Weathering

Rose AnnAgo IV-6 BEEd

WHITTLING WIND Bryce Canyon in Utah is a weathering wonder.

Weathering and erosion have whittled away the rocks there for millions of years.

Today huge hoodoos rise from the canyon floor. Hoodoos are rock pillars with shapes on their tops. They tower nearly 610 meters (2,000 feet) above the ground.

The hoodoos' story began millions of years ago. That is when ancient rivers washed sediment off nearby mountains into a lake. Over time, the sediment turned into rock.

Next, ocean water flooded the area. Mud and skeletons from ancient sea creatures drifted to the seafloor. These too turned to rock.

Then the ocean dried up. A mountain of rock rose out of the receding water. The ocean had protected the rock. Now the forces of weathering lashed out at it.

A rushing river flooded the area. The water sliced its way through the rocks. It loosened softer rocks. It then washed them away.

The harder rocks remained. The river now churned around those rocks. It carved the rocks into hoodoos.

Rainwater splashed onto the hoodoos. It seeped into cracks. The water turned to ice in cold weather. The ice split apart the hoodoos. Bits of rock then fell to the ground far below.

Wind also chipped in. It blasted the hoodoos, blowing crumbling rocks away. Sediment rained down from the hoodoos.

All this took time. The forces of weathering and erosion work slowly, but they never stop. They still batter Bryce Canyon today. They will continue long after they have destroyed all the hoodoos they once carved.

Weathering

weathering is a basic part of the rock cycle and thus a key process in Earth system.

Weathering breaks down and loosens the surface minerals of rock so they can be transported away by agents of erosion such as water, wind and ice.

Weathering

• weathering is a basic part of the rock cycle and thus a key process in Earth system.

• Weathering breaks down and loosens the surface minerals of rock so they can be transported away by agents of erosion such as water, wind and ice.

• Weathering causes the disintegration of rock near the surface of the earth.

Types of Weathering

• Mechanical Weathering- when rocks undergo a mechanical weathering, it is broken into smaller and smaller pieces, each retaining the characteristics of the original material.

• Frost Wedging- repeated cycles of freezing and thawing of water represent an important process of mechanical weathering. Liquid water has the unique property of expanding about 9% when it freezes.

• Unloading- the outer layers expand more than the rock below and thus separate from the rock body. Rock breaks off into leaves or sheets along joints which parallel the ground surface caused by expansion of rock due to uplift and erosion; removal of pressure of deep burial.

Sheeting- caused by the expansion of crystalline rock as erosion removes the overlying materials the overlying

materials.

• Biological Activity- accomplished by the activities of organisms, including plants, burrowing animals, and humans. Plant roots in search of minerals and water grow into fractures, and as the root grows they wedge the rock apart.

• Chemical Weathering Chemical weathering involves the

complex processes that alter the internal structures of minerals by removing and/ or adding elements.

Water and Carbonic Acid- water is by far the most important agent of chemical weathering. Oxygen dissolved in water will oxidize some materials.

•Rain dissolves some carbon dioxide as it falls through the atmosphere, and additional amounts released by decaying organic matter are acquired as the water percolates through the soil.

Clay minerals- are the end product of weathering and are very stable under surface conditions. Consequently, clay minerals make up a high percentage of the inorganic materials in soils. Moreover, the most abundant sedimentary rock, SHALE contains high proportions of clay minerals.

Water and Carbonic Acid- water is by far the most important agent of chemical weathering. Oxygen dissolved in water will oxidize some materials.

• Weathering of Silicate Minerals• Silicate Minerals make up most of

Earth’s crust and that these minerals are composed essentially of only eight elements. When chemically weathered, silicate minerals yield sodium, calcium, potassium and magnesium ions, which form soluble products that may be removed by groundwater. The three remaining elements- aluminum, silicon, and oxygen- join with water to produce residual clay minerals.

• Spheroidal WeatheringWhen angular rock masses are attacked by

water that enters along joints, the rocks tend to take a spherical shape. Gradually the corners and edges of the angular blocks become more rounded.

• Rates of Weathering• Rock Characteristics- encompass all of the

chemical traits of rocks, including minerals composition and solubility, In addition, any physical features, such as joints (cracks) can be important because they influence the ability of water to penetrate rocks.

• In Bowen’s reaction series. We see that olivine crystallizes first and is therefore the least resistant to chemical weathering, whereas quartz, which crystallizes last, is the most resistant.

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• Climate- climate factors, particularly temperature and moisture, are crucial to the rate of weathering. The optimum environment for chemical weathering is a combination of warm temperatures and abundant moisture.

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Soil• Soil covers most land surfaces. It is one of our

most indispensable resources. Also like air and water, soil is taken for granted by many of us.

• Soil is a combination of mineral and organic matter, water and air.

Soil types

Pedalfers- characterized by an accumulation of iron oxides and aluminum-rich clays in the subsoil.

Pedocal- derived from the Greek pedon meaning “soil” and the first three letters of calcite (calcium carbonate). As the name implies, pedocals are characterized by an accumulation of calcium carbonate.

Soil types

Pedocal- derived from the Greek pedon meaning “soil” and the first three letters of calcite (calcium carbonate). As the name implies, pedocals are characterized by an accumulation of calcium carbonate. A calcite enriched layer called CALICHE may be present in the soil. In these areas, little of the rains that falls penetrate to great depths.

Laterite- In hot, wet tropical climates, soils called Laterite may develop. Chemical weathering is intense under such climate conditions, so these soils are usually deeper than soils developing over a similar period in the midlattitudes. These soils are usually deeper than soils developing over a similar period in the midlattitudes. Because bacterial activity is great in the tropics, laterites contain practically no humus.

•Soil Profiles Soil formation begins first with the

breakdown of rock into regolith. Continued weathering and soil horizon development process leads to the development of a soil profile, the vertical display of soil horizons

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• O Horizon• At the top of the profile is the O horizon. The O

horizon is primarily composed of organic matter. Fresh litter is found at the surface, while at depth all signs of vegetation structure has been destroyed by decomposition. The decomposed organic matter, or humus, enriches the soil with nutrients (nitrogen, potassium, etc.), aids soil structure (acts to bind particles), and enhances soil moisture retention.

A Horizon The marks the beginning of the true mineral soil. In this horizon organic material mixes with inorganic products of weathering. The A horizon typically is dark colored horizon due to the presence organic matter.

• E Horizon• The E horizon generally is a light-colored

horizon with eluviation being the dominant process. Leaching, or the removal of clay particles, organic matter, and/or oxides of iron and aluminum is active in this horizon.

Eluviation, Eluviation (elu- get away from, via- a way) water percolating downward also dissolves soluble inorganic soil components and carries them to deeper zones. This depletion of soluble materials from the upper soil is termed leaching. The removal of inorganic and organic substances from a horizon by leaching

• ;LEACHING- The removal of inorganic and organic substances from a horizon by leaching

• B Horizon• Beneath the E horizon lies the B horizon. The accumulation of fine material leads to

the creation of a dense layer in the soil. In some soils the B horizon is enriched with calcium carbonate in the form of nodules or as a layer. This occurs when the carbonate precipitates out of downward moving soil water. B horizon or the subsoil.

The O, A, E, and B horizons together constitute the solum or true soil. It is in the solum that the soil-forming processes are active and that living roots and other plant and animal life are largely confined.

• C Horizon• The C horizon represents the soil parent

material, either created in situ or transported into its present location. Beneath the C horizon lies bedrock.