3. Formation of volcanic soils

Soils of residual origin evolve from in situ weathering, and normally, they are characterized by a finer granulometry close to the surface where the alteration has been more intense. Despite this generalization, there are residual soils that reflect greater alteration in depth; this is often

The soils derived from volcanic ash are those formed from the weathering of deposits of materials from volcanic ejections. According to the Committee for the Recognition of Soils [24], these soils are called Andisols, a name derived from ando soil; etymologically, "an"

The central concept of the Andisols covers two fundamental aspects: (1) parental material of volcanic origin (ash, pomace, slag, pyroclastic, etc.) and (2) soils whose colloidal fraction is

Under this concept, the specific properties of these soils have been attributed basically to the predominance of allophane in the colloidal fraction; however, the results found by Shoji and Ono [22] in soils without the presence of this mineral showed that the properties of the Andisols are not necessarily given by the allophone and indicate that the Al-humus and Fe-

Based on these results, new criteria were established to define the Andisols as soils developed from volcanic ejections or volcanoclastic materials whose colloidal fraction is dominated by non-crystalline materials and/or Al-humus complexes. It was also determined that the andic properties are the result mainly of the presence of significant amounts of Al-humus, allophane,

The physical, mechanical, and chemical properties of these soils make them considered as being of great importance worldwide due to their high productive potential, high carbon and

Around the volcanic zones of the entire American continent are deposits of residual soils formed from the weathering of volcanic ash. Studies on similar soils and their performance in engineering works in regions such as Indonesia, New Zealand, India, Dominica, and Japan show that this type of soil has unusual properties compared to sedimentary soils [18, 20, 28].

The soils that currently cover the regions surrounding the volcanoes of the Andes Mountains in Colombia have their origin in pyroclastic materials that emanated during the volcanic eruptions of the last 25,000 years [9]. These deposits correspond to residual soils formed from the physical and chemical alteration of volcanic ash. Worldwide, volcanic ash soils represent approximately 0.84% of soils and are located predominantly in tropical regions [10, 13, 17, 21]. The soils derived from volcanic ash in Colombia occupy about 11.6% of the national territory and are located in regions of significant demographic and economic growth. In the Colombian

nitrogen accumulation, high storage capacity, and improved water quality [10, 23].

the case of soils derived from volcanic ash [13].

90 Soil Moisture

dominated by non-crystalline materials.

imogolite, or ferrihydrite complexes [10, 16].

In: soils derived from volcanic ash in Colombia [13].

2. Localization and distribution

means dark and "do" means soil in Japanese language [10, 21, 27].

humus complexes also influence the properties of these soils [10].

Volcanic ash is generated from the fragmentation of magma and materials in the cone of the volcano from previous eruptions [2, 13, 29]. Three mechanisms have been identified as the main generators of volcanic ash: the rupture of the magma due to vesiculation, the fragmentation due to high thermal stresses, and the pulverization of the lava in the walls of the volcano's chimney during eruption.

The mechanism of ash formation defines the block or vesicular morphology. The block ashes have flat surfaces resulting from the vitreous fracture of the magma. Vesicular ashes may have water drop textures or surfaces formed by the rupture of the material through areas that had air bubbles [13, 29].

The amount of water consumed in the transfer of thermal energy into mechanical energy also affects the production of volcanic ash. Dry eruptions (completely consumed water) lead to the formation of thickly laminated lapilli layers and thick ash layers (scale: dm–m). Wet eruptions (partially consumed water) lead to thin ash layers (scale: cm) [2].

Volcanic ash is composed predominantly of light primary minerals and mainly volcanic glass [14]. This primary mineral plays an important role in the formation of the minerals currently found. In a more advanced stage of alteration of the volcanic glass, halloysite is formed, a quasi-argillaceous primary mineral that is less evolved as a gel with a 1:1 Si/Al ratio. Most of the ashes that have led to soil formation in Colombia are dacitic, rich in plagioclase feldspar, volcanic glass, amphiboles, and pyroxenes, and poor in quartz [1, 13].

