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Transcript
Weathering, Soil, and Erosion Chapter 5 Weathering Def: the breakup of rock due to exposure to processes that occur at Earth’s surface 2 types: Mechanical- the breakdown of rock that takes place when a rock is broken into smaller pieces of the same material without changing its composition Chemical- the breakdown or decomposition of rock that takes place when minerals are changed into different substances Mechanical Weathering Processes Frost wedging Def: a process in which water freezes in the cracks of a rock and wedges it apart Mostly in porous rocks and in rocks with many cracks In places where there are frequent freezes and thaws Ice Heaving- creates potholes; ice lifts pavement up and it collapses when it thaws Examples of Frost Wedging and Ice Heaving Mechanical Weathering cont… Abrasion Def: the wearing away of rock material by grinding action Water, wind and ice are capable of moving rocks. Sand is a product of abrasion. Mechanical Weathering cont… Plants and Animals Growth contributes Roots wedged into tiny pores and crevices Burrowing Digging contributes holes into soil Bringing rock fragments to surface Mechanical Weathering cont… Upward Expansion Exfoliation- the peeling of surface layers from exposed bedrock Rock is uplifted by tectonic forces (ex: granite) Overlying rock is worn away which reduces pressure Upward expansion causes the granite to break along curved joints Large sheets of loosened rock break away Upward Expansion Examples Chemical Weathering Water Hydrolysis- the chemical weathering by reaction of water with other substances Acids: seeps into the ground and reacts chemically with many common minerals Calcite Dissolves completely Underground caverns Chemical Weathering cont… Acid Rain Def: rainwater that contains unusually high amounts of acids that can be traced back to pollutants Increases the rate of chemical weathering Chemical Weathering cont… Oxidation Def: chemical reaction of oxygen with other substances Effective with minerals containing iron Formation of rust, or iron oxides Rates of Weathering Weathering is usually a slow process Factors that affect the rate of weathering: Surface More Exposure surface exposed, weathers more quickly Composition of Rock Various rocks are affected differently by weathering processes Climate Warm/wet climates: both chemical and mechanical Cold/dry climates: mainly mechanical Soil Def: loose, weathered rock and organic material in which plants with roots can grow Formed by weathering Contains air, water, organic material, mineral matter Parent material Def: material from which a soil is formed Residual soil- soil whose parent material is the bedrock below Transported soil- soils formed from transported materials Deposits left by winds, rivers, and glaciers Soil Profile Def: cross section of earth exposed by digging Soil horizons- three distinct zones of mature soil A-horizon Darker, topsoil contains humus (organic material), sandy B-horizon- subsoil Red or brown, iron oxides, clay from topsoil, calcium and magnesium C-horizon Weathered parent material, rock fragments Soil Composition 3 noticeable parts: sand, silt, and clay Affects Factors soil’s ability to hold water and air that affect composition: Time Parent material Plants and animals Topography Climate- MOST IMPORTANT! 12.3 Mass Movements and Erosion Mass movements- the downward transportation of weathered materials Gravity causes materials to fall, slide, or move at slow speeds to lower levels Erosion- the removal and transport of materials by natural agents such as wind and running water Mass Movements Talus- rock fragments that have been weathered from a cliff and pulled down by gravity Landslide- movement of a mass of bedrock or loose soil and rock down the slope of a hill, mountain, or cliff Steep slopes Regions near volcanoes and in earthquake-prone regions Mass Movements Creep- slow, imperceptible movement of soil down a slope Causes fence posts, poles and other objects fixed in soil to lean downhill Slump- a block of land tilts and moves downhill along a surface that curves into the slope Tends to occur because bottom of slope can no longer support top of slope Mass Movements Earthflows- the downslope movement of a mass of earth materials that have been saturated with water Slower and less fluid than a mudflow; velocity affected by amount of water present, the composition of the soil, and the steepness of the slope Mudflows- the downslope movement of water that contains large amounts of suspended clay and silt Rapid movement; capable of moving rocks, boulders, trees, and houses; lahars- volcanic mudflows Erosion Topography- uplifting and weathering/erosion are happening at same time More uplifting- rugged and sharp (Himalayas) More erosion- smooth and rounded (Appalachians) Climate- in humid areas, water is primary agent and causes rounded topography Composition of rock- some types are more resistant than other rock types Volcanic neck- the solidified lava filling the center vent of an extinct volcano (picture pg 270) METHODS OF STABILIZING SOIL What can we do??? FARMING PRACTICES TO KNOW…