WEATHERING

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WEATHERING
The process by which rocks and minerals break
down at or near the surface of the Earth.
EROSION
The process by which moving water, wind, ice
or gravity carries away pieces of rock and
deposits it elsewhere. WEATHERING and EROSION
are inter-related. WEATHERING speeds EROSION.
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WEATHERING PROCESSES
MECHANICAL WEATHERING
MECHANICAL WEATHERING breaks a mineral or rock
into smaller pieces but does not change the
chemical make-up of the pieces. Turns big rocks
into little rocks. Mechanical Weathering
increases the surface area that can later be
chemically weathered.
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FROST WEDGING
Water expands when frozen. Expands 9. Water
trapped in cracks freezes and expands. Actively
fractures the rock. Works best where
temperatures fluctuate above and below 0?C
(32?F). When water melts, it seeps deeper into
the crack and then refreezes.
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FROST WEDGING
Breaks off blocks or slabs of rock. Broken pieces
fall downslope. Accumulate as TALUS.
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FROST WEDGING
FROST HEAVES AND POTHOLES
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CRYSTAL GROWTH
Salt water, usually from the ocean, gets into
fractures. When it evaporates, crystals grow that
expand. Expansion of crystals breaks the rock.
Cleopatras Needle Central Park, NY
Before After
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THERMAL EXPANSION and CONTRACTION
Heat causes external layers of rock to
expand. Mineral expand at different rates. Quartz
expands more than feldspar. Those minerals that
expand more, exert pressure on those that
expand less. Generally affects only the surface
layer of a rock. (Rock is a poor conductor of
heat) Forest Fire High alternation of
temperatures (deserts) Water or moisture speeds
the process.
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MECHANICAL EXFOLIATION
When overlying mass of rock and sediment is
released, pressure on the underlying rock is
released. Allows the rock to expand. Expansion
takes place outward from the exposed
surface. Sheets of rock will fall off.
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MECHANICAL EXFOLIATION
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MECHANICAL WEATHERING OTHER TYPES
ROOT WEDGING
Trees grow in cracks in rocks and the force
related to expansion with growth breaks the
rocks.
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MECHANICAL WEATHERING OTHER TYPES
ABRASION
Contact of weathered and eroded particles with
other rock during erosion also leads to
mechanical breakage due to ABRASION.
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CHEMICAL WEATHERING
Causes a change in the chemical composition of
rocks and minerals being affected. Attacks rocks
and minerals that are unstable at the Earths
surface first. Produces stable byproducts. Mineral
s that are stable at the Earths surface are
less affected by chemical weathering. Most
change takes place through contact with
water. Water carries ions from place to
place participates in the reaction
itself carries away the products erosion.
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CHEMICAL WEATHERING
Chemical weathering occurs faster when
weathered material is broken up first by
mechanical weathering. Increased surface area
allows chemical weathering to occur at a faster
rate.
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CHEMICAL WEATHERING
DISSOLUTION
Water removes ions or ion groups from a rock
or mineral and carries them away. Precipitate
later when water evaporates. Due to the bipolar
nature of water molecules, ions become dissolved
and are transported in solution.