6. Causes and effects of masal removal

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

In a general way, it can be said that the structure, the state of efforts, and the flow of water in any type of soil change when it is exposed to the intense cycles of drying and wetting, typical of the climatic conditions of the tropics. These changes affect the physical properties and mechanical behavior of the soil, which can lead to geotechnical problems (e.g., erosion, slope

Soils derived from volcanic ash in Colombia are located in regions where a bimodal rainfall regime occurs during April to May and October to November and very dry periods occur between these stages. During periods of low precipitation and high temperature, high water

The evaporation produces contraction and increase of the suction forces in fine soils (silts and clays), for the states of complete saturation or partial saturation, respectively. The desiccation evolves occasionally toward the formation of cracks. These cracks can be understood as a consequence of the stresses produced by desiccation. Cracks in the surface of the soil make up areas susceptible to problems of erosion and instability, often observed on slopes with little plant cover, continuously exposed to drying processes. On the other hand, during humid periods, characterized by permanent and intense rains, the infiltrated water reduces the capillary effects and causes volumetric changes that can lead to swelling or collapse of the soil

In Colombia, the natural slopes in soils of volcanic origin reach heights between 10 and 20 m with slopes greater than 60 [8, 13, 19]. Despite this, the slopes are susceptible to instability, erosion, and cracking depending on the climatic conditions and vegetation cover. In the Colombian Coffee Region, landslides detonated by intense rainfall or locally intense earthquakes are often reported. These landslides can have a high potential for destruction in

The soils of the region are characterized by steep slopes of 30 (67%) to 35 (78%), extensive slope lengths; the shape of the concave slope is favorable to the accumulation of surface and

densely populated areas in mountainous reliefs of great length and high slope.

evaporation occurs between the pores of the soil, causing its drying.

of secondary minerals.

92 Soil Moisture

instability, etc.).

structure [13].

5. Erodability

4. Soil-water relationship

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 infiltrates through permeable surface of volcanic ash.

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 overload and negative "lever action."

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 vegetation cover that counteracts the runoff associated with degadation phenomena gives origin to loss of soils and biodiversity and the alteration of the hydrological cycles of the basins or rivers of the region. This determines that areas of productive vocation, which are close to the micro-basins, that have lost their protective capacity of the ecosystems of strategic interest, are also affected due to the factors that undermine the stability of the soil, thus diminishing the potential to offer environmental services, of which the populated communities of the region are beneficiaries, limiting the production processes, and, therefore, their social and economic life.

development of low-density bulk floors, high porosity, high water retention (high saturation, field capacity, and tension of 1.5 MPa), and high limits (upper plastic limit or liquid limit— LPS and liquid plastic lower limit—LPI) of plasticity. The retention of available water (field capacity humidity at 1.5 MPa) is also usually high and limit liquid or water flow in the form

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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Although the gravimetric water retentions are usually very high (up to 2–3 times the mass of dry soil when saturated), they are not so much on a volumetric basis due to the low apparent densities, although they are still higher than in other soils. The high retention of moisture even at high voltages and the poor connection between pores means that in humid climates, even with good drainage, conditions of poor aeration at shallow depths that restrict root development remain in the Andisols. In any case, to achieve such high moisture retentions requires a degree of weathering of volcanic ash, with formation of halloysite and accumulation of organic matter, since with very recently formed ashes, generally with sandy loam to gravel, the volumetric capacity Water retention is usually

With drying, up to 30–50% of the water-retention capacity and a large part of its plasticity are irreversibly lost. It has been pointed out that the change of the plasticity indexes with the drying of the soil is the main property that distinguishes the Andisols from other soils where

The drastic and irreversible changes of properties of the Andisols derived from changes in

The greater the inclination of the soils, the instability increases soils and, with it, the greater the susceptibility to mass movements, the more rainwater is infiltrated and less lost by runoff (accumulation). Mass movements depend on the interaction of several factors, especially slope; lithology; soil type; intensity, duration, and continuity of rainfall; surface and internal drainage

By virtue of the above, it is technically demonstrated that in Andisols, where a limiting layer has been formed for internal drainage at shallow depths and a high rate of surface infiltration is maintained, increases in moisture content negatively affect the stability of the soil material

1. Increase in pore water interstitial pressure, which reduces the flow resistance in saturated

2. Development of a hydraulic gradient or pressure in the direction of flow below the surface

3. Lubrication of the limiting layer or sliding plane, which facilitates the movement of the

5. Decrease in the cohesion between particles and aggregates and once the soil is saturated,

of water is near, in soils not altered to the point of saturation.

humidity have much to do with the erosion processes in these soils.

conditions; vegetation cover; and management.

soil over the restricted drainage layer.

that can gradually lead to sub-surface erosion.

development of positive pressures in the pores [15].

4. Increase in the mass of moist soil, sometimes 2–3 times its dry mass.

very low [15].

crystalline clays predominate.

facing landslides by:

material above it.

Other determining factors of the drastic hydrological imbalances of the micro-basins of the region, which contribute significantly to the increase of flows, both surface water and infiltrated, which are the cause of landslides and mass erosion phenomena, are as follows:


The deforestation of the areas of interest for the protection of the micro-basins and the presence and increase of the areas in natural pastures in the study area are some of the causes of the decrease in water flows, which are associated with degradation of soils and aquatic and terrestrial flora and fauna and the alteration of the hydrological cycles of the basins, when climatic variables reach the most critical levels. The productive areas to intervene surrounding the micro-basins as ecosystems of strategic interest are also affected by climate change, which affects soils, reducing the supply of this environmental service to the beneficiary communities.
