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Transcript
Weathering, Soil, and Mass Movement What is Weathering? Is the breaking down and changing of rocks near Earth’s surface ◦ Two Types: Mechanical (physical) and Chemical What is Mechanical Weathering? Mechanical Weathering: Physical forces break rock into smaller and smaller pieces without changing the rock’s mineral composition. Three Types of Mechanical Weathering Frost Wedging Unloading Biological Activity Frost Wedging Expansion of freezing water in cracks and crevices Eventually breaking rocks into pieces • Sections of rock that are wedged loose are called talus Unloading • The uplift and erosion of rocks overlying igneous rocks because pressure on igneous rocks is reduce • Exfoliation—slabs of outer rock separate and break loose Biological Activity • The activity of organisms, including plants, burrowing animals, and humans • Plant roots wedge into rocks breaking them apart What is Chemical Weathering? Chemical weathering: the transformation of rock into one or more new compounds. Agents and Evidence of Chemical Weathering Water: most important agent of chemical and mechanical weathering. It picks up CO2 and SO2 in the air which forms acid rain. Granite: Weathering of potassium feldspar produces clay minerals, soluble salt (potassium bicarbonate), and silica in solution. Quartz remains unaltered. Silicate Materials and Spheroidal Weathering Weathering of Silicate Minerals: Produces insoluble iron oxides and clay minerals Spheroidal Weathering: Causes the corners and edges of rock to be more rounded Rate of Weathering How fast the rocks erode Two factors • Rock characteristics • Mineral composition and solubility • Climate • Temperature and moisture • Favors high temperature and abundant moisture Soil Soil: part of the regolith that supports the growth of plants. Regolith: layer of rock and mineral fragments that covers most of Earth’s land surface. How is Soil Formed? Soil is formed by rock being eroded away. Parent material Residual soil ◦ parent material is the bedrock Transported soil ◦ parent material has been carried from elsewhere and deposited Characteristics of Soil Soil Composition Soil has four major components A. Mineral matter (broken-down rock) B. Humus (decayed remains of organisms) C. Water D. Air Characteristics of Soil Soil Texture Texture refers to the proportions of different particle sizes. A. Sand (large size) B. Silt – feels like flour C. Clay (small size) D. Loam (a mixture of all three sizes) is best suited for plant life. Characteristics of Soil Characteristics of Soil Soil Structure Soil particles clump together to give a soil its structure. Time, Climate, Organisms and Slope Time: Important in all geologic processes. The longer a soil has been forming, the thicker it becomes. Climate Greatest effect on soil formation Organisms Furnish organic matter to soil Slope Steep slopes often have poorly developed soils. Soil Profile O Horizon: Humus A Horizon: Topsoil E Horizon: Eluviation layer B Horizon: Subsoil C Horizon: Regolith R Horizon: Bedrock Soil Types Soil Types Location Contents Pedalfer under forest vegetation iron oxides and aluminum-rich clays in the B horizon Pedocal drier grasslands Calcium carbonate Laterite Hot, wet, tropical climates Intense chemical weathering to the top layers of soil How does water erode the soil? Rain uses gravity as a force to move soil. Flash flooding and runoff of water causes erosion Strong winds move particles Processes of Water Erosion Sheet erosion 2. Rills (tiny streams) 3. Gullies (trenches) 4. Transports sediments for deposits. 1. How can humans control erosion? Planting rows of trees called windbreaks Terracing hillsides Plowing along the contours of hills Rotating crops What is Mass Movement? The transfer of rock and soil down-slope due to gravity Triggers of Mass Movement Water Heavy rains and rapid melting of snow Oversteepened Slopes The steeper the slope the greater the chance for movement Removal of vegetation Roots keep the soil intact. Removing plants causes erosion Earthquakes Aftershocks dislodges rocks causing movements Classification of Mass Movements Rockfalls occurs when rocks or rocks fragments fall freely through the air. Classification of Mass Movements Avalanches --extremely rapid movement of earth material or snow Classification of Mass Movements Slides In a slide, a block of material moves suddenly along a flat, inclined surface. Slides that include segments of bedrock are called rockslides. Classification of Mass Movements Slumps A slump is the downward movement of a block of material along a curved surface. Classification of Mass Movements Flows Flows are mass movements of material containing a large amount of water. Mudflows move quickly and carry a mixture of soil, rock, and water that has a consistency of wet concrete. Earthflows move relatively slowly and carry clay-rich sediment. Classification of Mass Movements Creep is the slow, downhill movement of soil and regolith. slowest type of mass movement