Weathering and Soils

Entisol

Young soils having limited development and exhibiting properties of the parent material; productivity ranges from very high for some formed on recent river deposits to very low for those forming on shifting sand or rocky slopes

Soil Horizons

A ____ is a layer generally parallel to the soil crust, whose physical characteristics differ from the layers above and beneath. Each soil type usually has three or four ____. ____ are defined in most cases by obvious physical features, chiefly colour and texture. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material (i.e., "coarser" or "sandier" than the ____ above and below). The differentiation of the soil into distinct ____ is largely the result of influences, such as air, water, solar radiation and plant material, originating at the soil-atmosphere interface. Since the weathering of the soil occurs first at the surface and works its way down, the uppermost layers have been changed the most, while the deepest layers are most similar to the original parent material.

Residual Soils

A soil formed by the weathering of the bedrock immediately beneath it. A ____ is formed 'in place'. It is made up of rock particles weathered from the bedrock below and it is therefore chemically similar to that bedrock. It will also contain organic material derived from plants and animals living in the area.

Mollisols

Dark, soft soils that have developed under grass vegetation, generally found in prairie areas. Humus-rich surface horizon that is rich with calcium and magnesium. Soil fertility is excellent. Also found in hardwood forests with significant earthworm activity. Climate range is boreal or alpine to tropical. Dry seasons are normal.

E Horizon

Short for eluviated, ____ is most commonly used to label a horizon that has been significantly leached of clay, iron, and aluminum oxides, which leaves a concentration of resistant minerals, such as quartz, in the sand and silt sizes. These are present only in older, well-developed soils, and generally occur between the A and B horizons.The ___ often has a pale color that is generally lighter in color than either the horizon above or below it. ____ are commonly found in soils developed under forests, but are rare in soils developed under grasslands. In regions where this designation is not employed, leached layers are classified firstly as an A or B according to other characteristics, and then appended with the designation "e" (see the section below on horizon suffixes). In soils that contain gravels, due to animal bioturbation, a stone layer commonly forms near or at the base of the ____.

B Horizon

Subsoil: Subsurface layer reflecting chemical or physical alteration of parent material. This layer accumulates iron, clay, aluminum and organic compounds, a process referred to as illuviation.

Rills

In hillslope geomorphology, a ___ is a shallow channel (no more than a few tens of centimetres deep) cut into soil by the erosive action of flowing water. Similar but smaller incised channels are known as micro__; larger incised channels are known as gullies. Artificial ___ are channels constructed to carry a water supply from a distant water source. In landscape or garden design, constructed ___ are an aesthetic water feature.

frost shattering and hydration shattering

- freezing of water in pores and fractures the specific volume (vol./unit mass) of water increases by 9% upon freezing producing stress that is greater than the tensile strength of all common rocks - therefore the stress generated by the crystallization of ice is the most pervasive mechanism of weathering, effects all rocks However, the effectiveness of freezing water is influenced by: 1. lack of confinement: if more than 20% of pore space is empty, then the tensile stress may be less than the tensile strength, thus frost shattering is most effective in saturated rock; ice under pressure deforms plastically and thus will extrude through daylighted fractures and pores 2. decreased freezing point with increasing pressure (supercooled water) and impurities (e.g. salt) 3. necessary frequency and magnitude: extent of frost shattering is a function of the combination of frequency, duration and intensity (rapidity and degree) of freeze-thaw cycles -hypotheses to account for apparent effectiveness of frost shattering; hydrofracturing: 1. thin (monomolecular) films of water do not freeze even at low temperatures, given strong capillary adhesion to rock; powerful molecular forces in these thin films of semicrystalline water draw water along microfractures opening and propagating them 2. shallow freezing forces films of capillary water along microfractures, disintegrating rocks well below the depth of freezing; e.g. hydrofracturing in the Allegheny Mountains (southern Appalachians of West Virginia and Pennsylvania) extends to 12-15 m, while frozen ground rarely extends below 1 m

Gullies

A ___ is a landform created by running water, eroding sharply into soil, typically on a hillside. ___ resemble large ditches or small valleys, but are meters to tens of meters in depth and width. When the __ formation is in process, the water flow rate can be substantial, causing a significant deep cutting action into soil.

Transported Soil

A soil that has been transported (eroded) and then deposited in a region where it was not originally formed. ____ are the result of erosion and deposition by wind, water, and ice. _____ may have properties very different from the bedrock beneath them since they are unrelated. Most soils are ____. This is because the forces of erosion and deposition are constantly at work.

