Sinkholes are mostly found in limestone regions. They are huge depressions in the earth that are shaped like a funnel. Sinkholes are caused by many factors like a decline in the water level or the disturbance of the soil.
Concentration of water and storing water in huge quantity as in case of dams and basins can also cause a sinkhole. Human activity like vibration caused by traffic or blasting during mining could also be the reason.