this thing, all things devours.this thing, all things devours. birds, beasts, trees, flowers. birds,...
TRANSCRIPT
• 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 ProcessesDestructional 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.
U-shaped Valley, Main Trunk, Hanging ValleyGlacial Erosion
http://www.ndsu.nodak.edu/instruct/schwert/anaglyph/
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
WeatheringWeathering
Carlsbad Caverns
White Sands
Guadalupe M
ountains
Weathering and SoilsWeathering and Soils
• Mechanical Weathering
• Chemical Weathering
• Soils
Prof. A.H.Thompson, Dirty Devil River, 1872Thompson Construction of Topographic Maps Flipbbok
Powell and Thompson Exploration of the Colorado RiverUSGS geologists studying weathering in the Mancos Shale
Almon Harris ThompsonAlmon Harris Thompson
Evidence of Evidence of Frost Frost Wedging in Wedging in Wheeler Wheeler Park, Park, NevadaNevada
Source: Tom Bean/DRK Photo
2. Chemical Weathering2. 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
DissolutionDissolution Weathered and Weathered and
Unweathered Unweathered Limestone Limestone BouldersBoulders
Source: Ramesh Venkatakrishnan
CaCO3 +2HCl => H2CO3 + Ca++ + 2Cl-
H2CO3 => H2O + CO2
1414
Hydrolysis – Feldspar to ClayHydrolysis – Feldspar to Clay
Mechanical fracture due to chemical weathering
Feldspars become
Vegetation and Soil DevelopmentVegetation and Soil DevelopmentNeed the extra humic acid to
dissolve limestone
Bowens Reaction Series and Weathering
Mg2SiO4 + 4CO2 + 4H2O => 2Mg+ = 4HCO3- + H4SiO4 (aq)
2KAlSi3O8 + 2H2CO3 + 9H2O => Al2Si2O5(OH)4 + 4 H4SiO4 (aq) + 2K+ + 2HCO3 -
Soil FormationSoil FormationFactorsFactors
• Climate: Climate: – Temperature 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 Rainfall • increases chemical weatheringincreases chemical weathering
• Parent Rock characteristics Parent Rock characteristics – Limestone easily dissolved, Basalt easily oxidized, Granite easily hydrolyzed, Limestone easily dissolved, Basalt easily oxidized, Granite easily hydrolyzed,
Sandstone resistant to soil formationSandstone resistant to soil formation
• TimeTime• SlopeSlope• OrganismsOrganisms
Equator to Poles Climate Factors
Equatorialand tropicalrain forests
SavannahsLow-latitudedeserts andsemi-deserts
Grasslands(steppes)
Temperate regionsand mixedboreal forests
Arcticandtundraregions
EquatorA
nnua
l pre
cipi
tatio
nIn
crea
sing
dep
thof
wea
the
ring
1800mm
600mm
40ºC
30ºC
20ºC
10ºC
Precipitation
Temperature
Evaporation
Bedrock ator very nearsurface
Soil Soil
Bedrock
Deeply weatheredbedrock(~40 - 50 meters deep)
Tem
per
atur
e
30 degrees Latitude
Climate
Chemical weatheringby dissolution Limestone
Weathering-resistant sandstone yields little soil
SoilSoil Soil
Feldspar-richgranite
Iron-richbasalt Chemical
weatheringby oxidation
Chemicalweatheringby 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 Parent Rock ResistantResistant
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 Parent Rock SolubleSoluble
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.
TimeTime
SlopeSlope
• 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
http://www2.jpl.nasa.gov/srtm/virginia.html
Soil thickness depends on many factors, including parent rock weather-ability, and slope.