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.

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

Residual Soils

Transported PM Soils

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

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.

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

Anatomy of a GlacierSteve 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 advancesto near Minnesota River

Minnesota Glaciations

Minnesota Glaciationshttp://mrbdc.mnsu.edu/mnbasin/flash/glaciers/glaciation_animation.html

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

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

Beach Ridge

Lake Plain

Wind 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 GLACIERShttp://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+tourists&hl=en&emb=0

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.

Soil Forming Factor - Climate

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 MinnesotaLI = Precipitation - Evapotranspiration

LI

Leaching Index = 0 to 12 in Minnesota

LI = 8 LI = 4 LI = 2

CaCo3 Zone