Weathering, Erosion, Deposition, and Soil

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. 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. 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