Soils and Environment

Introducing soils:

An important consequence of the factors we just listed is that in some regions, weathering products hang around and continue to interact with weathering agents and parent material. The result is soil. Terms:


Land use planning:

Waste disposal:


Study of Natural Hazards: Climate patterns:

Soil Profiles:

Transport of weathering products: The mineral component can form either:


The ideal soil profile -the succession of distinctive horizons (a new term for layers or strata, when applied to soils) from the surface down to the bedrock (unaltered parent material). All soil profiles contain the following, in some form or other: In the real world, soil profiles are influenced and constrained by their environments, such that the relative thickness (or even the presence) of horizons is highly variable. Compare:


Soil Fertility:

Soil Classification:

Engineering properties of soil:


Strength: The ability of the soil to resist deformation when a load is applied to it. This represents a complex interaction of:


Sensitivity: A soil's change in strength upon being vibrated or disturbed.

Compressibility: The tendency to compact under load. Coarser material is typically less compressible.

Erodibility: A soil's vulnerability to erosion by agents of transport. Typically:

Hydraulic conductivity (K): A soil's ability to transmit groundwater. Essentially a function of:

Note: Clay rich fine grained soils may contain much water but, because of its electrostatic interactions with the grains, allow very little to pass through.

Corrosion potential: A measure of the speed with which chemical reactions in the soil will corrode buried objects. Generally a function of:


Ease of excavation: What kind of machinery is needed to excavate(More a measure of human technology than of soil):


Shrink-swell potential: (A live issue in our region.) The degree to which soils expand and contract when wet or dry. Many clay minerals, especially montmorillonite, can accept water molecules into their crystal lattices, expanding to up to 15 times their original volume in the process. Expansive soils rich in such clays may swell from 25 to 50% of their dry volume, damaging foundations and disrupting other constructions. Associated issues:

Environmental problems of soil:


Agriculture: Naturally impacts soil health because plowing:

As a result, an estimated 30% of topsoil - the nutrient-rich O and upper part of the A horizons - has been lost in the US. Note that soils form at rates less than 1 mm/year. If erosion outstrips soil formation, soils will be lost. Extreme cases in history include the destruction of the native soils of Iceland by Norse settlers (right). Mitigation strategies:


Urbanization: Influences soil health in varied ways:


Off-road vehicles: In some ways mimic the effects of agriculture and in others the effects of urbanization:

Soil pollution:

In nature, soils are the primary location of the biological filtration system in which bacteria break down organic pollutants. They can, however, become reservoirs for industrial contaminants that the natural filtration system can't deal with, especially as these tend to adhere to fine grains.

Remediation is onerous and expensive, including soil removal, incineration, or bioremediation.