*2.2.1 Leachate waters*

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

and environmental problems [26, 28, 40].

mental problems are common in Sivas.

mining area [24].

Hafik (Sivas) and Zara (Sivas), developed in different sizes and gypsum formation, are used for agricultural production [24, 25]. However, these lands are also used as settlement area, forest area, pasture area, natural parks, natural sports and tourism resort area, raw material acquisition (e.g., plaster, cement industry), and

The sudden generation of collapse dolines in areas underlain by gypsum constitutes great danger for both lives and property. Karst features, such as sinkholes, near-surface caves, and collapse structures, which are formed in water-soluble rocks, constitute potentially serious hazards. Groundwater in karst areas is an important resource, which needs to be developed and protected [23]. Water percolates over or through gypsum and dissolves the highly soluble rock; and this causes the formation of sinkholes, caves, natural bridges, disappearing streams, and springs. Thus, natural hazards include damage and/or collapse of houses, buildings (such as dams, bridges, highways, and farmlands) [26, 28]. Such events can cause great economic hardship, disruption of lives, and even loss of life. Conclusively, the study area is located on the gypsums on the Hafik Formation and geologic units with gypsum intercalation (**Figure 1a**). Therefore, karst structures such as fractures, cracks, dissolution caves, and deterioration areas specific to karstic areas are very extensive in these units. Moreover, the geological formation of the study area does not change, the Hafik Formation and karstic structures in this formation continue throughout the study area [3]. The full ranges of gypsum-karst features are present in the region, and there is a number of striking examples of karst hazards

Therefore, collapses in karst terrains constitute very serious geological hazards and can damage engineering structures and cause groundwater contamination [29]. In these areas, very shallow soil could develop, or there is no soil development, and the outcropped karstic area is open to external factors and processes. Therefore, this unit mainly consisting of massive gypsum and gypsum interfingered fractured rocks has a structure that is easily dissolved under the impact of atmospheric processes [6]. Thus, cracks and intense joint systems in various directions have developed in gypsums of the Sivas basin. These are causing the fall of rocks (blocks) in parts where bevels are steep at rocks [13]. These natural hazards and their environ-

**2.2 Natural hazards and environmental problems caused by gypsum areas**

Natural hazards and environmental problems that occur in gypsum areas depending on the karstic characteristics of a gypsum unit and the geochemical, hydrogeological and atmospheric characteristics of its mineralogical composition may lead to different effective problems in human/plant/animal health and their living environments. Every detail is important in urban planning since the selection of gypsum areas as new settlement areas will cause problems in planning studies that increase with urbanization. These problems can be listed as foundation and drainage works in unplanned/out-of-plan construction works, constructions, which cannot be completed on time, safety problems that may arise due to the wrong material selection, and enabling the formation of new pollution areas [5, 30, 31]. While making site selection in these cases, if there is an area, which is zoned or will be zoned for construction, planning will be different according to them in the works to be done. Therefore, the reduction of costs and the correct orientation of investments can be ensured by examining the issues related to site selection and very large-scale events. Another important issue is related to carrying out scientific studies because different preparations will be made with different studies in site selection depending on the geological characteristics of

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Surface waters or groundwaters contacting with gypsum lead to the dissolution of gypsum. Thus, the concentration of ion dissolved in water increases, and the water transmitted threatens the soil fertility and the life of living beings by leaking into the soil in the areas where it transmits. Furthermore, the waters brought by precipitation through washing the surfaced gypsum impair the quality of potable or tap waters and soil quality by mixing into surface waters and leaking into underground waters. In urban areas, corrosion, salinization, mineral transformation, and dissolution cause damage to the ground and structures in places where building foundations and substructure systems exist. As a result of this, safety problems arise in buildings or on the ground (**Figures 2–5b,c**). For example, hazardous leachate waters or gases in buried pipes damaged by corrosion erosion may mix into the soil and then underground waters, which means the formation of a source of pollution [5, 6].
