Transcript Weathering
Warm Up 10/11/12 • Answer the following questions based on the demonstration: 1. Which dissolved faster rock salt or granulated salt? 2. Describe, in terms of surface area, why? Weathering Earth Systems TYPES OF WEATHERING • There are three major types of weathering: • physical (mechanical) • chemical • biological Physical Weathering • AKA Mechanical weathering • Physical weathering breaks rocks down into smaller pieces. Chemical Weathering • Chemical weathering breaks rocks down chemically adding or removing chemical elements, and changes them into other materials. Chemical weathering consists of chemical reactions, most of which involve water. Biological Weathering • Biological weathering breaks down rocks and minerals due to the chemical and/or physical agents of an organism. The types of organisms that can cause weathering range from bacteria to plants to animals. TYPES OF PHYSICAL WEATHERING • Frost wedging - water expands when it freezes, breaking rocks into angular fragments TYPES OF PHYSICAL WEATHERING • Exfoliation – outer rock layers are stripped away. • Often results in dome-shaped formations, like that of Stone Mountain. TYPES OF PHYSICAL WEATHERING • Thermal expansion heat causes expansion; cooling causes contraction. • Different minerals expand and contract at different rates causing stresses along mineral boundaries. • Repeated daily heating and cooling of rock causes the rock to break down. TYPES OF CHEMICAL WEATHERING • Dissolution – Carbonation is the reaction with carbonic acid, which forms when carbon dioxide from the atmosphere dissolves in rain water: CO2 + H2O H2CO3 (Carbon dioxide gas + water carbonic acid) – Hydration is addition of the entire water molecule to the mineral structure and commonly occurs in clay minerals, sometimes causing them to swell. TYPES OF CHEMICAL WEATHERING • Hydrolysis is an exchange reaction involving minerals and water. Free hydrogen (H+) and hydroxide (OH)- ions in water replace mineral ions and drive them into solution. • As a result, the mineral's atomic structure is changed into a new form. It is a process whereby silicate minerals like potassium feldspar are weathered and a clay mineral is formed. TYPES OF CHEMICAL WEATHERING • Oxidation is the process by which ironbearing minerals weather to produce iron oxides (or "rust"). – Iron-bearing silicate minerals which also contain aluminum undergo both oxidation and hydrolysis, forming both iron oxides and clays. Iron-bearing alumino-silicate minerals weather to form the red clayey soils, such as are found in Georgia. CHEMICAL WEATHERING • Factors which affect the rate of chemical weathering are: – Particle size - Smaller the particle size the greater the surface area and hence the more rapid the weathering – Composition – Climate – Type and amount of vegetation