Surface Processes

The Hydrologic Cycle and its Consequences

Soils

¥      weathering produces  = a layer of sediment

-> the regolith or pedosphere (unconsolidated sediments):

 soil = upper part of the regolith or pedosphere

 

                           A.  Components = what is in soilÉ..

 

                      1.  Sand, silt and clay

                      2.  Organics (litter & humus)

                      3.  H2O & nutrients

 

Controls => what determines how much or how fertile a soil is?

 

         1.  substrate : residual vs. transported soils

 

                           ->controls texture and amount of nutrients

 

         2.  duration: controls soil maturity-> amount and quality

 

3.  Climate: most important factor=> soil type

 

       4.  Topography:    slope angle => gravity

                                    aspect = amount of sunlight.......

 

         5. Vegetation - plant types

 

Soil profile: * soil horizons.......

                                   

1.  O-horizon => organics (litter and humus)

 

2.  A1& A2-horizons => zone of leaching:

                  O+A = topsoil

 

3.  B-horizon => zone ofaccumulation: subsoil

 

4.  C-horizon => broken up parent material (bedrock)

 

Soil types: climate affects character of soil horizons => soil type

 

       1.  Temperate = pedalfer: moderate leaching of Fe&Al from A: good accumulation of humus..É

 

 

2. Arid =pedocal: little leaching in A: evaporation=> precipitation of calcite= caliche: poor input of organics

 

3.  Tropical = laterite: thorough leaching in A: left with insoluble Fe&Al - oxides: little or no humus=> decay in the tropics is very efficient....É

 

=> paradox of tropical soils

 

=> Detailed Soil types

 

 

- UNESCO = 110 different soil types

 

- United States = 10 major types ÒSoil Orders of the

Seventh ApproximationÓ - 12,000 total types

 

- Based on where soil forms

and types of horizons

 

Importance of soil:

             

       => A non-renewable natural resource

      

       => soil erosion: a natural process enhanced by humans

 

       => soil erosion has environmental and economic implications...

 

Mass Wasting: a surface process controlled by gravity....

 

Controls:

 

1) topography

2) type and orientation of rocks

3) nature of unconsolidated material: effects angle of repose;

4) amount of water and vegitation;

5) tectonism

 

Types of Mass Wasting

 

       1. Flow;  2. Slide; and 3. Fall

 

1. Flow = unconsolidated regolith; fluid movement

 

         a) creep -> slow soil movement

 

       b) debris flow-> fluid; coarse grained

 

       c) mudflow-> fluid; fine grained

                       

2. Slide = regolith or bedrock move as large blocks

                 

                   a) slump -> blocks of regolith slide along curved surface

                           (a fault)

 

b) rockslide -> blocks of bedrock slide down a slope.......É

 

3. Fall: -> requires steep slopes

 

Mass Wasting => often triggered by human activities

                   => oversteepened slopes

 

Other triggers

¥     loading slopes

¥     Sudden shocks

¥     Water

¥     Streams and Ocean waves

 

Prevention

¥     Stabilize Slope

Р  Bolts

Р  Rip-rap

¥     Shields

Р  Fences and retaining walls