Weathering - ROCK
CYCLE
 WEATHERING
 • 

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Unformatted text preview: ROCK
CYCLE
 WEATHERING
 •  the
physical
breakdown
(disintegra5on)
and
 chemical
altera5on
(decomposi5on)
of
rocks
 at
or
near
Earth's
surface
 •  Slow
but
constant
 •  Plenty
of
5me
 SURFICIAL
or
EXTERNAL
PROCESSES
 •  Affects
the
top
150
feet
‐
just!
 WEATHERING
 scenery
 WEATHERING
 scenery
 •  The
Bridestones

 WEATHERING
 human
problems
 Mechanical
Weathering
 •  rocks
are
broken
down
into
smaller
and
 smaller
pieces
‐
BUT
retain
the
 characteris5cs
of
the
original
material
 •  more

 Surface
 area
 Bryce
Canyon
 Hoodoos
 hKp://faculty.plaKsburgh.edu/carol.treadwellsteitz/Bryce%20Canyon/ Bryce_‐_Marge_Simpson.JPG
 Mechanical
Weathering
 •  Boulders
 •  Cobbles

 •  Pebbles
 –  All
larger
than
 2mm
 Mechanical
Weathering
 •  Sand
 –  2mm
‐
1/16th
mm
 •  Silt
 –  1/16
th
mm
‐
1/256
 •  Clay
 –  Less
than
1/256
 Joints
faults
 Mechanical
Weathering
 mechanisms
 frost
wedging
 •  Water
freezes
to
ice
‐
expands
10%
 •  Repeated
over
and
over
 frost
wedging
 •  Talus
slope
at
base
 Salt
crystal
growth
 •  solutions seep into cracks and joints in the rocks and evaporate, leaving salt crystals behind. thermal
expansion/contrac5on
 •  •  •  •  Temperatures are high in the day, Cools greatly at night. Rock heats up and expands by day, Rock cools and contracts by night •  Stress is exerted on the outer layers. Sediments
and
soils
 thermal
expansion/contrac5on
 •  Also by fire Unloading
‐
pressure
release
 •  overlying materials (not necessarily rocks) removed (by erosion, or other processes), •  causes underlying rocks to expand and fracture parallel to the surface. Joints
cooling
 Animals
and
plants
 •  Birds
 •  Prairie
dogs
 Animals
and
plants
 •  Root
wedging
 product
:
clasIc
sediment
 talus
 Chemical
Weathering
 •  complex
process
of
breaking
down
the
 components
in
a
rock,
crea5ng
new
minerals
 and
releasing
elements
(ions)
into
the
 environment
 •  New
‐
more
stable
‐
minerals
 •  Water
‐
most
important
 Chemical
Weathering
 mechanisms
 dissolu5on
 •  Dissolved
by
water
 •  H20
‐
bipolar
molecule
 •  product:
ions
in
solu5on
 dissolu5on
 •  •  •  •  •  Water
aKracts
water
 Water
breaks
apart
compounds
 E.g.
salt
 Na+
in
solu5on
 Cl‐
in
solu5on
 dissolu5on
 •  Acids
drama5cally
increase
weathering
 •  Water
+
Carbon
dioxide
=
carbonic
acid
 





H2O

+

CO2 
 
=


H2CO3
 Carbonic
acid
has

H+


and
HCO3‐


 H+
is
very
reac5ve
 dissolu5on
 •  Calcite
+
carbonic
acid

 





CaCO3


+
H2CO3
(H+

and
HCO3‐)
 
 
 
=
calcium
ion
+
Bicarbonate
ion
 
 
 
 
Ca2+





and


2HCO3‐
 •  Creates
caves
 •  Calcium
ions
move
to
oceans
to
remake
calcite
 (shells
etc)
 dissolu5on
 •  Calcite
and
salt
caves
 oxida5on
 •  oxida5on
of
iron
minerals
 •  Iron
and
steel
“rust”

