Sinkholes are most apparent as physical holes or depression on land surfaces. Not all sinkholes, however, are visible or dramatically deep as a home or roadway that looks as if it had been sucked under the ground. Many times, sinkholes do not manifest on land surfaces, making some of them hard to detect. Lands that sit on top of limestone are more vulnerable to sinkhole phenomena. Limestone is porous and can crack, break and dissolve. Increased sinkhole activity can be attributed to urban land development as it changes the earth’s surface and adds weight on the soil beneath it.