Sinkholes are not unique to the state of Florida, and as any resident knows Florida has its fair share. Florida’s unique geology is perfect for sinkhole development, and every year this natural hazard is responsible for costly damage to buildings, homes, and roads across the state. Most residents have a negative view of sinkholes for good reason, but sinkholes are a feature of Florida’s natural environment that is vital to the health of the state’s drinking water supply. This article provides an overview of what sinkholes are, how they form, and why they are so important.
What is a Sinkhole? Sinkholes are depressions that occur on the surface of the earth caused by erosion of underlying soil and bedrock. Sinkhole depressions vary greatly in size and can measure from just a few feet in diameter to hundreds of feet in diameter. Regardless of size, sinkholes are a fascinating natural phenomenon that provides a unique opportunity to explore Florida’s geology.
Sinkhole Development Geologically, the land you see in Florida is situated on top of a bedrock foundation of limestone. Limestone is any sedimentary rock that is composed of at least 50 percent calcium carbonate, the main mineral found in sea shells and egg shells. Limestone forms over very long periods of time from the accumulation of sea shells, coral, and algae in regions with warm shallow seas.
One of the characteristics of limestone is that it dissolves slowly when it comes in contact with mild acids. The dissolving of limestone, called dissolution, occurs naturally with an acid called carbonic acid. Carbonic acid is created when rainwater absorbs carbon dioxide from the atmosphere and soil.
In addition, the burning of fossil fuels from cars and industrial production can produce mild acids that can further contribute to the dissolution of limestone bedrock.
The process of dissolution eventually creates a landscape that geologists call karst topography.
Karst topography is created as groundwater rich with carbon doxide moves freely through cracks and crevices in the bedrock, slowly dissolving the surrounding limestone. Over a period of hundreds of thousands of years, these cracks and crevices grow large enough to create caves, tunnels, cavities, and most notably sinkholes.
Types of Sinkholes Sinkholes are the most visible feature of a karst landscape, and they can develop several different ways. Solution sinkholes develop when the underlying bedrock is very close to the earth’s surface. The bedrock gradually dissolves creating a bowl-shaped depression. Solution sinkholes are usually shallow, and they generally do not cause severe damage to property like cover collapse sinkholes.
Cover collapse sinkholes occur when the ceiling of an underground cave or cavity gives way. When the ceiling of an underground cave collapses, the overburden composed of soil, gravel, and clay covering the cave falls into the void leaving a depression on the earth’s surface. Damage from cover collapse sinkholes can be rapid and catastrophic.
Cover subsidence sinkholes can also be very damaging, but develop more gradually. Cover subsidence sinkholes are very similar to solution sinkholes, but they develop much deeper under the surface of the earth. As subsidence sinkholes develop, the overburden gradually filters into the developing cavity causing a surface depression.
When and Where Do Sinkholes Occur in Florida? Sinkholes can occur any time of the year, but certain weather patterns such as drought can increase sinkhole development. During a normal year Florida’s limestone bedrock contains large amounts of water that helps to support the weight of the overburden above the bedrock. During long periods of drought, the water contained in the bedrock decreases and the support goes away allowing sinkholes to develop with greater frequency.
The opposite weather pattern can also contribute to sinkhole development. During periods of above average rainfall, the overburden becomes so saturated with rainwater that the ceiling of a cave or cavity may not be able to support the excess weight causing a collapse.
Location is another important factor for sinkhole development in Florida. Sinkholes can develop anywhere in the state, but some regions are particularly susceptible to sinkhole formation. The most notable region for sinkhole development is central peninsular Florida, but some areas of the northern panhandle also see a lot of sinkhole activity. While sinkholes are a nuisance, one benefit of Florida’s karst topography and sinkhole development is that residents and visitors have lots of opportunities to swim in crystal clear natural springs that result from the natural dissolution of the limestone bedrock.
Sinkholes: an Important feature of Florida’s Natural Environment
Living with sinkholes is just part of living in the state of Florida. Every year this natural hazard causes millions of dollars worth of damage to homes, building, and roads, but sinkholes are also an important feature of Florida’s environment and for Florida’s residents and visitors.
The way that Florida’s aquifer gets replenished with water is from rainfall that seeps into the underground bedrock primarily through sinkholes. Sinkholes are the gateway between rainwater and the aquifer, which means that anything that goes into sinkholes like chemicals used in lawn maintenance may potentially enter the state’s drinking water supply. This is an important consideration, especially, for people that have a sinkhole on their property.
Sinkholes are a fascinating feature of Florida’s natural environment that can be a devastating natural hazard. But they are also vital for maintaining Florida’s drinking water supply that millions of Floridians rely on every day. If you are interested in learning more about sinkholes and Florida’s karst environment, there are several great state parks you can visit to get up close and personal with Florida’s unique geology.
The following state parks provide recreational and educational opportunities to learn more about sinkholes, aquifers, and karst environments.
Manatee Springs State Park
http://www.floridastateparks.org/manateesprings/
Devils Millhopper Geological State Park
http://www.floridastateparks.org/devilsmillhopper/
Rainbow Springs State Park
http://www.floridastateparks.org/rainbowsprings/default.cfm
Peacock Springs State Park
http://www.floridastateparks.org/peacocksprings/default.cfm
Sources used in this article
Florida Department of Environmental Protection
http://www.dep.state.fl.us/geology/geologictopics/sinkhole.htm
University of Florida Extension
http://plants.ifas.ufl.edu/guide/sinkholes.html
