General Geology: Weathering and Soil

1. General Geology: Weathering and Soil Instructor: Prof. Dr. Boris Natalin

2. Principle processes • Weathering – disintegration and decomposition of rocks at or near the Earth’s surface • Mass wasting – the transfer of rock fragments downslope under influence of gravity • Erosion – the incorporation and transportation of material by mobile agents as water, wind, or ice

4. Types of weathering: - Mechanical weathering - Chemical weathering Mechanical weathering increases rock surface for chemical attack

5. Fragmentation of rocks • Frost wedging • Expansion resulting from unloading • Thermal expansion • Organic activity

6. Unloading

7. Frost wedging Water expands about 9% upon freezing Ice Broken fragments fall to the base of the cliff and create talus Talus

8. Steep slopes covered by talus

9. Joints

10. Thermal expansion Rounded pebble disintegrated due to the rapid cooling (during desert sunder storms?)

11. Organic activity Weathering is accomplished by: • Plants • Burrowing animals • Human beings

12. Chemical weathering Breaks down rock components and minerals Formation of new minerals Minerals stay, if they are stable in surface environments Water is a good solvent • Dissolution • Oxidation • Hydrolysis

13. Dissolution Sodium and chlorine ions are attacked by the polar water molecules Once removed, these ions are surrounded and held by a number of water molecules

14. Acid increases the corrosive force of water • Transformation of solid into soluble • H+ is active ion • Formation of carbonic acid: CO2 + H2O ↔ H2CO3 • Water is a weak acid CaCO3 + 2[H+(H2)O] → Ca2+ + CO2↑ + 3(H2)O

15. Dissolution of stone monuments

16. Acid precipitation • Burning releases sulfur and nitrogen • In addition to CO2, they are converted to acids • Dissemination over vast territories • Dissolution of aluminum and formation of toxic material • Leaching nutrient minerals in soil • Poisoning of fish

17. Oxidation • 4Fe + 3O2 → 2Fe2O3 • Hematite (Fe2O3) and limonite [Fe2O3(OH)] • Mine acid Hydrolysis • Chemical reaction during which molecules of water (H2O) are split into hydrogen very active cations (H+) and hydroxide anions (OH−). • H+ replaces positive ions in silicate • Destruction of crystal lattice • Natural water also contains CO2 which makes H2CO3 (carbonic acid)

18. Decomposition of potassium feldspar Potassium forms soluble potassium bicarbonate KHCO3

19. Products of granite weathering 1) K+ as nutrient for plants 2) Clay as inorganic material of soil 3) Dissolved silica 4) Resistant quartz as a beach maker

20. Alteration caused by chemical weathering • Decomposition of unstable minerals • Retention of minerals that are stable at the Earth’s surface • Physical change of outcrops - Sharp corners are attacked more readily - Spheroidal weathering

21. Spheroidal weathering

22. Spheroidal weathering

23. Rates of weathering • Rock characteristics • Climate • Topography

24. Rock characteristics

25. Rock characteristics granite marble

26. Climatechemical weathering Warm, moisture Arid 3500 years in Egypt 75 years in New York

27. + acid rains Rain but not acid

28. Topography • Humid regions – rolling hills covered by soil (chemical weathering dominate) • Arid regions – jagged topography (mechanical weathering dominate) • Differential weathering

29. Soil is the bridge between life and the inanimate world

30. Soil • Regolith – a layer of rocks that consists of mineral fragment produced by weathering • Soil – combination of minerals and organic matter, water and air • Humus – decayed remains of animal and plant life

31. Composition of soil Growth of plants depends on humus, water and air

32. Soil formation • Parent material • Time • Climate • Plants and animals • Slope

33. Parent material • Parent material is a weathered matter from which soils develop • Type of this material controls the rate of soil formation (consolidated or unconsolidated) • Similar material may produce different soil • Residual soil is underlain by bedrocks • Transported soil – layer of unconsolidated sediments

34. Residual and transported soil

35. Time in soil formation • Short time – parent material • Long time – other factors, especially climate

36. Climate and soil formation • Wet and hot climate produces a thick layer of chemically weathered rocks • Dry climate produces a thin layer of chemically weathered rocks • Precipitation leaches accumulated material from soil and controls the soil fertility

37. Plants and animals • Their main function is to supply organic matter to the soil • Soil fertility depends on amount of organic matter • Organic decay creates nutrients and enhance the fertility of soil • Microorganisms speed up the organic decay and create the humus • Earthworms mix the soil

38. Slope in soil formation • Steep slope • Bottomlands and valleys • Flat-to-undulating upland surfaces • Slope orientation

39. Soil profile A soil profile is a vertical cross-section from the surface down to the parent rocks

40. Soil profile humus Topsoil 30% humus True soil (solum) subsoil Time span of soil formation: Layer A needs hundreds to several hundreds years to be formed Layer B needs 10,000 to 100,000 years

41. Soil type

42. Soil type Pedalfer Pedocal Laterite

43. Laterite Angkor Wat (Cambodia) is the largest  Hindu temple complex in the world (the early 12th century). It is made of laterite brick.

44. Soil erosion • It is a natural process • Human being can increase the fertility of soil • Human being can damage or destroy soil

45. Soil erosion • Sheet erosion • Rills • Gullies

46. Soil erosion • 9 billion metric tons per year • 24 billion metric tons per year • Wind erosion • Filling water reservoirs with sediments • Filling water reservoirs with pesticides and nutrients

47. ??