Chapter 4

How might a forest fire influence mass wasting?

Large scale mass wasting events frequently follow forest fires because their were sudden changes made to the vegetative cover. The vegetative cover refers to trees, bunchgrasses and grasslands, legumes, and shrubs with an expected life span of at least 5 years. After the vegetative cover is destroyed by a forest fire, it leaves the hillsides bare which causes normal rainstorms to saturate the ground and cause mudslides that do tremendous damage.

In the Rocky Mountain region of the United States, north-facing slopes (downhill direction is toward the north) are typically moister and more heavily forested than south-facing slopes. Why?

North-facing slopes receive about the same amount of precipitation as south-facing slopes; less moisture evaporates from north-facing slopes.

From the land surface downward to the unweathered bedrock, which of the following is the correct order of the different soil horizons?

O, A, E, B, C, bedrock

Deforestation of rain forests exposes tropical soils that are famous for their low fertility, despite the fact that they had previously hosted a lush tropical forest. Which soil type would describe these soils?

Oxisols—Soils that occur on old land surfaces unless parent materials were strongly weathered before they were deposited. Rich in iron and aluminum oxides, Oxisols are heavily leached, hence are poor soils for agricultural activity

In your own words, describe the difference between weathering, erosion, and mass wasting.

Weathering generally restricted to material breakdown in place. The physical and chemical changes that occur in rocks happens at the interface of the Earth's hydrosphere and atmosphere. Mass Wasting is when material falls under influence of gravity with little or no transporting agent. And erosion refers to processes that move material to another site under the influence of transporting agents such as water, ice, and/or wind.

How does deforestation by fire or human activity contribute to mass wasting? a) It allows excess rainfall runoff to erode the landscape, triggering mass wasting. b) It kills tree roots that help hold the slopes in place, allowing mass movement. c) It allows the wind to blow across the slopes, imparting a stress that triggers landslides. d) It allows farming activity that exposes soil to erosion and mass wasting.

b) It kills tree roots that help hold the slopes in place, allowing mass movement.

Which of the following is most resistant to both chemical and physical weathering? a) clay minerals b) quartz c) a granite d) a limestone

b) quartz

The word topsoil is commonly used, but not always correctly. The proper definition is ________. a) the A, E and B horizons b) the dark, organic rich layers of O and A c) the entire soil down to the base of the C horizon d) only the O horizon

b) the dark, organic rich layers of O and A

Which of the following statements concerning mudflows is NOT true? a) Mudflows may be caused by heavy rains or melting snow. b) In hilly areas, mudflows move down the canyons and stream valleys. c) Mudflows deposit talus slopes. d) Mudflows can move and carry very large boulders and other coarse debris.

c) Mudflows deposit talus slopes.

Which one of the following statements best describes erosion? a) disintegration and decomposition of rocks and minerals at the surface b) movement of weathered rock and regolith toward the base of a slope c) the process by which weathered rock and mineral particles are removed from one area and transported elsewhere d) the combined processes of leaching, eluviation, and mass wasting

c) the process by which weathered rock and mineral particles are removed from one area and transported elsewhere

Rounding of angular edges of rock outcropping and formation of insitu, spherical boulders are both indications of ________.

chemical weather and associated spheroidal weathering

All of the following are factors that affect rates of weathering except for ________. a) rock characteristics b) surface area c) climate d) geologic age of earth materials

d) geologic age of earth materials

Which one of the following statements concerning mechanical weathering is NOT true? a) reduces grain sizes of rock particles b) allows for faster rates of chemical weathering c) is important in the formation of talus slopes d) involves a major change in the mineral composition of the weathered material

d) involves a major change in the mineral composition of the weathered material

Which one of the following statements concerning mechanical weathering is not true? a) reduces grain sizes of rock particles b) allows for faster rates of chemical weathering c) is important in the formation of talus slopes d) involves a major change in the mineral composition of the weathered material

d) involves a major change in the mineral composition of the weathered material

What two factors speed up rates of chemical reaction and weathering in rocks and soils? a) low temperatures; very dry b) low temperatures; very moist c) high temperatures; very dry d) warm temperatures; very moist

d) warm temperatures; very moist

A geologist is looking at deposits along a river below a large volcano. She finds large boulders mixed with sand and mud, and all of the material is comprised of volcanic rocks, particularly the mud which is volcanic ash. She quickly realizes these deposits represent an ancient ________.

lahar

Limestone and marble weather faster than granite because ________.

limestone and marble can be dissolved by weak acids in rain

Climate change and human activity like overgrazing of grasslands is leading to large areas subject to "desertification" where native grass cover dies out during drought periods, exposing soil to erosion. What is potentially the greatest initial soil erosion potential during this type of an event?

loss of topsoil by wind erosion on a large scale

One important relationship between chemical and mechanical weathering is ________.

mechanical weathering can produce smaller pieces of rock that have more surface area for chemical weathering to work on.

Mass wasting, a process that often occurs between weathering and erosion, involves ________.

the transport of material due to gravity