Carbonation = Acidification
• Text calls weathering of rocks by
H2CO3 (carbonic acid) carbonation
• Process is one type of acidification
Rock to Soil
Granite
Element
P
Ca
Si
Fe
In Rock
0.057
1.07
32.9
2.5
In Soil
0.035
0.23
21.8
8.54
Chemical weathering of
igneous and metamorphic
rocks
• Rocks higher in Fe and Mg will tend
to weather faster
• Will lose Fe and Mg in the process
• Secondary minerals that are the
result of weathering will have higher
Si, lower Fe, Mg
Weathering process
%Change
-38
-79
-34
+242
Which mineral would you
expect to form a fertile soil?
• Primary minerals
Secondary
minerals (including clays)
• Generally associated with loss of Si,
P, K, Mg…
• Increase in prevalence of Fe and Al
clays
• More on this later...
Where would you expect
rocks to weather faster?
• Quartz- SiO2
• Olivine - (Mg,Fe)2SiO4
1
Where would
you expect
rocks to
weather
faster?
Both sites
(Alaska and Puerto Rico)
are wet
Higher temperatures in
Puerto Rico will
accelerate weathering
process
Where would you expect
more rapid chemical
weathering?
Puerto Rico,
Oxisol
Alaska, Gelisol
Where would you expect
more rapid chemical
weathering?
Desert vs Tropical
Rainforest
• Temperature regime is similar
• Water will accelerate
weathering process
• Physical weathering will be
predominant mechanism in
desert
2
Where would you expect
expansion of water due to
freezing to play a greater role
in weathering?
Utah, Aridisol
Puerto Rico, Oxisol
Where would you expect
expansion of water due to
freezing to play a greater role
in weathering?
Greenland vs Vermont
• For freezing water to play an
important role in weathering, it has to
thaw as well
• Freeze, thaw cycles accelerate
weathering process
It may not seem like fun,
but….
• What process is going on here?
3MgFeSiO4 + 2H2O
H4Mg3Si2O9 +
SiO2 + 3FeO
• And here?
4FeO + O2
2Fe2O3
Alaska, Gelisol Vermont, Spodisol
3
Weathered Rocks from the
lithosphere are the parent
materials for soils
Types of Parent Material
•
•
•
•
•
•
Residual
Colluvial
Water
Ice
Wind
Organic material
Residual:
Parent material in place
Nature of the parent
material
will greatly influence time it
takes to make soil and the
nature of the soil that is
formed
Colluvial debris:
Rocks that have fallen down
hills
•
Water:Alluvial
deposits
Sediment that is deposited by rivers
Woodson soil series, KS
formed from sediment
4
•
Water:Alluvial
deposits
Sediment that is deposited by rivers
Water:Marine (sediments deposited
by oceans)
Glacial till:
Material
transported
by glacial ice
Water:Lacustrine (materials
deposited by lakes)
Glacial till: Material
transported by glacial ice
Pleistocene Epoch
2 million years
5
Eolian:
Materials transported by wind
Loess
Eolian:
Materials transported by wind
Volcanic ash
Organic:Wet areas where
accumulation> decomposition
Peat bogs
(1)Parent materials + 4 other
factors of soil formation
•
•
•
•
Climate
Topography
Time
Biota
6