Module 13

What is salt weathering?

the formation of minerals in rock cracks during the evaporation of salty water, forcing rock apart

What do freeze-thaw and salt weathering have in common?

Both freeze-thaw and salt weathering require rain and force rocks apart physically.

The major determining factor for the chemical break down of rocks is their chemical composition. For example, granite and basalt are both igneous rocks with different chemical composition and structure and, therefore, different weathering rates. Rocks with minerals that crystallize late in Bowen's reaction series, like granite, are usually more resistant to chemical weathering than those with minerals that crystallize early, like basalt. Besides chemical composition, a secondary factor that affects the rate of weathering in such rocks is the amount of cracks/fractures present. Rank the rocks in order of the rate of chemical weathering they would experience, assuming they are all located in the same warm wet climate. Rank from slowest to fastest.

Granite, with very few or no cracks Granite, with abundant cracks Basalt with few to no cracks Basalt with abundant vesicles (holes)

Read the following descriptions of several different environments. Based on the information given, sort each environment into the correct bin for an environment that would experience predominantly mechanical weathering or predominantly chemical weathering. Drag the appropriate items into their respective bins.

Mechanical weathering would predominate. A cold wet environment at high elevation, in which freezing and thawing is common. A cold dry environment experiencing uplift, in which material is being removed by erosion from an underlying pluton/intrusive igneous rock. Chemical weathering would predominate. A hot environment with many short but intense rainstorms.A hot humid climate with heavy precipitation that occurs all year.A warm wet environment with above average yearly rainfall and several stormy seasons each year.

During hydrolysis, ions and clay minerals are produced by the decomposition of which of the following Earth materials?

Quartz is extremely resistant to all forms of chemical weathering.

Considering the following list, which is not an example of chemical weathering?

exfoliation

Why does water frozen in the cracks of a rock help to break down the rock?

Water expands when frozen and physically forces the rock apart.What is salt weathering?

The chemical weathering process known as dissolution is most effective in the breakdown of which of the following minerals?

calcite

Look at the descriptions below of scenarios and determine whether the scenario inhibits weathering or enhances weathering. Drag the appropriate items to their respective bins.

limits weathering Rows of trees are planted on the border of a field to slow the wind and deflect it upward. Promotes weathering Humans remove trees and other vegetation in order to develop an area of land. LIchens, which secrete acids, are present on the surface of a rock. Animals burrow into the ground loosening the soil. Consistent grazing by a herd of cattle.

Of the following processes, which is not an example of mechanical weathering?

oxidation

The chemical weathering process known as oxidation would be most effective in the breakdown of which of the following Earth materials?

pyroxenes