Hydrogeology of the karst of Puerto Rico

About one-fifth of Puerto Rico is covered by a tropical karst formed on a series of six limestone formations ranging in age from middle-Oligocene to middle Miocene. These formations strike east to west and crop out over the north coast of the island. Structurally, the rocks form a simple wedge abutting southward against a mountain chain of volcanic origin and thickening northward to about 1,400 meters by the seashore. All stages of karstification are present: from the incipient, found at the western end of the belt to the residual, found at the eastern end. Maximum development of sinkholes occurs on the Aguada Limestone and upper part of the Aymanom Limestone. These formations have a CaCO₃ content range from about 85 to 95 percent. The denudation rate of the Limestone belt through solution is computed as 0.70 mm per year with some evidence that abrasion may increase the denudation rate locally by as much as 40 percent.