1) Soil is formed through the weathering of rock and minerals and is important for plant growth, land use planning, waste disposal, and understanding climate and natural hazards. 2) Soil formation involves chemical, physical, and biological processes that break down parent materials over time into distinct soil horizons. 3) Soil type depends on climate, vegetation, parent material, and other factors and influences properties like texture, structure, fertility, and engineering characteristics. 4) Improper land use can damage soils through erosion, pollution, loss of structure and fertility. Sustainable practices are needed to conserve and protect soils.

1. ENVIRONMENTAL
GEOLOGY
GEO-305
Soil and Environment
1

2. 2

3. Introduction
• Regolith is a layer of loose, heterogeneous superficial
material covering solid rock. It includes dust, soil,
broken rock, and other related materials and is present
on Earth, the Moon, Mars, some asteroids, and other
terrestrial planets and moons.
• Soil scientists define soil as upper layers of regolith
that support plant growth.
• Engineering geologists define soil very broadly to
include all unconsolidated material overlying bedrock.
3

4. Why soil is Important to Humans?
• Soil and land use planning
• Land capability for urbanization, timber management,
and agriculture
• Soil and waste disposal
• Soil and natural hazards
• Soil and climatic signals
4

5. Formation of Soil
• Soil is produced by weathering, a term that encompasses
a variety of chemical, physical, and biological processes
acting to break down rocks and minerals.
• Residual soil and transported soil.
• Soil characteristics are function of climate, topography,
parent material, Time and biological processes.
5

6. Some essential Terminologies
• Eluviation - The process of washing down material such
as organic matter or minerals through the soil.
• Illuviation - The deposition in a soil horizon of
minerals, humus and other materials.
• Leaching - The dissolving and washing down of
calcium and other bases through the soil as a result of
percolating rain water. Bases are substances which react
with an acid to form a salt and water. Some bases
dissolve in water and are then called alkalis e.g. the
hydroxides of sodium, calcium and potassium.
6

7. 7
Approximate composition of Soil
Soil Aeration
Saturated vs Unsaturated Soils

8. Soil Profile and Soil Horizons
• Vertical and horizontal movements of the materials
in a soil system create a distinct layering, parallel to
the surface, collectively called a soil profile. The
layers are called zones, or soil horizons.
8

9. 9
O. Horizon is composed mostly of organic materials including decomposed or
decomposing leaves, twigs, etc. The color of the horizon is often dark brown
or black.
A. Horizon is composed of both mineral and organic materials.
The color is often light black to brown. Leaching, defined as the
process of dissolving, washing, or draining Earth materials by
percolation of groundwater or other liquids, occurs in the A
horizon and moves clay and other material such as iron and
calcium to the B horizon.
E. Horizon is composed of light-colored materials resulting from
leaching of clay, calcium, magnesium, and iron to lower
horizons. The A and E horizons together constitute the zone of
leaching.
B. Horizon is enriched in clay, iron oxides, silica, carbonate, or other
material leached from overlying horizons. Horizon is known as the zone of
accumulation.
C. Horizon is composed of partially altered (weathered) parent material;
rock is shown here but the material could also be alluvial in nature, such as
river gravels in other environments. The horizon may be stained red with
iron oxides. R. Unweathered (unaltered) parent material.
Soil Horizons

10. 10
Soil Types
Pedalfer Pedocal Laterite
Under forest
Vegetation
Drier Grasslands Hot, wet tropical
Climates
Iron Oxide and
Aluminum-rich clays
in the B-Horizon
Calcium
Carbonate
Intense chemical
weathering to the
top layer of soil

11. Soil Properties
• Color
Depending on the amount of organic matter, consituents
minerals, aeration or aerification, soil drainage.
• Texture
Relative proportions of sand, silt, and clay-sized particles,
affect soil’s strength and ability to retain water and nutrients.
• Structure
Aggregates of soil as peds.
The more developed with time, the more complex a soil’s
structure, from granular to blocky to prismatic.
11

12. 12
Figure 12.6
(Environmental
Geology by C.W.
Montegomery)
Soil-texture
terminology reflects
particle size, not
mineralogy.
Diagram simplified
from U.S. Department
of Agriculture
classification scheme.

