Transcript Weathering and Erosion

Weathering
Weathering and Erosion
 Weathering
is the chemical or physical breakdown
of a rock or mineral due to exposure to the
atmosphere.
 Erosion is the removal or transport of material by 5
possible agents: running water, glaciers, waves,
wind, and gravity.
 www.gg
- wind, water, waves, gravity, glaciers
 Humans and animals may also play a part in erosion.
Types of Weathering
 There
are two major types of weathering:
 1. Physical (mechanical) – mechanical breakdown
of rock or mineral. Just breaks it into smaller
pieces, composition of the material is NOT
changed!!
 2. Chemical – decomposition of material. The
composition IS changed!!
Mechanical Weathering – Video Clip
Physical (Mechanical) Weathering
There are several different types of physical weathering:
 1. Frost or Ice Wedging – alternating freezing and
thawing of moisture in rock openings causing rock
disintegration.

Water expands as it freezes, this breaks the rock into angular
fragments.
 Occurs A LOT in Western New York – causes most potholes!!
 Will ONLY occur in areas where the temperature alternates
above freezing and below freezing!!!

Frost Wedging animation
Physical (Mechanical) Weathering
Exfoliation – Erosion of upper rock causes
underlying rock to expand resulting in
cracking and peeling of rock in slabs.
Think of onion skin layers and peeling
them off!!
 2.
Pictures of Stone
Mountain, Georgia –
exfoliation here has
caused an overall
rounded shape to the
mountain.
Physical (Mechanical) Weathering
Organic Activity – plant roots or animals like
burrowing worms can cause rock to breakdown.
 3.
Physical (Mechanical) Weathering
 4.
Wetting and Drying - addition of water to
mineral structure causes structure to expand.
Physical (Mechanical) Weathering
 IMPORTANT!!
 Physical
weathering increases the surface area of
rocks/minerals.
 Taking a rock/mineral and breaking it up into
smaller pieces causes it to take up more space
(surface area) and will eventually increase the rate
of chemical weathering to occur.
Chemical Weathering – Video Clip
Chemical Wethering
 There
are also several different types of chemical
weathering:
 1. Hydrolosis – chemical reaction between water
and other substances.
 Silicate
minerals will often form clay from this process.
Kaolin mine, central Georgia (feldspar
weathered into clay by hydrolosis)
Chemical Weathering
Carbonic Acid – dissolving of substances by
acids in water often leaving insoluble remains.
 2.
Chemical Weathering
Oxidation – chemical reaction of a substance
with oxygen causing a rust material to form.
 3.
Weathering and Climate
 Climate
plays a very important role in weathering.
 The temperature and amount of moisture
influences the type of weathering that will occur.
 Warm and wet climates produce mostly chemical
weathering. Never any frost wedging.
 Cool and slightly wet climates produce mostly
physical weathering.
Cleopatra’s Needle in
Egypt – warm dry
climate – little to no
weathering occurs
Cleopatra’s Needle was moved to
New York and has weathered
considerably in only 80 years due
to the cold and wet climate.
Weathering and Resistance
 The
harder the rock or mineral is, the more
resistant it will be to weathering.
 Any rock with quartz will be quite resistant due to
quartz’s hardness.
 What
is quartz’s hardness??
7
 Rocks made mostly of calcite, a very soft mineral, will
be easily weathered.
 What is calcite’s hardness??
3
Porosity and Permeability
 Porosity:
material
The percentage of pore space in a
 Permeability:
The ability of a material to
let liquid (water) pass through it.
 Impermeable:
When something will not let
liquids pass through it (usually water is the
liquid).
Does the grain size or the size of
the sediment affect the porosity?
NO!!!!!
 Smaller
pieces have smaller gaps between them
but there are lots of gaps.
 Larger pieces have fewer gaps, but they are
larger gaps.
 So…the
amount of pore space (porosity) does
not change with grain size.
MIXED grain sizes WILL affect the porosity though
because the small pieces fill in the space between the
big pieces.
Sorted
Unsorted
Permeability
 If
something has
Low Porosity, then
permeability will be
SLOW
 If
something has
High Porosity, then
permeability will be
FAST