7 Weathering, Soil, and Mass Wasting

7 WEATHERING, SOIL, AND MASS WASTING Weathering Weathering - the decomposition and disintegration or wearing away of material at or near Earth’s surface. Mechanical Weathering - breaking down rock into smaller pieces through: 1. Frost wedging - expansion of freezing water by 9% 2. Salt crystal growth 3. Thermal expansion 4. Sheeting - generates layers and exfoliates domes. 5. Biological activity - burrowing animals, organisms, and plants growing in cracks. Chemical Weathering - breaking down the internal structure of a rock by removing or adding elements. Water plays an important role in weathering; Why?... 1. Oxygen dissolved in water oxidizes material 2. Carbon dioxide dissolved into water forms carbonic acid and then alters the material ☆ Weathering of potassium feldspar produces clay minerals, soluble salt, and silica in solution. ☆ Weathering of silicate minerals produces insoluble iron oxides and clay minerals. ☆ Advanced mechanical weathering aids chemical weathering by increasing the surface area. Factors that affect rates of Weathering: 1. Rock Characteristics 2. Climate 3. Differential weathering Soil Erosion - the incorporation and transportation of material by water, wind, ice or gravity. Soil - a combination of 45% mineral matter, 25% water, 25% air, and 5% organic matter that is an interface in the Earth System Regolith - rock and mineral fragments that support the growth of plants. Residual Soil- when parent material is already in the bedrock. Transported Soil - when parent material has been carried from elsewhere and deposited. Soil Horizons - the zones or layers of soil. Soil Textures - a reference to the sizes of particles present in the soil: (largest to smallest) 4. Sand 5. Silt 6. Clay Controls of Soil Formation: 1. Parent materials 2. Time 3. Climate 4. Plants and animals 5. Topography Soil Structure - the structure product of the soil particles bound together: 1. Platy - flat and plate-like units that are generally laid horizontally causing plates to overlap. 2. Prismic -long, vertical units with the tops shaped like a prism. They are bounded by flat or rounded vertical faces. 3. Blocky - block-like units that consist of six or more flat or slightly rounded surfaces. 4. Massive - no apparent structure; soil particles cling together with no uniform masses. 5. Columnar - units that are similar to prisms but have normally rounded edges. These are bounded by flat or slightly rounded vertical faces. 6. Crumb - small, porous units that are weakly bounded. 7. Granular - spherical or polyhedral units that are small, porous and strongly bounded. 8. Single grain - no apparent structure; soil particles exist as individuals, not bounded to form aggregates. - Mass Wasting Mass Wasting - the downslope movement of rock and soil due to the controlling influence of gravity. Mass Wasting triggers: 1. Saturation of water - Water adds weight and destroys cohesion between particles. 2. Over steepening of slope - Over steepened slopes are unstable; a stable slope is called the angle of response. 3. Removal of anchoring Vegetation 4. Ground vibrations from earthquakes Mass Wasting types are defined by the material involved, what is moved, how it moves, and how fast it moves. Types of Movement - fall, slide, and flow. Forms of Mass Wasting: 1. Slump - rapid movement along a curved surface, along over steepened slopes. 2. Rockslide - rapid movement of blocks of bedrock down a slope. 3. Mudflow - rapid movement of debris that is often confined to channels. This is an issue in dry areas with heavy rain. 4. Earthflow - rapid movement on hillsides in humid regions where water saturates the soil. 5. Creep - slow movement of soil downhill which causes poles and fences to tilt. Liquefaction - a special type of earthflow that is sometimes associated with earthquakes.