GLY1010 Chapter 6 Test - Weathering and Soil

What are three (3) major processes of chemical weathering?

1. Dissolution 2. Oxidation 3. Hydrolysis

What are four (4) important physical processes that lead to the fragmentation of rock? (i.e. mechanical weathering)

1. Frost Wedging 2. Salt Crystal Growth 3. Sheeting 4. Biological Activity

What are four (4) stages of soil erosion by water?

1. Once soil forms, erosional forces (e.g. *water* and wind) move soil components from one place to another. 2. In a process called *sheet erosion*, thin sheets of water flow across the surface for a relatively short distance, carrying away the dislodged soil particles. 3. Threads of current typically develop, and tiny channels called *rills* begin to form. As the rills enlarge, even deeper cuts of soil, called *gullies*, are created. 4. Once in the stream channel, the soil particles, now referred to as *sediment*, are transported downstream and eventually deposited.

What are five (5) controls of soil development?

1. Parent Materials 2. Climate 3. Plants & Animals 4. Time 5. Topography

What are the two (2) components of a solution?

1. Solute 2. Solvent

What are two (2) ways in which time influences soil formation?

1. The nature of soil is strongly influenced by the length of time different geological processes have been operating. 2. The longer soil has been forming, the thick it becomes and the less it resembles its parent material. 3. The amount of time weathering has been taking place determines the amount of influence the parent material has on soil characteristics. (i.e. more recent weathering = stronger influence of parent material; older weathering = less influence of parent material)

What are two (2) ways in which parent materials influence soil formation?

1. The type of parent material (underlying bedrock or unconsolidated sediment) influences the rate of weathering and thus the rate of soil formation. 2. The chemical makeup of the parent material affects the soil's fertility, which influences the character of the natural vegetation the soil can support.

What are three (3) agents of chemical weathering?

1. Water 2. Oxygen 3. Carbon Dioxide

Weathering

Involves the physical breakdown (disintegration) and chemical operation (decomposition) of rock at or near the Earth's surface.

Topspoil

Made up of the O and A soil horizons

Biological Activity

Physical process accomplished by the activities of organisms, including (1) plants, (2) burrowing animals, and (3) humans.

Unloading

Physical process that contributes to sheeting in which a great reduction of pressure occurs as overlying rock is eroded away.

Creep

Slower form of mass wasting that involves the gradual downhill movement of soil and regolith, partly due to the repeating expansion and contraction of the surface material caused by freezing and thawing or wetting and drying.

Residual Soils

Soils whose parent material is underlying bedrock

What is the role of water in dissolution?

Water acts as a solvent of the products (i.e. minerals) of dissolution.

Give a real-world example/application of a lahar

Redoubt Volcano in Alaska: An eruption of this volcano on Alaska's Kenai Peninsula sent lahars down the valley of the Drift River.

Debris Slide

Refers to a rapid form of mass wasting similar to a rockslide, except the material involved is largely unconsolidated.

Regolith

Refers to the layer of rock and mineral fragments that are produced by weathering and which cover the majority of the Earth's land surface

Solifluction

Refers to the slower form of mass wasting in which masses of soil saturated with water may flow downslope at a rate of a few millimeters per day or per year; means 'soil flow'.

Debris Flow

Relatively rapid type of mass wasting that involves a flow of soil and regolith containing a large amount of water; it can also be described as a moving tongue of well-mixed mud, soil, rock, and water. These processes pose a serious hazard to relatively dry mountainous areas such as southern California.

Transported Soils

Soils whose parent material is unconsolidated sediment

Rockslide

Rapid form of mass wasting that is an example of a transitional slide and occurs when blocks of bedrock break loose and slide a relatively flat slope or surface with little to no rotation or backward tilting.

Soil Profile

A vertical section through a plot of soil showing its succession of horizons and its underlying parent material.

Describe the general structure of a soil profile.

A well-developed soil profile consists of five distinct, identifiable horizons; from the surface downward, they are designated as O, A, E, B, and C.