Residual soils derived from volcanic ash are developed through processes of physical and chemical alteration of volcanic ash deposits (dissolution, leaching, and precipitation of compounds). These processes of alteration transform the minerals, the shape and size of the particles, and the porosity. Its influence is controlled by climatic conditions and weather. Climatic conditions (such as precipitation, temperature, humidity, and wind) determine the presence of available fluids for chemical reactions, the rate at which these reactions occur, the migration of compounds, and the erosion, among other processes [4, 26]. Time, on the other hand, governs the sequence for the synthesis of secondary minerals and the distribution of particle sizes.

As a soil-forming factor, the effect of the parent material is more important in the initial stages of soil formation than in advanced stages. The weathering of the parent material depends on the presence of acidic or basic minerals. In general, acid minerals (e.g., quartz, feldspar, hornblende, mica, etc.) are more resistant to weathering than basic minerals (e.g., olivine, pyroxene, and calcium plagioclase [13, 26]).

During weathering, an elemental composition rich in Si, Al, and base cations (e.g., Na and Ca) is generally obtained. The Si and the basic cations are dissolved and removed from the surface layers and the Al tends to remain. As the climate becomes more humid, greater dissolution occurs and more aluminum (Al) is removed [13, 14, 30]. The mechanisms of dissolution and leaching are very important for the formation of soils derived from volcanic ash since they lead to highly porous surface areas and the availability of the necessary solutions for the synthesis of secondary minerals.

sub-surface waters. In addition to the detonating agent, the occurrence of a landslide is determined by previous conditions related to deficient plant cover, or the misuse or management of the soil, the poor disposition of agricultural production systems, the indiscriminate felling of forests for planting of pastures and livestock production and their precarious man-

The Humidity of the Volcanic Soils and Their Impact on the Processes of Mass Removal in Colombia

http://dx.doi.org/10.5772/intechopen.80399

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The coffee axis is located in a tropical zone that presents great climatic changes due to altitude changes and has a bimodal climatic regime given by two humid periods and two dry periods. The zone receives an annual precipitation varying between 1500 and 2250 mm. Surface landslides (depth < 1.5 m) are usually activated during periods of heavy rains, April to May and October to November, in which the accumulated rainfall during 1 or 2 days exceeds 70 mm

The superficial soils predominant in the area have deficiencies in the properties of resistance to the cut, since they are recently formed volcanic ash, unconsolidated, and sandy (Ruiz and Cerro Bravo volcanic complex in the Department of Caldas). These materials generally have low plasticity and cohesion due to their loose grain condition with sandy textural appreciations. The cohesion is drastically reduced (or even disappears) when the soil becomes saturated (reduction in the suction capacity), during the occurrence of intense rainfall, for example

The landslides have a flat and irregularly shaped surface defined by the contact between the layer of soils derived from volcanic ash and the layer that underlies it, composed of materials of vulcano-detrital origin, that are moderately or slightly weathered and/or evolved and they often come in slices. Slides of greater depth (depth: 3–10 m) are produced with detonating precipitation less than 50 mm, when the previous accumulated precipitation exceeds 200 mm [13, 25]. Dramatic differences in the permeability of these strata layers or horizons of these soils lead to the formation of a hung phreatic level that reduces effective efforts and increases

Erosive processes are due to natural causes such as contact between geological units, in particular, a geometrically unfavorable contact between the upper volcanic ash (sandy and permeable and without aggregation) and the underlying igneous and metamorphic sedimentary rocks (compact, massive, and impermeable). This contact coincides with the fault surface of many of the landslides that have occurred and favors the accumulation of water that

High torrentiality of permanent and intermittent drainage channels and lines exists in the region. Trees and very heavy shrubs on the crown of steep slopes generate a significant

The deforestation of the protection areas of the micro-basins, and the areas dedicated to pastures in the study area, becomes an accelerating factor due to the lack of protection of

agement and essentially physical causes inherent or intrinsic to these soils.

(the suction is lost and the natural cements dissolve).

instability or susceptibility to erosion.

overload and negative "lever action."

6. Causes and effects of masal removal

infiltrates through permeable surface of volcanic ash.

[13, 25].
