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Geosciences LibreTexts

9.7: Lab Exercise (Part C)

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  • Part C - Magma Viscosity

    The following questions address what factors control how fast a magma or lava can flow. The resistance to flow (viscosity) depends primarily on the magma or lava composition but is also affected by temperature.

    9. Intermediate lavas can flow _____ than mafic lavas, due to the _______viscosity.

    a. slower, higher

    b. slower, lower

    c. faster, higher

    d. faster, lower


    10. Let’s relate food items to magmas of different viscosity; if we compare how honey and water flow when poured from a container:

    a. Then, the honey represents felsic magma while the water represents mafic magma

    b. Then, the honey represents mafic magma while the water represents felsic magma.


    11. Imagine putting the honey in the refrigerator overnight; will its viscosity be affected?

    a. Yes. The viscosity will increase.

    b. Yes. The viscosity will decrease. 

    c. No. There will be no change as the composition stays the same.


    12. Keep the honey in mind while you answer this question: when it first erupted, basalt lava typically erupts at 1200°C; after flowing away from the vent, the temperature falls, therefore the viscosity of the basaltic lava will:

    a. increase

    b. decrease

    c. stay the same

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