**2.1 Regional features of gypsum karst morphology in the study area and its surroundings: examples from Sivas (Turkey)**

Karst is a morphological term and it is important to analyze karst morphology in terms of natural hazards, because the gypsum unit is a type of karst and can be solved if it contacts water. Gypsum can transform to anhydride as a result of geological and atmospheric processes in near-surface karsts, or vice versa. In other words, with the introduction of water into the anhydrite structure through these processes, an anhydrite unit can transform into a gypsum unit. These transformations also occur in the Hafik Formation, in Sivas (**Figure 1a**). The Hafik Formation is an Oligo-Miocene aged unit presenting wide spread in the Sivas evaporite basin

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**Figure 1.**

*August 12, 2018)).*

*Identification and Assessment of Hazard of Development in Gypsum Karst Regions: Examples…*

and mostly consisting of massive gypsums [17–19, 20]. Upon examining **Figure 1a**, it is observed that the Sivas tertiary basin shows a northeast-southwest extension [21]. On the other hand, this basin starts from Gemerek in the southwest of Sivas and extends along the Sivas center, Hafik, Zara, and Imranlı. In **Figure 1a, b**, the study area is located in the Sivas basin and occurs from the Hafik Formation. This basin is one of the largest Central Anatolia basins, which was formed in the collision zone and is located in the most important gypsum karst area of Turkey. However, the areas of gypsum outcrops occur in Central and Eastern Anatolia, and gypsum formations are found mostly in Ankara, Çankırı, Çorum, Kırşehir, Kayseri, and Sivas regions (**Figure 1a**). In addition, dissolution dolines are found in the youthful karst areas between Sivas and Zara; some of the most important collapse dolines are found in the mature karst area between Hafik and Zara [15, 20, 22, 23, 26, 27]. The dolines on gypsum have solution and collapse characteristics, and it was observed that population rates were low in these areas [24]. According to the study by Hadimli and Bulut (2000) because of the dense surface karst in these gypsum areas is observed; these areas do not offer suitable environments for human life. Therefore, in Turkey, in areas where macrokarst structures (poly, uvala, doline) are observed, even despite a continuous population, it has been observed that the areas with microkarst structures (lapya) observed are used periodically [24]. Furthermore, in karstic fields, karstic structures (such as doline bases) are used for agricultural area needs (due to need), although they do not show high agricultural potential. In particular, large doline-based areas around

*(a) Study area (rearranged from [23, 25], and (b) the locations of figures (arranged from Google Earth, 2018,* 

*DOI: http://dx.doi.org/10.5772/intechopen.83684*

*Identification and Assessment of Hazard of Development in Gypsum Karst Regions: Examples… DOI: http://dx.doi.org/10.5772/intechopen.83684*

and mostly consisting of massive gypsums [17–19, 20]. Upon examining **Figure 1a**, it is observed that the Sivas tertiary basin shows a northeast-southwest extension [21]. On the other hand, this basin starts from Gemerek in the southwest of Sivas and extends along the Sivas center, Hafik, Zara, and Imranlı. In **Figure 1a, b**, the study area is located in the Sivas basin and occurs from the Hafik Formation. This basin is one of the largest Central Anatolia basins, which was formed in the collision zone and is located in the most important gypsum karst area of Turkey. However, the areas of gypsum outcrops occur in Central and Eastern Anatolia, and gypsum formations are found mostly in Ankara, Çankırı, Çorum, Kırşehir, Kayseri, and Sivas regions (**Figure 1a**). In addition, dissolution dolines are found in the youthful karst areas between Sivas and Zara; some of the most important collapse dolines are found in the mature karst area between Hafik and Zara [15, 20, 22, 23, 26, 27]. The dolines on gypsum have solution and collapse characteristics, and it was observed that population rates were low in these areas [24]. According to the study by Hadimli and Bulut (2000) because of the dense surface karst in these gypsum areas is observed; these areas do not offer suitable environments for human life. Therefore, in Turkey, in areas where macrokarst structures (poly, uvala, doline) are observed, even despite a continuous population, it has been observed that the areas with microkarst structures (lapya) observed are used periodically [24]. Furthermore, in karstic fields, karstic structures (such as doline bases) are used for agricultural area needs (due to need), although they do not show high agricultural potential. In particular, large doline-based areas around

#### **Figure 1.**

*(a) Study area (rearranged from [23, 25], and (b) the locations of figures (arranged from Google Earth, 2018, August 12, 2018)).*

