Weathering and Soils Weathering and Soils Marble Graniteheadstones

Weathering and Soils

Weathering and Soils Marble Graniteheadstones headstone in Southern Vermont

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

Mechanical Weathering

Mechanical Weathering Tectonic Jointing

Mechanical Weathering Exfoliation

Chemical Weathering Solution: H 2 O + CO 2 = H 2 CO 3 ( H+ + HCO 3 - ) in air (acid rain) acid Limestone dissolves readily gas Ca. CO 3 + 2 H+ (aq) = Ca+2 + CO 2 + H 2 O

Chemical Weathering Solution: Karst Topography

Chemical Weathering Karst Sinkhole- Florida

Chemical Weathering Tower Karst - China

Chemical Weathering Oxidation: Fe 2 Si. O 4 + ½ O 2 = Fe 2 O 3 + Si. O 2

Chemical Weathering

Chemical Weathering Differential Weathering

Chemical Weathering Differential 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.

Zone of Leaching Idealized soil profile from a humid climate at middle latitudes

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 Temperature hot laterites hot pedocals pedalfers tundra soils cold undra soils low 50 cm/yr Precipitation cool high

Principal soil types in the USA

Effect of climate on soil types A typical pedocal with white caliche (Ca. CO 3) deposits in a shallow B horizon

Effect of climate on soils Making laterite bricks Tundra soil Laterite Temple at Angkor Wat Cambodia (700 yrs old)

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