity as lava cools.
Composition and Silica Content
- Silica content significantly impacts magma behavior:
- Felsic rocks (high silica, >70%) lead to viscous lavas and shorter flows.
- Mafic rocks (low silica, ~50%) produce fluid lavas capable of traveling extensive distances prior to congealing.
- Viscosity hierarchy: Felsic > Intermediate > Mafic with higher silica content leading to increased viscosity.
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