Feb 26, 2012 Photo taken on Feb. 26, 2012 shows a big hole formed during the land sink in Yuejiaqiao Town, Yiyang City of central China's Hunan Province. (Xinhua/Long Hongtao) Since Jan 1, 2012, karst cave-ins have occurred in many places of Yuejiaqiao Town, Yiyang City of central China's Hunan Province. Yiyang city has seen 693 karst cave-ins, including 537 in farmland and 150 in rivers. The geo…