*2.2.3.3 Ground damage*

*Natural Hazards - Risk, Exposure, Response, and Resilience*

is very low (about 0–50°C) [33–35]. For example, the solubility of gypsum in pure water at 20°C is 2.531 g/L [34, 36]. Gypsum is about 10–30 times more soluble than limestone, and it commonly has a lower mechanical strength [3, 15, 23, 33, 34]. However, between 0 and 30°C, the range encompassing most natural waters, the solubility of gypsum increases by 20%, reaching a maximum (about 2.66 g/L) at 43°C [34]. Therefore, sudden collapses in gypsum areas are a great danger for both life and property [3]. Therefore, the quality of water in the basins where the rock types formed by these minerals dominate is easily impaired, and surface and underground waters in which evaporite group minerals are dissolved are naturally polluted [4, 6, 38]. These polluted waters also pollute fertile soils if they leak into

*(a) Gypsum samples collected from the northeast and south-southeast of Sivas (Turkey) (photo: Sevda Özel, 2005, 2007, and 2010). (b) Surfaced gypsum in the northeast of Sivas (Turkey) (photos: Sevda Özel, 2015) (c) Gypsum karstic deformation structures (cave, fracture, crack, collapse) from Hafik Formation in Sivas* 

Evaporite units tend to expand and swell depending on their origin, and these unites may also involve areas where underground waters are collected, and the sources where underground waters rise to the surface [3]. Upon examining **Figure 1** it is observed that, a shallow or deeper ground cover may develop or soil development may not occur at all in these areas. If the karstic area is surfaced, these areas are open to external factors (e.g. precipitation, wind, temperature) and processes (e.g. dissolution, erosion, deterioration). In this case, cracks in various directions, dense joint systems, melting areas, and various karstic structures begin to occur in gypsum areas. Moreover, larger fractures or new faults may occur as a result of seismic activity and collapse events. Furthermore, rock (block) fall events may also occur in rocks where slopes are perpendicular [12]. According to all these geological characteristics, significant ground problems are encountered in the existing buildings in the area or during and after new construction with the use or selection of gypsum areas as settlement areas (**Figure 1a,b**). These areas should be included in the class of areas with risky areas, especially if such areas continue to be selected as new settlement

There is always a risk of pollution in soil and underground/surface waters in gypsum areas. This pollution problem takes place as a result of salinization. Gypsum units may lead to salinization by ion decomposition resulting from the contact with water. Waters with the intense ion content formed during salinization threaten underground waters, surface waters, soil quality, and the life of plants, animals, and humans in the places of their passage, as leachate waters. In other words, leachates are the waters containing inorganic pollutants, and they also interact with other materials. This also reduces the existing underground/ surface water quality and decreases the soil fertility, plant diversity, and the

**118**

areas.

*2.2.3.2 Pollution*

the soil.

**Figure 5.**

*(Turkey) (photo: Sevda Özel, 2017).*

Since gypsum units geologically have swelling-expansion characteristics due to their mineralogical structure, they cause swelling in the ground. Thus, ground and structure deformations caused by the swelling of gypsum grounds, and material damages occur on superstructure grounds and in substructure systems (**Figures 2a,b** and **5b**). In these situations that endanger the safety of buildings, the life of human and living beings will also be under risk due to the safety problem (**Figure 2**). On the other hand, gypsum units may also be covered with alluvial units in some places. In this case, similar ground swelling problems may occur if units with swelling properties like clay are found in the alluvial filling material. Therefore, it is necessary to control leachate and underground waters in the construction areas in both cases.
