Limesink Ponds

Limesink ponds, sinkholes and small depressions are common geological formations all over the world as a result of the dissolving of underlying limestone. Many exist throughout the United States, but our personal research will focus specifically on North Carolina and Carolina Beach State Park, where there are many limestone rock formations.  Each limesink pond has its own ecological environment with different plants and animals. As residents of Southeastern North Carolina, students should be aware of the geological history of North Carolina and the potential aspects that human development can have on the area’s geological and ecological environment.  


Limesink pond vegetation example: Cypress Pond Photo by Rita Russ, June 2011GEOLOGICAL CHARACTERISTICS

Limesink ponds are depression ponds formed by sinkholes in areas where limestone, or a similar rock containing the shells of sea animals, have dissolved over a very long period of time and have caused the surface soil to form a depression.  They occur throughout the world and can be shallow or deep, small or large, but all are a result of the dissolving of the underlying limestone.

 Sinkholes are the result of water movement through the limestone rock formations. Normal rainwater is weakly acidic. As the water moves through the natural cracks in these formations, the limestone, or shell fragments made of calcium carbonate in the rock formations, is slowly dissolved leaving open spaces in the rock structure. Over time, more of the limestone is dissolved and more water flows along the enlarged pathways in the rock. When enough limestone has dissolved to weaken the rock, the sand and loose surface soil above it begin to sink slowly, forming into a cone shaped depression commonly called a sinkhole. The size of the sinkhole is dependent on severalLimesink pond example: Grass Pond Photo by Rita Russ, June 2011 factors including groundwater level, surface water infiltration rate, overburden depth, and water chemistry (acidity). Once formed, a sinkhole can grow in size unpredictably, based on conditions specific to that area and, in some cases, can collapse into huge gaping holes rather than small depressions.  Hydrologic conditions, including lack of rainfall, lowered water levels, or, conversely, excessive rainfall in a short period of time, can all contribute to sinkhole development. People can cause sinkholes, too. Human activities that change groundwater levels, flow directions and flow rates can increase the speed at which sinkholes form. Ground water extraction and road construction have resulted in the rapid formation of sinkholes in many areas, including in the lower Cape Fear area. 


CAPE FEAR REGION LOCATIONS

According to the Carolina Beach State Park website, three limesink ponds can be found in the park. Each is vegetated by a unique plant community. Cypress Pond is the most unusual limesink pond in the park and is dominated by a dwarf cypress swamp forest. Lily Pond is occupied by water lilies, which cover its waters in late spring and early summer. Grass Pond, which dries out almost every year, is filled with a variety of aquatic sedges. Carnivorous plants, such as the Sundew, thrive in the boggy soil around its edge and in the park's acidic, mineral-poor soil.    


LIMESINK OR SINKHOLE?

A Limesink is only a word variation of sinkhole.  Limesinks are not as deep as what we have come to expect sinkholes to be due to movies, newspapers, and television accounts. No cars or houses disappear into the depths of them and they don't form in a matter of minutes or hours.

Sinkholes are depressions or holes in the land surface that occur throughout the world. They can be shallow or deep, small or large, but all are a result of the dissolving of the underlying limestone.

Hydrologic conditions, including lack of rainfall, lowered water levels, or, conversely, excessive rainfall in a short period of time, can all contribute to sinkhole development.

Comments