Nat sci 3 earth science and astronomy chapter iii earth processes
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NAT. SCI. 3 – Earth Science and Astronomy CHAPTER III: Earth Processes. RONALDO T. BIGSANG, M.Sc. SURFACE PROCESSES: Weathering, Soil and Erosion. OBJECTIVES. Describe weathering as an important force in the rock cycle; Identify the types of weathering and the sub-processes under each;

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NAT. SCI. 3 – Earth Science and Astronomy CHAPTER III: Earth Processes

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Nat sci 3 earth science and astronomy chapter iii earth processes

NAT. SCI. 3 – Earth Science and AstronomyCHAPTER III:Earth Processes

RONALDO T. BIGSANG, M.Sc.


Surface processes weathering soil and erosion

SURFACE PROCESSES:Weathering, Soil and Erosion


Objectives

OBJECTIVES

  • Describe weathering as an important force in the rock cycle;

  • Identify the types of weathering and the sub-processes under each;

  • Discuss the components and horizons of soil;

  • Name some soil-forming factors; and

  • Explain the agents of erosion.


Weathering

WEATHERING

  • surface process that breaks or decompose rocks into smaller pieces (i.e. sand, gravel, soil, etc)

  • involves little or no movement of decomposed rocks and minerals

  • 2 types: mechanical and chemical


Mechanical weathering

MECHANICAL WEATHERING

  • also called PHYSICAL weathering

  • DOES NOT alter the chemical composition of weathered rocks

  • includes:

    • pressure-release fracturing

    • frost or ice wedging

    • abrasion

    • organic activity

    • thermal expansion and contraction


Mechanical weathering1

MECHANICAL WEATHERING

  • pressure-release fracturing

    • tectonic force lift up buried rocks to the surface

    • erosion of the overlying rocks and sediments remove the pressure

    • buried rocks expand and fracture


Mechanical weathering2

MECHANICAL WEATHERING

  • frost or ice wedging

    • water seeps into cracks in rocks

    • when temperature is very low, water freezes

    • ice expands and wedges the rock apart


Mechanical weathering3

MECHANICAL WEATHERING

  • abrasion

    • weathering of rocks by friction and impact


Mechanical weathering4

MECHANICAL WEATHERING

  • organic activity

    • cracks in rocks are expanded by tree or plant roots


Mechanical weathering5

MECHANICAL WEATHERING

  • thermal expansion and contraction

    • when temperature changes rapidly (heating and cooling processes)

    • surface heats up (expands) or cools down (contracts) faster than the interior


Chemical weathering

CHEMICAL WEATHERING

  • ALTERS the chemical composition of the weathered rock

  • rapid in tropical regions --- moist and warm

    • contrast to desert and polar regions?

  • includes:

    • dissolution

    • hydrolysis

    • oxidation

Table 1. Rate of chemical weathering in different climatic conditions.


Chemical weathering1

CHEMICAL WEATHERING

  • dissolution

    • rock or mineral dissolves forming a solution

    • ACIDIC pH (lower pH than pure water)

      • CO2 + water = carbonic acid

    • BASIC pH (higher pH than pure water)


Chemical weathering2

CHEMICAL WEATHERING


Chemical weathering3

CHEMICAL WEATHERING

  • hydrolysis

    • mineral reacts with water and form a new mineral with water as part of its crystal structure

    • i.e: feldspar  kaolinite

    • 2KAlSi3O8 + H2O + 2H+ = Al2Si2O5(OH)4+ 2K+ + 4SiO2


Chemical weathering4

CHEMICAL WEATHERING

  • oxidation

    • mineral decomposes when it reacts with oxygen


Weathering1

WEATHERING

  • salt cracking

    • saltwater seeps into rock cracks

    • water evaporates, salt crystallizes

    • salt crystals expands and widen cracks in the rocks


Weathering2

WEATHERING

  • exfoliation

    • concentric plates or shells split away from a main rock mass

    • pressure-release fracturing VS hydrolysis-expansion weathering


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