GEOG 2051 : Geog2051 Exam2 AllNotes
Chemical Weathering
• Oxidation
o Rusting
o If a rock has metallic minerals in it, and they are exposed to water, a chemical
reaction takes place called “oxidation”
o Oxygen binds to the Iron and caused iron oxide to be formed
o Many rocks are porous and will absorb water
o Freeze-thaw breaks the rock down further
• Hydrolysis
o Involves water
o Attacks minerals called silicates
o Water molecules strip out elements from those minerals, creating new compounds
o Which, again, weakens the rock
o Ex: feldspar, a common mineral in granite, is attacked by hydrolysis and breaks
down into two other elements
• Carbonation
o A specific type of solution
o Certain substances, when dropped in water, will dissolve
o This process is enhanced when the water is acidified
o Ex: when rain is acidic
▪ Gases, like carbon dioxide, can dissolve into the rain water and make it a
weak acidic
o Rocks with carbon are very susceptible to this acidic water
o Calcium carbonate (limestone) is very susceptible
o Ex: gargoyles in France used to have elegant detail, now are worn away
o Since the industrial revolution, the acid rain has grown stronger and carbonation
happens even faster now (this rain will sometimes have a PH of 4!)
• Pinnacle Karst (caused by carbonation)
o Karst Topography
o Pinnacle Karst
▪ Karst and spires
▪ Water runs through the cracks and faults and breaks off the rock
o Tower Karst
▪ Remnant stumps are left behind from the original bedrock material
o Sinkholes
▪ Depressions on the surface
▪ 2 types:
• Solution sinkholes
o Result from the dissolution of the bedrock from
carbonation
• Collapse sinkholes
o The remaining material is too weak to support the structure
and then collapse
o Disappearing streams
▪ Streams that flow along the surface and then disappear
▪ Flow into a collapse sinkhole into a subterranean cavern system
o Karst valleys
▪ A sequence of sinkholes that have merged and grown together; looks like
a river bed
o All Karsts are underlain by cavern and caves
▪ Erosional (creates caverns)
• Rock saturated with water, carbonation takes place, water carries
off excess sediment, when water level drops, left with cavern
▪ Deposition
• Drip stones:
o Stalactites
▪ Water soaks down through bedrock, the droplet
hangs on the end of the limestone, and when the
water evaporates, the limestone is left
o Stalagmites
▪ If those same drops of water are falling on the floor,
they form stalagmites
▪ “G” for ground!
• Stalactites:
o Soda straws
o Drip curtain
Slopes and Mass Movements
• Slope
o Formal: A curved or inclined surface that represents the boundary of a
landform
o Informal: The side of a hill
• Steepness of the slope
o Angle
▪ Measure the angle of the slope with respect to a horizontal surface
o Tangent
▪ Tangent = Rise/Run
▪ Tangent of the slope is the ratio of the rise (vertical) over the run
(horizontal); how much we go up for every unit we go forward
▪ Given as a decimal number
▪ Tangent = 5/50 = 0.1
o Gradient
▪ Derived from the tangent
▪ 0.1 * 100 = 10% gradient
• Slopes as a system
o Inputs
▪ Material from weathering
▪ Materials keep building up, making the slope steeper and steeper
o Outputs
▪ Mass movement: general term that covers the processes for
materials to move downhill
▪ When the slope is too steep, the material has to go down
o Angle of repose
▪ The steepest angle that a slope can maintain
• Forces acting on a slope
o Driving force
▪ Gravity
▪ Driving force pushes rock down hill
▪ Water
o Resisting force
▪ Gravity
▪ Resisting force hold rock to hill
▪ Friction
• Smooth, round rocks won’t be able to maintain as steep a
slope as square rocks (marble vs. dice)
▪ Cohesion
• Water holding sand together
• Plant roots holding soil together
o Fd < Fr = stable
o Fd > Fr = unstable
Review
• Chemical Processes
o Solution, carbonation, oxidation, hydrolysis (oxygen molecules are stripped out of
a substance)
• Karst Topography
o Solution of limestone (CaCO3)
• Surface
o Sinkholes (solution, collapse)
o Karst valleys
o Disappearing streams
o Tower karst
o All karsts are underlain by caverns
• Caverns
o Erosion and deposition
o Dripstones (stalactites - ceiling, stalagmites - ground, columns, drip curtains, soda
straws, etc.)
• Slope
o Angle, tangent, gradient
o Inputs (weathering)
o Outputs (transport)
o Equilibrium (angle of repose)
• Forces and stability
o Gravity (driving, resisting)
o Friction (resisting)
o Cohesion (resisting)
▪ Anything that causes particles to stick together
▪ Wet sand vs. dry sand
o Role of water (buoyancy, lubricant)
Document Summary
If those same drops of water are falling on the floor, they form stalagmites: g for ground, stalactites, soda straws, drip curtain. Slope elements: soil processes, physical and chemical weathering, waxing slopes - increasing (convex surface, fall/free face (steepest portion of the slope, transportation, coarse materials, debris slope, deposition, waning slope decreasing, fine materials. Mass movements: general term for processes that carry material downhill, moisture content, dry completely saturated, speed, moving a few centimeters per year vs. 70 mph, type of material, earth, mud, debris flows. Slope development: controls, rock strength, climate, process balance, time, theories, decline, parallel retreat, replacement. The sea shrank, eventually into two pieces, and less water meant greater concentration of salt and pollutants: ocean, 40 units lost to atmosphere 40 units lost atmosphere over land. 40 units excess precipitation to land surface 40 units rivers, groundwater: solar energy powers the hydrologic cycle; causes pressure differences in atmosphere, wind, that moves water; evaporation, groundwater.
