Transcript Weathering
Recognise that weathering involves the breakdown of rock in situ and, as such, should be distinguished from erosion. • Describe what is meant by different types of weathering – physical/mechanical (freeze-thaw action, exfoliation), chemical (carbonation, oxidation) and biological. • Explain the main factors influencing the type and rate of weathering – climate and rock features (mineral composition, grain size of the rock, presence of lines of weakness). The influence of climate on the rate of weathering could be illustrated with reference to simple explanation as to why weathering is more rapid in humid tropical regions of the world than in temperate regions. Weathering is the breakdown of rock in situ Erosion involves the removal of weathered material by the action of gravity, water, wind or ice The two types of weathering are: 1. physical or mechanical weathering 2. chemical weathering 3. Biological weathering the breaking of rocks into smaller fragments without changing their mineral or chemical composition joints are cracks in rocks formed by tectonic forces 1. frost action – rocks break as water freezes in cracks Click for animation! 2. pressure release – rocks fracture as they expand when exposed from beneath the Earth’s surface exfoliation – outer layers of rock peel off following pressure release or insolation weathering 3. insolation weathering – rocks break due to exposure of extremes of temperatures resulting in repeated expansions and Click for contractions animation! 4. biological weathering a. rocks break as plant roots grow in cracks b. rocks and minerals break down as animals burrow and move Click for animation! the minerals or chemicals in rocks are altered and new substances are formed water is needed for chemical reactions to take place iron leaching 1. leaching – water dissolves chemicals in rocks and washes them away 2. hydration - certain minerals absorb water and produce new substances (ex. feldspar + water → kaolinite, a type of clay used in pottery) 3. oxidation – certain minerals combine with oxygen in air or water forming oxides (ex. iron + oxygen → rust) 4. carbonation weathering – rocks with calcite (ex. limestone) are dissolved away by carbonic acid produced from water combining with CO2 5. acid rain – sulfur and nitrogen oxide air pollutants combine with rain droplets forming acids that break down rocks 6. biological weathering a. chelation – organisms such as lichens and moss produce acids that break down rocks 6. biological weathering b. organisms can influence environmental factors that may enhance weathering (ex. moisture and pH) 1. 2. The bigger and more numerous the joints in a rock, the faster is the rate of weathering. Climate affects the rate of weathering. a. Frost action depends on rain, snowfall and temperature ranges. b. Chemical weathering is enhanced in humid climates. 3. The mineral composition of a rock may make it more or less susceptible to weathering. a. Quartz is resistant to both physical and chemical weathering. b. Calcite is easily dissolved away by carbonic acid. 1. 2. 3. 4. 5. 6. 7. rock fragments rock formations limestone caves soil sediment nutritional minerals for plants solutes in bodies of water abrasion chelation exfoliation oxidation • • • • abrasion chelation exfoliation oxidation abrasion chelation exfoliation oxidation abrasion chelation exfoliation oxidation Watch the following slideshow in silence. Look at each picture. Be sensitive to the feelings and ideas each one evokes. Choose the picture that made the most impact on you. Describe it. How did it make you feel? What thoughts and ideas came to you? Write a short reflection (5 to 10 sentences) about it.