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Clicking on the Video Tutorial link below will open a video hosted on youtube. As the cache owner, I represent that this file is safe to download, as I have created it myself. The file has not been checked by Groundspeak or by a Reviewer for possible malicious content, and therefore, you are downloading this file at your own risk.
FLORIDA SINKHOLES- The posted coordinates will take you to the very spot where a sinkhole occurred on December 8, 2002 according to FCIT. This reported sinkhole is based on data gathered by the Florida geological Survey (FGS) and the Florida Department of Evironmental Protection (FDEP). Broward Maps! The hole has since been filled but will be a good place to learn about Florida sinkholes.
Sinkholes are most commonly thought of as physical depressions or holes in the surface of the land. Not all sinkholes, however, are as visible or dramatic as a home or roadway falling into the ground. Many times, sinkhole activity never manifests itself on the surface of the land, making it harder to detect. The entire state of Florida sits on top of thousands of feet of limestone. Limestone is a porous rock, capable of cracking, breaking and dissolving. The most significant factor in the development of sinkholes is the dissolution of the limestone underlying Florida by acidic waters. As water moves through the soil, it becomes more acidic as it reacts with living and decaying plant matter. This water reaches the underlying limestone, it slowly begins to dissolve the rock and creates voids and cavities. The soil resting on top of the limestone then collapses or subsides into the caverns and voids and causes sinkholes. A rapid increase in sinkhole activity can be attributed to the development of land, which changes the earth’s surface as well as the weight or load on the soil beneath it. The creation of retention ponds, new buildings and homes, roadways, and changes in ground water levels can all trigger sinkhole activity.
SINKHOLES are considered a type of land subsidence, because they involve a vertical downward movement of the land surface. There are three types of sinkholes, each of which forms in a different way. Collapse sinkholes are the most hazardous to humans because of how suddenly they can form. There are 3 types of sinkholes.
TYPE 1: SOLUTION SINKHOLE
Solution sinkholes form where soluble bedrock (i.e., limestone, dolomite, marble, and rock salt) is exposed at the land surface and thus subjected to weathering by dissolution. Surface water collects in natural depressions and slowly dissolves a sinkhole.
TYPE 2: SUBSIDENCE SINKHOLES
Subsidence sinkholes are similar to solution sinkholes, except that the soluble bedrock is covered by a thin layer of soil and/or sediment. Surface water infiltration dissolves cavities where the bedrock is most intensely fractured, and the overlying sediment gradually moves downward into the expanding cavity.
The formation of a subsidence sinkhole is illustrated below. Note that the geologic conditions include soluble bedrock (such as limestone) covered by relatively thin deposits of sediments. This type of sinkhole tends to form naturally and is not greatly affected by human activities.
(1) Initially the bedrock contains fractures and small cavities that have formed by dissolution, but no land subsidence has occurred.
(2) Small cavities and cracks grow larger through time, and sediments from above are slowly carried down by infiltrating rainwater to fill the voids forming in the bedrock.
TYPE 3: COLLAPSE SINKHOLE
Collapse sinkholes form when surface materials suddenly sink into a subsurface cavity or cave. The cavities form slowly over time, as groundwater moves along fractures in soluble bedrock and enlarges them through dissolution, and the actual collapse can occur in two different ways:
a. When a cavity gets sufficiently large, the "roof" becomes too thin to support the weight of any overlying rock or sediment, so it collapses into the cavity.
b. Caves are sometimes able to support the weight of overlying sediments because they are filled groundwater. However, if groundwater levels are lowered, then the overlying sediment will first erode and then collapse into the dewatered cavity.
Collapse sinkholes are the most dramatic of the three sinkhole types; they form with little warning and leave behind deep, steep-sided holes. One mechanism for the formation of a collapse sinkhole is illustrated below. Notice that the geologic conditions include soluble bedrock (such as limestone) covered by relatively thick deposits of sediments. This type of sinkhole can form naturally but is often affected by human activities.
(1) There is no evidence of land subsidence, but small- to medium-sized cavities have already formed in the bedrock.
(2) Cavities in the bedrock continue to grow larger but remain filled with groundwater. Water pressure helps to support the thinner, weaker roof of a large cavity.
(3) As groundwater levels drop naturally during the dry season (or are drawn down by pumping), the cavities become dewatered. The weight of overburden now exceeds the strength of the cavern roof, and the overburden collapses into the cavern, forming a sinkhole.
Let's Make our own SINKHOLE
MATERIALS
Styrofoam cup
Scouring pad
Bowl with small amount of water
Sugar in a cup
Sand in a cup
Scissors
Half piece of construction paper
Tape
MAKING SINKHOLE
-Using your thumb, make a hole about the size of a quarter in the bottom of the cup.
-Cut a circle the size of the bottom of the cup from the scouring pad.
-Place this circle into the bottom of the cup.
-Make a tube by rolling up the piece of construction paper.
-Tape it so that it does not unroll.
-Place the tube inside the center of the cup.
-Pour the sugar inside the tube.
-Pour the sand on the outside of the tube – make sure to go all the way around to fill the cup.
-Carefully remove the paper tube by pulling it straight up.
-Place a thin layer of sand over the sugar.
-Look at your bowl – the water in the bowl represents groundwater.
-Place the cup with the sugar and sand in the water.
-You may need to lift the cup gently for your sinkhole to form.
CLICK HERE FOR VIDEO TUTORIAL
Thank you to Soflfamily for the very educational video tutorial.
Credit for Cache: (Send via email. Do Not Post answers in log)
1) Survey the area at the posted coordinates, what evidence is there that a sinkhole developed?
2) Do you think the SINKHOLE you created is the same that occurred here in 2002? Explain.
3) Using the experiment as a guide, describe how the sinkhole formed at this site?
4) How long did it take for the SINKHOLE to form in the experiment?
5) OPTIONAL - post a photo of you and your SINKHOLE in your log.