Platinum Earthcache Masters
INTRO: Welcome to the tiny blip of land that is Craig Key. Craig Key is not a natural island, but was originally a flag stop on the Overseas Railroad, a rail line running to Key West that operated from 1912-1935. It also served as a vacation spot, as some land was built up on the side of the railroad for docking boats and buildings. In 1935, the Great Labor Day Hurricane struck and decimated Craig Key (among others) and the railroad. Craig Key is the technical landfall site for the hurricane, although just the eye of the storm was eight miles across, dwarfing the island.
SITE: This site here caught my eye when I noticed this abandoned house on the island. We dipped right off the bike trail here and found this great swimming spot, with clear water, fish, jellyfish, and fossils along a riprap shorline. This is a great, very accessible spot with a relatively large example of coral fossils used in an engineering project meant to prevent erosion.
GEOLOGY: The constant wave action and salt water can cause a lot of problems for the tiny islands of the Keys. Some islands are losing up to 3 feet of shoreline a year due to erosion (Clark, Florida DNR). Craig Key was at a much higher risk for significant erosion, since it is a man-made island. The waves and hurricanes of Florida are no joke, and after Craig Key got wiped out by the Great Labor Day Hurricane of 1935, city planners needed a way to rebuild permanently. In 2009, Florida Department of Transportation took over and settled on a type of erosion control called a riprap shorline. A riprap shoreline is a design element consisting of rocky material piled up along the bank, with rocks ranging anywhere from 4 inches to over 2 feet in diameter. Sometimes, concrete filler will be poured in between the rocks as a sort of "glue" to hold them together. The goal of the riprap is to create a rougher, heavier shoreline that will not be so susceptible to erosion. This can be applid to ocean shorelines, lakeshores, or even fast moving rivers that are causing problems. For Craig Key, the goal is to provide a solid foundation for the Overseas Highway and adjoining plots of land, and prevent (or at least slow) the inevitable erosion from waves. The rocks were strategically placed along both sides of the highway (here at the site, and the additional waypoint) to protect from waves on both sides. "[Craig Key] is surrounded by water on the east by Channel 2 and the Atlantic Ocean and on the west by Channel 5 and Florida Bay" (Wilkinson, History of Craig Key). The size of the rock material needed is dependent on the steepness of the slope and how fast the water is moving. The rough tides and storms off the southern coast of Florida mean that relatively large rocks were needed for this infrastructure project to prevent further erosion. The larger rock pieces used here help weigh down the shoreline, and are heavy enough to not be disturbed by the daily onslaught of the tides. Originally, Craig Key and nearby Keys had coarse sandy beaches, and this small, fine material was being washed away at a rapid rate. The riprap shoreline modification that has been implemented is focused on keeping Craig Key and the Overseas Highway safe and stable.
Secondly, stone here along the Florida Keys is called Key Largo Limestone. It is a fossilized coral reef that extends from Soldier Key to Bahia Honda Key. The formation is visible above water at multiple sites (including here) and underwater just offshore of the keys themselves. These fossilized remains offer an opportunity to step into the geologic history of the Florida Keys. The limestone is white and light gray, containing fossils of corals, mollusks, and bryozoa. The grains that compose the limestone are similar in size to grains of sand, and made of calcite. “There are five primary coral species found within the Key Largo Limestone: star coral (Montastrea annularis), porous coral (Porites astreoides), and brain corals (Diploria stigosa, Colpophyllia natans, Diploria labyrinthiformis)” [Florida State Parks, 2018]. This stone at the site was sourced from nearby Windley Key, which has been known to uncover a ton of fossils. There is also a riprap shoreline example across the street, listed as an additional waypoint. Located here at the earthcache site is one of the three types of coral. Corals make up about a third of the limestone formation. Older and deeper parts of the limestone were formed in deeper water, whereas shallower and/or above sea-level parts are younger and were formed in shallower water.
The formation is estimated to be roughly 130,000 years old, from the Pleistocene era.
Below are pictures of 1) star coral, 2) porous coral, 3) brain coral. You will get to determine which type of coral is present at this site!
1) 
2)
3)
LOGGING: Upon discovering the fossils, send a message containing the following:
- Name of this cache and number of people in your group
- Using the pictures provided, which type of coral is before you?
- Compare the stones of the shoreline (not just the fossil specimen) here to the stones of the riprap shoreline at the additional waypoint. Do you think the stones across the street are made up of Key Largo limestone? What about their appearance makes you think so?
- If you have a smartphone, look up the current tide height at the time of your visit. Is it high tide or low tide?
- Based on what you observe, does the current erosion control seem to be doing its job? What indicators did you look for to reach a conclusion?
- What side of the highway would you think experiences a higher rate of erosion?
Enjoy the discovery and please practice some CITO at the cache site if you notice any trash nearby!
SOURCES:
https://www.floridastateparks.org/learn/geology-windley-key-fossil-reef-geological-state-park
https://en.wikipedia.org/wiki/Craig_Key
https://en.wikipedia.org/wiki/1935_Labor_Day_hurricane
https://en.wikipedia.org/wiki/Key_Largo_Limestone
https://www.dianeburko.com/fossil-reef-limestone
https://floridadep.gov/sites/default/files/CarbonateBeachesOfFlorida-NoAppendices.pdf
https://www.ayresassociates.com/what-is-riprap-and-why-it-rocks/
http://www.keyshistory.org/CRK-Craig-Key.html