PHSC 210 QUESTIONS AND ANSWERS LATEST EDITION GRADED A+
Weathering
physical and/or chemical breakdown of a rock in place
the process by which larger rocks get broken down into smaller pieces
the disintegration and decomposition of rock
Erosion
the removal of weathered material
Soils
a mixture of mineral and organic matter
Loam
a well-balanced soil (roughly equal sand/silt, organics, clay)
Rain
most important for soil-making
moderate rainfall (30-50 in/yr) helps foster deep soil formation
Soil Horizon
O horizon = humus, organic, dead decaying plant & animal remains
A horizon = topsoil, below O, organic & mineral
E horizon = leaching zone, below A, occurs where there is a lot of rainfall
B horizon = subsoil, zone of accumulation, organic, clay, small pieces of bedrock
C horizon = parent material, weathered bedrock, composition dependent on bedrock,
Chemical weathering
occurs when a rock disintegrates due to chemical reactions that happen within the
environment
Formation of carbonic acid
Water + Carbon Dioxide <--> Carbonic Acid
H2O + CO2 <--> H2CO3
Carbonic Acid chemically erodes limestone (calcite CaCO3)
The solution of calcite by carbonic acid
Calcite + Carbonic Acid <--> Calcium + Hydrogen + Bicarbonate
CaCO3 + H2CO3 <--> Ca+2 + 2H+ + 2CO3-2
Rusting of rocks
Iron + Oxygen --> Rust (Hematite)
4Fe + 3O2 --> Fe3O4, If iron is present in rocks combined with oxygen to make iron
oxide (rust)
Mechanical weathering
the physical or mechanical breakdown of a rock into smaller pieces. Types of
Mechanical Weathering: Frost Wedging, Frost heaving, Thermal expansion/contraction,
Root wedging, Unloading (pressure release), Water abrasion, Wind abrasion, Hydraulic
action, Cavitation, Fire, Groundwater sapping
Frost wedging
when water gets into the cracks of a rock and then proceeds to freeze (expanding)
Frost heaving
, when freezing water lifts (and cracks) the road causing damage that must be repaired
the next summer
Root wedging
as the roots force open even small fractures, this leads the way to other weathering
processes, such as frost wedging in the winter
Isostatic rebound
when a landscape responds to a large amount of rock being removed (by
erosion/glacier melting) by expanding upward as a result of the lost material.
Pressure release / Unloading
when the weight of a landscape is unloaded, or the pressure of the overlying rock is
released, the rocks respond by slightly expanding, pulling the rock apart. This is
mechanical weathering and is called pressure release or unloading
Water Abrasion
smoothing a rock's rough spots by current or flow tumbling it in a stream
Hydraulic action
the breaking rocks apart by the sheer force of moving water
Cavitation
occurs when very fast moving water flows over small depressions in bedrock. When this
happens, small vacuum bubbles form and then implode (like a mini sledge hammer
pounding on the rock)
Groundwater sapping
a process that occurs as groundwater pushes from the inside-out of a rock face. It will
typically happen in an area where a spring is flowing out of a rock
Spheroidal weathering
when rocks (typically granites) become weathered into rounded shapes because at
least 2 sets of perpendicular joints crisscross the granite. Mechanical and chemical
weathering attacks the joints and widens them turning cubes into spheres.
Differential weathering
when one rock types weathers faster than another (eg. shale weathers faster than
limestone/sandstone)
Thermal expansion/contraction
why sidewalks have cracks
Mass-Wasting (or Mass-Movement)
large-scale transport of rock, soil, etc.
