Soil Formation, Degradation, and Conservation
Mechanical or Physical Weathering: Rock Fragmentation
Mechanical or physical weathering occurs without altering the chemical composition of rocks, deserts, and minerals. Intense examples can be seen in Lost Montana.
Unloading Pressure
When rocks outcrop due to the elimination of covering materials by erosion, they experience decompression. This decompression leads to the appearance of several cracks, such as:
- Relaxation or expansion cracks
- Contraction differential cracks due to large temperature variations between day and night (common in deserts). Different minerals expand and contract at different rates, generating internal tensions. Repeated expansion and contraction cycles cause superficial rock disintegration.
Gelivation or Gelifraction
Liquid water penetrates cracks in rocks. When it freezes, its volume increases, exerting pressure against the crack walls. This process enlarges cracks and eventually fragments the rock. The resulting fragments fall due to gravity and accumulate in lower areas, forming scree, cones, or stony washouts.
Action of Living Beings
Plant roots can penetrate rock cracks. As they grow in thickness, they increase the size of the cracks, ultimately breaking up the rock.
Haloclasty
Water containing salts crystallizes in fissures, increasing in size and causing rock fractures. This mechanism occurs in coastal areas and arid zones.
Chemical Weathering
Hydrolysis
The crystal structure of some minerals breaks down in ionic form due to the action of water. This reaction is one of the most important in silicates, such as the alteration of feldspars.
Solution
Water dissolves some rocks and minerals, especially saline minerals. Small channels often form on the surface of these rocks.
Hydration
Some minerals incorporate water molecules into their lattice. This process is common in clay minerals, which expand when they incorporate water and contract when they lose it.
Carbonation
Water carries dissolved CO2, forming carbonic acid. This acid reacts with carbonates in limestone, transforming them into bicarbonates, which are water-soluble.
Oxidation
Atmospheric oxygen combines with metallic elements in some minerals, converting them into other, usually more easily disintegrated minerals.
Action of Living Beings
Living organisms release various substances that can alter rock minerals.
Soil Components
- Inorganic Components (minerals, water, and gas): These originate from the weathering of parent rock. They consist of rock fragments of different sizes, iron oxides and hydroxides, various dissolved salts, water, and air pores.
- Organic Components: These include living organisms inhabiting the soil (plants, bacteria, fungi, animals) and dead organic matter, which constitutes humus.
Soil Formation Factors
- Type of Bedrock: Bedrock composition determines the soil’s mineral components, influencing the type of vegetation that can establish itself.
- Climate: Climate is a crucial factor, determining the intensity and type of weathering and the vegetation that will develop. Key climatic factors include temperature (influencing soil reactions) and precipitation (contributing to material creep and solution).
- Living Beings: Living organisms contribute to soil development, facilitate weathering, and provide organic matter. Plants are the primary source of organic matter and protect the soil from erosion with their root networks.
- Topography: In steep terrains with pronounced slopes, soil is poorly developed due to slope erosion and difficult water infiltration. Gently sloping reliefs favor soil development.
- Time: Soil formation time varies greatly depending on the climate, ranging from a few decades in hot, humid climates to several millennia in dry climates.
Soil Uses and Degradation
Soil is used for food production, timber harvesting, mineral and energy resource extraction, water management, and building support. However, soil productivity can be lost due to various factors.
Soil Degradation
Soil degradation is a process that reduces the current and potential capacity of soil to produce goods and services, both quantitatively and qualitatively.
Degradation Processes
- Chemical Degradation: Causes loss of soil fertility, salinization, acidification, etc.
- Physical Degradation: Loss of soil structure due to compaction.
- Biological Degradation: Loss of humus due to the elimination of humidifying organisms.
- Erosion: Removal of soil by water or wind, which can be exacerbated by human activities.
Problems Derived from Soil Loss
- Water Loss: Decreased water holding capacity, leading to flooding or drought.
- Energy Loss: Reduced water flow to reservoirs.
- Loss of Arable Land: Decreased agricultural production, especially in irrigated areas.
- Ecosystem Disruption: Due to sediment accumulation.
- Desertification: Human activities transform areas into deserts or semi-deserts.
Measures to Avoid Soil Degradation
- Proper Cultural Practices: Cultivation techniques that respect soil characteristics and prevent gully formation.
- Reforestation: Repopulate deforested land, preferably with native species.
- Forest Management: Sustainable forestry practices, such as pruning and incentives.
- Rural Land Management: Prevent the abandonment of agricultural land.
- Erosion Prevention Measures: Construct plant or artificial barriers or increase soil cover.
Desertification in Spain
Other factors contributing to desertification in Spain include soil loss through erosion, fires, and overexploitation of aquifers. Desertification is considered severe in 31.41% of the Spanish territory.
Erosion, Transport, and Sedimentation
Erosion
Erosion is the process by which the Earth’s surface is dismantled by geomorphic agents like water, ice, or wind. Erosion results in the mobilization of materials previously disintegrated by weathering.
Transport
Transport is the displacement of weathering minerals from their origin to a more distant location. It depends on the transporting agent and the material being transported.
Sedimentation
Sedimentation is the deposition of materials transported by erosion, called sediments.
- By Gravity: Gravity acts on solid materials when the transporting agent loses energy. If the agent is fluid, material is selectively deposited by precipitation-del-peso.
- Chemical Function: If dissolved materials are transported in water, sedimentation occurs upon supersaturation.
Sedimentary Basins
Sedimentary basins are areas where surface sedimentation occurs. They are located in low areas where sediments accumulate and often experience subsidence due to various causes.
Diagenesis
Diagenesis is the set of physical, chemical, and biochemical changes that occur in sediments after sedimentation, taking place at low pressure and temperature. It results in the formation of sedimentary rock and comprises five processes: compaction, dissolution, displacement, recrystallization, and metasomatism.
Sedimentary Rocks
- Fragmental Rocks: Composed of mineral fragments of different sizes, obtained from the alteration of other rocks and deposited after transport.
- Chemical Rocks: Formed by precipitated dissolved substances in water.
- Biochemical Rocks: Formed by the accumulation of remains of living organisms in the sedimentary basin.