Lecture 4a Soil Forming Factors

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Lecture 4aSoil Forming Factors

• Parent Material
• Climate
• Vegetation
• Topography
• Time
• Soils vary from place to place because the
  intensity of the factors is different at
  different locations.

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Soil Parent Materials

• Residual - Soil formed from Bedrock. In
  Minnesota only the following are close enough to
  the surface to have a soil formed from them
• Sandstone
• Limestone
• Basalt
• Granite

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Transported PM Soils
Basalt Gabbro
Residual Soils

Granite
Sandstone
Limestone
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Transported Parent Materials

• Water - Rivers Alluvium
• Wind - eolian sand or silt (loess)
• Gravity colluvium
• Ice Glacial Drift - all materials transported
  by ice or as a result of glacial activity

alluvium
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Minnesota Glaciation

• Ice left Minnesota-Iowa border about 12,000 YBP
  (years before present)
• 40,000 YBP is the oldest glacial till in Minn.
  That is a soil parent material (SE Mn.)
• 10,000 YBP ice left MN-Canadian border
• Ice thickness 1000 to 5000 ft. over the state
• There were at least 4 advances of the ice and
  that complicates the history and the kinds of
  glacial parent materials.
• Glacial till in Minnesota is not all the same.

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A. Unsorted Glacial Materials

• Glacial Till unsorted deposits left by the
  retreating ice - made of sand, silt ,clay,
  gravel, boulders, stones and large rocks. Till
  can be deposited into various shapes
• Moraines- ground moraine - gently rolling
  plain
• End moraine - large hill or series of hills
• Drumlins - low hill shaped by the ice

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Anatomy of a GlacierSteve Dutch- Natural and
Applied Sciences,University of Wisconsin-Green
Bay
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A Typical Glacial Advance and Retreat
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As long as Accumulation Ablation, the Glacier
Front Remains Fixed
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If Accumulation Exceeds Ablation, the Glacier
Advances
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If Ablation Exceeds Accumulation, the Glacier
Retreats
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Eventually, Material Trapped in the Ice Reaches
the Terminus
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A Typical Glacial Advance and Retreat
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Continental Glacier Landforms
Steve Dutch -Natural and Applied
Sciences,University of Wisconsin-Green Bay
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Maximum extent of Wisconsin Glaciation
http//geology.isu.edu/Digital_Geology_Idaho/Modul
e12/extent.gif
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Minnesota Glaciations 15,000 B.P.(before
present)
Superior Lobe advances to near Minnesota River
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Minnesota Glaciations
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Minnesota Glaciations

• http//mrbdc.mnsu.edu/mnbasin/flash/glaciers/glaci
  ation_animation.html

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Glacial Tills of Minnesota

• Superior Lobe Till - red in color, sandy in
  texture, acid, rocks of granite, basalt, and
  sandstone
• Des Moines Lobe Till - gray or tan in color,
  loam to clay loam in texture, calcareous (free
  calcium carbonate present), rocks present-
  limestone and shale

DesMoines Lobe Till
Superior Lobe Till
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Sorted Parent Materials

• Water
• Outwash - often stratified sand or sand
  and gravel
• Lacustrine - lake deposited - silt or
  clay in texture - fine sediments - flat terrain,
  former lake bottom

Lake Plain
Beach Ridge
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Wind

• Loess - wind blown silt (.05 - .002mm diameter)
• Sand - dune sand - wind blown sand
  (eolian sand)

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• Dyad Where have you seen evidence of glaciers
  . One for each person..
• VIDEO OF GLACIERS
• http//dsc.discovery.com/videos/discovery-project-
  earth-jakobshaven-glacier-retreat.html
• http//video.google.com/videosearch?qglaciermelt
  inghlenemb0aq5oqglacierqglacierextent
  hlenemb0start10
• http//video.google.com/videosearch?qglaciermelt
  inghlenemb0aqfqglaciermeltingtouristshl
  enemb0

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Soil forming Factors

• Parent Material
• Climate
• Vegetation
• Topography
• Time
• Soils vary from place to place because the
  intensity of the factors is different at
  different locations.

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Soil Forming Factor - Climate

• Temperature - Warmer Faster
  Cooler Slower --gt Soil
  Development
• Precipitation - higher rainfall greater
  leaching
• Leaching Zone - determined by location of CaCO3
  in the soil profile
• Leaching Index Pcpt. - Evapotranspiration the
  amount of effective rainfall that can cause soil
  leaching

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Temperature Precipitation vs. Clay, Depth to
Carbonates OM
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Leaching Index for MinnesotaLI Precipitation -
Evapotranspiration
LI
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Leaching Index 0 to 12 in Minnesota
CaCo3 Zone
LI 2
LI 4
LI 8
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The End
Sandstone Bedrock - a residual parent material