Chapter 6: Problem 5

Why do magmas rise from depth to the surface of the Earth? (B)

Short Answer

Expert verified

Magmas rise from depth to the surface of the Earth due to their composition, properties, and the buoyancy force acting on them. The less dense magma, caused by the expansion of dissolved gases and higher temperature, experiences an upward buoyancy force that makes it rise towards the surface. Pressure and temperature conditions also play a role in magma movement, as a decrease in pressure can cause the magma to solidify and further increase its buoyancy force. Ultimately, these factors lead to magma rising to the Earth's surface, resulting in volcanic eruptions or intrusions into the crust.

Step by step solution

Understand the composition and properties of magma

Magma is a mixture of molten or semi-molten rock, volatiles (such as water, carbon dioxide, and other gases), and minerals. When rock in the Earth's mantle or crust heats up to a sufficient temperature, it becomes partially molten and forms magma. This can happen due to the Earth's internal heat and interactions with other tectonic processes, such as subduction or plate divergence.

Explain the buoyancy force acting on magma

Buoyancy force occurs due to differences in density between the magma and the surrounding solid rock. Magma is generally less dense than the surrounding rock because the higher temperature of the magma causes it to expand, reducing its density. As a result, the magma experiences an upward buoyancy force, causing it to rise towards the surface.

Discuss the role of pressure and temperature in magma movement

The pressure and temperature conditions in the Earth's crust and mantle play an essential role in magma movement. As magma rises, the pressure decreases, and this may cause the dissolved gases in the magma to expand and form bubbles. This further reduces the density of the magma, enhancing the buoyancy force and causing the magma to rise more quickly. Additionally, a decrease in pressure may cause the magma to partially solidify (crystallize), further increasing the buoyancy force as solid crystals are more buoyant than semi-molten magma.

Conclusion

Magmas rise from depth to the surface of the Earth due to their composition and properties, and due to the buoyancy force acting on them. The less dense magma experiences an upward buoyancy force as it is lighter than the surrounding solid rock. The pressure and temperature conditions experienced by the magma as it rises contribute to this force, causing the magma to rise to the surface where it may form volcanic eruptions or intrusions into the crust.

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Why do magmas rise from depth to the surface of the Earth? (B)

Short Answer

Step by step solution

Understand the composition and properties of magma

Explain the buoyancy force acting on magma

Discuss the role of pressure and temperature in magma movement

Conclusion

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