GeologyLesson 4 of 5 in the course Earthquakes and volcanoes

Magma: Composition, Melting, Differentiation, and Ascent

5 flashcards · 5 quiz questions · 5 match pairs · 4 fill-in sentences · English

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Summary

Magma is the molten or partly molten material from which igneous rocks form. Understanding what magma contains and how its composition varies helps explain why volcanoes produce different kinds of lava and rocks.

Magma is naturally occurring molten or semi-molten material beneath a planet’s surface. It may include liquid rock, suspended crystals, and gas bubbles. The term lava is used for magma that has erupted onto the surface; the two terms are related but are not interchangeable.

All flashcards

How does magma differ from lava?
Magma is molten or partly molten material below the surface; lava is magma erupted onto the surface.
What is equilibrium crystallization?
Crystals continue to equilibrate with the melt, so the overall composition of melt plus crystals is retained.
What is a crystal mush?
A magma mixture containing abundant crystals; at high crystal content it may behave more like a solid than a fluid.
What is a non-silicate magma?
Magma not dominated by silicate material; carbonatite, iron-oxide, and sulfur magmas are examples.
What are cumulates?
Layered accumulations of crystals that settle to the bottom of a magma body.

Quiz questions

  1. What commonly happens to dissolved gases as magma rises and pressure decreases?Answer: They come out of solution and form bubbles.
  2. Why does increasing silica content generally increase magma viscosity?Answer: Silica tetrahedra link into larger networks.
  3. What does the liquidus mark for a rock or magma?Answer: The temperature above which the material is completely liquid.
  4. How does fractional crystallization change a magma?Answer: Removing crystals as they form changes the composition of the residual melt.
  5. What is a common result of slow cooling of magma underground?Answer: Intrusive rock with more time for crystals to grow.

Based on the Wikipedia article Magma, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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