Weathering, Erosion, Deposition, and Soil

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

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

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

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

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

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

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

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

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

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

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

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