Lecture 5 Flashcards
Why can magma composition differ between ultramafic, mafic, intermediate, and felsic?
Magma composition depends on the source-rock composition and processes like partial melting, assimilation, and magma mixing.
Source-rock composition can include ultramafic mantle or continental crust.
What does Bowen’s Reaction Series tell us about mineral crystallization in cooling magma?
It predicts the order in which minerals crystallize: mafic minerals form at higher temperatures, while felsic minerals crystallize later at lower temperatures.
How does igneous activity vary with different tectonic settings?
Igneous activity varies as follows:
* Divergent boundaries: decompression melting produces mafic magma
* Convergent boundaries: addition of volatiles + heat transfer produces intermediate or felsic magmas
* Hot spots: mantle plumes rise by decompression, forming shield volcanoes, potentially evolving to more felsic compositions.
What are dikes, sills, and batholiths in intrusive igneous settings?
Definitions:
* Dike: magma cuts upward across rock layers
* Sill: magma intrudes parallel to rock layers
* Batholith: large, deep-seated igneous body formed by multiple magma injections.
What is a volcano, and how does a volcanic eruption occur?
A volcano is an outlet on Earth’s surface where molten rock, pyroclastic debris, and gas escape. An eruption occurs when pressure within the chamber is released, allowing magma to surface.
What determines the speed (flow) of magma or lava?
Viscosity determines the speed, affected by:
* Silica content
* Temperature
* Volatile content
* Crystal content.
What are some common basaltic (mafic) lava flow features?
Features include:
* Lava tube
* Pillow lava
* Pāhoehoe
* ‘A‘ā.
How do andesitic and rhyolitic (intermediate-felsic) flows differ from basaltic?
They are more viscous, move more slowly, create blocky flows or lava domes, and can trap more gas.
What role do volcanic gases play, and which rocks show evidence of gas escape?
Volcanic gases affect eruption style and form bubbles in lava. Vesicular basalt or pumice can form when gas escapes.
What is pyroclastic debris (tephra), and how does it differ in mafic vs. felsic eruptions?
Pyroclastic debris is fragmental material ejected from a volcano.
* Mafic eruptions may include basaltic fragments.
* Felsic eruptions produce finer ash and can generate pyroclastic flows.
Distinguish between effusive and explosive eruption styles.
Effusive eruptions involve hot, less viscous lava; explosive eruptions involve cooler, more viscous magma that traps gases.
What are the main parts of a typical volcano?
Main parts include:
* Conduit (vent)
* Crater.
Describe the four common types of volcanoes.
Types include:
1. Shield volcano
2. Cinder cone
3. Stratovolcano
4. Caldera.
Where do volcanoes commonly occur, and what is a hot spot volcano?
Volcanoes occur along plate boundaries (divergent, convergent) and hot spot volcanoes arise from rising mantle plumes.
What hazards arise from volcanic eruptions?
Hazards include:
* Lava flows
* Pyroclastic flows
* Ash fall
* Lahar
* Blast, landslides, earthquakes, tsunami
* Volcanic gases.
