About the Islands:
The Cayman Ridge is a long, underwater mountain chain found in the Caribbean Sea, stretching from the southeastern tip of Cuba nearly to Belize in the Gulf of Honduras. The ridge was formed due to the interaction between the North American and Caribbean tectonic plates over millions of years and lies to the north of the Cayman Trough which is approximately 150 miles wide and reaches depths in excess of 3 miles. The Cayman Islands were formed when these tectonic plates forced rock upward, breaking the surface of the ocean. So, in a way, when walking about the low-lying limestone base surrounded by coral reefs that make up the islands you are actually traversing the top of a large mountain, which is mostly hidden by the sea. At this location you are visiting the island of Grand Cayman, which is by far the largest of the Cayman Islands, its two "Sister Islands", Cayman Brac and Little Cayman lie to the Northeast.
Geologic research of these islands has revealed that the Caymans have a granodiorite base, followed by a cap of basalt. This base, is usually found deep within the earth and is only found exposed where uplifts, such as the one which formed the island, have occurred. The surface geologic layer of the Caymans is composed mostly of carbonates, which were formed by living organisms (corals, algae, and shells) and were laid down during sea level changes over the past 30 million years. Limestone forms due to the accumulation and consolidation of these limey muds, calcium-carbonate rich sands and shell fragments. This usually occurs on the ocean floor. Similar to limestone is dolomite, which also contains magnesium and forms in the same way as limestone, often alongside it. As sea levels dropped over millions of year, these limestone and dolomite features were exposed.
About Hell:
The rocks that form the Hell formation are a bed of limestones and dolomite that has undergone extreme erosion due to activities of small tropical organisms, known as phytokarst. “Phyto” meaning plant and “karst’ meaning eroded form that consists of formation of holes and pockets. The shallow water at the base of the formation supports the algae which slowly eats away at the limestone/dolomite and removing the calcium, through a process known as bio-erosion. The result is the pock-marked pinnacles you see here. The rocks are actually white, like the corals you see throughout the Caribbean Basin, but as the algae eats away at the limestone it also stains the rock giving it this unique black color. Most algae need water to stay alive, so the areas of this phytokarst formation above the water are no longer being eaten away by algae but are still subject to rainwater erosion.
The Questions:
1. From the coordinates, calculate the approximate height of the tallest Hell Formation spires visible here. In your opinion, based on what you have learned here, why do you think the spires have a similar height across the formation and why is this height limited?
2. There is an information board at the location that explains the geology of this unique area, it mentions an additional environmental factor crucial in the creation of the pinnacles through solution, what is this factor and based on the information do you believe that the erosion process has increased or decreased in the last 500 years.
3. The water level among the pinnacles fluctuates depending on recent rainfall and evaporation. By observing the formation what is the immediately obvious difference in the stone above and below the usual water line, and why do you think the difference is so dramatic?
4. Based on information in the cache page and the information on site, what does this difference tell you about the continuing processes that shape this formation today?
*Information used in the creation of the cache page from: The Cayman Islands: A Geologic View; Matt Unruh. http://academic.emporia.edu/aberjame/student/unruh1/webpage.html
Granodiorite, Wikipedia article. http://en.wikipedia.org/wiki/Granodiorite