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Weathering of volcanic tuff (~1970).

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Weathering of volcanic tuff 1970' – PowerPoint PPT presentation

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Title: Weathering of volcanic tuff (~1970).


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Weathering processes tend to slow, but can be
observed over your life time.
Weathering of volcanic tuff (1970).
1980
1990
3
Chemical weathering of an Egyptian obelisk after
arriving in Central Park, New York.
Egyptian obelisk survives over 3000 year in the
aridity of the Sahara Desert.
4
Mechanical weathering processes, such as frost
wedging shown above, will cause the break-up of
rock into smallerclasts without changing the
mineralogy of the rock.
5
Joints facilitate weathering by exposing more
surface area and allowing water to infiltrate at
depth.
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Fire-induce spalling
Mechanical Weathering Processes
Bioturbation
Freeze-thaw/Frost Wedging
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Production of carbonic acid and bicarbonate ions
H2O CO2 H2CO3
H1 HCO31-
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Eocene oxisol, Ione, CA Iron oxide laterite (red)
overlies kaolinite clay (white). Formed on
alluvium derived from eroded Sierra Nevada
volcanics in a tropical climate 38 m.y. ago.
12
A Horizon
Goethite
B Horizon (goethite yellow precipitate and
hematite red precipitate)
4FeO 2H2O O2 2FeOOH
Dehydration to form Hematite
2FeOOH Fe2O3 H2O
Modern soil formed in laterite of Eocene Ione
Formation
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Soils can form in unconsolidated sediment.
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Soils can form in residual bedrock.
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A Horizon
B Horizon
C Horizon
(Partially weathered parent material)
Soil forming in granitic bedrock.
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A
Bwk
Formation of caliche soils in arid climates.
Bk
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A Horizon
B Horizon (goethite and hematite)
Eocene oxisol, Ione, CA
Modern soil formed in laterite of Eocene Ione
Formation
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solum
Unweathered parent material (glacial till)
  • Soil development versus position on a moraine
    slope. Compare solum depth at crest versus the
    flank of the moraine

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Soil development on a 13,000 year old moraine,
Snoqualmie Pass, WA.
35
Soil development on 75,000 and 150,000 year old
moraines.
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Entisols Soils with little of no morphological
development because the parent material has only
recently accumulated. Quartz sand is also
conducive to formation of entisols. Often occur
in young alluvium or very steep slopes.
38
Inceptisols are typically young soils that are
just starting to show horizon development. The
soil on the right is forming in young colluvium
(slope wash) and the solum is less than 2 feet
thick. Inceptisols commonly form in alluvium and
young glaciated terrains.
39
Histosols Organic-rich soils. Histosols form
where the rate of organic decomposition is less
than the rate of accumulation, such as peat bogs,
swamps or tundra.
40
Aridisols are soils of arid or semi-arid
environments where moisture is scarce.
Calcification and salinization are important soil
forming processes. Soils are typically alkaline.
41
Andisols are soils that are developed in parent
material that is at least 50 volcanic ash. They
tend to be fertile and support a dense vegetative
cover in moist climates.
42
Vertisols are clayey soils with a shrink-swell
capacity. During drying cracks can develop and
organic matter will be swallowed into the cracks
and become inverted profiles. Slickensides are
often present on ped faces.
43
Mollisols are typically the most fertile soils
on earth. They tend to have deep A horizons and
high nutrient status (K, Na, Ca, Mg) and possess
high moisture retention. They typically form in
grasslands and steppe climatic regimes.
44
Spodosols are typically found in cool, moist
climates under conifer forests. Decomposition of
conifer needles forms weak organic acids and
remove base ions (Ca, Na, K, Mg) to produce
acidic soils. Typically will possess and E
horizon from major leaching of bases and organics.
45
Alfisols are soils developed undeer temperate
forests at mid-latitudes. Eluviation is moderate
and base status (Ca, K, Na, Mg) high. These soils
are well-developed and contain an argillic
(clay-rich) horizon.
46
Ultisols share many of the same properties as
oxisols in that they are stained red/yellow
reflecting the oxidation of iron and aluminum.
Unlike oxisols they have an illuvial clay layer.
They are typically found in the moist subtropical
climatic zones.
47
  • Oxisols is found in moist tropical climate
    under broadleaf vegetation. Chemical weathering
    and leaching of soluble ions is high, leaving
    residual soils containing high concentration of
    iron and aluminum oxides (sesquioxides). Heavy
    leaching leaves a soil that is nutrient poor and
    not well-suited for agriculture.

48
Gelisols soils that form on permafrost (within 2
m of the surface). The soils can be rich in
either mineral and/or organic material. They are
common in the tundra and have experienced
cryoturbation (frost-churning) due to annual
freeze-thaw cycles.
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