4 What is weathering?Weathering is the breakdown and alteration of rocks and minerals near or at the Earth’s surface.The two types of weathering are: physical or mechanical weathering 2. chemical weathering
5 Physical Weatheringthe breaking of rocks into smaller fragments without changing their mineral or chemical compositionjoints are cracks in rocks formed by tectonic forces
6 Physical Weathering1. frost action – rocks break as water freezes in cracksClick for animation!
7 Physical Weathering2. abrasion or impact weathering – rocks break down when exposed to agents of erosion
8 Physical Weathering2. abrasion or impact weathering – rocks break down when exposed to agents of erosion
9 Physical Weathering3. pressure release – rocks fracture as they expand when exposed from beneath the Earth’s surface
10 Physical Weatheringexfoliation – outer layers of rock peel off following pressure release or insolation weathering4. insolation weathering – rocks break due to exposure of extremes of temperatures resulting in repeated expansions and contractionsClick for animation!
11 Physical Weathering 5. biological weathering a. rocks break as plant roots grow in cracksb. rocks and minerals break down as animals burrow and moveClick for animation!
12 Chemical Weatheringthe minerals or chemicals in rocks are altered and new substances are formedwater is needed for chemical reactions to take place
13 Chemical Weatheringiron leaching1. leaching – water dissolves chemicals in rocks and washes them away
14 Chemical Weathering2. hydration - certain minerals absorb water and produce new substances (ex. feldspar + water → kaolinite, a type of clay used in pottery)Click for animation!
15 Chemical WeatheringClick for animation!3. oxidation – certain minerals combine with oxygen in air or water forming oxides (ex. iron + oxygen → rust)
16 Chemical Weathering4. carbonation weathering – rocks with calcite (ex. limestone) are dissolved away by carbonic acid produced from water combining with CO2
17 Chemical Weathering5. acid rain – sulfur and nitrogen oxide air pollutants combine with rain droplets forming acids that break down rocks
18 Chemical Weathering 6. biological weathering a. chelation – organisms such as lichens and moss produce acids that break down rocks
19 Chemical Weathering 6. biological weathering b. organisms can influence environmental factors that may enhance weathering (ex. moisture and pH)
20 Rate of WeatheringThe 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.
21 Rate of WeatheringThe 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.
22 Products of Weathering rock fragmentsrock formationslimestone cavessoilsedimentnutritional minerals for plantssolutes in bodies of water
29 Reflection: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.