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Questions and Answers
What is the primary material ejected during the formation of cinder cone volcanoes?
What is the primary material ejected during the formation of cinder cone volcanoes?
Which type of volcano is primarily characterized by alternating layers of ash and hardened lava?
Which type of volcano is primarily characterized by alternating layers of ash and hardened lava?
What is the relationship between pressure and temperature in the Earth's crust and mantle?
What is the relationship between pressure and temperature in the Earth's crust and mantle?
Which type of magma is associated with the most explosive eruptions?
Which type of magma is associated with the most explosive eruptions?
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What defines the explosivity of a volcano?
What defines the explosivity of a volcano?
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What type of eruptions are typically associated with oceanic-continental subduction volcanoes?
What type of eruptions are typically associated with oceanic-continental subduction volcanoes?
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What is a common characteristic of eruptions at divergent boundaries?
What is a common characteristic of eruptions at divergent boundaries?
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Which structure is responsible for storing magma beneath the Earth's surface?
Which structure is responsible for storing magma beneath the Earth's surface?
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Which type of volcano is characterized by broad, gently sloping sides and results from nonexplosive eruptions?
Which type of volcano is characterized by broad, gently sloping sides and results from nonexplosive eruptions?
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What occurs when magma emerges from a volcanic vent?
What occurs when magma emerges from a volcanic vent?
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What distinguishes the formation of chains of volcanoes over stationary hotspots?
What distinguishes the formation of chains of volcanoes over stationary hotspots?
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What is a caldera?
What is a caldera?
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What is formed when lava flows out of long cracks in the Earth's crust?
What is formed when lava flows out of long cracks in the Earth's crust?
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Study Notes
Zones of Volcanism
- Volcanism occurs at convergent plate boundaries, divergent plate boundaries, and hot spots.
- Oceanic-continental subduction zones cause mantle melting and magma rising, forming volcanoes. Most land volcanoes result from this type of subduction, known as explosive eruptions.
- Divergent boundaries typically produce nonexplosive eruptions. Pillow lava is formed at divergent boundaries on the ocean floor.
- Hot spots are unusually hot areas in Earth's mantle. High-temperature plumes of mantle material rise to the surface in these locations.
Hotspots and Plate Motion
- Chains of volcanoes over stationary hotspots show plate motion.
- Flood basalts are formed when lava flows out of long cracks in Earth's crust, called fissures.
Anatomy of a Volcano
- Crater: A bowl-shaped depression at the volcano's summit surrounding the vent.
- Caldera: Larger depressions at the summit of a volcano.
- Magma Chamber: A region below Earth's surface that stores molten material known as magma.
- Vent: The opening where lava emerges.
- Conduit: A tube-like structure that transports magma from the magma chamber to the vent.
Types of Volcanoes
- The appearance of a volcano depends on the materials that form the volcano and the eruptions.
- Volcanoes are classified as shield volcanoes, cinder cones, and composite volcanoes.
Shield Volcanoes
- Shield volcanoes have broad, gently sloping sides and a nearly circular base.
- They form from layers of lava accumulated during nonexplosive eruptions.
- Shield volcanoes are the largest type of volcano.
Cinder Cone Volcanoes
- Cinder cones have steep sides and are the smallest type of volcano.
- These volcanoes are formed when eruptions eject small pieces of lava into the air, forming tephra.
- Tephra falls back to Earth and piles up around the vent.
Composite Volcanoes
- Composite volcanoes are formed from layers of ash and hardened lava chunks from violent eruptions, alternating with layers of lava.
- These volcanoes form cone-shaped structures with concave slopes before solidifying.
Eruptions
- A volcano erupts when pressure from the magma forces its way to the surface.
Making Magma
- Pressure increases with depth due to overlying rock weight.
- As pressure increases, temperature also increases.
- This explains why most rocks in Earth's lower crust and upper mantle are solid, while those in the core are liquid.
Types of Magma
- Volcano explosivity depends on magma composition.
- Basaltic: Forms when upper mantle rock melts. Associated with quiet eruptions.
- Andesitic: Found along oceanic-continental subduction zones. Intermediate explosivity.
- Rhyolitic: Results when molten material mixes with the overlying continental crust. Extremely explosive.
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Description
Explore the fascinating world of volcanism, including its occurrence at convergent and divergent plate boundaries, as well as hot spots. Learn about the structures of volcanoes, their eruptions, and how plate motion is linked to these geological phenomena.
