1. Weathering, Erosion, Deposition, and Soil

2. Weathering
Weathering – is the process by which rock materials are broken down by the action of physical or chemical processes.
Mechanical Weathering – the breakdown of rock into smaller pieces by physical means
Chemical Weathering – the process by which rocks break down as a result of chemical reactions

3. Mechanical Weathering
Ice
The alternate freezing and thawing of soil and rock – frost action
Ice wedging – water seeps into cracks, water then freezes and expands causing the crack to widen
Abrasion – the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles
Wind
Water
Gravity

4. Plants
Plant roots grow into existing cracks in rocks and expanding roots become so strong that the crack widens
Animals
Any animal that burrows causes mechanical weathering (ants, worms, mice, coyotes, and rabbits)
Mixing and digging by animals can also cause chemical weathering

5. Chemical Weathering
Water – dissolving of water into a rock can break the rock down over years
Acid Precipitation – rain, sleet, or snow, that contains a high concentration of acids
Caused by burning fossil fuels
High level of acidity can cause very rapid precipitation

6. Air – oxygen in the air reacts with iron and forms rust
Acid in Groundwater – chemical reactions occur between the acid in the groundwater and rock and breaks the rock down
caverns
Acid in Living Things
Lichens – grow on rocks and trees and slowly breaks down the rock
Air – oxygen in the air reacts with iron and forms rust
oxidation

7. Rate of Weathering Composition of rocks
Amount of time that rock is exposed to weathering
The amount of exposed surface
More joints or cracks easier broke down

8. From Bedrock to Soil The source of soil
Soil – a loose mixture of rock fragments, organic material, water, and air that can support the growth of vegetation
Soil is made from weathered rock fragments, the type of soil that forms depends on the type of rock that weathers
Parent rock – a rock formation that is the source of soil
Bedrock – the layer of rock beneath soil

9. Soil Properties Soil Texture and Soil Structure Soil Fertility
Humus – dark, organic material formed in soil from the decayed remains of plants and animals
Soil Horizons – soil often ends up in a series of layers, with humus-rich soil on top, sediment below that, and bedrock on the bottom
Horizon tells you the layer the rock is in horizontal
Top layer of soil is often called topsoil and contains more humus than the layers below
Soil pH

10. Soil Conservation
Soil conservation – is the method to maintain the fertility of the soil by protecting the soil from erosion and nutrient loss
The importance of soil – soil provides minerals and other nutrients for plants and all animals get their energy from plants
Housing – soil provides a place for animals to live
Water Storage – without soil to hold water, plants would not get the moisture of the nutrients they need. Soil also keeps water from running off

11. Contour Plowing and Terracing
Soil Damage and Loss – can be caused by overuse, poor farming techniques or overgrazing
Soil Erosion – the process by which wind, water, ice, or gravity transport soil and sediment from one location to another
Contour Plowing and Terracing
Contour Plowing – plowing across the slope of hills
Terracing – changing one steep field into a series of smaller flatter fields
Cover Crop and Crop Rotation
Cover crops – crops that are planted between harvest to replace certain nutrients and prevent erosion
Crop rotation – planting different crops

12. River Systems and Deposition
Streams join other small streams to form larger ones and eventually all of the water flows into one and forms a river
Network of streams and rivers that drains an area is its runoff.
Tributary – a stream that flows into a lake or into a larger streams.
Watershed (drainage basin) – is the area of land that is drained by a water system
Divide – the boundary between drainage areas that have streams that flow in opposite directions
Load – the material that is carried by a stream
Deposition – the process in which material is laid down or dropped. Rock and soil that is deposited by streams are called sediments

13. Reshaping Earth’s Surface
Sand dunes – a mound of wind-deposited sand that keeps its shape even though it moves
Glaciers – a large mass of moving ice
Mass movement – is the movement of any material, such as rock, soil, or snow, down a slope