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DEVELOPMENT OF SOIL What are the 5 Factors which aid in soil formation? 1. 2. 3. 4. 5. 5 Factors which aid in soil formation? 1. Parent Material (unconsolidated bedrock) 2. Climate 3. Living organisms 4. Landscape position 5. Time (300 to 1000 years to form!!!!) Weathering by Temperature Extremes Plant Roots Effects on Rocks Lichens are common primary colonisers of surfaces They cause chemical weathering, releasing small quantities of organic acids which can dissolve limestone Foliose lichen Wind Effects on Rocks Water Effects on Rocks Ice Effects on Rocks Man Made Effects on Rocks What are the stages of Soil Development? Stages of Soil Development Weathering of rock produces soil. Through time - vegetation grows on the land surface Rainwater moves through the soil, carrying weathering products from the surface to lower depths Forming soil horizons Organic matter accumulates at the surface when vegetation dies forming topsoil (A horizon) Then, mineral subsoil begins to oxidize (C horizon) Water translocates weathering products of clay, iron oxides, and caliche into a layer called B horizon With time, soils get thicker, gain horizons, and become clay-rich and redder. What is the difference between soil formation and weathering? What is the difference between soil formation and weathering? All soils initially come from rocks, ‘parent material’. The Parent Material may be directly below the soil, or great distances away (wind, water or glaciers have transported the soil) The soil formation process is termed 'pedogenesis'. Climatic conditions are important factors affecting both the form and rate of physical and chemical weathering of the parent material. Soil formation is a combination of the products: Of weathering of structural development of the soil, of differentiation of that structure into horizons or layers, and lastly of its movement or translocation In fact there are many ways in which soil may be transported away from the location where it was first formed. Weathering? Weathering Breakdown of rock to form sediment Types of Weathering? Physical or mechanical weathering (Biological weathering) & chemical http://facstaff.gpc.edu/~pgore/geology/geo1 01/weather.htm 5 Factors in Weathering of Minerals 1. _____________ alterations that crack rock 2. _______________that pry cracks in rocks open 3. _____________ grinding of wind, water, and ice 4. ____________producing organic acids that chemical react with rocks to further weaken it. 5. ___________weathering occurs over eons of geological time 5 Factors in Weathering of Minerals Temperature alterations that crack rock Plant roots that pry cracks in rocks open Abrasive grinding of wind, water, and ice Lichens and microbes producing organic acids that chemical react with rocks to further weaken it. Time weathering occurs over eons of geological time Weathering All materials are susceptible to weathering. Weathering is a natural process. Mechanical weathering is the physical breaking up of rocks. (ie. plant roots, freeze & thaw, shifting of the earth’s surface) Chemical weathering is the actual altering of rock, changing it into a different substance. (Water combines with carbon dioxide to create carbonic acid) Erosional agents – wind, water, and glaciersalso disintegrate rock particles even further. What is the difference between Mechanical & Chemical Weathering? Mechanical or Physical Weathering Freezing and Thawing - can literally grind mountains down over time! Heating and Cooling - expand and contract. The effect is less pronounced that that of freezing and thawing but over time this can become significant. Wetting and Drying - soils that swell and shrink. Clay minerals in particular exhibit this property. Grinding or Rubbing - most obvious on the beach, grinding of particles against each other leads to particle disintegration. This is why beach pebbles become smooth. Abrasion similarly breaks down the soil particles. Mechanical or Physical Weathering Organisms - Soil is home for a wide range of organisms. If plants can push through concrete - soil presents little obstacle! Worms churn their way through soil, mixing and aerating it all through their lives and there can be thousands of worms in a field. Unloading - when pressure is placed upon soil it becomes compressed. Never mind tractors, imagine the weight of a glacier! When ice melts a huge weight is lifted and the soils may react accordingly by uplifting and expanding. What are 3 examples of natural erosional agents? – This was stated in mechanical weathering Water is the main chemical weathering agent Oxygen dissolved in water will oxidize with certain materials. Also, as rain falls through the atmosphere it dissolves some carbon dioxide to from carbonic acid. The result is that water everywhere on Earth’s surface is slightly acidic and this acid destroys certain minerals’ crystalline structure. Clay minerals are generally the end product of chemically weathering. Define Erosion Erosion The wearing away and transportation of the earth’s weathered surface What are the 4 natural forces that may cause erosion? 1. 2. 3. 4. Erosion 1. Wind 2. Water 3. Glacial action 4. Gravity (from a point of high elevation to a lower elevation) Explain the 5 different types of parent material based on how they were transported? 1. 2. 3. 4. 5. How did the soils get there? Types of parent material? 1. Sedentary – soils that weather from bedrock and remain in place Bedrock – solid unweathered rock lying beneath surface deposits of soil 2. Colluvial – soils that have moved in response to gravity 3. Alluvial – Soils that are carried in water such as rivers. These are deposited on flood plains and at deltas 4. Aeolian – Soils that are transported and deposited by winds 5. Glacial till – Soils deposited by glaciers How wind erodes the soil? Define the following forms of wind erosion - Saltation – How wind erodes the soil??? Saltation – Fine and medium sand-sized particles move mainly by saltation “bouncing particles”. 50-80% of the total soil is moved this way Most soil movement is within a foot of the ground How wind erodes the soil? Suspension – Suspension – Very fine soil particles are lifted from the surface by the impact of saltation This “dust” is carried high into the air for long distances Small % of the total soil moved by wind is this way These particles are the most fertile part of the eroded soils How wind erodes the soil? Surface creep – Surface creep – The movement of larger (sandsized) soil particles along the surface of the soil. Loosened by saltation particles Too large to be lifted off the ground in most winds Rolling motion along the surface 25% of the soil is moved this way What are the 5 Major types of erosion by water and explain each type? 1. 2. 3. 4. 5. Soil Erosion by Water Water causes about 2/3 of the erosion on our land. Soil is the largest pollutant in our waterways Our soil erosion problems began in colonial times…. “When our fore-fathers settled here…the Land being new they depended upon the Natural Fertility of the Ground…and when they had worn out one piece they cleared another…” - Jared Eliot, Ct. minister, doctor, and farmer, 1748 A Natural Stream A Damaged Stream Long-term accumulations of sediment, nutrients, and pesticides have damaged vital aquatic resources.. Major types of erosion by water: SPLASH EROSION – Soil particles loosened by water drops SHEET EROSION – Surface carrying soil particles detached by water drops RILL EROSION – Small eroding channels or water paths GULLY EROSION – Large volumes of soil removed by scouring the sidewalls. Creating verticle walls MASS EROSION OR SLUMPING – Large areas of soil slide or creep downhill. Potential for gully erosion What are the best agricultural soils? What are the best agricultural soils? They are loam Most alluvial and glacial till soil is best Colluvial soils are coarse textured and contain undesirable chemical and physical qualities Aeolian soils are finely textured and vary greatly in their productivity Sedentary soils may be useful for agriculture if they have not lost their nutrient elements How do sedentary soils loose their nutrients?