13. 13

14. • A weakly developed soil profile: A horizon directly over a C
horizon (no B horizon or it is very weakly developed),
relatively young few hundreds to a few thousands years old.
• A moderately developed soil profile: A horizon overlying an
argillic Bt horizon that overlies the C horizon, from at least
the Pleistocene (more than 10,000 years old).
• A well-developed soil profile: Redder colors in the Bt
horizon, more translocation of clay to the Bt horizon, and
stronger structure, may have K horizon; older than 40,000
years.
Relative Soil Profile Development
and Chronosequence
14

15. Soil Fertility
• Soil’s capability to supply nutrients needed for
plant growth, such as N, P, K
• Fertility changes
• Increase: Applying fertilizers or mixing materials to
improve soil texture
• Decrease: Leaching or soil erosion
15

16. Water in Soil
• Soil pores are filled with air or liquid
• Saturated and Unsaturated Soils
• Saturation level: changes with climate and seasons
(hardly saturated in arid climate)
• Movement of water: Important in pollution
monitoring and management
16

17. Engineering properties of soil
• Soil strength is its ability to resist deformation, function of cohesive and
frictional forces between particles.
• Soil sensitivity is measure of changes in soil strength from disturbances.
• Soil compressibility is its tendency to consolidate or decrease in volume.
• Soil erodibility is the ease with which soil is removed by wind or water
• Soil hydraulic conductivity is the ease with which water moves through a
material.
• Soil corrosion potential is slow weathering or chemical decomposition
that proceeds from the surface into the ground.
• Shrink-well potential is the tendency of a soil to gain or lose water.
• Ease of excavation the degree of ease to remove soil using certain
equipment during construction 17

18. Rates of Soil Erosion
• Volume, mass, or weight of soil removed from a
specific area during a specific period of time, kilograms
per year per hectare.
• Types of soil erosion; splash erosion, sheet erosion, rill
erosion and gully erosion.
• Factors affecting erosion rates; Physical and chemical
properties of soil, land use, climate, topography,
tectonics.
• Various approaches for measuring soil erosion.
18

19. The Universal Soil Loss Equation
The Universal Soil Loss Equation is 𝑨 = 𝑹𝑬𝑳𝑺𝑪𝑷
where
• A = long-term average annual soil loss for the site being considered
• R = long-term rainfall runoff erosion factor
• E = soil erodibility index
• L = hillslope/length factor
• S = hillslope/gradient, or slope factor
• C = soil cover factor
• P = erosion-control practice factor
19

20. Sediment Pollution
• Sediments - one of the greatest pollutant.
• Choking the waterways, burying vegetation, causing dust storm.
• Adverse impact on water and air quality land quality, productivity
using dust storms.
• Preventive measures
• tailoring development to the natural topography,
• exposing a minimal amount of land,
• providing protection for exposed soil,
• minimizing surface runoff from critical areas
• and trapping eroded sediment on construction sites
20

21. Land-use and Soil Problems
• Influencing the pattern, amount and intensity of surface-water
runoff, erosion and sedimentation.
• Agriculture: Estimated 10 percent of the world best agricultural
land damaged due to soil erosion and overuse of soil during the last
50 years
• Better practice to sustain soils
• Contour plowing
• No-till agriculture (no plowing)
• Terracing slopes, retaining walls for steep slopes
• Planting more than one crop, particularly in tropical areas 21

22. • The conversion of agricultural, forested, or rural land to highly
urbanized land causes dramatic changes.
• The process of urbanization directly affects soils in several ways:
• Soil may be scraped off and lost. Once sensitive soils are disturbed, they may have
lower strengths when they are remolded.
• Materials may be brought in from outside areas to fill a depression before construction,
resulting in a much different soil than was previously there.
• Draining soils to remove water may cause desiccation, or drying out, and other changes
in soil properties.
• Soils in urban areas are susceptible to soil pollution resulting from deliberate or
inadvertent addition of chemicals to soils. This problem is particularly serious if
hazardous chemicals have been applied. 22
Land-use and Soil Problems

23. Soil Pollution
• Soil pollution: By any materials detrimental to
human and other living organisms, such as organic
chemicals, inorganic chemicals, toxic substances
• Intentionally or accidentally applied to soils
• Inappropriate disposal of waste materials
• Treatment: excavation, disposal, incineration, and
bioremediation
23