photo: The man-made lake Miguel Alemán. Photo by Teddy Garlock.

What and where is this cave system?

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. There are two major known resurgences in the Cerro Rabón - the Río Uluopan resurgence and an unnamed resurgence under the lake Miguel Alemán. Connecting these resurgences to the cave systems above would make for ~1500m deep cave systems, tens of kilometres in length.

The first cavers to see the resurgence known as the Río Uluapan visited there in the spring of 1980 during the 1980 Rio Iglesia Expedition to nearby Huautla which resulted in the first 1 kilometre deep cave in the western hemisphere by connecting two major caves -  Li Nita and San Agustin. It was not until 1986 that the Río Uluapan was first explored by American cave explorers Bill Stone and Noel Sloan. 

Whey they drove to Ayautla, the closest town to the Río Uluapan resurgence, they found that the bridge to Ayautla was completely destroyed by the summer floods - which issued from the Río Uluapan resurgence resurgence.  The flow was still enormous, but no longer zero viz brown.

Bill Stone recalls: We spent the entire next day chopping a steep trail up the left side of the raging arroyo leading up to the entrance. The water coming out the entrance was frightening.  I still remember taking a photo of Noel standing beside it. The water flying out over the travertine falls was deeper than Noel was tall and it arc'd out a good 20 meters before disappearing in a cloud of impact-induced spray and fog.  We seriously considered aborting right then. But further investigation showed that the breakdown on the floor of the entrance chamber right there at the entrance was diffusing the flow - enough so that despite that ferocious waterfall just meters away, the deep, dark, long lagoon leading back into the mountain was tranquil, still.  

The following day, using 1984 Pena Colorada diving kit (S-glass composite tanks, Y-valves, and specially modified Sherwood regulators that handled 5,500 psi) borrowed from Zambrano, Sloan and I suited up while the four sherpas watched on.  It has been 33 years since that day but I still remember the exchange I had with Noel before entering the water. He gestured with his arm towards the back of the blue-black lagoon and began nodding. Then he looked at  me and said, "have you ever seen the movie Caltiki - the Immortal Monster ?"  I looked at him, and off towards the back of the lagoon, then back at him and said, "unfortunately, yes. why the hell did you have to bring that up ?" It *was* a spooky place.

We inflated our BCs and swam as far as we could into the entrance chamber lagoon, to where it takes a westward jog.  We tied off there and submerged. Each of us had two back mounted 9-liter tanks at 5,500 psi (air), so we were somewhat limited in what we could do.  We did, however, have a lot of line with us. We stayed on the right wall at roof level, trying to keep as high as possible. We had pretty good primary cave lights, but probably nowhere near as tight and powerful as what we have today.  Nonetheless, we spotted what appeared to be sculpted sand on the bottom, perhaps 30 meters below. The left wall was out of sight in the blackness. I remember the right wall being stratified and curving upwards. We tied off at 280 meters penetration when we hit thirds on our gas supply.  We had no backup whatsoever so we were playing it conservative.  

This exploration then remained a secret amongst a few of them until 1994, during the famous and tragic San Agustin expedition, when Bill Stone and Barbara am Ende discovered Sump 9, now known as “The Mother of all Sumps”, in Sistema Huautla.  At that time Bill gave a full debrief on what they had done to cave divers Tom Morris and Jim Brown. They readily expressed interest and, in the spring of 1995, returned with Paul Smith and Bill Farr. Only Brown and Farr dived; Brown essentially reached the limit of exploration set by Sloan and Stone. Farr then ostensibly reached a point 430m from the end of the entrance pool where he surfaced to conditions that have either been garbled or intentionally obfuscated. Nobody then returned to this resurgence until 2019.