Weathering and Soil Formation Chapter 4 Weathering and Soil Formation

4.1 - Mechanical and chemical forces break down rocks. Weathering – process by which natural forces break down rocks. * Two types – Mechanical & Chemical

Mechanical Weathering – breaking up of rocks by physical force Ice wedging – frozen water expands and is forceful enough to split rocks. Pressure Release – causes rocks to expand and cracks to form resulting in exfoliation.

Exfoliation – process in which layers or sheets of rock gradually break off. Plant Root Growth – plants can root in cracks in the rock which can result in a completely split rock. Abrasion – process of wearing down by friction, the rubbing of one object or surface against another.

Chemical Weathering – breakdown of rocks by chemical reactions that change the rocks’ makeup. * WATER is the main cause of Chemical Weathering.

Dissolving – minerals completely “fade away” in water Rusting – oxygen and water react with minerals (IRON) to form rust

Weathering occurs at different rates. Surface Area – the more of a rock’s surface that is exposed, the faster it will break down. Rock Composition – what a rock is made of determines the rate it will break down.

Climate Chemical weathering occurs FASTER in how, wet regions. It occurs SLOWER in cold, dry regions. Mechanical weathering occurs more often in cold regions.

4.2 – Weathering and organic processes form soil. Soil is a mixture of four materials: Weathered rock particles Organic matter – 5% Water Air 20-30%

Humus – decayed organic matter in soil Kind of soil depends on… Kind of rock in the area Area’s climate Landforms (mountains and valleys) Plant cover Animals and organisms Time

Soil horizons – layer of soil with properties that differ from those of the layer above or below it. A horizon – TOPSOIL; upper layer of soil; contains most organic matter B horizon – little organic matter; red or brown in color C horizon – deepest layer; largest & least weathered particles; yellowish-brown in color

4 types of soil Tropical Desert Temperate Arctic

Organisms affect soil Plants (form humus) Microorganisms (decomposers and fungi) Animals (loosen and mix soil)

Properties of soil Texture – determined by sand, silt, and clay Color – red, brown, yellow, green, black, and white Pore Space – spaces between soil particles Chemistry – acidity of soil

4.3 – Human activities affect soil. Soil sustains life by… supporting the growth of plants, purifying water, and recycling nutrients.

Land-use can HARM soil. Farming Construction & Development Mining Adds nutrients to soil Loss of soil, overgrazing, desertification (expansion of desert conditions in areas where the natural plant cover has been destroyed) Construction & Development Mining

How can we protect and conserve soil? Crop Rotation – planting different crops on the same field in different years or growing seasons; *maintains soil fertility Conservation Tillage – reducing the number of times fields are plowed in a year

Terraces – flat, steplike areas built o a hillside to hold rainwater and prevent it from running downhill Contour Plowing – plowing along the curves of a slope Windbreaks – rows of trees planted between fields to “break” the force of wind