Ch. 5, p. 124: #4-6, 12, 13

4.  Why do stone buildings tend to weather more rapidly in cities than in rural areas?

Air pollution in urban areas makes water more acidic and more effective at dissolving rock material.  Pollution of that sort is not as common in rural settings.

5.  Describe at least three processes that mechanically weather rock.

In frost wedging, the expansion of ice that freezes in cracks causes the cracks to widen with each generation of freezing.  In pressure release, rocks that form at depth under great pressure may expand when overlying rock material is eroded away.  Biological activity, including root growth of plants and animal burrowing may loosen and break up rocks.

6.  How can mechanical weather speed up chemical weathering?

Mechanical weathering increases the overall surface area when it breaks down the rock into smaller fragnments.  Increased surface area provides more surface for chemical weathering to attack the rock, allowing chemical weathering to speed up.

12.  Physical disintegration of rock into smaller pieces is called:

d.  mechanical weathering

13.  The decomposition of rock from exposure to water and atmospheric gases is called:

a.  chemical weathering

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