WEATHERING
Weathering - physical &/or chemical breakdown of rocks & minerals. Unweathered rocks
are stronger
Agents of Weathering
1) water
2) air
3) waves
4) ice
5) gravity
Types of Weathering - all operate at the same time
1) Physical (Mechanical) - disintegration, breaking up of rocks from large to small pieces
2) Chemical - decomposition, change in the particles’ chemistry, caused primarily by
chemicals in the atmosphere (primarily CO2, O2, & water vapor)
3) Organic - roots of plants, effects of man, etc.
4) Mobile Agents - wind, water, glaciers
Physical/Mechanical
1) Frost Action - water expands when it freezes & causes rocks to crack
i) Frost Wedging - caused by alternate freezing & thawing
ii) Frost Heaving - caused by expansion of soil causing rocks to be pushed upward
2) Salt Cracking - soluble salts wedge into pore spaces & crystallize
3) Hydration - expansion of salt minerals when water is added
3) Abrasion - grinding away of rock by friction and impact during transportation
4) Pressure Release - reduction of pressure (unloading) on a body of rock. Sheet-like
(sheeting) layers of bedrock break off (exfoliation), ex: granite, Stone Mt. in GA
Chemical
1) Carbonation & Solution - reaction of minerals with water (ex: acid rain). Also chemical
combinations of minerals with CO2
2) Oxidation - oxygen combines with certain metallic elements, ex: Fe, Mn, S
3) Hydrolysis - water reacts with silicate minerals converting them into clays.
Organic
Examples: strip mining
search for gold
industrial processes
plant roots,
burrowing animals
Mobile Agents
will be considered separately
MASS WASTING
Mass Wasting (Mass Movement) - downslope movement of material (rock & soil) due to
gravity. May be slow or fast, wet or dry, gentle or steep.
Types of Motion
1) Fall - movement involves the free-fall of detached individual pieces of any size
2) Slide - movement involves material that remains fairly coherent & moves along a well-defined surface
3) Flow - material moves downslope as a viscous fluid
Factors Controlling Mass Movements
1) slope angle
2) local relief
3) thickness of debris
4) orientation of planes of weakness
5) climatic factors
6) vegetation
Causes of Mass Movements
1) earthquakes
2) added weight to upper part of slope
3) undercutting of bottom of slope
4) water
Fast Movement Examples
1) Rock Slides (hard material) - friction must be overcome first. An earthquake, blasting, heavy rains can
set it off. Movement occurs along surfaces of weakness within the bedrock. The rocks at the base
are called talus.
zones of weakness - ex: foliation, bedding planes, joints, faults
2) Landslides (soft material - soil & rock) - mass of soil & weathered rock that moves as a unit on a slip
fault
2 types
a) glides (translational) - slippage is planar
b) slumps (rotational) - slippage is concave upward; can be caused by undercutting (ex: waves in
California) or earthquake
3) Avalanches - snow & ice
4) Flows - soil & water slurries
- resembles that of a viscous fluid
types
a) earthflows - characteristic of grass covered earth movement
b) debris/mudflow
c) lahars - volcanic mudflows
Slow Movement Examples
1) Soil Creep
- slow glacier-like movement of shallow soil downslope with surface levels moving fastest & rate
of movement decreasing with depth. Primarily due to expansion & contraction (expands when wet, gets
warm, or freezes; contracts when dries, cools, or thaws); also due to gravity & rainfall & no vegetation
2) Solifluction - rising up of soil due to alternate freezing & thawing over permafrost