Slump

Rapid form of mass wasting that is an example of a rotational slide and refers to the downward sliding of a mass of rock of consolidated material moving as a unit along a curved surface of rupture.

True or False: Oxygen has to be present in order for oxidation to occur.

*False*: Oxygen is *not* necessarily an inherent agent of oxidation.

Give a real-world example/application of a rockslide

*Gros Ventre, WY*: The side of Sheep Mountain when the titled sandstone bed that had been cut through by the river could no longer maintain its position atop the saturated bed of clay

Give a real-world example/application of a slump

*Point Fermin, CA*: Waves undercut the base of the steep slope, making it unstable.

B-Horizon

- By itself, this horizon makes up the subsoil - Often referred to as the zone of accumulation, because it is here that much of the material removed from the E-Horizon by eluviation is deposited - This accumulation of fine clay particles enhances this horizon's ability to retain water - In extreme cases, clay accumulation can form a very compact, impermeable later called hardpan.

Describe the relationship between mechanical weathering and chemical weathering.

- Mechanical weathering increases surface area, adding to the effectiveness of chemical weathering because chemical weathering can occur only on exposed surfaced - Chemical weathering weakens the outer portions of some rocks, making them more susceptible to being broken down by processes of mechanical weathering.

C-Horizon

- Soil horizon partially characterized by partially altered and easily identifiable parent material - In this horizon, parent material undergoes changes that will eventually transform it into soil - The parent material has not yet crossed the threshold that separates regolith from soil;

O-Horizon

- The upper-most horizon in a soil profile which is subdivided into an upper and lower portion - This horizon consists of loose and partly decayed organic matter (i.e. humus) and mineral matte - Contains litter/debris of recognizable (partly decayed) & unrecognizable (fully decayed) plant - Also teeming with microscopic life (e.g. bacteria, fungi, algae, and insects) which contribute oxygen, carbon dioxide, and organic acids to the soil

E-Horizon

- Third-down, light-colored soil horizon that contains little organic matter - As water percolates downward through this zone, finer particles are carried away and soluble inorganic soil components are dissolved and carried further downward to deeper zones - Zone of eluviation and leaching

What are four (4) products of hydrolysis? (hydro = water; lysis = loosening)

1. Clay Minerals (e.g. kaolinite) 2. Quartz Grains 3. Hematite 4. Limonite

Give two (2) examples of slow forms of mass wasting in order of descending rate of speed

1. Creep 2. Solifluction

What are four (4) ways in which organic matter (furnished by organisms) influences soil formation?

1. Decomposed organic matter supplies important nutrients to plants, as well as to animals and microorganisms living in the soil. 2. The amount of organic matter present can influence soil fertility 3. Organic matter has a high water-holding ability and thus aids water retention in soil. 4. Organic matter contains nutrients for organisms, like earthworms, who feed on it, mixing the soil in which they live in the process, often moving and enriching many tons of soil per acre each year.

What are some products of oxidation?

1. Ferromagnesian minerals (e.g. olivine, pyroxene, hornblende, and biotite) 2. Hematite (reddish-brown iron oxide) and limonite (yellowish-colored rust), which are formed when oxygen readily combines with the ferromagnesian minerals

What are three (3) products of dissolution?

1. Halite 2. Calcite 3. Sulfuric Acid

What are the two (2) main categories of weathering?

1. Mechanical weathering 2. Chemical weathering

Describe the activities of the three (3) agents of biological activity (i.e. plants, burrowing animals, and humans.)

1. Plant roots in search of nutrients and water grow into fractures, and as the roots grow, they wedge apart the rock. 2. Burrowing animals further break down rock by moving fresh material to the Earth's surface, where physical and chemical processes can more effectively attack it. (Decaying organisms also produce acids that contribute to chemical weathering.) 3. Humans contribute to mechanical weathering when performing certain activities, like those which involve rock being blasted from the Earth's surface in search of minerals (i.e. mining) or for road construction.

