A geohazard is a naturally occurring geological condition that may damage property or pose a threat to the safety of people. Many hazards to man-made structures can be related to a particular type of underlying rock, the presence of faults, and other terrestrial processes. Earthquakes are the hazards that receive the most press coverage and are the most well-known, but landslides, overgrown soils, and floods annually cause more damage than earthquakes because they occur more often. Karst hazards also cause less damage than earthquakes or landslides, perhaps half a million to $2 million in economic losses annually, but can still have devastating effects on individuals.                                                                                              

Four geological hazards are associated with karst. Two common geological hazards associated with karst - sinkhole collapses and sewer overflows - cause the most damage to buildings. A third karst hazard is relatively high concentrations of radon gas, which is sometimes found in basements and crawl spaces of homes built on karst. Finally, the head and geology of karst aquifers make groundwater vulnerable to contamination, and this vulnerability can also be considered a type of geological hazard.              

             Karst is a common phenomenon in different regions of Iraq. Karst features are developed due to the dissolution of limestone or gypsum. The main type is sewers, which are developed in different shapes and dimensions. The main problem with karst, which makes it one of the geological hazards, is when underground forms are developed. If not recognized and located, it will certainly cause serious damage to any type of engineering structure built on top of it. A good example of this is rocks Tiling factory in Haqlaniya (Sissakian et al. 2005).                                 

In the southern part of the island, along the left bank of the Euphrates River, large caves are formed in the gypsum layers of the Fatha Formation and carbonate rocks of the Euphrates Formation. A few kilometers north of the city of Hit, a large cave is formed in the plaster layers of the plateau adjacent to the Euphrates Valley. The cave entrance is about 130 meters above sea level. The name of the cave is Umm Jadoo’ (Figure 1). It is an oval cave, connected to the surface by two small entrances. The area of the cave is about 300 square meters. The cave is a dome-shaped dome with a ceiling height of two meters. Two closed joints 3-5 cm wide are observed on the surface. The partitions are in a north-south direction. At the base of the southern wall, there is a small drainage hole. Through this hole, the water that enters the cave is drained in the winter and then rises in the form of a spring at the base of the Euphrates River cliff. The cave is rich in dripping stones (stalactites, stalagmites) created by water falling from the cave ceiling. The stalactites and stalagmites are thick and have a palm trunk shape from which the cave gets its name. The cave is likely of early Pleistocene age and was developed at the same time as the terrace level was uplifted (Hamza, 1997). 

Figure (1) A photograph of the Umm Gthoaa cavity in the Hit area (Abed, 2013)

 In the Haditha area, on both sides of the Euphrates River, sinkholes and caves are well developed in the breccia layer, which represents an unconformity layer between the Anah Formation of Oligocene age and the Euphrates Formation of Miocene age. This layer consists of limestone fragments derived from the Anah Formation, stabilized by carbonate, and its thickness ranges between 0 and 8 meters. Sissakian et al (1986) mapped 43 holes. They linked the formation of sewers through the layer of concretions and the formation of its foundation. The authors dated the karst to the Pliocene or even the end of the Miocene. There are simple and complex caves spread between Al-Baghdadi and Haditha. Dozens of simple caves can be observed along the left escarpment of the Euphrates River within the city of Haditha. Caves are individual rooms for each cave. One of them is the hollow of Shamut Wahat in the city of Barwanah within the Haditha area (Figure 2).   

Figure (2) A picture of Wadha Shamout Cave in the Haditha area(Abed, 2013)

These caves represent a source of danger to civilian and military facilities, as they are considered a weak area that could collapse at any moment.      

Researchers from the Department of Applied Geology at the College of Science, University of Anbar, were interested in this dangerous phenomenon and began geophysical studies, which photograph the structure of the rock layers beneath the surface and the caves, voids, and fractures they contain. Several research papers have been published in international peer-reviewed journals. Through these studies, we believe that it is necessary to activate the role of the geologist in studying the areas over which buildings, investment projects, educational institutions, etc. are planned to be constructed.

References

Abed, A. M., 2013. Comparison between 2D Imaging Survey and Traditional Electrode Arrays in Delineating Subsurface Cavities in Haditha-Hit Area (W-Iraq). Unpublished Ph.D. Thesis University of Baghdad, College of Science, Department of Geology, Baghdad, Iraq

Hamza, N. M. , 1997 . Geomorphology map of Iraq explanatory text , series of geological maps of Iraq (GEOSURV) , sheet No. 3 (first edition)47p.

Sissakian, V., Ibrahim, E., Ibrahim, F., and AL-Ali, N., (1986),

Sinkholes of Haditha area, Journal of Water Recourses. Vol. 5, No. 1, pp. 1-14.                                                                                                         

Sissakian, V., Ibrahim, E., Ibrahim, F., and AL-Ali, N., (2005), Explanatory of Geological Hazard Map of Iraq 1st Edition,(Scale 1:1000000) D. Geol. Surv. (GEOSURV) Min. Invest, Baghdad.