Chapter 8
At end of period you will
get a class work grade for
attentiveness and note
completion…and you will
have a QUIZ on the
notes.
Chapter 8
Weathering: the
metamorphose process in
which rock goes from one state
of appearance and/or chemical
structure into another
Weathering
•Mechanical Weathering
•Chemical Weathering
•Erosion
Mechanical Weathering
Mechanical weathering:
type of weathering that
breaks rock into smaller
pieces without changing its
chemical composition.
Mechanical Weathering cont.
Ice wedging: when large
amounts of water gets into
the cracks of rocks and it
repeatedly freezes and thaws.
Mechanical Weathering cont.
Frost action: When small
amounts of water gets into
the cracks of rocks and it
repeatedly freezes and thaws.
`
Mechanical Weathering cont.
Plant and root action: when the
force of plants, trees, and/or
roots break apart rock into
smaller pieces.
Exfoliation: the peeling of
surface layers from a rock
structure.
Mechanical Weathering cont.
Wetting and drying: clay
particles in rock
repeatedly get wet and
then dry out making the
rock swell and shrink.
Mechanical Weathering cont.
Spheroidal weathering:
edges of a rock wear away
faster than the center of a
rock making it spherical in
shape.
Mechanical Weathering cont.
Abrasion: grinding action
of rock produces rounded
boulders, pebbles, and sand
grains.
Practice Link
Chemical Weathering
Chemical weathering:
type of weathering that
uses water and/or air to
change the chemical
composition of rock or
dissolve it away.
Chemical Weathering cont.
Hydrolysis: chemical
reaction of water with other
substances.
Oxidation: chemical
reaction of oxygen with other
substances.
Chemical Weathering cont.
Carbonic acid: carbon
dioxide and water form a
weak acid which dissolves
away certain minerals in
rock.
Chemical Weathering cont.
Natural acids: natural
acids from plants and
animals combine with water
to dissolve away certain
minerals in rock.
Erosion
USGS states, “soon as a rock
particle (loosened by one of
the two weathering processes)
moves, we call it erosion or
mass wasting. Mass wasting is
simply movement down slope
due to gravity.
Erosion
Rock falls, slumps, creeps,
avalanches, and debris
flows are all examples of
mass wasting. We call it
erosion if the rock particle
is moved by some flowing
agent such as air, water or
ice.
Creep or Earth flow
Erosion cont.
So, here it is: if a particle is
loosened, chemically or
mechanically, but stays put,
call it weathering. Once the
particle starts moving, call
it erosion.
Weathering and Erosion: A Dynamic
Duo
• Frost action / ice wedging may
lead to rock falls
• Exfoliation can lead to rock
slides
MASS WASTING SITE
Practice