This thing, all things devours.This thing, all things devours. Birds, beasts, trees, flowers. Birds, beasts, trees, flowers. Gnaws iron, bites steel. Gnaws iron, bites steel. Grinds hard stones to meal. Grinds hard stones to meal. Slays kings, ruins towns, Slays kings, ruins towns, and beats high mountains down.and beats high mountains down. J. R. R. Tolkien: The Hobbit Destructional Processes Glacially-modified topography associated with the Prairie Coteau of SD, ND, MN. During the Wisconsinan, the glacier divided into two southward-flowing lobes. Paraphrased from here. Paraphrased from here U-shaped Valley, Main Trunk, Hanging Valley Glacial Erosion

Eastern New Mexico, northwestern Texas. Included is the area of White Sands National Monument and Guadalupe Mountains National Park Destructional Landforms are shaped by Weathering and Erosion Weathering Carlsbad Caverns White Sands Guadalupe Mountains

Weathering and Soils Mechanical Weathering Chemical Weathering Soils Prof. A.H.Thompson, Dirty Devil River, 1872 Thompson Construction of Topographic Maps Flipbbok Powell and Thompson Exploration of the Colorado River USGS geologists studying weathering in the Mancos Shale Almon Harris Thompson

Frost Wedging 1. Mechanical weathering

Evidence of Frost Wedging in Wheeler Park, Nevada Source: Tom Bean/DRK Photo

Salt Weathering

Unloading = Exfoliation

Thermal Expansion and Contraction Source: Tom Bean

Spalling Frost Fire

Tree Roots Growing in Rock Fractures Animal Burrows Source: Runk/Schoenberger/Grant Heilman

Mechanical Weathering, Cubes/Surface Area

2. Chemical Weathering Major processes of chemical weathering Dissolution –Soluble ions contained in underground water Oxidation –Chemical reaction where compound loses electrons –Important in breaking down mafic minerals –Rust colored weathering of Basalt Hydrolysis H + or OH - ions –Reaction of any substance with water –Water’s ions replace different ions in mineral –Feldspars, most abundant crust minerals, become fine clay particles. Easily transported. Role of Water

Dissolution Weathered and Unweathered Limestone Boulders Source: Ramesh Venkatakrishnan CaCO 3 +2HCl => H 2 CO 3 + Ca Cl - H 2 CO 3 => H 2 O + CO 2

14 Hydrolysis – Feldspar to Clay Mechanical fracture due to chemical weathering Feldspars become

Vegetation and Soil Development Need the extra humic acid to dissolve limestone

Oxidation of Basalt Rust (Iron Oxide) forms

Bowens Reaction Series and Weathering Mg 2 SiO 4 + 4CO 2 + 4H 2 O => 2Mg+ = 4HCO H 4 SiO 4 (aq) 2KAlSi 3 O 8 + 2H 2 CO 3 + 9H 2 O => Al 2 Si 2 O 5 (OH) H 4 SiO4 (aq) + 2K + + 2HCO 3 -

An idealized soil profile 3. Soils

Remember the different horizons OAEBCOAEBC Organic Activity Exited Back Crushed Rock

pedalfer pedocal laterite tropicsShortgrass Evergreen forests Note no E or C in some

Rainfall seasonal "Laterite"

Soil Formation Factors Climate:Climate: –Temperature chemical weathering faster hot climateschemical weathering faster hot climates Rates of frost wedging increased by fluctuations of temperature around freezingRates of frost wedging increased by fluctuations of temperature around freezing Thermal expansion & contraction extreme in hot cloudless areasThermal expansion & contraction extreme in hot cloudless areas –Rainfall increases chemical weatheringincreases chemical weathering Parent Rock characteristicsParent Rock characteristics –Limestone easily dissolved, Basalt easily oxidized, Granite easily hydrolyzed, Sandstone resistant to soil formation TimeTime SlopeSlope OrganismsOrganisms

Equator to Poles Climate Factors Equatorial and tropical rain forests Savannahs Low-latitude deserts and semi-deserts Grasslands (steppes) Temperate regions and mixed boreal forests Arctic and tundra regions Equator Annual precipitation Increasing depth of weathering 1800 mm 600 mm 40ºC 30ºC 20ºC 10ºC Precipitation Temperature Evaporation Bedrock at or very near surface Soil Bedrock Deeply weathered bedrock (~ meters deep) Temperature 30 degrees Latitude Climate

Chemical weathering by dissolution Limestone Weathering-resistant sandstone yields little soil Soil Feldspar-rich granite Iron-rich basalt Chemical weathering by  oxidation Chemical weathering by hydrolysis Factors related to bedrock composition "Parent Rock"

Sandstone in humid climates develops very poor soil on which the dominant natural vegetation is woodland as in this forest in PA From Drury, Ch. 4 Parent Rock Resistant

Limestone 1. Prolonged chemical weathering of carbonates in humid climates leaves a thin residual veneer of clay-rich soil, which is often quite fertile, as in Kentucky However, the extremely good internal drainage may preclude all but the largest surface streams. The often low-lying surface is generally pock-marked by many depressions over sink holes. From Drury, Ch. 4 Parent Rock Soluble

Limestone 2. In recently glaciated areas, such as northern England, soil development has not been possible over limestones despite very humid conditions. Vegetation only occupies those surfaces veneered with glacial till.Time

Slope and Soil Thickness

Slope Massanutten Mt., Va., a syncline Ridges sandstone Valleys limestone and shale are less resistant The north and south forks of the Shenandoah River flank Massanutten Mountain. Note the meanders on floodplains of thick, fertile soils Soil thickness depends on many factors, including parent rock weather-ability, and slope.