Unit 1 Soil and Rock of the Earth PDF

Unit 1 Soil and Rock of the Earth Geo-Environmental Fundamentals Introduction Rocks Igneous Sedimentary Metamorphic Strongest when newly formed, become weaker and softer when exposed to weathering forces. Soils Formed by the weathering of rocks In-situ – residual soils...

Unit 1 Soil and Rock of the Earth Geo-Environmental Fundamentals Introduction Rocks Igneous Sedimentary Metamorphic Strongest when newly formed, become weaker and softer when exposed to weathering forces. Soils Formed by the weathering of rocks In-situ – residual soils Transported soils – wind, ice, and water – followed by deposition  Definitions *Definitions printed from: Physical Geography Glossary of Terms: http://www.physicalgeography.net/glossary.html *Igneous Rock Rocks formed by solidification of molten magma either beneath (intrusive igneous rock) or at (extrusive igneous rocks) the Earth’s surface. *Metamorphic Rock Rocks formed from the re-crystallization of igneous, sedimentary, or other metamorphic rocks through pressure increase, temperature rise, or chemical alteration. *Sedimentary Rock Rocks formed by the deposition, alteration and/or compression, and lithification of weathered rock debris, chemical precipitates, or organic sediments *Parent Material The mineral material from which a soil forms *Physical Breakdown of rock and minerals into small-sized particles through mechanical stress. Weathering *Chemical Breakdown of rock and minerals into small-sized particles through chemical Weathering decomposition. Residual Soil Soil developed directly from the weathering of the bedrock below *Lithification The process – generally compaction and/or cementation – of converting sediments into sedimentary rock  Definitions Continued Boulders Large fragmented rock that has a diameter greater than 256mm Sand Mineral particle with a diameter between 0.075mm and 4.75mm Silt Mineral particle with a diameter between 0.002mm and 0.075mm Clay Mineral Particle with a diameter less than 0.002mm Soil Profile A vertical section of the soil through all of its horizons and extending into the parent material. Soil Horizon A layer of soil differing in properties and characteristics from the adjacent layers below or above Definition of Soil and Rock Soil – from an engineering sense, is defined as “all fragmented minerals at or near the earth’s surface plus the air, water, organic matter, and other substances of unconsolidated sediments and deposits of solid particles that have resulted from the disintegration of rock”. Includes: - soft spongy peat - coarse grained sands - soft clays - gravel - loams - stiff clay - silts - shale Definition of Soil and Rock cont. Rock – In geological terms, rock is any naturally formed, consolidated aggregate of mineral matter making up part of the earth’s crust. References to rock include bedrock; a hard mineral substance great in size as well as regolith; rock fragments created from the weathering of bedrock. Stronger Weaker Blocks of rock are separated by naturally formed surfaces such as: bedding EXTRA NOTE: FORMED FROM PARENT MATERIAL planes, joints, faults and shears. These are all considered weaknesses and reduce the strength of large masses of rock. Geological Classification of Rock Igneous Rocks Formed by the solidification of molten materials, either by: intrusion – at depths within the earths crust – or extrusion – at the earths surface. The degree of crystallinity and the grain size of the rocks vary based on the rate at which the magma was cooled at the time of formation. Fast cooling = smaller mineral crystals Slow cooling = larger minerals, coarse texture Geological Classification of Rock Sedimentary Rocks Formed by the lithification (compaction and cementation) of sedimentary soils. The sediments are deposited in water environments. Over time, the weight of newly accumulated sediment will compact the existing sediment and the mineral matter contained within the water will be left behind as the water moves through the sediment, resulting in the cementation of the sediment particles. Examples of sedimentary rock include limestone, sandstone, shale and mudstone.  Geological Classification of Rock Metamorphic Rocks Originally igneous, sedimentary or metamorphic that have been altered by the application of intense heat and/or pressure and plastic flow. Plastic flow (rock): the slow viscous movement and rearrangement within the rock mass as it changes and adjusts to the pressure created by external forces.  “Remember, any rock can become any other type of rock” The Rock Cycle - YouTube Video - CIVL-2015 (242765) Geotechnical Fundamentals (rrc.ca) Formation of Soils There are 2 important factors involved in the weathering process which contributes to the creation of soil: Mechanical Chemical Weathering -The physical disintegration and chemical decomposition of rocks in response to environmental conditions at or near the earths surface. *Recall that the definition of soil contains the phrase “all fragmented minerals at or near the earth’s surface ….. that have resulted from the disintegration of rock.” Formation of Soils Mechanical Weathering - The process by which rocks break down by physical forces such as wind, rain, running water and ice. In this process the smaller fragments of rock maintain the same mineral composition as the original parent rock from which it was created. freeze thaw cycles (frost action) the force of water the abrasion of boulders and gravel carried by water ways glaciers temperature changes (thermal expansion) natural activities (erosion) animal and human activity Formation of Soils Chemical Weathering The decomposition of rock due to chemical reactions in the rock material that occur from exposure to the atmosphere: temperature, water/other fluids, climate, topography, drainage and vegetation impact the rate of chemical weathering. Formation of Soils Chemical Weathering - otherwise known as decomposition, occurs as a result of the reaction of the rock minerals with water, carbon dioxide, oxygen, organic acids from decayed materials, dissolved salts, etc. Rock minerals go through a chemical change and form new minerals with different chemical and physical properties as compared to the original parent rock from which they were created. 1. Reduction – reactions that take place without oxygen. Influenced by anaerobic bacteria. 2. Oxidation – rocks rich in iron will rust in the presence of water and air, decomposing the rock. 3. Acid Rain - carbon dioxide dissolves in water, carbonic acid is formed, which can dissolve minerals and cause decomposition. 4. Carbonation – carbons are modified into coals, petroleum or gas under high pressure. 5. Hydrolysis – minerals take up OH-ions (from water) and decompose into soil particles. Formation of Soils Newly formed soils will either remain in place – residual soils – or be transported and deposited in a new location – transported soils. Transportation/deposition agents include gravity, wind, water, glaciers. It’s important to recognize that the formation of rock and soil is an ongoing process that takes place over time. Often hundreds or thousands of years.  Formation of Soils Deposition River and Stream Deposits Flowing bodies of water carry soil in suspension, or rolling along the bottom of the river. Soils carried by and deposited by rivers are classified as alluvial deposits. Lacustrine deposits form in open water – finer silt and clay Ice Born Deposits Ice is the major eroding agent in the mountains. Its principal deposit is Till. Till is an unsorted mixture of clay, silt, sand and gravel/boulders. It’s typically hard and dense. If melted water is dammed by high topography, a large inland lake may be formed (Lake Agassiz). Soil Profiles and Horizons The transition of soil types in both horizontal and vertical directions may be gradual or abrupt. With time, soils become deeper and develop distinct layers or horizons. The soil profile in mineral soils has three horizon types, from the surface down, called A, B, and C. A soil profile is a vertical section of the soil from the surface through all of its layers (horizons) into the parent rock. They appear as layers in a soil profile. There are 4 general horizons. Horizon A contains organic matter (topsoil) usually black or brown in colour small clay particles are washed out compressible, elastic, unstable and a poor foundation layer Horizon B defined as “sub-soil” enriched with clay particles, oxides and soluble carbonate particles abundant clay makes it hard when dry and sticky/gummy when wet. iron oxides make it brown or yellow relatively stable Horizon C weathered parent material that has been broken from bedrock (parent material) Relatively stable, desirable as a foundation layer sometimes referred to as till Horizon D (Biggs, Soil Horizons 2021) massive, undisturbed bedrock (parent material) Resources: Glossary of Terms. PhysicalGeography.net. (n.d.). http://www.physicalgeography.net/glossary.html Anthoni, F. (2000). Soil Geology. https://www.seafriends.org.nz/enviro/soil/geosoil.htm Biggs, W. (2021). Soil Horizons. Wikimedia Commons. Retrieved August 23, 2024, from https://commons.wikimedia.org/wiki/File:Soil_Horizons.svg.