Chapter Weathering and Soil

What is weathering? Weathering is process of breaking down and changing of rock at or near Earth’s surface. The two types of weathering are mechanical and chemical weathering.

What is mechanical weathering? Mechanical weathering is the process of physical forces breaking down rocks into smaller and smaller pieces without changing the type of rock. The causes of mechanical weathering are Frost wedging, Unloading, and Biological activity.

What is frost wedging? Frost wedging is a rock break-up caused by the expansion of freezing water in cracks and crevices. The broken down pieces are known as talus.

What is unloading? Unloading is when large masses of igneous rock are exposed through uplift, and erosion of over lying rocks. This reduces the pressure on the rock causing the rock layers to break away which is known as exfoliation.

What is biological activity? Biological activity are the activities of living organisms that cause the breaking up of rock. – Roots of trees break rock apart – Burrowing Animals move rocks to the surface where weathering is more rapid. – Decaying Organisms- produce acid compounds that cause chemical weathering. – Humans- accelerate mechanical weathering through deforestation and blasting in search of minerals or in the creation of new roads.

What is chemical weathering? Chemical weathering is the process when rock turns into one or more new compounds. – Analogy: mechanical – tearing paper chemical – burning paper Water is the most important agent of chemical weathering. – water absorbs gases from the atmosphere and ground. – these dissolved substances chemically react with various minerals. Rust - is iron oxide that forms when iron containing objects are exposed to water. Acid rain – is forms when rain absorbs carbon dioxide as it falls. This acid breaks down rocks.

Spheroidal Weathering Chemical weathering can change both the physical appearance of rocks as well as the chemical composition. Water enters the joints in parts of the rocks which then reshape the rock giving it a Spherical shape.

What are 3 factors that affect the rate of weathering? Mechanical weathering – Breaks rock into smaller pieces, which increasing the surface area of exposed rocks & accelerates chemical weathering by. Rock Characteristics – Physical characteristics such as cracks can effect the ability for a rock to be penetrated. – Mineral composition increase or decrease rate of weathering. Climate – controls the frequency of freeze-thaw cycles and affects the rate of mechanical weathering.

What is Regolith & Soil? Weathering produces a layer of rock and mineral fragments called Regolith. It covers nearly all of the Earth’s land surface. Soil is the part of the regolith that supports the growth of plants.

What are the three characteristics of soil? The 3 characteristics of regolith are: Composition Texture Structure.

What are the major components of soil? Mineral Matter Organic Matter (humus) Water Air

What is soil texture? A soil’s texture is the particle size And the soil’s ability to support plant life.

What is soil structure? Soil Structure determines how easily a soil can be cultivated And how susceptible it is to erosion.

What causes soil formation? Parent material: – The source of the mineral matter in soil – Determines the rate of erosion. Time: – The longer the formation, the thicker the soil. Climate: – The greater the variations in temperature and precipitation, the greater the influence on the rate, depth, and type of weathering. Organisms: – Organic matter releases nutrients when it decades and contributes to fertilizing soil. – Burrowing animals mix the minerals and organic matter in the soil. Slope: – Variations of the land can result into different types of soil. – On steep slopes, erosion is accelerated. – Flat areas have little erosion and poor drainage.

What is erosion? Erosion is when Earth’s surface is transported by factors such as water, wind, glaciers, gravity and other agents. These factors move soil from one place to another.

How do other erosion factors affect soil? When it rains, rain drops strike the soil with force, then the broken-up particles are carried away by water flowing across the surface. Sediment deposition is a natural occurrence that is strongly influenced by humans, such as land clearing, agriculture, deforestation, etc.