When it rains, rainwater, which is slightly acidic, soaks into the ground and becomes more acidic as it moves through the soil. When this water comes in contact with the bedrock, it reacts with the limestone, dissolving it. As the water flows through the ground, it carries the dissolved limestone away with it, enlarging the natural holes and cracks that were already present in the rock. Over time, large cavities may form in the bedrock. Sinkholes often form when the overlying sediments become too heavy for the ceiling of an underground cavity to support. The ceiling gives way and the overlying sediments collapse into the cavity.