The Rio Uluopam in flood. Photo by Ernie Garza.

The Cerro Rabón, located in the Mexican state of Oaxaca, is home to some of Mexico’s largest cave systems. The most impressive of these is the Kijahe (Xontjoa), mapped to a length of over 24 kilometres and a depth of over 1.2 kilometres. While these cave systems have been extensively explored and mapped since the 80s, the resurgences of these cave systems remain unexplored.

It is these resurgences where the large amounts of rain which falls in the wet season, draining into the caves hidden away in the rain forests on top of the Cerro Rabón, exits the mountain 1.5 kilometres lower in altitude in the form of large rivers. These underground rivers are fully submerged and hence can only be explored by cave divers. The exploration and mapping of two of the major resurgences in this region, the Rio Uluopam and an unnamed resurgence under the lake Miguel Alemán, is the goal of this expedition.

The expedition’s first objective is the resurgence known as Rio Uluopam which has been last explored in the early 90s by American cave explorers Bill Stone and Bill Farr. These explorers had to abort their efforts less than 500 metres into the cave when, after a dive, they surfaced underneath a massive waterfall surrounded by vertical walls which stopped these explorers from exiting the water.

Building on experience with these sort of circumstances over the last few years, we will now repeat this dive and use modern climbing techniques to scale this waterfall to then continue exploration and mapping further into the mountain.

A map or the Rio Uluopam (note the different spellings of this cave).

The expedition’s second objective is a resurgence to the north-east of the Carro Rabón, located under a dammed lake known as Miguel Alemán. While locals have been reporting large boils of water seen on the lakes surface when rain falls in the Cerro Rabón, this resurgence has to date remained unexplored.

While there have been several hypothesis of drainage patterns in the Cerro Rabón, possibly explaining why there are two major resurgences in this area, none of these theories have ever been proven. We will conduct a dye tracing experiment, putting dye into some hypothesized sinks, to understand the flow patterns through this complex karst area.

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