Five major mechanisms of mechanical weathering

Abrasion Crystallization of ice (frost shattering) Thermal fracture Hydration shattering Exfoliation or pressure

R Horizon

Bedrock: The parent material in bedrock landscapes. This layer denotes the layer of partially weathered bedrock at the base of the soil profile. Unlike the above layers, ____ largely comprise continuous masses of hard rock that cannot be excavated by hand. Soils formed in situ will exhibit strong similarities to this bedrock layer. These areas of bedrock are under 50 feet of the other profiles.

USDA Soil Taxonomy

Developed by United States Department of Agriculture and the National Cooperative Soil Survey, ____ provides an elaborate classification of soil types according to several parameters (most commonly their properties) and in several levels: Order, Suborder, Great Group, Subgroup, Family, and Series.

Frost wedging

Fracturing of rock by the expansionary pressure associated with the freezing of water in planes of weakness or in pore spaces.

Histosol

Organic soils with little or no climatic implications. Can be found in any climate where organic debris can accumulate to form a bog soil. Dark, potentially decomposed organic material commonly referred to as peat.

Alfisols

Moderately weathered soils that form under boreal forests or broadleaf deciduous forests, rich in iron and aluminum. Clay particles accumulate in a subsurface layer in response to leaching in moist environments. Fertile, productive soils because they are not too wet nor too dry

O Horizon

Organic matter: Surficial organic deposit with litter layer of plant residues in relatively non-decomposed form.

C Horizon

Parent rock, also known as substratum: The parent material in sedimentary deposits. Layer of large unbroken rocks. This layer may accumulate the more soluble compounds .

Exfoliation

Rocks which form under the surface form under pressure - confining pressure. When that pressure is released, the rock will expand. Pressure is released as the rock is brought to the surface - tectonics, isostasy, erosion. As it expands the outer layers break free in sheets - _____.

Vertisol

Soils containing large amounts of clay, which shrink upon drying and swell with the addition of water. Found in subhumid to arid climate, provided that adequate supplies of water are available to saturate the soil after periods of drought. Soil expansion and contraction exert stresses on human structures

Spodosol

Soils found only in humid regions on sandy material. Common in northern coniferous forests and cool humid forests. Beneath the dark upper horizon of weathered organic material lies a light colored horizon of leached material

Aridosols

Soils that develop in dry places where there is insufficient water to remove soluble minerals; may have an accumulation of calcium carbonate, gypsum, or salt in the subsoil; low organic content

Oxisols

Soils that occur on old land surfaces unless parent materials were strongly weathered before they were deposited. Generally found in the tropics and subtropical regions. Rich in iron and aluminum oxides, oxisols are heavily leached and hence are poor soils for agricultural activity.

Ultisol

Soils that represent the products of long periods of weathering. Water percolating through the soil concentrates clay particles in the lower horizons. Restricted to humid climates in the temperate regions and the tropics, where growing season is long. Abundant water and a long frost-free period contribute to extensive leaching, hence poorer soil quality.

A Horizon

Surface soil: Organics mixed with mineral matter. This layer of mineral soil contains the most organic matter accumulation and soil life. This layer eluviates (is depleted of) iron, clay, aluminum, organic compounds, and other soluble constituents. When eluviation is pronounced, a lighter colored "E" subsurface soil horizon is apparent at the base of the ___. _____ may also be the result of a combination of soil bioturbation and surface processes that winnow fine particles from biologically mounded topsoil. In this case, the ____ is regarded as a "biomantle".

Soil Profile

The ____ is an important tool in nutrient management. By examining a ____ we can gain valuable insight into soil fertility. As the soil weathers and/or organic matter decomposes, the ____ changes. For instance, a highly weathered, infertile soil usually contains a light-colored layer in the subsurface soil from which nutrients have leached away. On the other hand, a highly fertile soil often has a deep surface layer that contains high amounts of organic matter. With clues provided by ____, we can begin to predict how a soil will perform under certain nutrient management conditions.

Abrasion

The grinding action of other rock particles due to gravity or the motion of water, ice or air. _____ is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion. After friction, the moving particles dislodge loose and weak debris from the side of the rock. The intensity of ____ depends on the hardness, concentration, velocity and mass of the moving particles.