Which two (2) climatic elements are considered to exert the strongest impact on soil formation?

1. Precipitation 2. Temperature

What are five (5) ways in which plants and animals influence soil formation?

1. The types and abundance of plants and animals strongly influence the physical and chemical properties of different types of soil. 2. Plants and animals furnish organic matter in soil 3. Certain microorganisms aid soil fertility by converting atmospheric nitrogen into soil nitrogen. 3. Fungi, bacteria, and single-celled protozoa and other microorganisms also play an active role in the decay of plant and animal remains, whose end-product is a material called humus. 4. The decay of plant and animal remains causes the formation of various complex organic acids, which hasten the weathering process. 5. Burrowing animals create burrows and holes, which aid the passage of water and air through soil.

How do temperature and precipitation affect soil formation?

1. Variations in these temperature and precipitation determine whether chemical weathering or mechanical weathering will predominate. 2. Temperature and precipitation influence the rate and depth of weathering 3. The amount of precipitation influences the degree of *leaching* (i.e. the process in which various minerals are removed from the soil by percolating water)

What are ways in which topography influences soil formation?

1. Variations in topography can lead to the development of a variety of localized soil types 2. The length and steepness of slopes significantly affect the amount of erosion and water content. (Ex 1. Steep slopes experience more accelerated erosion, resulting in poorly developed soil, causing rapid run-off. This means less water soaks into the soil, resulting in low moisture content that may not be sufficient for vigorous plant growth. Furthermore, accelerated erosion on steep slopes results in soil that is thin or even non-existent.) (Ex 2. Flatter/lower slopes found in bottomlands often contain poorly drained and water-logged soils. These soils are usually thick and dark in color due to the large quantity of organic matter that accumulates because saturated conditions slow the decay of organic matter. Lowland slopes experience good drainage, minimum erosion, and sufficient water content.) 3. Slope orientation, or the direction a slope is facing, determines the amount of (direct) sunlight that the soil receives. (Ex 1: In the mid-latitudes of the N. Hemisphere, south-facing slopes receive/absorb much more direct sunlight than north-facing slopes. A steep, north-facing slope in these latitudes may receive no sunlight at all.) 4. The amount of solar radiation (i.e. sunlight) received causes differences in soil moisture and temperature, which in turn influences the nature of vegetation and character of the soil.

What is the role of water in hydrolysis?

1. Water usually contains other substances that contribute additional hydrogen ions, thereby greatly accelerating the process of hydrolysis. The most common of these substances is carbon dioxide, which dissolves in water to form carbonic acid, which then disassociates to form hydrogen ions and bicarbonate ions.

What are five (5) products of mechanical weathering?

1. Wind 2. Waves 3. Glacial ice 4. Running water

Soil

A combination of mineral and organic matter, water, and air.

Soil Horizon

A layer of soil that has identifiable characteristics (color, texture, structure) produced by chemical weathering and other soil forming processes.

Carbon Dioxide

Agent of chemical weathering that combines with active precipitation (i.e. falling raindrops) to form a weak acid, called carbonic acid, which works to dissolve rock.

Oxygen

Agent of chemical weathering...

What portion of regolith supports the growth of plants?

Air

Oxidation

Any chemical reaction in which a compound of radical loses electrons.

List different components of soil and explain why and how they vary to make up different types of soils.

Characteristics of soil that vary between types include chemical/physical composition, texture, structure, and color. Because soil-forming processes operate from the surface downward, these characteristics evolve differently at varying depths (i.e. vertically.) These vertical variations usually become more pronounced over time.

How does climate influence soil formation?

Climatic conditions are an important control on the types and numbers of plant and animal life present in soil. Also, climate is considered the most influential control of soil formation.

Lahar

Debris flows mostly composed of volcanic materials and occurring on the flanks of volcanoes

What are three (3) examples of external processes?

