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click to enlargeRio La Venta flows between deeply carved walls with a meandering course. The current route was established when the Rio crossed a plain and the river’s current flowed lazily, forming itself into wide loops. Then, about 90,000 years ago, the block to the northeast of the great fault, which has since been the western border of the limestone range, began to rise. Since then the block has been raised an average of 5 millimetres a year, resulting in a total rise of 400 metres today.
The raising of the limestone block corresponded to the progressive down-cutting of the canyon. Currently, at various heights on the vertical walls which trap the river, the remains of ancient ‘river terraces’ can be found, being level surfaces which formed during the evolution of the canyon due to the lateral wanderings of the water course during the pauses in its vertical deepening. The summit of the mountain range, strongly modelled by erosion and especially by karst processes, is what remains of the original level plain where the ancient Rio La Venta peacefully flowed. It is in this time period and context that the underground karst network originated and evolved. The rain waters which fell on the forest passed, and still pass through, the karst conduits which over time grew and changed. The conduits lead the underground streams to several emergences at the base of the canyon walls, adding themselves to and increasing the Rio La Venta’s flow.
In the Rio La Venta karst area, over 250 caves are known with a total of over 60 km of surveyed underground passages. The sector in which the speleological explorations were able to completely reveal the structure of the underground karst network is that of López Mateos, a small settlement reachable in about two hours with an off road vehicle from Municipio de Cintalapa, road conditions permitting. The López Mateos underground system is currently made up of 20 caves, segments of that underground network which allows the waters falling on the slopes starting at the southwest edge of the limestone, to head north and eventually pour into the Rio La Venta canyon.
In the westernmost part of the mountainous area, the draining of the water takes place partly on the surface and partly through underground conduits. The topography is characterised by closed basins, within which the waters gather themselves into surface streams which are then swallowed by karst conduits probably laid out on layers with a slight slope to the north. These passages pass a little way beneath the ‘cone’ karst landscape and emerge from resurgences inside other closed basins, again flowing along the surface until swallowed by a new sinkhole. In the western area about fifteen caves have been explored, some are hundreds of metres long while others are over a kilometre in length, like Cueva del Naranjo (2.5 km), Cueva de las Cotorras, and the Cueva Ejidal.
click to enlargeIn the central part of the mountain, at about 700 m altitude and on the edges of one of these closed basins, is the village of López Mateos. The level bottom of the large basin is carved out by the Rio Osman, whose flow is very variable and averages between 1 and 2 m3/s. Following it upstream, several bifurcations are reached, each leading to a cave-spring: Cueva del Cafetal (1,000 m long), Cueva del Rio Osman (680 m), and Cueva Monterosa III (240 m). In the Cueva del Rio Osman, the discovery of a connecting passage allowed the resurgence and sinkhole (Cueva Ejidal) to be joined, making the cave traversable from end to end. In the others, a connecting passage is not possible due to the presence of collapses or siphons. In some, a higher and richly decorated fossil level is found, while the active part containing the underground stream is about ten metres below. Downstream, Rio Osman reaches the edge of the López Mateos plain and disappears, swallowed up by the Traforo di Osman at 680 m elevation. From here on it stays underground until the resurgence in the Rio La Venta canyon. In the eastern sector, the river that disappears into the Traforo di Osman is found again downstream, still underground, in Sumidero I and then flows under the Sotano del Quetzal to finally enter, several hundred metres further along, the Cueva del Rio La Venta. This last cave can be completely traversed in a spectacular descent into the canyon. In 1995, the passing of some unstable collapsed blocks in Sumidero II, through which a light air current passed, brought the speleologists to the shores of the Lago degli Ignavi (Lake of the Slothful), the previous year’s exploration limit that had been reached by climbing up the stream from the canyon side. The journey in the dark is nearly 13 kilometres long and is accompanied by a strong draught and the stream water. In some places the stream flows peacefully, at times rests in lakes, and sometimes explodes down roaring waterfalls. The names given to the various places by the explorers evoke magical images, sometimes surprising and sometimes ominous: Salone della Cascata (Chamber of the Waterfall), Kinich Ahau Chamber, Chaac Rapids, Gallerie Via Col Vento (Gone With The Wind Galleries), Bella Addormentata (Sleeping Beauty), Forra dei Sogni (Gorge of Dreams), Salone Porte del Caos (Doors of Chaos Chamber), Galleria Segnali di Fumo (Smoke Signals Gallery), Salone della Città Perduta (Chamber of the Lost City)… From its appearance in Cueva del Rio La Venta, the water flows though passages which are more inclined compared to the nearly horizontal ones seen in the upstream caves. Continuing towards the canyon, the inclination increases while, above the speleologist’s heads, the outside surface gets farther away. Finally, at 275 m altitude, a large gallery leads to a majestic portal, through which one can see daylight once again. In the final tract, the water follows narrow fissures and emerges as a spring on the shores of the Rio La Venta.
To the north of Rio Negro, a left hand tributary of Rio La Venta, is an underground system which has hydro-geological features similar to those of the Cueva del Rio La Venta. This is the Pecho Blanco system, explored for over 6 kilometres by speleologists from Rome and made up of different caves with connecting tracts which are only partly physically passable by humans. This group of conduits allows the Selva del Mercadito waters to flow from the western edge of the range towards Lake Malpaso.
In the sector to the right of the Rio La Venta, Selva El Ocote, territorial explorations have not progressed so much, mainly because of the difficulties involved in penetrating the virgin forest where progression is extremely slow. Ways through the thick tangle of vegetation have to be opened with machete, ridges have to be crossed, and deep folds descended, all the while trying to keep a straight line given by the compass, which is indispensable for not losing oneself in the labyrinth of corridors and cockpits. The exploration of the heart of the forest was motivated by clues such as the grandiose sotanos which are visible on satellite images, but everything which remains hidden in the thick vegetation is still unknown. The most remote sotano, a hole with a diameter of over 50 m called Ombligo del Mundo, was reached with great effort and descended in 1998 and then again in 2008. It was bottomed at 177 m depth without finding any continuation.
Another large opening, Fundillo del Ocote, had been reached a few years previously and explored to its base 85 m down, where the forest extends just as luxuriantly as on the surface. All around the heart of the forest, the search has led to the discovery of numerous caves, such as sotanos, pits, and horizontal galleries, which together extend for several kilometres. At the base of the canyon’s wall, always to the right of the river, French speleologists have explored over 5 km of the large Los Bordos resurgence, which drains the waters from a sector of the southern karst area.
Despite the massive amount of work carried out, which over the years has involved more than 200 people including speleologists, archaeologists, researchers, guides, and companions, there is still much to do in the Rio La Venta karst area. Both to the left and right of the river, several caves still need to be thoroughly explored and many others have yet to see an explorer’s light for the first time. The canyon itself contains many cave entrances, at different heights, which have never been reached by the speleologists.
The way traced by the research carried out by the La Venta Association is very clear: to continue to explore, describe, document, and divulge, so that mankind can get to know this extraordinary territory, appreciate its value and protect it. This is a constantly evolving process which cannot be interrupted, both in regard to the local resident population as well as the political and technical authorities who determine the territory’s use and conservation strategies.
We can only hope that other speleologists and researchers follow in our footsteps and carry the knowledge forward. We would like it if it were done with the same spirit of sharing and co-participation with the areas’ inhabitants, which we have always tried to stick to, so that slowly the young locals will also become speleologists and learn to protect their land, both above and below the surface.

 


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