Sheeting

The process by which thin sheets, slabs, scales, plates, or flakes of rock are successively broken loose or stripped from the outer surface of a large rock mass in response to release of load. Also known as exfoliation.

Thermal Fracture

The result of rapid temperature change, as by fire, volcanic activity or day-night cycles (as in the formation of grus), all of which rely on the differences in thermal expansion among a mixture of minerals. Rock has a low thermal conductivity - tends to make a good insulator. When rock is heated on a surface that heat does not travel inward very rapidly. The heated exterior of the rock will expand more rapidly than the cool interior, causing the exterior to fracture - spalling.

Root Wedging

____ occurs when a plant, especially trees, sink root systems into existing joints and fractures. As the root grows it forces the fracture to expand. Relatively minor weathering force in rocks, but is very important for soil development.

Inceptisol

Weakly developed young soils in which the beginning of the profile development is evident. Most common in humid climates, they exist from the arctic to the tropics. Native vegetation is most often forest.

Chemical Weathering

____ weathering involves the direct effect of atmospheric chemicals or biologically produced chemicals also known as biological weathering in the breakdown of rocks, soils and minerals. While physical weathering is accentuated in very cold or very dry environments, chemical reactions are most intense where the climate is wet and hot.

Andisols

Young soils in which the parent material is volcanic ash and cinders, deposited by recent volcanic activity

Gelisol

Young soils with little profile development that occur in regions with permafrost. Low temperatures and frozen conditions for much of the year, slow soil forming processes

Frost weathering

____ is a collective term for several mechanical weathering processes induced by stresses created by the freezing of water into ice. The term serves as an umbrella term for a variety of processes such as frost shattering, frost wedging and cryofracturing. The process may act on a wide range of spatial and temporal scales, from minutes to years and from dislodging mineral grains to fracturing boulders. ____ is mainly driven by the frequency and intensity of freeze-thaw cycles and the properties of the materials subject to weathering. It is most pronounced in high altitude and latitude areas and is especially associated with alpine, periglacial, subpolar maritime and polar climates but occurs wherever freeze-thaw cycles are present.

The Rock Cycle

____ is a group of changes. Igneous rock can change into sedimentary rock or into metamorphic rock. Sedimentary rock can change into metamorphic rock or into igneous rock. Metamorphic rock can change into igneous or sedimentary rock. Igneous rock forms when magma cools and makes crystals. Magma is a hot liquid made of melted minerals. The minerals can form crystals when they cool. Igneous rock can form underground, where the magma cools slowly. Or, igneous rock can form above ground, where the magma cools quickly. When it pours out on Earth's surface, magma is called lava. Yes, the same liquid rock matter that you see coming out of volcanoes. On Earth's surface, wind and water can break rock into pieces. They can also carry rock pieces to another place. Usually, the rock pieces, called sediments, drop from the wind or water to make a layer. The layer can be buried under other layers of sediments. After a long time the sediments can be cemented together to make sedimentary rock. In this way, igneous rock can become sedimentary rock. All rock can be heated. But where does the heat come from? Inside Earth there is heat from pressure. There is heat from friction . There is also heat from radioactive decay (the process that gives us nuclear power plants that make electricity). So, what does the heat do to the rock? It bakes the rock. Baked rock does not melt, but it does change. It forms crystals. If it has crystals already, it forms larger crystals. Because this rock changes, it is called metamorphic. Remember that a caterpillar changes to become a butterfly. That change is called metamorphosis. Metamorphosis can occur in rock when they are heated to 300 to 700 degrees Celsius. When Earth's tectonic plates move around, they produce heat. When they collide, they build mountains and metamorphose (met-ah-MORE-foes) the rock. ____ continues. Mountains made of metamorphic rocks can be broken up and washed away by streams. New sediments from these mountains can make new sedimentary rock. _____ never stops.

Humus

____ is dark, organic material that forms in soil when plant and animal matter decays. When plants drop leaves, twigs, and other material to the ground, it piles up. This material is called leaf litter. When animals die, their remains add to the litter. Over time, all this litter decomposes. This means it decays, or breaks down, into its most basic chemical elements. Many of these chemicals are important nutrients for the soil and organisms that depend on soil for life, such as plants. The thick brown or black substance that remains after most of the organic litter has decomposed is called ____. Earthworms often help mix ____ with minerals in the soil.

Weathering

____ is the breaking down of rocks, soil and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters. ____ occurs in situ, roughly translated to: "with no movement", and thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity and then being transported and deposited in other locations. The materials left over after the rock breaks down combined with organic material creates soil.