Examples include... 1. Cliff erosion 2. Volcanic eruption 3. Sedimentation at the mouth of a river

Joints

Important rock structures produced by activities (e.g. expansion; contraction during the crystallization of magma; the occurrence of tectonic forces during mountain building) that allow water to penetrate to depth and start the process of weathering long before the rock is exposed, and generally form a definite pattern.

Solum

Means "true soil", and refers to the first four horizons of a soil profile (i.e. O, A, E, B).

Give four (4) examples of rapid forms of mass wasting in order of descending rate of speed

Rapid Forms of Mass Wasting: 1. Slump 2. Rockslide 3. Debris flow 4. Earthflow

Hydrolysis

Most important process of chemical weathering, in which hydrogen or hydroxide ions replace the cations in a mineral to change the mineral.

Give a real-world example/application of an earthflow

Mountain Valley near Durango, CO: Triggered by heavy rains, this event caused a massive gathering of material downslope, blocking railroads and significantly narrowing the adjacent stream channel.

Where and why does chemical weathering occur?

Occurs at or near the Earth's surface / because atoms of elements react and bond (i.e. valence electrons)

Permafrost

Occurs extensively in areas located in the N. Hemisphere (i.g. Alaska and Canada) where summers are too short and too cool to melt melt more than shall surface layer, so ground at deeper depths remains frozen year-round.

Frost Wedging

Physical process in which water works its way into the cracks of rock and then freezes, enlarging the cracks, which results in angular fragments eventually breaking off.

Salt Crystal Growth

Physical process that begins when sea spray from breaking waves or salty groundwater penetrates crevices and pore spaces in rock. As the water evaporates, salt crystals form. As these salt crystals grow larger, they weaken the rock by pushing apart the surrounding grains or enlarging tiny cracks in the rock.

Sheeting

Physical process that occurs when large masses of igneous rock, particuarly granite, are exposed at Earth's surface by erosion, causing concentric slabs to begin to break loose, generating onion-like layers in the rock.

Leaching

Process in which various minerals are removed from the soil by percolating water

Dissolution

Process of chemical weathering in which minerals dissolve in water. Most minerals (e.g. halite) readily dissolve in pure water, but some minerals (e.g. calcite) only dissolve in water that is acidic.

External Processes

Processes that affect the Earth's surface and are powered by solar energy.

Exfoliation Dome

Product of the physical processes sheeting and unloading that occurs when continued weathering eventually causes the slabs of rock to separate and peel off. (Ex. Stone Mountain , Georgia, and Half Dome and Liberty Cap in Yosemite National Park.)

Solvent

The component of a solution that dissolves something else

Solute

The component of a solution that gets dissolved

Mass Wasting

The down-slope movement of rock, regolith, and soil under the direct influence of gravity

Humus

The end-product of decayed plant and animal remains in soil by microorganisms

Water

The most important agent of chemical weathering; referred to as the universal solid solvent

Soil Erosion

The removal of topsoil (i.e. the O and A Horizons)

A-Horizon

The second upper-most horizon in a soil profile made up largely of mineral matter combined with humus (up to 30% in some instances) and containing high biological activity

Parent Materials

The source of the weathered mineral matter from which soils develop; can either be underlying bedrock (for residual soils) or unconsolidated sediment (for transported soils.)

Eluviation

The washing out of fine soil components; most commonly occurs in the E-Horizon of a soil profile

Earthflow

These rapid forms of mass wasting most often occur on hillsides in humid areas during times of heavy precipitation or snowmelt. When water saturates the soil and regolith on a hillside, te material may break away, leaving a scar on the slope and forming a tongue- or teardrop-shaped mass the flows downslope.

What is the role of water in oxidation?

Water greatly speeds up a reaction, called rusting, that takes place during oxidation.

Chemical Weathering

Weathering that involves a chemical transformation of rock into one or more new compounds by the addition or removal of elements/atoms.

Mechanical Weathering

Weathering that is accomplished by the physical forces that break rock into smaller and smaller pieces without changing the rock's mineral composition (i.e. each retaining the characteristics of the original material from which they were broken down)