1. Introduction

An important part of the Colombian territory is located mainly around and in the vicinity of the volcanoes and is covered with deep mantles as deposits of volcanic ash soils modeling the landscape of mountains and especially the central mountain range.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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 case of soils derived from volcanic ash [13].

coffee zone, it is estimated that about 350,000 ha of soils grown with coffee correspond to Andisols. These soils extend from the Eje Cafetero (Departments of Antioquia, Caldas, Risaralda, and Quindío) in the center of the country, to the departments of Tolima, Cauca,

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

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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

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

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

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,

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

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,

(partially consumed water) lead to thin ash layers (scale: cm) [2].

volcanic glass, amphiboles, and pyroxenes, and poor in quartz [1, 13].

and Nariño to its south west.

chimney during eruption.

air bubbles [13, 29].

particle sizes.

pyroxene, and calcium plagioclase [13, 26]).

3. Formation of volcanic soils

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

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 dominated by non-crystalline materials.

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

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, imogolite, or ferrihydrite complexes [10, 16].

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

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