Mechanical Weathering

• Weathering occurs on a rocky substrate (bare rock or bedrock) due to climatic factors, resulting in two types of alterations.

Mechanical Weathering

• Involves the fragmentation of the parent rock due to various causes.

• Hydroclasticity: Rocks subjected to alternating wet and dry periods experience disruptive effects, leading to surface scaling and fracturing along existing planes of fissibility.

• Gelifraction or Gelivation: Water penetrates pores, and its freezing expansion breaks the rocks, with a 9% volume increase when water turns to ice.

• Thermoclasty (Dilatation-Contraction): Humidity and temperature changes, such as insolation, cause volume changes that fracture rocks.

• Haloclasty or Crystallization: Rock fragmentation occurs due to tension from the volume increase of saline crystals formed when water evaporates. These salts, lodged in rock fissures, exert pressure, widening them like wedges. The expansion of crystals, as they absorb water, causes rock fractures by applying pressure.

• Abrasion: The size of particles is modified through mechanical wear, especially by rubbing.

Chemical Weathering

• Occurs simultaneously with mechanical weathering and involves alterations to rock minerals in contact with air and water.
• The main chemical alteration processes include oxidation-reduction, dissolution, hydration, hydrolysis.
• Dissolution: Incorporates molecules of a solid into a solvent, like water, dissolving sedimentary rocks composed of salts left from evaporated water.
• Hydration: Water chemically combines with a compound, and when water molecules enter the crystalline networks of rocks, it causes a pressure inducing a volume increase, which can reach 50%. When these transformed materials dry, they contract and crack.
• Oxidation: Oxygen, typically released in water, causes oxidation, with a simultaneous reduction, as oxidizing substances gain electrons from what oxidizes. This produces reddish, ochre, or brownish rock substrates from the oxidation of iron content.
• Hydrolysis: A substance's chemical decomposition occurs through water, transforming water into ions that react with minerals, breaking their crystalline networks, forming most of the known clay materials.
• Carbonation: Carbon dioxide's capacity to act alone or dissolve in water creates small amounts of carbonic acid. Carbonated water reacts with rocks whose predominant mineral is calcium, magnesium, sodium, or potassium, producing carbonates and bicarbonates.
• Installation of Living Beings: Living organisms (vegetation, microorganisms, etc.) are on inorganic substrates, which is a phase of significance. Organisms, with their vital and metabolic processes, produce substances that continue weathering of minerals initiated by strictly inorganic mechanisms. Lichens, for example, produce acids that dissolve the rock, allowing the absorption of salts for nutrition. Additionally, plant and animal remains incorporate into the soil after decomposing through putrefaction and fermentation.

Zonal Soils

• Zonal Soils: Characteristics influenced by climate impacts.
• High Latitude Soils: These tundra soils exhibit little chemical weathering due to low temperatures, supporting limited vegetation like mosses and lichens. They are poorly drained, leading to water saturation, with minimal bacterial activity due to cold, a process called gelification.
• Mid-Latitude and Cold Climate Soils: Include three primary types.
  • Podsols: Also known as gray soils, podsols exhibit a surface layer of ash colored clay. They are rich in sparsely processed acidic humus and typically support coniferous forests (pines, firs, cypresses...) and heathlands. Adequate rainfall generally favours the leaching of bases and the cold climate slows bacterial activity.
  • Brown Forest Soils: These soils are typical of milder climates and deciduous forests. Rich in humus, they have a sparsely developed B horizon.
• Mid-Latitude and Temperate to Warm Climate Soils: This category includes a broad range of soils with distinct features.
  • Mediterranean Soils: Summer drought duration is fundamental, determining several subtypes of soils. These soils support Mediterranean forests typical of holm oaks and shrub vegetation. Types include red soils, southern brown earth, and vertisols.
  • Vertisols: These soils are identifiable by their colors, levels of organic matter, and fine textures, with a corresponding amount of expansive clays. In Spain, vertisols are abundant in Mediterranean climate zones and clay-rich areas, such as the Guadalquivir Depression (Andalusia), the Ebro Valley, and regions of La Mancha. The soils prove fertile but mechanically difficult to manage. Mediterraneans Red Soil (Ferralsols): Reddish soils characterized by few nutrients and an elevated concentration of iron, commonly found in southeastern Spain, such as Almería and Granada.
• Chernozems: Highly fertile, dark soils defined by a deep, dark-colored horizon A with abundant organic matter, formed in temperate to semiarid climates with cold winters and moderately warm summers, typical of steppes that are ideal for cultivating wheat and corn. While not naturally occurring in Spain, similar regional attributes are in the Ebro Valley.
• Calcisols: Calcium carbonate-rich soils with a calcic B horizon that accumulates lime, usually found in arid and semiarid climates with limited rainfall, which facilitates the collection of salts. It is fertile but requires prudent irrigation to avoid salinization and is present in semiarid areas of Spain like Almería, Murcia, and southeastern parts of Castilla-La Mancha.
• Other Types: Soils formed over magma-rich rocks, less evolved and known as rankers.
• Desert Soils: Very undeveloped, composed of rough loose materials shaped mostly by weathering; contain no vegetation.
• Loess: A sedimentary deposit comprised of silt, clay, and sand particles transported by wind during glacial periods. Generally porous, easily eroded, yellow or beige colored and has high mineral content which makes it notably fertile for agriculture. In Spain, mostly found in the Ebro Valley and inland areas of Castilla y León, also common in parts of central Europe such as Germany and Ukraine.
• Intertropical Latitude Soils: These soils undergo strong chemical weathering, yielding thick soils typical of humid jungle vegetation. The most typical include laterites, with nearly an absence of horizons A and B. This soil type forms mainly through intense weathering (decomposition) of rocks in warm and humid environments, where water promotes the leaching of soluble minerals and the accumulation of oxides.

Azonal Soils

• Azonal Soils: Soil type wherein climate isn't the key factor, they are immature, or have seen little development.
• Lithosols: They exhibit very little development, forming directly on the bedrock with a thin profile that is less than 10 cm deep, possess no leached salts, are without defined horizons are are often.
• Regosols: A young soil that is underdeveloped with a thin surface that lacks well-defined horizons. It is commonly made up of loose substances such as sands, gravel, or silt within regions of active decay or new sedimentation. Soils exhibit limited capacity for water and nutrient retention which limits overall fertility. In semiarid areas of Spain, the regosols are often found on erosion and recent fluvial or eolian sediments.
• Histosols: Formed by an accumulation of organic matter under water saturation in marshes and peat bogs. It has poor drainage, is naturally carbon-rich, and used for conservation. Development is driven by organic accumulation rather than climate.

Intrazonal Soils

• Intrazonal Soils:

  • Alluvial Soils: Found on riverbanks are well-suited for agriculture.
  • Volcanic Soils: Linked with basalt, unsuitable for agriculture.
  • Halomorphic Soils: Influenced by salts, hindering growth and humus formation.
  • Gypsisols: Soils with gypsum accumulation, common in dry regions.
  • Gleysols: Develops in wet, low-oxygen areas, with unique coloring.

• Current land utilization is crucial due to its scarcity and population growth.

• Indiscriminate exploitation and contamination alter soils, rendering them non-recoverable.