Section 12.1 Weathering

2 major types of weathering Mechanical Chemical

Mechanical weathering Ice and water frost wedging – water seeps into cracks in rock. It expands when it freezes causing the crack to expand. When this occurs over and over rocks can break into smaller pieces.

Abrasion Striking rock with sand, pebbles, and even other large rocks.

Plants and animals The breakdown of rock due to plant and animal activity.

Upward expansion Rock outcrops are lifted exposing them to weathering.

http://www.classzone.com/books/earth_science/terc/content/visualizations/es1201/es1201page01.cfm

Chemical weathering Hydrolysis as water leeches through the soil it picks up ions that are often deposited in caverns below.

Oxidation when oxygen reacts with rock outcrops, breaking them down. This process usually produces rust.

Rates of Weathering Surface Exposure Composition of rock Climate More surface area more weathering Composition of rock Some rocks weather better than others Climate Some climates are more conducive to weathering

Section 12.2 Soil

How soil forms Soil loose weathered rock and organic matter. Parent material the material in which soil is formed from.

Where soil comes from Residual soil Transported soil Soil that sits above the bedrock it was formed from Transported soil Soil that has been transported to a new location

Soil profile Soil horizons A cross section of the soil that makes up a particular area. Soil horizons The individual zones or layers that make up the soil profile

Types of soil Topsoil Subsoil C horizon A horizon, top layer dark in color, and it contains humus (organic matter) Subsoil B horizon, red or brownish due to greater iron content, contains clay C horizon Older more weather layer, larger fragments of rock

Soil composition Soil is dependant on the climate. Temperature Precipitation Plant matter Bedrock

Section 12.3 Mass Movements and Erosion

Mass movement vs. erosion Mass movement is the downhill transportation of material caused by gravity. Erosion is the transportation of material due to wind or water.

Mass movement Landslide – the mass movement of bedrock downhill Talus – weathered rock fragments that have been pulled downhill

Creep slow movement of soil downhill

Slump occurs when the underlying rock is eroded and the soil above give way.

Earthflow vs. Mudflow Earthflow is a landslide that occurs in water saturated areas. Mudflow is a massive movement of water downhill that contains high amounts of clay and silt.

Section 12.4 Soil as a resource

Soil fertility Soil fertility is the ability for soil to grow plants. The amounts of minerals, water, and organic matter determine what plants are able to survive in that particular area.

Soil depletion occurs when soil gradually looses its nutrients and can no longer sustain crops. How can we prevent this from happening?

Salinization is when irrigation brings in minerals that can add salt deposits to the soil decreasing its fertility.

Erosion and soil concervation Windbreaks slow the wind preventing or decreasing wind erosion.

Contour farming is a method of farming that inhibits water from flowing downhill rapidly.

Terraces are flattened areas along slopes that slow the speed of runoff.

Strip-cropping is a method where farmers alternate different types of crops. Some maybe tall crops like corn while others are ground covering crops like alfalfa.

What other methods can we use in order to prevent erosion? What methods are used around here?