The Making of a Sinkhole at A. L. Anderson Park EarthCache

A sinkhole is a natural depression in the Earth’s surface caused by some form of collapse of the surface layer. Some are caused by chemical dissolution-karst process (the chemical dissolution of carbonate rocks) or suffosion process. Most sinkholes are formed by the suffosion process. When loose soil, loess or other material lies on top of a limestone substratum containing fissures and joints, rain and surface water gradually wash this material through these fissures into caves beneath. Over time this creates a depression on the landscape of varying depth. Sinkholes can develop gradually or can be brought on by sudden catastrophic collapse of subsurface cavaties. These are often triggered by the decline in the level of groundwater aquifers or by increased groundwater flow, both of which are affected by pumping.

The kind of sinkhole we see in Florida is called a cover-collapse sinkhole. It usually occurs in clay, because clay holds soil together like glue. As the soil leaches into a cave below the rock, it creates a void in the soil that moves upward. You can’t see it on the surface. Then suddenly the bridge over the top of the void can’t hold anymore and it collapses.

Sinkholes vary in size in both diameter and depth, as small as a pothole or large enough to swallow an entire house or building. Sinkholes are found worldwide. In Guatemala two of the world’s largest and deepest sinkholes opened within three years of each other. In Florida, sinkholes are a natural landform. Collapse sinkholes are the ones that make the news in Florida. On a map of Central Florida you can see numerous circular lakes. These are ancient sinkholes that have collapsed and filled with surface water. One of the largest sinkholes in Florida opened in 1981. It grew to 350 feet wide and 75 feet deep. It swallowed an entire city block including a home and Porsches from a nearby car dealership. The sinkhole eventually filled with rainwater and is now known as Lake Rose in the Winter Park area.

Discolored water, wilting vegetation, and structural cracks in walls or floors are all warning signs that a sinkhole may be forming.

To log a find for this EarthCache, you will need to answer the following questions. The answers to most of them can be found at GZ. Email the answers to furshore.

1. What surrounds the smaller sinkhole on the ground?

2. Estimate the width of the smaller sinkhole and the elevation at GZ.

3. What is the name of each sinkhole?

4. What diving legend mapped the caves in these sinkholes?

5. What is the water like at the depth of 205’?

6. How deep did the divers go plotting the depth of these caverns?

7. Photos at GZ are encouraged but not required. http://en.wikipedia.org/

https://www.swfwmd.state.fl.us/hydrology/sinkholes/ http://www.dep.state.fl.us/geology/geologictopics/sinkhole.htm http://www.sjrwmd.com/watersupply/howsinkholesform.html http://www.baynews9.com/content/news/baynews9/news/article.html/content/news/articles/cfn/2013/8/12/sinkhole_quiz_test_y.html