Topography as a soil forming factor is related to the soil's position on the landscape. Topography refers to the shape or contour of the land surface. Some soils are going to occur on the summit of a hill, some on the side slopes, and some on the footslope. The position of the slope will have a great deal to do with the soils characteristics.
A typical slope profile would look like this:
In general soils at the summit and
backslope develop horizons the fastest. The steeper the slope the less
development the soil will have.
Soils on the shoulder develop horizons slower because :
At the footslope position the soils will collect sediment from upslope that can bury the horizons and slow down their development. If sediment is minimal, the increased water accumulating on the footslope from upslope will increase the leaching and the depth of horizon development.
Another complicating factor is the depth of the water table in relation to the slope position. This concept of soils being different because of the depth to the natural water table is called the"Catena Concept" or soils have different properties due to their depth to the water table.
This diagram indicates this relationship. Soils that are greater than 4 feet
to the water table are considered
Well Drained (WD) and do not have any
characteristics that indicate poor drainage. These features are called
redoximorphic features and are reflected in the soil as splotches of red or
gray color and are called mottles. Well drained soils have mottles greater than
4 feet. Another diagram showing this "Soil Catena Relationship" can
be found at Soil Catena
Soils that are Moderately Well Drained
(MWD) have gray and red mottles between 3 and 4 feet
These mottles indicate that the water table will be
at this level during some periods of the year. For the Somewhat Poorly Drained (SPD) soils the mottles
will occur from 2 to 3 feet. For the Poorly
Drained (PD) soils the entire soil below the dark surface will
be gray in color. Indicating that most of the iron has been reduced due to the
low O2 levels.
A typical profile of a poorly drained soil would look like this.
Note the gray colors immediately below the dark surface. Poorly drained soils
occur in depressions and low areas. Many areas of Minnesota prior to settlement
consisted of these kind of soils that today are known as wetlands. An area to
look for wetlands is north of the Twin Cities on the Anoka Sand Plain. The
Anoka Sand Plan has the poorly drained Isanti soils interspersed with the well
drained Zimmerman soils
.
The last component of topography is the aspect of the slope or the direction
the slope faces. 
This is important where the slopes are
steep enough to allow the southern aspect to become hotter from the direct rays
of the sun. As this occurs more water is evaporated and less leaching occurs,
thus lesssoil development takes place on southern exposures. In
southeastern Minnesota these southern exposures are sometimes called "goat
openings".
In summary, topography affects soil development by the location of the soil
on the slope profile, the direction the steep slope faces, and the depth to the
water table. See Block Diagram for topography factors
Soil Forming Factors
Chapter 4 Time as a Soil Forming Factor
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