This Earthcache is about sinkholes. We have all read about houses falling into sinkholes and mineshafts in this area.
Icefrog and I stumbled upon this sinkhole while caching one day.
How are sinkholes formed?
Sinkholes are bowl-shaped, funnel-shaped, or vertical-sided depressions in the land surface that form over underground voids. These depressions, which can range in size from a few feet to several hundred feet in diameter and depth, usually result from the natural collapse of the roofs of caves eroded in soluble bedrock, but they can also result from man-made activity such as mining, groundwater pumping, or the failure of sewer and storm water drains. Subsidence of the ground is usually gradual, but on occasions it can be sudden and dramatic.
In regions of carbonate bedrock such as limestone or dolomite, rainwater percolating though organic soil becomes slightly acidic and as it comes into contact with the bedrock, it slowly dissolves the carbonate minerals. Over time, this persistent process can create extensive systems of underground fissures and caves. The surface of such a region is often pocked with sinkholes and closed depressions. This type of topography is called karst terrain. In well-developed karst terrain, chains of sinkholes form what are known as solution valleys and streams frequently disappear underground.
A poor understanding of Karst terrain has led to land-use practices that pose significant economic and environmental impacts to households and communities. Sinkhole collapse, either slow or dramatic, regularly causes considerable damage to buildings, highways, rails, bridges, pipelines, storm drains, and sewers. In addition, sinkholes provide a pathway for surface water to directly enter groundwater aquifers, so the potential for pollution is high because of the minimal filtering of surface water.
Sinkhole formation is closely related to local hydrologic conditions, and human-induced changes to the local hydrology commonly accelerate the process. Diverting surface water, pumping groundwater, and constructing reservoirs all contribute to sinkhole collapse. An extreme example occurred in Florida on February 25, 1998, when, during the flushing of a newly drilled irrigation well, hundreds of sinkholes up to a hundred and fifty feet across formed over a twenty-acre area within a few hours. Runaway urbanization and development dramatically increases water usage, alters drainage pathways, and overloads the ground surface. According to the Federal Emergency Management Agency, the number of human-induced sinkholes has doubled since 1930, while insurance claims for related damages has increased 1,200 % from 1987 to 1991, costing nearly $100 million. Subsidence is not covered by standard homeowners insurance.
Signs of sinkhole formation:
Although a sinkhole can form without warning, specific signs can signal potential development:
- Slumping or falling fence posts
- Wilting vegetation
- Discolored well water
- Structural cracks in walls, floors, or foundations.
To claim this cache, email the following questions:
A. Using your GPS, in what directions is the fireroad running next to the sinkhole
B. What type tree is growing out of the sinkhole
C. Distance sink hole is from edge of trail (use your GPS)
And, in summer, wear tink repellent. A LOT of ticks in this area.