Weathering and Soils
Marble headstones in Southern Vermont Weathering and Soils Granite headstone in Southern Vermont
Weathering and Soils l Mechanical Weathering- the physical breakdown of rocks l Chemical Weathering- reaction of rocks with water, acids, oxygen, etc.
Mechanical Weathering
Tectonic Jointing Mechanical Weathering
Exfoliation
Exfoliation
Exfoliation
Chemical Weathering Solution: H 2 O + CO 2 = H 2 CO 3 ( H + + HCO 3 - ) H 2 CO 3 ( H + + HCO 3 - ) in air (acid rain) in air (acid rain) acid gas Limestone dissolves readily CaCO H + (aq) = Ca +2 + CO 2 + H 2 O Ca +2 + CO 2 + H 2 O
Chemical Weathering Solution: Karst Topography
Chemical Weathering Solution: Karst Topography
Chemical Weathering Karst Sinkhole- Florida
Chemical Weathering Karst Sinkhole- Florida
Chemical Weathering Tower Karst - China
Chemical Weathering Oxidation: Fe 2 SiO 4 + ½ O 2 = Fe 2 O 3 + SiO 2
Chemical Weathering
Chemical Weathering Differential Weathering
Weathering can preferentially dissolve out mafics & increase the sialic component in sediments to yield “granite”
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.
Idealized soil profile from a humid climate at middle latitudes Zone of Leaching
Horizon Development and Climate
Soil textural classes
Topsoil ecosystem in a temperate climate
Effect of climate on soil development
Chemical Weathering Transported Soils
Wind-blown Glacial Loess Deposits
The Principal Soil Types
Effect of climate on soil types tundra soils Precipitation Temperature cold hot cool lowhigh50 cm/yr pedalferspedocals laterites tundra soils
Principal soil types in the USA
Effect of climate on soil types A typical pedocal with white caliche (CaCO 3 ) deposits in a shallow B horizon
Effect of climate on soils Making laterite bricks Temple at Angkor Wat Cambodia (700 yrs old) Laterite Tundra soil
A Newer Classification of Soil Types Pf Pc Pf Pf, Pc L Pf, L
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
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
Soil Degradation l Erosion l Deforestation l Agricultural depletion l Contamination - Pollution F Salinization F Pesticides F Chemical additions and spills l Urbanization l Desertification l Overgrazing
Raindrop impact: millions in a single shower hit at ~ 30 mph Soil Erosion
Rill-wash and gullying in loose and poorly-consolidated soils Soil Erosion
Number of dust storms during the month of March, 1936 Soil Erosion
Effects of logging in Madagasgar
Soil Erosion Figure 3.12:(a) a natural forested slope (b) the same slope following a clearcut
Soil Erosion Figure 3.12:(c) the same slope after conversion to farmland (b) the same slope following urbanization
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
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
Soil Erosion 1985 photo of bulldozer and jeep tracks in Alaskan tundra made in 1946
Soil Erosion
Salt accumulation due to irrigation in an arid climate: San Fernando Valley
Worldwide Distribution of Salt-affected Soils
Chemical Contamination of Soils
Grain production levels off while population continues to grow
Strip-croppingand Contour plowing Combating Soil Degradation
Rice terraces in Asia Combating Soil Degradation
No-tillFarming