Lava Tubes of Cuernavaca

Nov. 1996 :

I just got back from a weekend of mapping lava tubes with Ramón Espinasa just south of Mexico City. He had tempted me with prospects of pushing crawls in the top of his second longest tube cave but fortunately decided (at my prompting) to ask and see if there weren't some new entrances that he hadn't seen before and which would likely be easier to explore. Sure enough, about 300m from the car (which was parked over the bottom end of his biggest tube system (Cueva Iglesia) we asked the local residents if they had any entrances in their back yard and received a positive reply. After seeing that one (called Cueva Mina by them) we asked if there weren't any more around - might as well find out where we are going to come out before we go in! So knowing that we had this one to come back to we went down hill in search of the obvious entrance after the water pipe. "You can't miss it" we were told. And we didn't - for a change. It turned out to be a pit entrance that Ramón and I looked at and figured on finding an easier way into. But we had young Tachi along (who Ramón had first met six years previously coming out of the other tube (Cueva Ferrocarril) on Ramón's second exploration trip to the area. Tachi was 13 at the time and so keen to get out exploring caves with real cavers that he skipped school the next day to go up and discover the entrance to Cueva Iglesia, now the longest in the area at 3.1 km and where our car was now parked) and he just proceeded to down climb into it pronouncing it quite do-able, which it was.

It trended downhill at a steady -20 degrees in mainly walking or stooping passage. And you sure made sure you stooped when it was necessary for there are no nice brittle, fragile, calcite stal to break off - in these lava tubes there are solid, pointy, and sharp basalt stal which draw blood for those unwise enough to bump them. There were also some nice levee structures left behind as the lava flowed along as a molten mass and the banks cooled leaving the equivalent of mud banks. Eventually we found the mud for real after about 400m downhill in one single, non-branching tube. Growing in the mud at the bottom were roots (we think) that looked very similar to a prickly cactus.

Going up hill from the entrance, but still in the cave, we passed some infill volcanic ash sediment which got Ramón quite excited as he is doing his M.Sc. thesis on these caves and this may give him an opportunity to date the eruption that dumped the ash and thus help bracket the age of the caves. (another geologic aside - A few weeks ago I went through the tourist cave of Chacahuamilpa with Ramón and saw a volcanic lahar (a mud a rock flow produced by cataclysmic eruptions) plastered to the walls which had come from a volcano 50 km up stream and which passed through the cave and continued 30 km further downstream - which we saw as we paddled past). We then passed underneath a sky light entrance that showed flow marks indicating that surface lava flowed into this entrance and we could see the horizontal lines where it had ponded before draining out the bottom. Very similar to the water features that you see in limestone caves, but here the evidence is solidified in rock for posterity. Neat stuff.

Shortly above this point the lava flowed right to the roof, and thus we had finished C. de la Tuberia at 428m long and 116m deep. Having knocked off that part and still not reached the first entrance we headed back there and surveyed down what is surely the same tube that unfortunately became blocked by a lava plug. No easy digging for a connection here. But a side passage near the entrance beckoned us up into a crawlway. Now having come all the way over from Guadalajara (a 7 hour, over-night bus ride) expecting to push crawls I should have been in there like a shot. But after almost 500m of easy stuff I wasn't too keen to donate blood to this cave despite Ramón insisting that this was only pahoehoe lava. Well I had to concede that it wasn't aa lava (so named because you go "aa aa" if you step on it) but it still didn't look too friendly for belly crawls. As we could see at least 15m that was passable I relinquished the lead tape position to Ramón and volunteered to record the distances as they shouted them back. As luck would have though, in his shouting I could tell he had broken out into a much bigger space and it was going strong. Through I went.

Things started getting big again and complicated this time as tubes branched off in multiple headings both upstream and down. We pushed on upwards trying to figure which was the biggest tube and thus have the best chance of going the furthest before choking. We added another 200m or so before running out of steam. Caving for 7 hours with no fluid intake is not a good idea. I was quite dehydrated, while the others didn't even have enough fluid left to pee in their generators and were thus getting low on light. A good day though in the new Cueva Mina and we decided against pushing a dome climb the next day in a limestone cave in favour of continued mapping in this growing, soon to be big, system.

Sunday morning had us going into yet another new entrance over by the top end of Cueva Ferrocaril. This one was only 8m away from another one that Ramón's brother had found from the inside of Ferrocaril. Being pretty sure we could easily connect with Ferrocaril below us we headed upstream again. Lots of comfortable walking passage with branches anastomosing all over the place. Again we tried to follow the one most likely to continue and ended up surveying a few loops as the likely one didn't go. The genesis of this part of the system involves the flowing lava melting through its own walls and breaching into a neighbouring tube. This may result in it cutting off the old one, or the new one with its left over solidified lava. We also saw evidence that supported Ramón's earlier thought that they also melt through their own floor creating an even larger tube probably due to the new increase in fresh lava.

After another 4-500m we were in an area of large wide tubes and we could hear the sound of music. Then we could hear foot steps of people running over head! The roof must be only a meter or so thick and we were obviously underneath the town. Which meant also that we were very near Cueva Iglesia, which we had suspected anyway. One tube had particularly nice levees and a flow that wrapped neatly around a heart shaped rafted block. Truly this was the heart of the whole system and was thus named the Heart Room.

Shortly upstream it pinched down again, but this time in a soft mud floor, just like the one Ramón remembered being in the bottom of Cueva Iglesia. Oh, so close. So we decided to head down stream on the eastern side of the heart where the tubes seemed to split, one half going down the Ferrocaril drainage and the other going down the Cueva Mina side that we had just mapped yesterday. We agreed on 10 more legs as funny enough, we were out of water again (those two not having brought any again!). The tubes here were 15m wide and some 10m high and a treat to cruise down. In less than 10 shots we connected into the line we had surveyed the day before confirming that the divide really did exist. So quite chuffed at this we headed back down to make the connection with Ferrocaril.

After surveying a couple of dead ends we finally crawled through into some good going passage. Which kept going and going and going. Where was the next bloody entrance? We knew that Ramón's brother only went 50m or so and we had just surveyed close to a 100m with tubes still going off in various directions. One junction had six passages leading away from it! Ramón was really wiped now so we sat and waited while the super kid ran up and down and back a couple times trying to locate that elusive entrance. With no luck. So close yet again. We must be underneath or beside the upper passages of Ferrocaril, but the connection will have to wait until another trip. I don't imagine that Ramón will have too much trouble rounding up a new crew this time as joining these three caves together will create one of the top ten longest lava tubes in the world. Not a bad weekend.

Update to 1999: That weekend did indeed provide the incentive to get the project going again and over the next year about 8 more km of tubes were mapped. I did one more trip, while other visitors also helped out. Cueva Iglesia and Ferrocaril went from being about 3.1km and 3km long respectively to 5.145 and 5.623km. We had gone right by the connection into Ferrocarril the day I was there as it turned out. Despite all the work though, the two main caves remain unconnected. Slowly the available tubes are being crossed off. The most recent attempt was by Ramón's brother once again and resulted in him popping out yet another new entrance that happened to be a very small enclosure for a rather large bull. Needless to say this surprised the bull enormously and it actually jumped right out of the enclosure and went raging through town. This did not go over well with the local residents, particularly the bull's owner. Luis figures it best to let the connection search wait for a year or two before returning.

By: Chris Lloyd, Photos By: Chris Lloyd

July 1999