Weathering and Soils

1
Weathering and Soils
2
Weathering and Soils
Marble headstones in Southern Vermont
3
Weathering and Soils

• Mechanical Weathering- the physical breakdown of
  rocks
• Chemical Weathering- reaction of rocks with
  water, acids, oxygen, etc.

4
Mechanical Weathering
5
Mechanical Weathering
Tectonic Jointing
6
Mechanical Weathering
Exfoliation
7
Mechanical Weathering
Exfoliation
8
Mechanical Weathering
Exfoliation
9
Chemical Weathering
Solution H2O CO2 H2CO3 ( H HCO3-
) in air (acid rain)
acid
10
Chemical Weathering
Solution Karst Topography
11
Chemical Weathering
Solution Karst Topography
12
Chemical Weathering
Karst Sinkhole- Florida
13
Chemical Weathering
Karst Sinkhole- Florida
14
Chemical Weathering
Tower Karst - China
15
Chemical Weathering
Oxidation Fe2SiO4 ½ O2 Fe2O3 SiO2
16
Chemical Weathering
17
Chemical Weathering Differential Weathering
18
Chemical Weathering Differential Weathering
Weathering can preferentially dissolve out mafics
increase the sialic component in sediments to
yield granite
19
Chemical Weathering
What happens when granite is weathered? The
biotite and hornblende will undergo hydrolysis to
form clay, and oxidation to form iron
oxides.
The feldspars will undergo hydrolysis to form
kaolinite (clay) and release Na and K ions into
solution
The quartz (and muscovite, if present) will
remain as residual minerals because they are very
resistant to weathering.
20
Idealized soil profile from a humid climate at
middle latitudes
Zone of Leaching
21
Horizon Development and Climate
22
Soil textural classes
23
Topsoil ecosystem in a temperate climate
24
Effect of climate on soil development
25
Chemical Weathering
Transported Soils
26
Wind-blown Glacial Loess Deposits
27
Wind-blown Glacial Loess Deposits
28
The Principal Soil Types
29
Effect of climate on soil types
tundra soils
30
Principal soil types in the USA
31
Effect of climate on soil types
A typical pedocal with white caliche (CaCO3)
deposits in a shallow B horizon
32
Effect of climate on soils
Making laterite bricks
Temple at Angkor Wat Cambodia (700 yrs old)
33
A Newer Classification of Soil Types
34
Rates of soil formation Central USA
1 cm/100 years in very porous and permeable
rock Humid N. Carolina 1 cm/5
years Granite may require over 1000 years for
a cm
35
(No Transcript)
36
Both Ends of the Erosion Problem
Serious soil erosion and gully formation related
to diversion of water runoff over a few months in
central California
Sediment pollution following heavy rains in North
Carolina
37
Soil Degradation

• Erosion
• Deforestation
• Agricultural depletion
• Contamination - Pollution
• Salinization
• Pesticides
• Chemical additions and spills
• Urbanization
• Desertification
• Overgrazing

38
Soil Erosion
Raindrop impact millions in a single shower hit
at 30 mph
39
Soil Erosion
Rill-wash and gullying in loose and
poorly-consolidated soils
40
(No Transcript)
41
Soil Erosion
42
(No Transcript)
43
(No Transcript)
44
Soil Erosion
Number of dust storms during the month of March,
1936
45
Effects of logging in Madagasgar
46
Soil Erosion
Figure 3.12 (a) a natural forested slope (b)
the same slope following a clearcut
47
Soil Erosion
Figure 3.12 (c) the same slope after conversion
to farmland (b) the same slope following
urbanization
48
Soil Erosion
1968 motorcycles first come to Deer Creek near
Bakersfield, CA
1972 after only 4 years of ORV use little
vegetation or topsoil remains
49
Soil Erosion
ORV users increased from 21 to 38 million between
1982 and 1992
ATVs rip through a marsh in West Virginia
Great Grizzly Hike, Montana
50
Soil Erosion
1985 photo of bulldozer and jeep tracks in
Alaskan tundra made in 1946
51
Soil Erosion
52
Salt accumulation due to irrigation in an arid
climate San Fernando Valley
53
Worldwide Distribution of Salt-affected Soils
54
(No Transcript)
55
Chemical Contamination of Soils
56
Grain production levels off while population
continues to grow
57
Combating Soil Degradation
Strip-cropping and Contour plowing
58
Combating Soil Degradation
Rice terraces in Asia
59
Combating Soil Degradation
No-till Farming