Weathering & Soil

Weathering dark Weathering & its effects Surface processes that break down rock. Sediments: sand, silt, & clay Weathering changes the Earth’s surface. dark

Mechanical Weathering Occurs when rocks are broken apart by physical processes. Caused by: Growing plants Burrowing animals Expanding ice

Ice wedging occurs where water enters cracks in rocks, freezes, & expands. As surface area increases, more rock is exposed to be weathered. Chemical Weathering Chemicals dissolve the minerals in rocks or change them into different minerals. Naturally formed acids can weather rocks chemically

Carbonic acid forms when Carbon dioxide mixes with water Carbonic acid forms when Carbon dioxide mixes with water. The acid reacts with calcite in limestone to form caves. Some roots & decaying plants give off acids that dissolve minerals in rock. Oxidation occurs when some materials are exposed to oxygen and water. (Rust)

Soil Effects of Climate Mechanical weathering occurs more in cold climates. Chemical weathering occurs more in warm, wet climates. Rock type can affect the rate of weathering in a particular climate. Soil A. Formation of Soil Weathering gradually breaks rocks into smaller and smaller fragments. Plants and animals add organic matter to the rock fragments.

Soil is a mixture of Weathered rock Decayed organic matter Mineral fragments Water Air Causes for soil formation include: Climate Slope Types of rock Types of vegetation Length of time that rock has been weathering

Composition of Soil Decayed organic matter turns into a dark-colored material called humus. Humus provides nutrients for plants. Burrowing creatures mix humus with the other rock fragments.

Soil Profile A Horizon (topsoil) Can be covered by litter, organic material that will eventually become humus and helps prevent erosion. B Horizon Lighter in color & contains less humus. Leeching is the removal of minerals that have been dissolved by water. Water reacts with humus & carbon dioxide to form acid.

C Horizon Made of partially weathered rock and is found at the bottom of a soil profile.

Soil Types Different types of soil vary in color, depth, texture, & fertility. The type of soil depends on the region’s climate. Deserts are dry, prairies are semi-dry, & temperate forests are mild & moist.

Soil Erosion Soil – An Important Resource Soil is eroded when it is moved to a new location by wind or water. Soil erosion removes topsoil that is important for plant growth.

Causes and Effects of Soil Erosion Human activities can increase the rate of soil erosion. Soil erosion occurs rapidly on steep slopes and areas that are not covered by vegetation. Forest harvesting & overgrazing contribute to the rate at which erosion can occur.

Preventing Soil Erosion Farmers reduce erosion by planting shelter belts, using no-till farming, and planting cover crops after harvesting. Contour farming and terracing are used to control erosion on slopes.

Rows of trees (windbreaks) are Rows of trees (windbreaks) are planted on the plains to reduce erosion caused by wind.