A Land Above All Else EarthCache

Note: There is an entrance fee to get to this location.

Standing at the GZ, look all around you. You are standing not to far from what is debated as the highest point in peninsular Florida situated along the Lake Wales Ridge. A ridge is a geological feature consisting of a chain of mountains or hills that form a continuous elevated crest for some distance. Ridges are usually termed hills or mountains as well, depending on size. The locals call this point Iron Mountain.

A unique aspect of this ridge and smaller ones around Florida is the abundance of fossils found in the earth just below your feet. Take a look to the west and on a clear day you will see huge stacks of earth. These are Gypsum stacks that come from the phosphate mining in the area. The huge draglines that move the earth in search for phosphate find fossils and bones nearly on a weekly basis. So many have been found, the local phosphate museum has added a number of them to their collection. This museum is located 25 miles West of Lake Wales in Mulberry, FL. This is where things get a little weird. Sea level has not been as high as the distinctive ridges that run down the length of Florida for millions of years. Yet recently deposited marine fossils abound in the ridges' sands.

Peter Adams, an Assistant Professor of Geology has an answer for that. He believes that the land that forms the sandy Trail Ridge running north to south from North Florida through South Georgia, as well as lesser-known ridges, was undersea at the time the fossils were deposited - but rose over time, reaching elevations that exceeded later sea level high stands.

"If you look at the best records, there's no evidence that global sea level has come close to occupying the elevation of these fossils since the time of their emplacement," Adams said, referring to Trail Ridge's elevation today, just under 300 feet above modern sea level. "The only thing that explains this conundrum is that Trail Ridge was underwater, but later rose to an elevation higher than subsequent sea levels."

At the heart of the phenomenon are Florida's unique weather patterns and geology, Adams said.

The state's abundant rain contains a small amount of carbon dioxide, which forms carbonic acid in lake and river water. This slightly acidic water slowly eats away at Florida's limestone bedrock, forming the karst topography for which Florida is so well known, replete with pockmarks, underground springs and subterranean caverns. The surface water washes the dissolved limestone out to sea, over time significantly lightening the portion of the Earth's crust that covers Florida.

A mass of slow-moving mantle rock resides 6 to 18 miles below the crust. As the Florida land mass lightens, this mantle pushes upward to equilibrate the load, forcing Florida skyward, Adams said. The process is known as isostatic rebound, or isostatic uplift. "It's just like what happens when you get out of bed in the morning. The mattress springs raise the surface of the bed back up," Adams said, adding that the uplift is similar to what takes place when glaciers retreat, with Maine and Norway, for example, also gaining elevation.

Glaciers melt off the land surface to drive isostatic uplift. But in Florida, varying rainfall rates during different periods have slowed or quickened the karstification just below the land. This has in turn slowed or quickened the mantle's push up from below. Additionally, sea level high stands do not always return to the same elevation, which creates a complex history of which beach ridges are preserved and which aren't, Adams said. For instance, during periods when sea level rose quickly, some pre-existing ridges were overtaken and wiped out. During other periods, however, when sea level rose slowly or did not reach a certain ridge's elevation, a beach ridge was preserved. In effect, Trail Ridge, Lake Wales Ridge and other lesser-known ridges are the remains of isostatically uplifted land that was kept out of harm's way, Adams said. The ridges carry with them the marine fossils that are the evidence of their lowly early beginnings.

• Time to Learn

To get credit for this Earthcache, you need to answer the following questions. Questions must be submitted to me or your log will be deleted. DO NOT place any answers in the logs or your log will be deleted. The picture portion is optional but recommended.

1) What is the elevation that you are standing at right now?

2) What is the geological process that created this elevation?

3) What area of the USA are you able to find similar soil and landscape?

4) Why is there an abundance of fossils in the ground beneath your feet?

5) Take a picture of you and your GPSr at the GZ. Please don't use old vacation photos. (Optional)

References: http://news.ufl.edu/2010/06/01/florida-rise/