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

erosion, and corrosion that directly occur in nature [4–6]. On the other hand, the rapid construction that comes with urbanization requires new settlement areas. Therefore, there are also constructions on gypsum units [3]. The reason why it is considered that gypsum areas will cause significant environmental problems in the future is natural hazards and environmental problems that will arise in the event when gypsum is mainly surfaced or very close to the surface especially in new places opened for settlement, as required by karst geology. This also suggests that there will be risks for the life of humans and living beings and that these risks will increase, especially in these kinds of areas in the future, along with the opening of an area consisting of evaporite units for construction. Geological structures specific to gypsum karst lead to the formation of caves/areas causing the danger of collapse under the ground of the building and also collapses along with the fact that dissolution caves and dissolution channels are merged over time and create large galleries. As a result of these events, concrete materials, pipes, and cable systems of buildings and substructure systems are damaged. This also means that substances that may leak liquid and gas are mixed into the soil, water, and even into the atmosphere or that there are energy losses. Thus, there will also be economic losses. For this reason, it was considered necessary to draw attention to the problems originating from gypsum, while they are examined with environmental problems and soil and water pollutions on the issues for environmental

monitoring purposes, and these problems should not be ignored [5].

all these issues were examined in this study.

**surroundings: examples from Sivas (Turkey)**

When natural-origin environmental problems described above are considered,

it is essential to reveal the geological, engineering, hydrogeological, and environmental impact models of the environment in the site selection for settlement purposes and in the site selection of other human-made constructional areas [7, 8]. Therefore, various maps on different topics and scales that define the gypsum area from all aspects and geological/geophysical sections of various sizes are prepared by the relevant experts and scientists [3, 9–16]. Thus, gypsum areas can be defined in detail by using mineralogical-petrographic and structural properties of geologically lithological units, their degree of weathering, geophysical-hydrological-physicomechanical properties, and meteorological status, and other surface and underground research methods. With these studies, risky areas at the horizontal-vertical or shallow-deep dimensions can be determined by preparing reports and maps to take precaution for natural hazards and environmental impacts. According to the results found, new and future sustainable planning and preparations can be made for these issues. Then, human/plant/animal health and their living environments can be maintained in a sustainable manner. Therefore, the problems of erosion and pollution may be reduced more effectively with the measures to be taken. In conclusion,

**2. Natural hazards environmental problems in gypsum karst regions**

**2.1 Regional features of gypsum karst morphology in the study area and its** 

Karst is a morphological term and it is important to analyze karst morphology in terms of natural hazards, because the gypsum unit is a type of karst and can be solved if it contacts water. Gypsum can transform to anhydride as a result of geological and atmospheric processes in near-surface karsts, or vice versa. In other words, with the introduction of water into the anhydrite structure through these processes, an anhydrite unit can transform into a gypsum unit. These transformations also occur in the Hafik Formation, in Sivas (**Figure 1a**). The Hafik Formation is an Oligo-Miocene aged unit presenting wide spread in the Sivas evaporite basin

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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 mining area [24].

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 and environmental problems [26, 28, 40].

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 environmental problems are common in Sivas.

#### **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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**Figure 2.**

*Identification and Assessment of Hazard of Development in Gypsum Karst Regions: Examples…*

gypsum, the parcel size of the building to be constructed, and building types. First of all, since the size of the area where the structure will be placed is different or the load to be imposed on the ground will be different depending on the size/number of floors of the buildings to be constructed, methods are selected accordingly and survey studies are initiated. If works are completed with correct planning when it comes to site selection, the gains brought along by them will be too much. However, in gypsum areas, the following natural hazards and environmental

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

If site selection is made or construction areas are selected for settlement purposes without getting engineering service, the problems of ground subsidence in gypsum areas, and rockfall in collapse areas and slope areas can be observed (**Figures 2a, b, 3b** and **5b, c**) [3]. They have a negative impact on human life and lead to material and moral losses. For example, subsidence and cracks occur in foundation ground due to dissolution in the gypsum unit (with the contact of leachate water), and this may cause damage to buildings. However, the rockfall constitutes a safety problem (e.g., in road, highway, and railway routes) [13] (**Figure 3b**). Consequently, various structural damages (cracks, dissolution, collapse, sinkholes,

*Gypsum-based ground deformations in the southeast Sivas city (Turkey) (photos: Sevda Özel, 2018). (a) As the* 

*) is filled with fill material (as a temporary measure) and* 

*).*

*DOI: http://dx.doi.org/10.5772/intechopen.83684*

problems are generally observed.

*2.2.1 Leachate waters*

pollution [5, 6].

*2.2.2 Subsidence/collapse/rock (block) fall*

*setting-collapse increases, the cavity (~1.0 × 2.5 m2*

*(b) a newly formed dissolution area under the pavement (~0.3 × 0.5 m<sup>2</sup>*

## *Identification and Assessment of Hazard of Development in Gypsum Karst Regions: Examples… DOI: http://dx.doi.org/10.5772/intechopen.83684*

gypsum, the parcel size of the building to be constructed, and building types. First of all, since the size of the area where the structure will be placed is different or the load to be imposed on the ground will be different depending on the size/number of floors of the buildings to be constructed, methods are selected accordingly and survey studies are initiated. If works are completed with correct planning when it comes to site selection, the gains brought along by them will be too much. However, in gypsum areas, the following natural hazards and environmental problems are generally observed.
