Chapter 6: Weathering & Soils

Which of the following external processes are clearly active/evident in the image above? Select the two that apply.

-Erosion -Mass wasting

Which of the following components make up a healthy soil?

All of these choices are needed.

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.

(Slowest) -Granite, with very few cracks or no cracks. -Granite, with abundant cracks. -Basalt, with very few to no cracks. -Basalt, with abundant vesicles (holes). (Fastest)

There are four main types of mechanical weathering: frost wedging in which rocks are broken by water freezing within cracks, salt crystal growth in which rocks are broken by salt freezing within cracks, sheeting in which rocks dome upward and peel off, and biological activity in which living things such as tree roots break rocks apart. You will visually identify these types. Note that one of the images is not an example of mechanical weathering.

1) Image of ice on mountains showing clone-shape roack piles/talus slope beneath--- Frost Wedging 2) Image of a rocky sea shore --- Salt crystal growth 3)Image of an exfoliation dome at Yosemite --- Sheeting 4)Image of a tree root growing into a rock fracture --- Biological activity 5) Image of a cave formed in limestone --- Not an example of mechanical weathering

Where does the clay that accumulates in the B horizon come from?

A and E horizons

The map below is the spatial representation of the soil distribution across the globe. You will determine the most dominant soil type in each subregion of the world.

1. Northern part of South America= Oxisols 2. The American Southwest= Aridisols 3. The American Midwest= Mollisols 4. The Sahara desert, northern Africa= Entisol 5. Other Regions= Gelisols

The processes of mechanical weathering transform rocks exposed at the surface over time. Match key terms to appropriate sentence. Be sure to complete each sentence before submitting your answer.

1. [Climate] has a crucial influence on the rates of all types of mechanical weathering. 2. [Salt crystal growth] can contribute to crumbling roadways in areas where salt is spread to melt ice and snow in winter. 3. The fissures formed as a result of [Sheeting] in exfoliation domes can be further enlarged by [Frost wedging] in areas subjected to seasonal freeze-thaw cycles. 4. The break down of rock by moving fresh materials to the surface by burrowing animals is an example of mechanical weathering due to [Biological activity.]

The processes of chemical weathering results in the decomposition of minerals within rocks over time. Fill in the sentences below to explore the different chemical weathering processes.

1. [chemical] weathering alters the internal structure of rock materials. 2. Potassium feldspar weathers in the presence of water containing [carbonic acid]. 3. Iron weathers through the process of [oxidation]. 4. A greenhouse gas called [carbon dioxide] influences the rate of chemical weathering.

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

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

Look at the image carefully. You will see several processes and features. Some of these are agents of mass wasting while others have resulted from the processes of mass wasting itself. Which of the following features is the result of mass wasting?

Boulders

Which of the three images in Figure 2 would be most susceptible to chemical weathering and why?

C: Physical weathering has created more surface area for chemical weathering to attack.

Using the choice you made for Part C, explain why that part of the rock would chemically weather the most quickly during spheroidal weathering.

Corners have the most surface area and provide three directions from which chemical weathering can attack.

Using what you know about spheroidal weathering, put the images in Figure 1 in order from the start of spheroidal weathering to the finish.

D, A, C, B

__________ is when various geologic materials exposed to the same environmental conditions will weather differently depending on their composition.

Differential weathering

Which part of the rock in Figure 2 will get chemically weathered the most quickly?

E (corner)

Which of the following statements regarding weathering and erosion is NOT true?

Erosion and weathering have the same definition and can be used interchangeably.

Which of the following locations will weather a block of marble the most quickly?

Honolulu, Hawaii

You will sort each example into its category of chemical weathering process.

Hydrolysis: -Feldspar in granite rocks weathering to clay Oxidation: -Red color of rocks in Arches National Park -Yellow-stained rocks that used to contain pyrite before it is weathered Dissolution: -Caves formed in limestone -The salty taste of ocean water

What is the definition of physical weathering?

Mechanical processes break substances into smaller pieces.

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.

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

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.

How did weathering destroy New Hampshire's Old Man in the Mountain?

Water migrated along fractures in the rock, where it froze and wedged the rock apart.

What is salt weathering?

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

Which soil horizon will contain the greatest amount of organic material?

O horizon

How will physical and/or chemical weathering contribute to create rounded shapes during spheroidal weathering?

Physical weathering will fracture a rock, which leaves more area for chemical weathering to attack.

How can plants physically weather a rock?

Plant roots exert outward pressures as they grow.

How does physical weathering cause chemical weathering to be more effective?

When a rock is physically broken into smaller pieces, there is more surface area on which chemical weathering can occur.

Which of the following is an example of chemical weathering?

a car fender getting rusty

Which of the following climates would have the greatest degree of ice wedging?

cold in the winter, warm in the summer, and with moderate precipitation

A hoodoo with a cap rock of sandstone and shale below is an example of __________.

differential weathering

Which of the following rocks would most likely experience sheeting?

granite

When sheeting develops in an igneous pluton, fractures will develop in an orientation __________ to the direction of expansion.

perpendicular

Which one of the following is NOT an example of a mechanical weathering process?

reactions that occur when rain mixes with carbon dioxide to form carbonic acid

Using the picture of the Entrada Sandstone in Figure 1, try to identify the evidence of physical and/or chemical weathering present.

rusty color and fracturing

Which of the following scenarios best describes how sheeting will develop in an igneous rock?

A subterranean pluton is exposed at the surface, releasing confining pressure.

With the addition of water, the minerals in granite rocks chemically weather into other minerals, known as products. Test your knowledge of the by-product of each mineral as a result of chemical weathering by labeling the minerals below with their respective products.

Feldspar= Clay Quartz= No chemical change Olivine= Limonite

Think about the soil horizons that make up the solum. Why isn't the C horizon part of the solum?

The C horizon contains unweathered parent material.

Both tombstones in Figure 1 are from the same cemetery and were erected within four years of each other. Why is the younger marble tombstone more weathered than the older granite tombstone?

The quartz and feldspars in the granite are more resistant to weathering than the calcite in the marble.

During the late Cretaceous, the Bisti Badlands were home to numerous animals including turtles, crocodiles, and even dinosaurs. What type of environment were they living in?

They were living along rivers and deltas on the edge of an inland sea.

How can the creation of ice result in physical weathering?

Water expands in volume when freezing, exerting pressure on a container.

What changes are occurring in the igneous pluton that would result in sheeting?

volume increase

Which of the following climates will have the highest rate of weathering?

warm, wet climates