Lecture 4a
Soil Forming Factors
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* Parent Material
* Climate
Vegetation
Topography
Time
Soils vary from place to place because the
intensity of the factors is different at
different locations.
Soil Parent Materials
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Residual - Soil formed from Bedrock.
In Minnesota only
the following are close enough to the surface to have a soil
formed from them:
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Sandstone
Limestone
Basalt
Granite
Transported PM Soils
Residual Soils
Transported Parent Materials
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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
Minnesota Glaciation
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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.
A. Unsorted Glacial Materials
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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
Anatomy of a Glacier
Steve Dutch- Natural and Applied Sciences,
University of Wisconsin-Green Bay
A Typical Glacial Advance and Retreat
As long as Accumulation = Ablation, the
Glacier Front Remains Fixed
If Accumulation Exceeds Ablation, the
Glacier Advances
If Ablation Exceeds Accumulation, the
Glacier Retreats
Eventually, Material Trapped in the Ice
Reaches the Terminus
A Typical Glacial Advance and Retreat
Continental
Glacier
Landforms
Steve Dutch -Natural and Applied Sciences,
University of Wisconsin-Green Bay
Maximum extent of Wisconsin Glaciation
http://geology.isu.edu/Digital_Geology_Idaho/Module12/extent.gif
Minnesota Glaciations – 15,000 B.P.(before present)
Superior
Lobe
advances
to near
Minnesota
River
Minnesota Glaciations
Minnesota Glaciations
http://mrbdc.mnsu.edu/mnbasin/flash/glaciers/glaciation_animation.html
Glacial Tills of Minnesota
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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
presentlimestone and
shale
DesMoines Lobe Till
Superior Lobe Till
Sorted Parent Materials
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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
Wind
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Loess - wind blown silt (.05 - .002mm
diameter)
Sand - dune sand - wind blown sand
(eolian sand)
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?q=glacier+melting&hl=en&emb=0&aq=5&
oq=glacier+#q=glacier+extent&hl=en&emb=0&start=10
http://video.google.com/videosearch?q=glacier+melting&hl=en&emb=0&aq=f#q=glacier+melting+touri
sts&hl=en&emb=0
Soil forming Factors
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Parent Material
Climate
Vegetation
Topography
Time
Soils vary from place to place because the
intensity of the factors is different at
different locations.
Soil Forming Factor - Climate
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Temperature - Warmer = Faster
Cooler = Slower --> 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
Temperature & Precipitation vs. Clay, Depth to Carbonates & OM
Leaching Index for Minnesota
LI = Precipitation - Evapotranspiration
LI
Leaching Index = 0 to 12 in
Minnesota
CaCo3 Zone
LI = 8
LI = 4
LI = 2