Chapter 8 - Wethering, Soil, and Mass Movement

How is carbonic acid formed in nature?

Atmospheric carbon dioxide dissolves in raindrops.

How is a fall different from creep?

Falls occur rapidly and in areas with high slope, whereas creep occurs slowly in areas with low slope.

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

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

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.

Why is soil considered an interface within the Earth system?

Changes in the climate in the atmosphere create changes in soil texture and composition. Water from the hydrosphere that is added to soil from various sources allows the soil to be able to sustain plant life, which returns the water to the geosphere when it expires.

Which of the following statements is associated with chemical weathering?

Chemical weathering changes the chemical composition of the rock

How are debris avalanches and flows related?

Debris avalanches are large, rapid flows of rock.

Which of the following options is true regarding the concepts of eluviation, leaching, zone of accumulation, and hardpan?

Eluviation washes out fine soil components in the E horizon, which is also where leaching (the depletion of soluble materials from the upper soil) occurs. As a result, the B horizon below is often referred to as the zone of accumulation, where sometimes a hardpan of impermeable clay forms.

Which of the following is true of lunar soil when compared with terrestrial soil? Select all that apply.

- It does not contain air. - It does not contain organic matter. - It cannot support life.

Which are factors that influence the type and rate of weathering a rock undergoes? Choose all that apply.

- The amount of precipitation in an area - The range of temperatures of an area - The size of the rock - Mineral composition of the rock

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.

What is the definition of physical weathering?

Mechanical processes break substances into smaller pieces.

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.

Which of the following is an example of chemical weathering?

a car fender getting rusty

Over time, mass wasting causes __________.

canyons to widen

Which of the following are classifications describing how rock and other material move downslope?

fall, slide, slump, creep, flow

Which type of mass movement event requires the addition of water?

flow

What is mass movement?

movement of material under the influence of gravity alone.

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

What rock type is the easiest for a river to cut through?

shale

A __________ is formed when vertical incision by a stream is the primary process, with relatively minimal mass wasting.

slot canyon

The processes of mechanical weathering transform rocks exposed at the surface over time. In frost wedging, seasonal freezing of water causes expansion of cracks in rock. Salt crystal growth within fissures or cracks in rock similarly causes expansion and mechanical weathering. Sheeting occurs when large sheets of rock dome upward and peel off when overlying rocks are eroded away, decreasing pressure. Biological activity can also cause mechanical weathering of rocks when living things such as the roots of plants or bacteria cause rocks to break apart. Fill in the sentences below to explore the four different mechanical weathering processes. 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*.

Drag and drop the events, processes, or one of the spheres of the Earth system to their correct location in the table below. The events and processes described in each row occur within the sphere in each row. Group 1 labels go in the first column for events. Group 2 targets go in the second column for results that occur from preceding events. Group 3 targets go in the third column for one of the spheres of Earth system. Drag the appropriate labels to their respective targets.

1. Event - a wildfire burns through a section of forest. - humans create a new highway road cut. 2. Process - saturates surrounding soil with water and increases evaporation - quickly and drastically loosens rock materials on a steep slope. - removes material from below the ground surface, allowing for subsidence or collapse of the ground. 3. Sphere - Biosphere - Atmosphere - Hydrosphere

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.

1. Mechanical weathering 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 are common. 2. Chemical weathering would predominate - 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.

Triggers of mass movement In this activity, you will explore and test your knowledge about triggers of four mass movement types. Slump: occurs on curved surfaces and involves the movement of unconsolidated materials. Slopes are considerably high in areas where a slump occurs. Flow: occurs when material moves downslope as a viscous fluid. Fall: this involves the freefall of rock pieces or masses. Fall occurs on slopes that are too steep for loose material to remain on the surface. Many falls occur when freeze and thaw cycles or plants roots weaken rocks to the point where gravity takes over. Creep: this involves the gradual downhill movement of soil or rock pieces. The major factor that facilitates this process is alternate expansion and contraction by freeze and thaw. Drag the appropriate labels to their respective targets.

1. Slump - triggered by curved oversteepened slopes. 2. Flow - triggered by large amounts of water and steep slopes. 3. Creep - triggered by repeated freezing and thawing of soils on gentle slopes. 4. Fall - triggered by ice wedging or plant activities on steep slopes.

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. Drag the appropriate labels to their respective targets.

1. frost wedging 2. Salt crystal growth 3. sheeting 4. Biological activity 5. Not an activity of mechanical weathering

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.

Slowest Chemical Weathering - Granite, with very few or no cracks. - Granite, with abundant cracks. - Basalt, with very few or no cracks. - Basalt, with abundant cracks. Fastest Chemical Weathering

How are slumps and slides related?

Slumps are a type of slide in the special case where the rupture surface is curved.

Which of the following correctly states the role of rivers and mass wasting in the formation of the Grand Canyon?

The Colorado River erodes downward, then mass-wasting processes move material from high to low areas, then the Colorado River transports material downstream.

Define mass wasting

The downslope movement of sediment and rock under the direct influence of gravity.

What would likely happen to a fence on a hill over time if the fence were built perpendicular to the hill's slope?

The top of the fence would likely bend uphill as creeping rocks moved under the fence and pushed the fence bottom downslope.

What is salt weathering?

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