JACKSONVILLE, FL – You may be surprised to know about a stretch of land just west of Jacksonville that towers higher than buildings in downtown and even above the Dames Point Bridge.
Trail Ridge is no ordinary hill, it’s an ancient shoreline, and its towering height is a clue to Florida’s fascinating geological history.
It runs along the eastern side of the Okefenokee Swamp and spans into northeastern Florida, extending around 100 miles and passes right near Kingsley Lake in Clay County.
Trail Ridge stands out for its unusual height, up to about 230 feet above today’s sea level.
How Trail Ridge formed
Trail Ridge is a natural formation made up of sand ridges that were created when sea levels were much higher during different periods in Earth’s history.
Over millions of years, these high sea levels created beaches and dunes that eventually turned into solid landforms as the water receded.
Today, the ridge stands much higher than any shoreline could have reached in recent times. So, why is it so tall?
The mystery of Trail Ridge’s height
Scientists, including Dr. Jessica R. Creveling, Jacqueline Austermann, and Andrea Dutton, have explored how Florida’s unique “karst” landscape plays a role in lifting the land.
Karst refers to a type of landscape formed by the dissolving of limestone or carbonate rock due to acidic water.
This process creates underground caves and empty spaces, which can cause the ground above to lift slightly over time.
In a 1984 study, researchers Opdyke and his team proposed that the karst rock below Trail Ridge gradually dissolved, creating empty spaces and pushing the land upwards.
They called this “isostatic uplift,” where the ground rises as the underlying rock dissolves. Based on calculations of how much rock dissolves in Florida each year, they estimated that the land could rise by about 3 feet every 38,000 years from karst dissolution alone.
Connecting Trail Ridge to past sea levels
Understanding the age of Trail Ridge has been tricky, but researchers have worked on ways to match ancient Florida shorelines with global climate changes, known as “marine isotope stages.”
These stages are periods when Earth’s temperature and sea levels changed, often due to melting ice sheets. By linking Trail Ridge to these stages, scientists can learn about how old the ridge might be.
In 2010, Adams and his team introduced a new model to figure out Trail Ridge’s age. This model tracked how Florida’s land responded to changes in sea level over millions of years, particularly how exposure to freshwater from lower sea levels sped up the dissolving process in the karst rocks below.
They calculated that Trail Ridge might have started forming around 1.4 million years ago.
Their findings matched up with some global sea level records, suggesting that Trail Ridge’s height is due to both ancient sea levels and the steady, upward lift caused by karst dissolution.