Chap 6 Weathering and Soil

Question 1

Erosion

Answer 1

Removal of weathered material by
water wind, ice, or gravity

Question 2

Mass wasting

Answer 2

Transfer of debris down slope under the influence of gravity

Question 3

Weathering types

Answer 3

Mechanical &
Chemical

Question 4

Mechanical weathering

Answer 4

= breakage and disintegration

1. Frost wedging = freeze thaw of water in fractures and cracks
2. Unloading = exfoliation/sheeting as a result of reduction in confining
   pressure
3. Thermal Expansion = alternate expansion and contraction due to temp
   fluctuation

Question 5

Chemical Weathering

Answer 5

= decomposition by reaction with water

1. Hydrolyses
   o any reaction involving water that leads
   to decomposition of a compound
   o Hydrogen ions most commonly cause
   hydrolysis
   o Breaks cation bonds in silicate minerals
   where hydrogen ions replace other cations - Hydrolysis of K-Feldspar forms a clay mineral = Kaolinite
2. Oxidation
   o Process of addition and combination of
   oxygen to minerals
   o Most active in the presence of
   moisture and result in hydrated oxides
   o Important in decomposing
   ferromagnesium minerals
   o Iron pyrite (iron sulphide mineral) =
   oxidation leads to sulfuric acid and Geothite (iron oxide)- Leads to acid mine drainage
   o Magnetite –> Hematite –> Limonite

Question 6

Factors Affecting rates of weathering

Answer 6

1. Exposed Surface area
2. Rock characteristics
    Calcite (marble and limestone) minerals dissolve in weak acids
    Silicate minerals weather in the same order of crystallisation
3. Climate = chemical weathering most active in warm, moist areas
4. Differential weathering = based on environmental factors

Question 7

Soil

Answer 7

= Combination of mineral and organic matter, water, and air

o Humus (organic matter) = small but essential

Question 8

Factors controlling soil formation

Answer 8

 Parent material
 Time
 Climate
 Plants and animals
 Topography