L13 - Soil forming processes

Question 1

When is soil formation fastest?

Answer 1

Warm, rainy summers in sedimentary rocks

Question 2

Where is soil formation slowest?

Answer 2

Arid, cold climates in igneous and metamorphic rocks

Question 3

Main soil forming processes?

Answer 3

1. Additions
2. Losses
3. Transformations
4. Transfers

Question 4

Name a rock with a low albedo and high albedo?

Answer 4

Basalt has a low albedo, low heat capacity and low thermal conductivity (surface temp very high). Chalk has a high albedo, high heat capacity and high thermal conductivity (more temperature distribution)

Question 5

Unloading

Answer 5

Breaking up when erosion removes the pressure on underlying rocks

Question 6

Thermal weathering (thermoclasty)

Answer 6

results from low and high variable thermal conductivity of minerals and rocks

Question 7

Gelifraction (freeze-thaw)

Answer 7

occurs when water in rock pores, joints and cracks freezes, expands by 9% and thus breaks rock.

Question 8

What is the loss of solutes and suspended material related to?

Answer 8

Precipitation frequency, intensity and surplus

Question 9

Leaching

Answer 9

organic and inorganic solutes are transported by percolating water

Question 10

Where does CO2 in soil come from?

Answer 10

respiration

Question 11

Where do H+ ions in soil come from?

Answer 11

Leaching from humus (organic acids) and cation exchange

Question 12

Hydrolysis

Answer 12

when acid rain reacts with rock-forming minerals such as feldspar to produce clay and salts which are removed in solution

Question 13

Weathering index

Answer 13

comparison between a chemical compound or mineral that is relatively stable with one that is readily removed by weathering

Question 14

What is the main source of electrons in soil?

Answer 14

Organic material

Question 15

Gley soils

Answer 15

caused by seasonal dynamics in soil water saturation. These soils have mottles (irregular arrangement of spots or patches of colour - cutans) from movement of iron and manganese by redox processes.

Question 16

What are some chelating agents?

Answer 16

Polyphenolics (occur in plants and leach from leaves) and humic and fulvic acids (leach from litter)

Question 17

Podzolization

Answer 17

occurs in temperate climates which are warm enough to support vegetation growth, but cold enough to limit rapid decomposition. There must also be high levels of rainfall. In this way, clay minerals are dissolved and transported down the soil profile through leaching and cheluviation, and OM builds up to create acidic conditions.

Question 18

Why is the E horizon bleached in podzols?

Answer 18

Due to organic acids e.g. carbonic, lactic and fulvic.

Question 19

Mechanical sieve effect

Answer 19

depends on size of transported material and pore sizes in deep soil. Chemical changes lead to lower solubility or suspension (peptisation) with precipitation as a result - increased pH