 •  
Iron
+
oxygen
=
hema5te
 
 
4Fe
+
3O2
=
2Fe2O3
 •  product:
iron
oxide
minerals
 oxida5on
 •  Weathering
rind
 •  Ferromagnesian
 minerals
(Fe,Mg)
 –  Olivine
 –  Pyroxene
 –  Hornblende
 •  Basalt
 •  gabbro
 Dissolu5on
+
oxida5on
 •  Pyrite
(FeS2)
and
 other
sulfide
 minerals
weather
to
 form
 •  Sulfuric
acid
+
oxides
 •  Result
‐
acid
mine
 drainage
 hydrolysis
 •  hydrolysis
of
silicate
minerals
(especially
 feldspar)
 •  product:
clay
minerals
 •  Needs
water
 hydrolysis
 •  K‐feldspar
+
carbonic
acid
+
water
 
2KAlSi3O8
+
2(H+
+
HCO3‐)
+
H2O
 
 
=
Kaolinite
(clay
mineral)
+
potassium
ions
+

 
 
Al2Si2O5(OH)4


 
+
2K+
 
 
 
bicarbonate
ions
+
silica
 
 
 
2HCO3‐








 
 
+
4SiO2
 hydrolysis
 Results
 •  Kaolinite
(clay
mineral)

 –  Paper

 –  Kaopectate
(original
recipe)
 –  Fine
china
 •  potassium
ions

 –  Used
for
reac5ons
needed
for
life
 –  Oceans
‐
salt
with
K+
 •  bicarbonate
ions

 •  Silica
 –  Flint
/
chert
(sedimentary
rocks)
 hydraIon
 Addi5on
of
water
to
a
mineral
 Anhydrite
to
gypsum
 Products
of
Chemical
Weathering
 –  Primary
minerals
 –  Secondary
minerals
 Goldich
stability
series
 •  Opposite
of
Bowen’s
reac5on
series
 Goldich
stability
series
 •  Resistance
of
primary
silicates

 •  Minerals
common
in
sedimentary
rocks,
and
 soils
 –  quartz,
feldspar,
muscovite,

 –  Pyroxene,
olivine
are
rare
 Other
minerals
 •  Resistance
 –  Hema5te
 –  Gibbsite
 –  quartz
 •  Weather
easily
 –  Halite
 –  Calcite
 –  olivine

 secondary
minerals
 •  Secondary
Minerals
such
as
kaolinite
and
 other
clay
minerals,
hema5te,
limonite
 –  Produced
by
chemical
reac5ons
 ions
in
solu5on
 •  Ca2+,
Na+
a
liKle
SiO2
from
hydrolysis
 •  form
chemical
sediment
 –  limestone
 –  gypsum
 –  halite
 –  chert
 Physical
and
chemical
weathering
 work
together
 •  Mechanical
 makes
things
 smaller
 •  More
surface
 area
‐
more
 chemical
 weathering
 Weathering
 •  parent
material
 –  Granite
‐
clear
wri5ng
 –  About
170
years
old
 Weathering
 •  parent
material
 –  Marble
(calcite)
weathers
easily
 Weathering
 •  rock
type
‐
differen5al
weathering
 Weathering
 •  joints
 spheroidal
weathering
 •  A
result
of
chemical
weathering
 –  Rounds
things
(mechanical
is
angular)
 Weathering
 •  slope
 Controls
on
rates
of
Weathering
 •  Climate
 •  Warm
and
wet
accelerates
chemical
 weathering
 •  Extreme
climate
changes
may
aid
weathering
 Cleopatra’s
needles
 •  Egyp5an
obelisks
 •  Now
in
London,
Paris
and
New
York
 •  originally erected in the Egyptian city of Heliopolis, around 1450 BC •  Granite •  The inscriptions were added about 200 years later by Ramesses II to commemorate his military victories. •  Toppled about 100 AD which preserved them from weathering Cleopatra’s

 needles
 Paris
 1833
 London
1819
 New
York
 1881
 Cleopatra’s
needles
 Egypt
 Central
Park
‐
now
 Weathering
 •  5me
 Sediment
(regolith)
 •  clasIc
or
detrital,
 primary
minerals,
 secondary
minerals
 •  chemical
ions
in
 solu5on
 ...
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