Cueva Ventana, Río Grande de Arecibo valley

Cueva Ventana, Río Grande de Arecibo valley

In Puerto Rico there are some 2,000 caves, of which about 415 have been explored, according to estimates by geologists, speleologists and explorers. The inventory of caves carried out by the Departamento de Recursos Naturales y Ambientales (DRNA, Department of Natural and Environmental Resources) lists 211 caves, but another 104 have been explored that have still not been documented in the inventory.

Caves are the best known of the karst formations, thanks to their mysterious and fascinating beauty. The word cave refers to a cavity that has formed naturally in rock and is sufficiently large for a person to enter and sufficiently deep that there are completely dark areas. Some caves are small in size, and others run for miles beneath the surface.

Caves form when the mineral calcium carbonate (CaCO3) is dissolved by the erosive and corrosive action of acidic water. Dissolution of karst is the result of the action of rain, which absorbs carbon dioxide (CO2) from the air and enters into contact with the soil, which acidulates it, or makes it acidic. This acidic water then filters through the fractures in the rock and slowly dissolves it, a process that may take millions of years.

Most caves in Puerto Rico are found associated with the karst zone (limestone rock). The largest extent of the zone runs across the northern part of the island from Loíza to Aguada. In the south, it occurs fragmentarily from Juana Díaz to Cabo Rojo. Other limestone formations are to be found in Aguas Buenas and Cayey, as well as on the islands of de Mona, Monito, and Caja de Muertos.

The best known system of caves in Puerto Rico is the Cavernas del Río Camuy between the municipalities of Lares, Camuy, and Hatillo. One part of the system has been developed as a tourist attraction known as the Parque de las Cavernas del Río Camuy (Camuy River Caverns Park), which is administered by the Compañía de Parques Nacionales de Puerto Rico (Puerto Rico National Parks Company). According to speleologists, the Río Camuy system, when it is at its peak, may be one of the most voluminous underground rivers in the world.

Another of the most important systems is the Cuevas del Río Encantado (16.9 km), which is found between the municipalities of Florida, Ciales, and Manatí. The system is in a recharge area associated with the valuable north-coast artesian aquifer, and a great part of the water that flows through it pours into the Río Grande in Manatí. Among the cavern systems that have been explored so far, it has one of the longest submerged passages through which human beings can pass.

Two other important cave systems in the northern area are Cueva Sorbetos and Cueva Mata de Plátano, both in Arecibo. Cueva Sorbetos is thought to be the most beautiful in Puerto Rico given the type of formations (speleothemas) in the shape of straws. Cueva Mata de Plátano, on the other hand, is characterized by the large number of bats that roost there and the constant presence of the Puerto Rican boa (Epicrates inornatus).

The Aguas Buenas system of caves extends for one kilometer and is made up of principal galleries of approximately that length. The Río Cagüitas, a tributary of the Río Grande of Loíza, has its origin here. Inside it are pre-Taino and Taino wall paintings. It is thought to be a refuge for wildlife, as 52 species have been identified, of which 50 percent are endemic.

In the south, the caves of the Bosque Xerofítico (Dry Forest) in Guánica stand out. There are 11 known caves that in general are rather short. The longest and most important in ecological terms are these: Cueva Murciélagos and Cueva Tortuga, which developed in Ponce limestone. Other, smaller ones are El Negro, El Refugio, Del Manglar, Los Granados, and Bosque Enano -all in Ponce Limestone and Cueva Las Latas in Juana Díaz limestone.

Between the municipalities of Peñuelas and Guayanilla, there is the Cuevas El Convento system, with a length of 500 meters. It is characterized by the abundance and diversity of its fauna and is unique in the southern area for the uninterrupted stream of water that flows through it (Quebrada El Cedro).

Secondary underground formations

Inside caves, secondary underground formations called speleothemas develop. This name derives from the Greek words spelaion (cave) and thema (deposits). The environmental conditions of an underground cavity are perfect for the formation of speleothemas. Most are formed from the mineral calcite, which is the principal component of limestone rock.

On the floor of the cave, decomposition of dead plants and animals produces a large amount of carbon dioxide (CO2). CO2 combined with water produces carbonic acid. This acidic water dissolves the calcite in limestone and carries the dissolved calcite along between the strata of rock. The mineralized water flows inward toward the subterranean cavities. When the liquid reaches a cavity, part of the CO2 is lost and the calcite precipitates in the form of crystals from which speleothemas begin to grow. This process takes place over millions of years.

The best known speleothemas are stalactites and stalagmites. Stalactites hang from the ceiling of caves. They form when mineralized water infiltrating through carbonate rock deposits crystals of calcite and produces a structure that grows wider and longer over time. Stalagmites rise from the floor of the cave and are made of the residual calcite from the water that drips from the ceiling of the cave.

The rhythm of formation of speleothemas varies and depends on several factors. Among the most important are the temperature of the environment, which affects the speed with which the plants and animals decompose (the amount of CO2 in the soil), and the amount of water that falls. The forms that the speleothemas take depends generally on how the water enters the underground cavity (by dripping, filtration, splattering or flow) and how the water flows or is obstructed after entering the cavity.

There is a wide variety of speleothemas. The best known, in addition to the stalactites and stalagmites, are the columns, straws, helictites or excentrics, flowstone, curtains, and cave coral or popcorn.

Speleothems in the shape of columns and straws inside a cave

Speleothems in the shape of columns and straws inside a cave

Caves are natural ecosystems of great value for the singular organisms they shelter. They are the habitat of nine species of insect-eating or fruit-eating bats. The excrement of bats (guano) is the basis of the food chain on which the rest of the species that live in caves depend. Throughout history, the extraction of guano for fertilizer has been a source of income, as it is rich in phosphorous and nitrogen.

Through the caves flow important bodies of underground water that are sources of supply for the population. Their spectacular characteristics are of great scenic and recreational value for visitors. They are sources of knowledge for the development of much scientific research. Caves hold archeological evidence, such as petroglyphs, pictographs, burial sites, ceramics and other materials of archeological and historical value. All these qualities make it necessary to protect and preserve cave resources.

In Puerto Rico, Public Law No. 111 of July 12, 1985, establishes the public policy of “protecting and preserving the caves, caverns and sinkholes of Puerto Rico, as they are a unique natural resource, given their beautiful formations of natural materials, their fauna adapted to the underground environment, their archeological and historical value, because they channel and store underground waters, and because they provide an environment that is apt for recreation and scientific research.”

In addition, Public Law 292 of August 21, 1999, known as the Law to Protect and Preserve Karst Physiography, sums up the importance of the karst region of northern Puerto Rico “as one of our most-prized natural, non-renewable resources, given its geomorphology and particular ecosystems. The karst region fulfills several functions that are vital for the natural and social survival of the island, such as providing shelter for a large number of species of flora and fauna, storing enormous supplies of underground water, possessing excellent land for agricultural use and great potential for recreation and tourism attributable to its natural characteristics.”

In terms of the underground world, the karst region of Puerto Rico is very impressive and offers a broad range of opportunities for study and research for the scientific community and the society as a whole.

Author: María A. Juncos Gautier
Published: August 27, 2014.

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