CHAPTER 6: WEATHERING AND SOIL

Hydrolysis

A chemical weathering process in which minerals are altered by chemically reacting with water and acids.

Soil

A combination of mineral and organic matter, water, and air; the portion of the regolith that supports plant growth.

Dissolution

A common form of chemical weathering, it is the process of dissolving into a homogeneous solution, as when an acidic solution dissolves limestone.

Horizon (soil)

A layer of soil that has identifiable characteristics produced by chemical weathering and other soil-forming processes.

Sheeting

A mechanical weathering process that is characterized by the splitting off of slablike sheets of rock.

Internal processes

A process such as mountain building or volcanism that derives its energy from Earth's interior and elevates Earth's surface.

External process

A process such as weathering, mass wasting, or erosion that is powered by the Sun and contributes to the transformation of solid rock into sediment.

Laterite

A red, highly leached soil type found in the tropics that is rich in oxides of iron and aluminum.

Soil Taxonomy

A soil classification system that consists of six hierarchical categories, based on observable soil characteristics. The system recognizes 12 soil orders.

Soil profile

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

Talus slope

An accumulation of rock debris at the base of a cliff.

Spheroidal weathering

Any weathering process that tends to produce a spherical shape from an initially blocky shape.

Which of the following statements about soils is false? Oxisols are highly-leached soils rich in iron and aluminum, but a poor soil for agriculture, and generally found in tropical rain forests. Aridosols are associated with areas of abundant rainfall and vegetation Gelisols are found in cold, high-latitude regions with permafrost and are frozen much of the year. Andisols are young soils where the parent material is volcanic ash and cinders deposited by recent volcanic activity

Aridosols are associated with areas of abundant rainfall and vegetation

Which of the following is/are most susceptible to chemical weathering by dissolution? Quartz Clay minerals Iron oxides Calcite

Calcite

Caliche is an excessive accumulation of... Calcite in the E horizon of Vertisols Clays in the A horizon of Spodosols Clays in hardpan layers of Oxisols Calcium carbonate in the B horizon of Aridosols (Pedocals)

Calcium carbonate in the B horizon of a pedocal.

Clay minerals formed from granite and diorite bedrock illustrate which kind of weathering? Chemical Proactive Syntropical Mechanical

Chemical

_______ describes a chemical weathering process where the products are typically _______. Precipitation / dissolved bicarbonate ions Oxidation / coal beds Dissolution / iron oxides (hematite) Hydrolysis / clay minerals

Correct Hydrolysis / clay minerals

Ferromagnesium minerals, such as olivine and pyroxene, that crystallize at high temperatures in Bowen's reaction series are generally less susceptible (more resistant) to chemical weathering than quartz. True False

False

Which one of the following is an important, mechanical weathering process for enlarging fractures and extending them deeper into large boulders and bedrock? Oxidation Eluviation Frost wedging Hydrologic cycling

Frost wedging

What two factors speed up rates of chemical reaction and weathering in rocks and soils? Low temperatures; very dry Low temperatures; very moist High temperatures; very dry High temperatures; very moist

High Temperatures and Moisture

Which of the following statements concerning humus is not true? Humus is typically found above the B soil horizon Humus consists of decaying and partly decayed leaves and other plant materials Humus is durable, resists leaching, and remains in the B horizon when subjected to weakly acidic, soil solutions Humus is less abundant in wet, tropical forested areas than in temperate, forested areas

Humus is durable, resists leaching, and remains in the B horizon when subjected to weakly acidic, soil solutions

What two chemical constituents cannot form by chemical weathering of feldspar minerals? Soluble sodium and potassium bicarbonates Insoluble iron oxides and soluble magnesium bicarbonates Silica and insoluble clay minerals Silica and soluble calcium bicarbonate

Insoluble iron oxides and soluble magnesium bicarbonates

Which one of the following statements concerning mechanical weathering is not true? Reduces grain sizes of rock particles Allows for faster rates of chemical weathering Is important in the formation of talus slopes Involves a major change in the mineral composition of the weathered material

Involves a major change in the mineral composition of the weathered material

Which term describes a soil formed by weathering of the underlying bedrock? Transformational Residual Relict Transported

Residual

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 A, B, C, D, E, bedrock E, A, B, C, O, bedrock D, E, C, B, A, bedrock

O, A, E, B, C, bedrock

Humus

Organic matter in soil that is produced by the decomposition of plants and animals.

The finely divided, red, brown, and yellow soil-coloring minerals originate by what process? Mechanical weathering of very fine-grained, blue-gray clays Precipitation of iron oxides during chemical weathering processes Chemical weathering of quartz and feldspars Mechanical weathering of feldspars and micas in granite and rhyolite

Precipitation of iron oxides during chemical weathering processes

Which one of the following statements concerning soil erosion is false? Sheet erosion, rills, and gullies develop mainly during prolonged droughts Soils form naturally by weathering; if protected from erosion, sound management can maintain or enhance their nutrient levels and textural characteristics Rates of soil erosion exceed rates of soil formation in many parts of the world Grasses and other vegetation, windbreaks, and contour cropping will help reduce losses of soil from cultivated lands

Sheet erosion, rills and gullies develop mainly during prolonged droughts

________ describes a mechanical weathering process that occurs when deeply-buried granite is slowly uplifted to the surface. As erosion removes the overlying rock, the granite expands due to the unloading, resulting in sets of fractures forming parallel to the rock surface. Sheeting Thermal cracking Pressure splitting Columnar jointing

Sheeting fractures

Regolith

The layer of rock and mineral fragments that nearly everywhere covers Earth's land surface.

Parent material

The material on which a soil develops.

Frost wedging

The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices.

Residual soil

Soil developed directly from the weathering of the bedrock below.

Transported soil

Soil that forms on unconsolidated deposits.

Frost wedging is the major weathering process contributing to the formation of which regolith material? Tropical laterites Talus slopes C soil horizons Mature pedalfers

Talus slopes

Leaching

The depletion of soluble materials from the upper soil by downward-percolating water.

Weathering

The disintegration and decomposition of rock at or near the surface of Earth.

Mass wasting

The downslope movement of rock, regolith, and soil under the direct influence of gravity.

What portion of an angular, fracture-bounded granitic block shows the highest rate of weathering? The unfractured interior The edges and corners The crack surfaces, not including edges and corners All portions of the granite block show equal rates of weathering

The edges and corners

Erosion

The incorporation and transportation of material by a mobile agent, such as water, wind, or ice.

Mechanical weathering

The physical disintegration of rock, resulting in smaller fragments.

Which one of the following statements best describes erosion? Disintegration and decomposition of rocks and minerals at the surface Movement of weathered rock and regolith towards the base of a slope The process by which weathered rock and mineral particles are removed from one area and transported elsewhere The combined processes of leaching, eluviation, and mass wasting

The process by which weathered rock and mineral particles are removed from one area and transported elsewhere

Chemical weathering

The processes by which the internal structure of a mineral is altered by the removal and/or addition of elements.

Oxidation

The removal of one or more electrons from an atom or ion. So named because elements commonly combine with oxygen.

Eluviation

The washing out of fine soil components from the A horizon by downward-percolating water.

Quartz is quite resistant to weathering and is an important component of sands in river beds and on beaches. True False

True

Removal of soluble chemical constituents from a soil is termed leaching. True False

True