when large quantities of rock or soil move downhill under the influence of gravity (like
landslides, rock falls, and slumps). GRAVITY primary force of mass wasting
Factors that often contribute to mass movements/mass wasting:
Gravity
Relief (difference between highest and lowest points)
Slope angle (makes it steep)
Lack of vegetation (roots hold a hillside together)
Water (adds weight to a hillside)
Seismic activity (can trigger a large slide or rock fall)
Amount of previous weathering (weaken a slope)
Character of the bedrock (if rock doesn't hold together well or is highly fractured in the
first place)
Weathering
physical and/or chemical breakdown of a rock in place
the process by which larger rocks get broken down into smaller pieces
the disintegration and decomposition of rock
Erosion
the removal of weathered material
Soils
a mixture of mineral and organic matter
Loam
a well-balanced soil (roughly equal sand/silt, organics, clay)
Rain
most important for soil-making
moderate rainfall (30-50 in/yr) helps foster deep soil formation
Soil Horizon
O horizon = humus, organic, dead decaying plant & animal remains
A horizon = topsoil, below O, organic & mineral
E horizon = leaching zone, below A, occurs where there is a lot of rainfall
B horizon = subsoil, zone of accumulation, organic, clay, small pieces of bedrock
C horizon = parent material, weathered bedrock, composition dependent on bedrock,
Chemical weathering
occurs when a rock disintegrates due to chemical reactions that happen within the
environment
Formation of carbonic acid
Water + Carbon Dioxide <--> Carbonic Acid
H2O + CO2 <--> H2CO3
Carbonic Acid chemically erodes limestone (calcite CaCO3)
The solution of calcite by carbonic acid
Calcite + Carbonic Acid <--> Calcium + Hydrogen + Bicarbonate
CaCO3 + H2CO3 <--> Ca+2 + 2H+ + 2CO3-2
Rusting of rocks
Iron + Oxygen --> Rust (Hematite)
4Fe + 3O2 --> Fe3O4, If iron is present in rocks combined with oxygen to make iron
oxide (rust)
Mechanical weathering
the physical or mechanical breakdown of a rock into smaller pieces. Types of
Mechanical Weathering: Frost Wedging, Frost heaving, Thermal expansion/contraction,
Root wedging, Unloading (pressure release), Water abrasion, Wind abrasion, Hydraulic
action, Cavitation, Fire, Groundwater sapping
Frost wedging
when water gets into the cracks of a rock and then proceeds to freeze (expanding)
Frost heaving
, when freezing water lifts (and cracks) the road causing damage that must be repaired
the next summer
Root wedging
as the roots force open even small fractures, this leads the way to other weathering
processes, such as frost wedging in the winter
Isostatic rebound
when a landscape responds to a large amount of rock being removed (by
erosion/glacier melting) by expanding upward as a result of the lost material.
Pressure release / Unloading
when the weight of a landscape is unloaded, or the pressure of the overlying rock is
released, the rocks respond by slightly expanding, pulling the rock apart. This is
mechanical weathering and is called pressure release or unloading
Water Abrasion
smoothing a rock's rough spots by current or flow tumbling it in a stream
Hydraulic action
the breaking rocks apart by the sheer force of moving water
Cavitation
occurs when very fast moving water flows over small depressions in bedrock. When this
happens, small vacuum bubbles form and then implode (like a mini sledge hammer
pounding on the rock)
Groundwater sapping
a process that occurs as groundwater pushes from the inside-out of a rock face. It will
typically happen in an area where a spring is flowing out of a rock
Spheroidal weathering
when rocks (typically granites) become weathered into rounded shapes because at
least 2 sets of perpendicular joints crisscross the granite. Mechanical and chemical
weathering attacks the joints and widens them turning cubes into spheres.
Differential weathering
when one rock types weathers faster than another (eg. shale weathers faster than
limestone/sandstone)
Thermal expansion/contraction
why sidewalks have cracks
Mass-Wasting (or Mass-Movement)
large-scale transport of rock, soil, etc.
when large quantities of rock or soil move downhill under the influence of gravity (like
landslides, rock falls, and slumps). GRAVITY primary force of mass wasting
Factors that often contribute to mass movements/mass wasting:
Gravity
Relief (difference between highest and lowest points)
Slope angle (makes it steep)
Lack of vegetation (roots hold a hillside together)
Water (adds weight to a hillside)
Seismic activity (can trigger a large slide or rock fall)
Amount of previous weathering (weaken a slope)
Character of the bedrock (if rock doesn't hold together well or is highly fractured in the
first place)
