How do columnar joints form? What will be an ideal ...

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How do columnar joints form? What will be an ideal response?

Question 2

How is the behavior of gases different in a quiet and an explosive eruption? What will be an ideal response?

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Answer to Question 1

In a lava flow, especially a mafic one, a distinctive pattern of columns bounded by fractures may form.
This occurs when the lava flow stops moving, contracts as it cools, and produces forces that cause
fractures to open. The fractures, called joints, appear as polygonal cracks that extend downward,
forming parallel columns with their long axes perpendicular to the cooling surface.

Answer to Question 2

When mafic magma rises toward the surface, the gases within it expand and are able to escape. Mafic
magmas usually erupt quietly. When felsic magma rises to the surface, the gases are unable to expand,
and the gas pressure increases. If the pressure becomes great enough, an explosion occurs and
pyroclastic materials are blown into the air

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Gracias!

[JaynaD87]

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