Parent Material

____ is the underlying geological material (generally bedrock or a superficial or drift deposit) in which soil horizons form. Soils typically inherit a great deal of structure and minerals from their ____, and, as such, are often classified based upon their contents of consolidated or unconsolidated mineral material that has undergone some degree of physical or chemical weathering and the mode by which the materials were most recently transported.

The Dust Bowl

____, also known as the Dirty Thirties, was a period of severe dust storms that greatly damaged the ecology and agriculture of the US and Canadian prairies during the 1930s; severe drought and a failure to apply dryland farming methods to prevent wind erosion (the Aeolian processes) caused the phenomenon. The drought came in three waves, 1934, 1936, and 1939-40, but some regions of the high plains experienced drought conditions for as many as eight years. With an insufficient understanding of the ecology of the plains, farmers had conducted extensive deep plowing of the virgin topsoil of the Great Plains during the previous decade; this had displaced the native, deep-rooted grasses that normally trapped soil and moisture even during periods of drought and high winds. The rapid mechanization of farm equipment, especially small gasoline tractors, and widespread use of the combine harvester contributed to farmers' decisions to convert arid grassland (much of which received no more than 10 inches (250 mm) of precipitation per year) to cultivated cropland. During the drought of the 1930s, the unanchored soil turned to dust, which the prevailing winds blew away in huge clouds that sometimes blackened the sky. These choking billows of dust - named "black blizzards" or "black rollers" - traveled cross country, reaching as far as the East Coast and striking such cities as New York City and Washington, D.C. On the Plains, they often reduced visibility to 1 meter (3.3 ft) or less. Associated Press reporter Robert E. Geiger happened to be in Boise City, Oklahoma, to witness the "Black Sunday" black blizzards of April 14, 1935; Edward Stanley, Kansas City news editor of the Associated Press coined the term "___" while rewriting Geiger's news story. While the term "___" was originally a reference to the geographical area affected by the dust, today it is usually used to refer to the event, as in "It was during ___". The drought and erosion of ____ affected 100,000,000 acres (400,000 km2) that centered on the panhandles of Texas and Oklahoma and touched adjacent sections of New Mexico, Colorado, and Kansas. ____ forced tens of thousands of families to abandon their farms. Many of these families, who were often known as "Okies" because so many of them came from Oklahoma, migrated to California and other states to find that the Great Depression had rendered economic conditions there little better than those they had left.

Spheroidal Weathering

_____ is a form of chemical weathering that affects jointed bedrock and results in the formation of concentric or spherical layers of highly decayed rock within weathered bedrock that is known as saprolite. When saprolite is exposed by physical erosion, these concentric layers peel (spall) off as concentric shells much like the layers of a peeled onion. Within saprolite, spheroidal weathering often creates rounded boulders, known as corestones or woolsack, of relatively unweathered rock. ____ is also called onion skin weathering, concentric weathering, spherical weathering, or woolsack weathering.

Regolith

______ is a region of loose unconsolidated rock and dust that sits atop a layer of bedrock. On Earth, _____ also includes soil, which is a biologically active medium and a key component in plant growth. _____ serves as a source of other geologic resources, such as aluminum, iron, clays, diamonds, and rare earth elements. It also appears on the surfaces of the Moon, other planets, and asteroids; however, the material found on other celestial bodies explored so far does not contain soil. The word is the Greek term for "blanket rock." On Earth, _____ is largely a product of weathering.

Mechanical Weathering

______ or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water, ice and pressure.

Soil

___is a mixture of minerals, organic matter, gases, liquids, and countless organisms that together support life on Earth. ____is a natural body called the pedosphere which has four important functions: it is a medium for plant growth; it is a means of water storage, supply and purification; it is a modifier of Earth's atmosphere; it is a habitat for organisms; all of which, in turn, modify the soil. ____ is called the "Skin of the Earth" and interfaces with its lithosphere, hydrosphere, atmosphere, and biosphere. The term pedolith, used commonly to refer to the ____, literally translates 'level stone'. ___ consists of a solid phase of minerals and organic matter, as well as a porous phase that holds gases and water. Accordingly, ___ are often treated as a three-state system of solids, liquids, and gases. ___ is a product of the influence of the climate, relief (elevation, orientation, and slope of terrain), organisms, and its parent materials (original minerals) interacting over time. ____ continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion.