Chapter 4 Lecture Earth Science PDF

Chapter 4 Lecture Earth Science Fourteenth Edition Weathering, Soil, and Mass Wasting Jennifer Mangan James Madison University © 2015 Pearson Education, Inc.  Earth’s External Processes Weathering – the disintegration and decomposit...

Chapter 4 Lecture Earth Science Fourteenth Edition Weathering, Soil, and Mass Wasting Jennifer Mangan James Madison University © 2015 Pearson Education, Inc.  Earth’s External Processes Weathering – the disintegration and decomposition of material at or near the surface Mass wasting – the transfer of rock material downslope under the influence of gravity Erosion – the incorporation and transportation of material by a mobile agent, usually water, wind, or ice © 2015 Pearson Education, Inc.  Weathering Two kinds of weathering – Mechanical weathering Breaking of rocks into smaller pieces – Chemical weathering Chemical transformation of rock into one or more new compounds © 2015 Pearson Education, Inc.  Increase in Surface Area by Mechanical Weathering © 2015 Pearson Education, Inc.  Mechanical Weathering Four important processes – Frost wedging – expansion of freezing water – Salt crystal growth – Sheeting – generates onion-like layers and exfoliation domes – Biological activity © 2015 Pearson Education, Inc.  Frost Wedging © 2015 Pearson Education, Inc.  Sheeting and Exfoliation of Igneous Rocks © 2015 Pearson Education, Inc.  Chemical Weathering Alters the internal structures of minerals by removing or adding elements Most important agent is water – Oxygen dissolved in water oxidizes materials – Carbon dioxide (CO2) dissolved in water forms carbonic acid and alters the material © 2015 Pearson Education, Inc.  Chemical Weathering Weathering of granite – Weathering of potassium feldspar produces clay minerals, soluble salt (potassium bicarbonate), and silica in solution – Quartz remains substantially unaltered – Weathering of silicate minerals produces insoluble iron oxides and clay minerals © 2015 Pearson Education, Inc.  Chemical Weathering Spheroidal Weathering – Generates rounded rocks – Weathering works inward from exposed surfaces © 2015 Pearson Education, Inc.  Rates of Weathering Advanced mechanical weathering aids chemical weathering by increasing the surface area Important factors – Rock characteristics Mineral composition and solubility Physical features such as joints © 2015 Pearson Education, Inc.  Rock Type Influences Weathering © 2015 Pearson Education, Inc.  Rates of Weathering Important factors – Climate Temperature and moisture are the most crucial factors Chemical weathering is most effective in areas of warm temperatures and abundant moisture © 2015 Pearson Education, Inc.  Rates of Weathering Differential weathering – Caused by variations in composition – Creates unusual and spectacular rock formations and landforms © 2015 Pearson Education, Inc.  Differential Weathering © 2015 Pearson Education, Inc.  Soil An interface in the Earth system Soil is a combination of mineral matter, water, and air – Regolith Rock and mineral fragments Supports the growth of plants © 2015 Pearson Education, Inc.  Soil Components © 2015 Pearson Education, Inc.  Soil Soil texture and structure – Texture refers to the proportions of different particle sizes Sand (large size) Silt Clay (small size) – Loam (a mixture of all three sizes) is best suited for plant life © 2015 Pearson Education, Inc.  Soil Texture © 2015 Pearson Education, Inc.  Soil Soil texture and structure – Structure Soil particles clump together to give a soil its structure Four basic soil structures – Platy – Prismatic – Blocky – Spheroidal © 2015 Pearson Education, Inc.  Controls of Soil Formation Parent material – Residual soil – parent material is the bedrock – Transported soil – parent material has been carried from elsewhere and deposited Time – Important in all geologic processes – Amount of time to evolve varies for different soils © 2015 Pearson Education, Inc.  Controls of Soil Formation Climate Plants and animals – Organisms influence the soil’s physical and chemical properties – Furnish organic matter to soil © 2015 Pearson Education, Inc.  Controls of Soil Formation Slope – Angle Steep slopes often have poorly developed soils Optimum is a flat-to-undulating upland surface – Orientation (direction the slope is facing) influences Soil temperature Moisture © 2015 Pearson Education, Inc.  Slopes and Soil Development © 2015 Pearson Education, Inc.  Soil Profile Soil Profile – Soil forming processes operate from the surface downward – Horizons – zones or layers of soil © 2015 Pearson Education, Inc.  Soil Profile Horizons in temperate regions – O – organic matter – A – organic and mineral matter – E – little organic matter Eluviation Leaching – B – zone of accumulation – C – partially altered parent material © 2015 Pearson Education, Inc.  Soil Profile Topsoil – Zones O and A together Solum – “True soil” – O, A, E, B together © 2015 Pearson Education, Inc.  Soil Horizons © 2015 Pearson Education, Inc.  Contrasting Soil Profiles © 2015 Pearson Education, Inc.  Soil Classifying soils – System for classifying soils in the United States is called the Soil Taxonomy Emphasizes physical and chemical properties of the soil profile Names of the soil units are combinations of syllables of Latin and Greek origin © 2015 Pearson Education, Inc.  Global Soil Regions © 2015 Pearson Education, Inc.  Soil Erosion Recycling of Earth materials Natural rates of erosion depend on – Soil characteristics – Climate – Slope – Type of vegetation © 2015 Pearson Education, Inc.  Soil Erosion Processes that erode soil – Water erosion Raindrops dislodge soil particles Flowing water carries soil away 2/3 of all U.S. soil erosion – Wind Erosion Occurs with dry soil conditions © 2015 Pearson Education, Inc.  Soil Erosion Soil erosion and sedimentation can cause – Reservoirs to fill with sediment – Contamination by pesticides and fertilizers © 2015 Pearson Education, Inc.  Soil Erosion © 2015 Pearson Education, Inc.  Soil Erosion Controlling soil erosion – Leave steep slopes undisturbed – Terrace crop planting – Grassed waterways – Tree windbreak barriers © 2015 Pearson Education, Inc.  Soil Conservation © 2015 Pearson Education, Inc.  Soil Conservation: Grassed Waterway © 2015 Pearson Education, Inc.  Mass Wasting The downslope movement of rock, regolith, and soil under the direct influence of gravity Gravity is the controlling force © 2015 Pearson Education, Inc.  Mass Wasting Triggers Saturation of the material with water – Destroys particle cohesion – Water adds weight © 2015 Pearson Education, Inc.  Mass Wasting Triggers Oversteepening of slopes – Unconsolidated granular particles assume a stable slope called the angle of repose – Stable slope angle is different for various materials © 2015 Pearson Education, Inc.  Mass Wasting Triggers Removal of anchoring vegetation Ground vibrations from earthquakes © 2015 Pearson Education, Inc.  Mass Wasting Processes Generally each type is defined by – The material involved – debris, mud, earth, or rock – The movement of the material Fall (free-fall of pieces) Slide (material moves along a well-defined surface) Flow (material moves as a viscous fluid) © 2015 Pearson Education, Inc.  Mass Wasting Processes Generally each type is defined by – The rate of the movement Fast Slow © 2015 Pearson Education, Inc.  Mass Wasting Forms Slump – Rapid movement along a curved surface – Occur along oversteepened slopes © 2015 Pearson Education, Inc.  Mass Wasting Forms Rockslide – Rapid – Blocks of bedrock move down a slope © 2015 Pearson Education, Inc.  Mass Wasting Forms Debris flow (mudflow) – Rapid flow of debris with water – Often confined to channels – Debris flows composed mostly of volcanic materials are called lahars © 2015 Pearson Education, Inc.  Mass Wasting Forms Earthflow – Rapid – Typically occur on hillsides in humid regions – Water saturates the soil – Liquefaction – a special type of earthflow sometimes associated with earthquakes © 2015 Pearson Education, Inc.  Mass Wasting Forms Creep – Slow movement of soil and regolith downhill – Causes fences and utility poles to tilt Solifluction – Slow movement in areas underlain by permafrost – Upper (active) soil layer becomes saturated and slowly flows over a frozen surface below © 2015 Pearson Education, Inc.  Creep © 2015 Pearson Education, Inc.  Solifluction © 2015 Pearson Education, Inc.