Geology 101 Outline of Last Lecture 1980 Mount St Helen s Eruption Nature of Eruptions Materials Extruded from a Volcano General Features of a Volcano Types of Volcanoes Other Volcanic Landforms Volcanic Eruptions and Plate Tectonics and Igneous Activity Outline of Current Lecture Earth s External Processes Two Types of Weathering Types of Mechanical Weathering Chemical Weathering Factors Affecting Rate of Weathering Soil Importance of Sedimentary Rocks Types of Sedimentary Rocks Common Detrital Sedimentary Rocks Earth s External Processes o Weathering physical breakdown and chemical decomposition of rock o Mass wasting the transfer of rock and soil downslope under the influence of gravity o Erosion physical removal of material by water wind ice or gravity Two types of weathering o Physical Mechanical Breaking down of rocks into smaller pieces o Chemical Chemically change rock composition o Two types work in concert Positive feedback Physical wreathing increases surface area Cube reference in class o Adds sides to cubes Making more surface area More cracks more surface area Chemical weathering weakens the attachment between grains Types of Mechanical Weathering o Frost wedging Geology 101 Due to water freezing o Unloading sheeting exfoliation domes Deeply buried igneous pluton Uplift and erosion of overlying rock Reduces pressure unequally Rock body expands Expansion and sheeting Exfoliation of dome Mt Georgia o Salt weathering by growth of salt crystals o Thermal expansion expansion contraction o Biological activity Plant roots Small fracture can become larger Animals o Joints formed by physical weathering Parallel Chemical Weathering o Most important agent is water o Major processes of chemical weathering Dissolution Aided by small amount of acid in water o halite dissolves in water polar water molecules attracted to halite sodium and chloride ions dissolved in water o calcium dissolves in water aided by carbonic acid forms limestone caverns Oxidation Type of chemical reaction when electrons are lost from one element o Iron and oxygen Hydrolysis Reaction of any substance with water A hydrogen ion attacks and replaces other ions Primary process for silicates to be decomposed Factors Affecting Rate of Weathering o Surface area o Rock characteristics Calcite marble limestone readily dissolve in weakly acidic solutions Silicate minerals weather in same order as their order of crystallization Olivine earlier than quartz o Climate Most effective in warm moist climate Geology 101 o Differential weathering Largely depend on composition of rock o Mineral and organic matter and water and air Regolith Rocks and mineral fragments produced by weathering Humus Decayed animal and plant remains Small Factors controlling soil formation Parent material Residual o Developed by bedrock being weathered o Above parent rock Transported o Developed somewhere else and was transported and deposited Stream deposit sediment Time o Depending on geologic and climate conditions Climate o Temperature o Precipitations Plants and animals Topography o Steep slopes often have poorly developed soils Soil profile Vertical difference are called horizons which are zones or layers of soil O organic matter A organic and mineral matter o O and A topsoil E little organic matter o Zone of eluviation and leaching B zone of accumulation clay o Transported from above o Subsoil C partially altered parent material Soil erosion Part of the natural recycling of all earth s material Natural rates of soil erosion depend on Soil characteristics Climate Slope Type of vegetation Soil conservation Windbreaks Soil o o o Geology 101 o Row of trees to slow wind Pattern of crop planting slow the rate of water running off Importance of Sedimentary Rocks o Small portion but at near surface Interface among geo hydro atmo and bio spheres o Contain evidence of past environments Provide information of Earth History Often contain fossils o Economically important Coal Petroleum and natural gas Source of Fe Al Etc Formation of Sedimentary Rocks o Weathering o Transportation o Deposition o Diagenesis Compaction and cementation Types of Sedimentary Rocks o Sediment originates from mechanical and or chemical weathering o Rocks based on source of material Detrital Transported sediments as solid particles Particle size distinguishes Chemical Sediment that was once in a solution Organic Coal Common Detrital Sedimentary Rocks o Shale Mud size particles in thin layers Most common o Sandstone Sand size particles Predominant mineral quartz Forms in a variety of environments Sorting particle shape and composition reveal environment