CEE 1030 1nd Edition Lecture 5 Weathering and Soils Outline of Last Lecture I Volcano resources II Nature of volcanic eruptions III Types of volcanic deposits a Basaltic lava flow types IV Basaltic volcanoes V Intermediate rhyolitic volcanoes VI Pyroclastic falls and flows VII Lahars VIII Volcanoes and climate IX Intrusive igneous activity X Hydrothermal systems XI Massive intrusions batholiths Outline of Current Lecture I Dangers of ash II Review III Earth s external processes IV Types of weathering V Soil formation Current Lecture I II III Dangers of ash a Planes flying through ash clouds can face serious problems i Ring of fire in overseas travel ii Volcano ash can spread across countries iii All commercial activity from North America to Asia goes over volcanoes important to monitor volcanic activity iv Ash tiny particles of abrasive glass causes massive damage to planes Review a Largest explosive volcanic eruption of historic times Tambora Indonesia 1815 b Factor likely to lead to highly explosive eruptions high viscosity Earth s external processes a Natural processes of change ex Old Man of the Mountain Finger of God These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute IV V b Weathering breakdown disintegration and chemical alteration decomposition of rock at Earth s surface c Erosion physical removal of material by mobile agents exposes fresh unadulterated rock to weathering d Leads to the formation of sedimentary rock e Different minerals affected by weathering to different extents Types of weathering a Mechanical weathering disintegration breaks rocks i Frost weathering water gets into cracks of rocks when it freezes it expands freeze thaw cycles crack rocks over time ii Root wedging tree roots grow down into cracks of rocks iii Salt wedging evaporation of water rich in dissolved species leads to the growth of salt crystals in cracks iv Thermal expansion large daily temperature changes creates expansion v Unloading uplift and erosion reduce pressure on rocks creates exfoliation sheets b Chemical weathering disintegration changes make up of rocks i Dissolution promoted by acidic water ii Hydrolysis reaction of minerals with water hydrogen ion attacks and replaces other ions iii Oxidation over exposure to particles in the air iv Products of chemical weathering 1 Placer deposits resistant economic minerals gold diamonds v Rates of chemical weathering 1 Surface area same volume of rock but smaller particles have greater total surface area smaller particles erode faster 2 Rock type rocks containing calcite marble and limestone readily dissolve in weakly acidic solutions a Silicate minerals weather in the same order as their order of crystallization 3 Climate temperature and moisture a Chemical weathering is most effective in areas of warm moist climates Soil formation a Regolith layer of weathering product s at Earth s surface rock and mineral fragments b Soil combination of mineral and organic matter plus water and air c Humus decayed plant and animal material d Residual soil developed in bedrock e Transported soil on unconsolidated deposits f Factors controlling soil formation i Climate ii Time iii Plants and animals iv Topography g Tropical soils laterites i Laterites highly leached soils ii Thin or absent humus layer nutrient poor h Tropical soils bauxite i More intense weathering ii Contains sources of aluminum
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