essay of freezing thaw weathering?

Answer 1

Weathering



Weathering refers to the group of physical, chemical, and biological processes that change the physical and chemical state of rocks and soils at and near the surface of the earth. Weathering is primarily a result of climatic forces. Because the effects of climate occur at the earth's surface, the intensity of weathering decreases with depth, with most of the effects exhibited within the first meter of the surface. The most important climatic force is water, as it moves in and around rocks and soil.

Physical weathering is the disintegration of rock into smaller pieces by mechanical forces concentrated along rock fractures. Abrasion of rocks occurs when wind or water carry particles that wear away rocks. Physical weathering due to frost is referred to as frost shattering or frost wedging. Because water expands when it freezes, it can break rocks apart from the inside when it seeps into cracks in a rock or soil. The specific volume (volume/unit mass) of water increases by 9% during freezing, which produces a stress that is greater than the strength of most rocks. Frost action is the most common physical weathering process, as frost is widespread throughout the world. Frost even occurs in the tropics at high elevations, and as a weathering force, is most effective in coastal arctic and alpine environments, where there are hundreds of frost (freeze-thaw) cycles per year.

Exfoliation is the breaking off of rocks in curved sheets or slabs along joints that are parallel to the ground surface. Exfoliation occurs when a rock expands in response to the removal of adjacent rock. Most commonly the release of stress upon a rock occurs when overlying rock is eroded away (i.e., when the pressure of deep burial is removed). The rock breaks apart along expansion fractures that increase in spacing with depth.

Another type of physical weathering is salt wedging. Most water as it moves through the earth contains dissolved salts; in some areas the salt content may be high, with possible sources being seawater or chemical weathering of marine sediments. As the saline water moves into rock fractures and subsequently evaporates, salt crystals form. As the process continues, the crystals grow until they act as a wedge and crack and break the rocks. Salt wedging most commonly occurs in dry landscapes where the groundwater is near the surface.

Hydration is a physical process that also results in weathering. Soil aggregates and fine-grained rocks can disintegrate due to wetting and drying cycles and the expansion and contraction associated with the cycles. Also air that is drawn into pores under dry conditions and then trapped as water returns to the soil or rock can cause fracturing.

Thermal weathering is another physical process. Repeated daily heating and cooling of rock results in expansion during heating and contraction during cooling. Different materials expand and contract at different rates, resulting in stresses along mineral boundaries.

Chemical weathering of rocks or soils occurs through chemical reactions when rocks or soils react with water, gases, and solutions. During these chemical reactions, minerals are added or removed or are decomposed into other materials such as clay minerals.

Carbon dioxide, a chemical weathering agent, dissolves in rain and forms a weak carbonic acid. This weak acid, through the process of carbonation, can dissolve rocks such as limestone and feldspar. Carbonation of limestone can result in the formation of karst topography that may include caves, disappearing streams, springs, and sinkholes.

In chemical oxidation weathering, rocks are transformed through reactions with oxygen dissolved in water. Iron, often found in silicate minerals, is the most commonly oxidized mineral element, when ferrous iron (Fe+2)) is oxidized to ferric iron (Fe+3). Color changes often indicate when oxidation has occurred, such as the "rusting" seen with the oxidation of iron. Other readily oxidized minerals include magnesium, sulfur, aluminum, and chromium.

Hydrolysis is the most common weathering process, where mineral cations in a rock or soil mineral are replaced by hydrogen (H+) ions. Pure water is a poor hydrogen donor, but carbon dioxide dissolved in water, which produces carbonic acid, acts as a source of hydrogen ions. Weathering products formed include clay minerals.

Biological weathering occurs when organisms aid in the breakdown of rocks and minerals. Plants such as lichens and mosses produce a weak acid that dissolves geological materials. Plant roots growing in the cracks of rocks, through the process of root pry, can make the crack larger and may loosen other types of materials.


Resources


Books

Ollier, Cliff, and Colin Pain. Regolith, Soils, and Landforms. New York: John Wiley & Sons Ltd., 1996.

Rolls, David, and Will J. Bland. Weathering: An Introduction to the Basic Principles. London: Edward Arnold, 1998.

Spickert, Diane Nelson, and Marianne D. Wallace. Earthsteps: A Rock's Journey Through Time. Golden, CO: Fulcrum Publishing, 2000.

Answer 2

The freeze-thaw section of this Wikipedia article should help you out with some of the information you need.

Answer 3

i'm no longer a geologists. freezing and thawing is at the same time as water receives into cracks then it freezes and expands and the repeating of this procedure makes the rock destroy down and breaks the rock it truly is likewise aside of weathering