Chapter 22: Problem 11

The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. How does lithosphere respond to the weight of glacial ice? (B)

Short Answer

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The lithosphere responds to the weight of glacial ice through the processes of isostatic depression and isostatic rebound. As glacial ice accumulates on the Earth's surface, the weight causes the lithosphere to adjust its thickness and sink deeper into the asthenosphere, a process called isostatic depression. When the ice melts or retreats, the lithosphere begins to rise back to its previous elevation through isostatic rebound, maintaining isostatic equilibrium.

Step by step solution

1. Introduction to lithosphere and glacial ice

The lithosphere is the solid, outer part of the Earth, comprising the Earth's crust and upper mantle. Glacial ice is the accumulation of snow over time that forms large ice sheets and glaciers. When these ice sheets and glaciers form on the Earth's surface, they exert a significant downward pressure on the underlying lithosphere due to their immense weight.

2. Introduction to Isostasy

Isostasy is the state of gravitational equilibrium between the Earth's lithosphere and the underlying, more fluid asthenosphere. It's a term used to describe how the Earth's crust tends to adjust its thickness so that lighter rocks float on denser mantle rocks over long geological timescales. This concept helps explain how the Earth's crust responds to the distribution of mass, like the weight of glacial ice, on its surface.

3. Response of the lithosphere to glacial ice

When a significant amount of glacial ice accumulates on the Earth's surface, it adds extra weight to the lithosphere. In response, the lithosphere adjusts its thickness to maintain isostatic equilibrium, causing the crust to sink deeper into the more fluid asthenosphere. This process is called isostatic depression, where the crust bends downward under the weight of the ice.

4. Isostatic rebound

After the ice melts or retreats, the weight on the lithosphere is removed, and the crust begins to rise back up to its previous elevation, a process called isostatic rebound. The rate of rebound is influenced by the Earth's crust's elasticity and the rate at which glacial ice is removed. This process may take thousands of years to reach a new equilibrium. To sum up, the lithosphere responds to the weight of glacial ice by adjusting its thickness through the processes of isostatic depression and isostatic rebound. The Earth's crust gets pushed down under the weight of the ice and rises back up when the ice melts or retreats, in order to maintain isostatic equilibrium.

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The letters following each Review Question refer to the corresponding Learning Objective from the Chapter Opener. How does lithosphere respond to the weight of glacial ice? (B)

Short Answer

Step by step solution

1. Introduction to lithosphere and glacial ice

2. Introduction to Isostasy

3. Response of the lithosphere to glacial ice

4. Isostatic rebound

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