NATURAL AND HUMAN-INDUCED SUBSIDENCE DUE TO GYPSUM DISSOLUTION: A CASE STUDY FROM INANDIK, CENTRAL ANATOLIA, TURKEY

Gypsum dissolves relatively quickly and gypsum karst can evolve on a rapid time scale that may be accelerated by human-induced change, often resulting in severe subsidence damage. The area close to İnandık stream in Central Anatolia, Turkey, is affected by subsidence in two ways: formation of collapse sinkholes on agricultural land and progressive subsidence in İnandık village that has damaged buildings. This study focuses on these subsidence phenomena. Seven large sinkholes were formed on a terrace where episodic incision of the fluvial system has led to reduced thickness and mechanical strength of the cavity roof; a process that also increases the hydraulic gradient and enhances cavity development in the terrace area. These processes formed a sinkhole-prone terrace surface. The other subsidence phenomena, which have increased progressively in the last decade, relate to human activity in İnandık village. Water consumption increased after domestic water service systems were installed in houses in 2007, and in 2012 a sewer system was built in the village. Due to cracks and breakage, leaking water from buildings and sewer pipes infiltrated the gypsum substratum, resulting in dissolution of the bedrock and superficial cavity formation, as shown by GPR and borehole data. The process leading to subsidence caused severe damage to buildings. Consequently, it was decided to relocate the village three km south of its current location because of the high level of damage.