Geology 111 Exam 3

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

A and E horizons

Which of the following components make up a healthy soil? water and air mineral matter organic matter organic matter and mineral matter All of these choices are needed.

All

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

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

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.

Which of the following is an example of chemical weathering?

a car fender getting rusty

Of the following processes, which is not an example of mechanical weathering? exfoliation oxidation frost wedging thermal expansion root penetration

Oxidation

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.

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

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

volume increase

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. Match each key term to the appropriate sentence. Be sure to complete each sentence before submitting your answer. You don't need to use all words.

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.

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.

Consider the marked locations in the figure below. Rank these locations based on rates of weathering as a function of climate. NOTE: Moisture is more important than temperature. Rank the rocks from fastest weathering to slowest weathering.

A,C,B Florida (Forest Soil), Canada (Wetland Soil), California (Desert Soil)

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

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.

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

Corner

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

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

Considering the following list, which is not an example of chemical weathering? Oxidation Removal of Calcite from rocks by water Dissolution Hydrolisis Exfoliation

Exfoliation

Rank the rocks from fastest weathering to slowest weathering.

Fastest to slowest: Peridotite Gabbro Diorite Granite

Sand dunes are typically dominated by quartz grains and very little other mineral matter. Why does this selection occur?

Quartz is extremely resistant to all forms of chemical weathering.

In temperate and polar regions, the accumulation of talus slopes at the base of steep, rocky cliffs is most often attributed to which of the following processes?

Frost Wedging

Pre-existing rocks are broken down into smaller particles by which of the following processes? oxidation frost wedging unloading lithification thermal expansion

Frost Wedging, Unloading, Thermal Expansion

Which of the following rocks would most likely experience sheeting? obsidian granite basalt rhyolite sandstone

Granite

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

Honolulu, Hawaii

Three types of chemical weathering processes are particularly important for transforming minerals within rocks into weathered products. These are hydrolysis, oxidation, and dissolution. Through hydrolysis reactions, minerals are weathered in the presence of water. Hydrolysis takes place when acid rain reacts with rock-forming minerals such as feldspar to produce soluble minerals that are removed in solution. Through oxidation reactions, iron-rich materials transform in the presence of oxygen in the air. Oxidation is responsible for why an apple may turn brown after your cut it open and place it in an open space. And through dissolution, minerals dissolve in water, making their chemical products ions within water. Example: Halite (NaCl) usually forms where ocean water evaporates. On the otherhand, it undergoes dissolution when placed in water. You will sort each example into its category of chemical weathering process.

Hydrolisis - 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.

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.

Image of ice on mountains showing clone-shape rock piles/talus slope beneath ----- frost wedging Image of a rocky sea shore ---- salt crystal growth Image of an exfoliation dome at Yosemite ---- Sheeting Image of tree root growing into a rock fracture ---- biological activity Image of a cave formed in limestone ---- Not an example of mechanical weathering.

What is the definition of physical weathering?

Mechanical processes break substances into smaller pieces.

______________ can contribute to crumbling roadways in areas where salt is spread to melt ice and snow in winter.

Salt crystal growth

The fissures formed as a result of ___________ in exfoliation domes can be further enlarged by __________________ in areas subjected to seasonal freeze-thaw cycles.

Sheeting, Frost wedging

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.

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 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.

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

differential weathering

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

pyroxenes

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

__________ has a crucial influence on the rates of all types of mechanical weathering.

Climate

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

Look at the descriptions below of scenarios and determine whether the scenario inhibits weathering or enhances weathering.

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

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.

Mechanical: 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: A warm wet environment with above average yearly rainfall and several stormy seasons each year. A hot humid climate with heavy precipitation that occurs all year. A hot environment with many short but intense rainstorms.

The production of tabular slabs of rocks caused by unloading of material overlying igneous bodies is known as _____.

Sheeting

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 to fastest: Granite with few or no cracks Granite with abundant cracks Basalt with few to no cracks Basalt with abundant vesicles

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.

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

calcite

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

feldspars

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

perpendicular

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 climates will have the highest rate of weathering?

warm, wet climates