Section 12.1Weathering

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– More surface area more weathering

• Composition of rock– Some rocks weather better than others

• Climate– Some climates are more conducive to

weathering

Section 12.2Soil

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– Soil that sits above the bedrock it was formed

from

• Transported soil– Soil that has been transported to a new

location

• Soil profile– 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– 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 12.3Mass 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 12.4Soil 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?