• Oct 8, 1996
• Exams (at end of lecture)
• Baraboo Field Trip (this Saturday)

• SUMMARY WEATHERING, EROSION, MASS WASTING
• WEATHERING PROCESSES

PHYSICAL

CHEMICAL

• SOILS
• VARIATION

• Uneven sidewalks
• Worms on walks after a rain
• Bumps along cracks in pavement
• Rocks on Roads (especially in Spring)
• Muddy rivers
• Old rocks are exposed in mountains
• Plants grow
• Floods fill houses with mud
• You exist!

• tied to geologic processes that regulate the surface of the earth, so called Surficial Geology.
• In the past weeks Dr. DeMets talked about ìInternal Dynamicsî or those forces that result from dynamic processes acting from within the earth.
• The interplay between these two forces are fascinating, and lead to shape and character of the earth we know.

TWO IMPORTANT FACTORS

• In its simplest form the processes of SURFICIAL GEOLOGY are regulated by two simple processes
• 1- The Force of Gravity
• 2- The Movement and Action of Water

GRAVITY

Gravity controls the movement of materials in the earth causing water to run down hill and rocks to fall from over-steepened slopes.

• In earth shaking terms:
• Water runs downhill, rocks fall

WATER

• Plays a major role in:
• 1- Regulating the earthís climate
• 2- Transporting materials to lower elevations (water AND ice)
• 3- Reacting with solid substances (rocks and minerals) that occur at the earth's surface

DRIVING FORCES

The interplay between these two factors (gravity and the effects of water) are the driving forces for all of surficial processes

• Physical and chemical processes acting at Earthís Surface
• Reaction with water and atmospheric gases to form materials more stable at earth surface temperature and pressure
• Carbon Dioxide (CO2), Oxygen ( O2) and Water (H2O) are principal agents

• Overlapping processes
• A continuum from weathering to mass wasting to erosion, all three acting in concert, but to various degrees in different environments
• Topically we can discuss each individually, but in reality they all act together in differing relative degrees.

Weathering

• generally restricted to material breakdown in place
• The physical and chemical (mineralogical) changes that occur in rocks in response to conditions that obtain at the interface of the Earth's hydrosphere and atmosphere.

Mass Wasting

• Refers to material that falls under influence of gravity with little or no transporting agent
• Processes range considerably in rate

Erosion

• Refers to processes that move material to another site under the influence of transporting agents such as, water, ice, or wind.

• CHEMICAL and PHYSICAL (mechanical)

• INORGANIC and ORGANIC elements

Physical and Chemical Processes

• In nature PHYSICAL and CHEMICAL processes work in combination to produce WEATHERING
• In different CLIMATES one or the other of the two processes may dominate over the other, but rarely does one act alone.

Physical Processes

• Gravity
• Stress relief (fractures)
• Frost heaving
• Surface area effects
• Heating and cooling (fire, ...)
• Tree roots, soil organisms (worms, ....)
• Salt growth in cracks and open spaces

FROST ACTION

• Water -> Ice (10% expansion)

Grain Size Important

• Weathering is a surface phenomenon
• More surface area means more access by water and the atmospheric gases CO2 and O2
• Permeability (connected pore space) allows water to move into the rock to promote weathering

SURFACE AREA

• Weathering occurs at surfaces of minerals
• Area of cube one cm on a side = ??

CHEMICAL PROCESSES

• Chemical weathering of mineral matter to other minerals and dissolved ions
• Biochemical breakdown of rock, mineral, and organic matter by soil microorganisms (bacteria, lichen, plant roots....)

PROCESSES

• Solution
• Precipitation
• Oxidation
• Carbonation
• Hydrolysis (Water splitting)

SOLUTION

• Action of water on minerals to produce dissolved ions
• Halite

NaCl + H2O -> Na+ + Cl-

• Gypsum

CaSO4ï2H2O + H2O -> Ca++ + SO4=

PRECIPITATION

• Reverse of solution
• Combination of dissolved ions to produce a solid mineral
• Evaporation of water
• Na+ + Cl- -> NaCl [Halite]

CARBONATION

• Weathering of calcite by ìcarbonated waterî (i.e. rain) - [pH = 5.6]
• ìCarbonic Acidî + Calcite
• CaCO3 + (H2O + CO2) -> Ca++ + 2HCO3-

OXIDATION

• Pyrite

Pyrite + water --> Hematite + dissolved sulfate and hydrogen ion

Can produce Acid Mine Drainage problems

• Your car/bike/truck

2Fe + 3O2 -> 2Fe2O3 (Hematite)

HYDROLYSIS

• Hydrolysis comes from ìhydroî and ìlysisî and literally means splitting of water.
• Combination of silicates with water to form a hydrous clay mineral plus dissolved ions

HYDROLYSIS OF FELDSPAR

• Feldspar + water --> clay minerals + (silica + Na, Ca, K, and OH) all dissolved
• Plagioclase weathering most important

Plagioclase + water + carbon dioxide = Kaolin + dissolved ions (Ca, Mg, ..)

• This is why major rivers are generally Calcium-bicarbonate type waters

ANOTHER EXAMPLE WITH:

• EQUATIONS!!!
• 2KAlSi3O8 + 9H2O + 2CO2 --> Al2Si2O5(OH)2 + 2K+ + 2HCO3- + 4H4SiO4
• K-feldspar + Water + Carbon Dioxide -> Kaolinite (a clay) + Dissolved potassium, bicarbonate, and silica

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