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Las Leñas: MCG in Argentina 2006

by Tim Francis

This year's team in Malargüe, February 2006, was just the usual three of us from the UK - Peat Bennett, Richard Carey and I - plus our friends from INAE. Again we had less than two weeks in the field so our focus was to really crack open the potential of the caves at Las Leñas. On the last trip in 2004, we had only cursorily looked at the valley but had noted more than 15 sites of interest including Cueva Naranja, Cueva Langosta, and Cueva de la Nieve.

Valle de Las Leñas

Not a lot has been written about the cave potential of the gypsum at Monte Leñas except for the exploration and survey (1997) of a very small cave, Cueva de Los Tunduques. This can be seen clearly from the road although you do need to get your feet wet to get to the entrance. It was considered that there was not much else to be had. I looked back at our original field notes from 2001:

"Due to the atrocious weather we virtually did not leave the car but did note one cave by the roadside [Actually just an undercut where water resurges]. The road was poor so we did not drive much beyond the resort. With hindsight I think this area would be worth further investigation."

Las Lenas

But in 2004 it was readily apparent that there was huge potential. The depth of the gypsum is significantly greater than that at Poti Malal, and with the mountains soaring to over 4000m it really was worth a proper look. We only had a few days at Las Leñas as our focus was to complete the survey of Cueva Miranda over at Poti Malal. But we noted resurgences at almost 3000m and 16 sites of spelaeological potential, not bad for an area considered to have no caves. The main discoveries were a big resurgence below Monte Leñas, Cueva Naranja and Rio Naranja, Cueva Langosta and Dead Colibri Cave. None of which are particularly long but there is hell of a lot of water coming out of the mountains. The problem we've found with Gypsum is that you just can't seem to follow the water very far before the cave closes down or collapses.

So in 2006 we were absolutely determined to focus on Las Leñas. Indeed we had muttered that we probably would not have time to visit Poti Malal which is almost sacrilege in these parts. Carlos lined us up some extremely cheap off-season accommodation at the ski resort; beds, a shower, an electric hob, a shop. This was true luxury compared to the usual cold and dusty camping. Indeed from our room's window we had a fantastic view of the gypsum mountains, "Cerro Yeseras", in the distance. Peat had a good pair of binoculars so we were even able to indulge in some armchair cave spotting.

The Resurgences of Las Leñas

The appeal of cave exploration in the valley is that you can do day trips from the end of the tarmac road. Indeed the furthest reaches of the Gypsum are only 3-4 hours walk away so there was no need for camping. Mind you, day after day of high altitude walking can get rather tiring to say the least. The caves are 500-1000m higher than at Poti Malal so they can be very cold. Mendip kit is definitely advisable for anything other than a quick recce.

Caves of Las Lenas

Cueva del Colibri

On the first day we thought we'd go for an evening's stroll to look at the main resurgence. Just follow the main river from the farmhouse at the end of the valley and you can't miss it. The others went up to Tunduques instead for a spot of tourist caving. Things had changed since 2004. The cliff face above the entrance had collapsed and there is now a nasty overhang. Not ideal.

Richard Carey in Cueva Colibiri

So instead I had a rummage in a scree slope on the left of the resurgence. Unbelievably I opened up a drafting hole within a matter of minutes. Another hour's digging on the following day and we were in. A couple of rubbly squeezes dropped us back down to stream level — the entrance collapse had been bypassed. The cave is low and wet and small. Despite our best efforts we couldn't keep out of the water which is essentially just snowmelt. It opens into a small section of walking-sized streamway before closing down at a grizzly looking bedding plane and boulder choke.

We tried to dig around the choke on the left but this looked long term. On the surveying trip Peat spotted that the main streamway was actually coming out of a low scoop on the right hand side. We duly surveyed into this but the streamway got lower and lower. Peat commented "this turned out to be a surveyor's hell involving crawling in freezing cold water. Enough was enough when I could hardly move my limbs due to the cold." We left it at a flat-out hypothermic bedding plane that twisted out of sight. On the final day, Peat and Rubèn did a mad dash to the end in full Mendip kit to see if they could push it. Again they were beaten back by the cold. It looks very unpromising but possibly in a thick wetsuit further progress might be possible. The current length stands at 125m.

Cueva Naranja

The object of the visit to this site was to see if we could dig out the large resurgence below the fossil cave entrance. We enthusiastically dug out the mud and rocks in the floor to try and lower the water level. This worked a treat but rather than the duck we'd hoped for it was revealed that the water flows out of a tiny bedding plane. Defeated again. The mud here has a high iron content so both the shivering team of diggers and the river in the valley were now bright orange. Intriguingly the resurgence at Colibri Muerto was flowing orange suggesting a connection somewhere to one of the meanders of the surface river.

Tim Francis at the dig in Cueva Naranja

Colibri Muerto

This was a small site we'd found in 2004 and so-named because of dead bird at the entrance. It's an unpromising grovel in the scree of gypsum on the left hand side of the huge resurgence on the other side of the valley from Colibri Cave. Towards the end of the trip Peat and I nosed around in every hole looking for a way passed the huge tumble of boulders that block the main resurgence. There really is nothing here but the nature of the gypsum means that it is worth checking every few years just in case. Just for the hell of it we looked at Colibri Muerto. This time there was a stream running down the cave whereas it had been bone dry in 2004.

Cueva de la Nieve

We had decided to traverse the whole of the valley side on the left and up into the upper valley. This took us past the small valley that Peat and Rubèn had looked at briefly in 2004. They'd found Cueva de la Nieve and spotted a couple of other possible locations before thunderstorms had cut short the day. Nieve is a delightful little cave with the roof festooned with gypsum crystals. It's also rather wet and loose. The entrance looks like it is going to collapse sooner rather than later so we didn't tarry too long.

Formations in Cueva de la Nieve

Anything above 2500m in this area seemed to be snow-plugged. We did come across a tiny resurgence and sink in a doline but not much else. The highlight of this tour of the hills was a natural rockarch carved out of glacial debris by a meltwater stream. This lay right at the foot of a tongue of ice and afterwards we realised that we could actually see it through the binoculars all the way from the ski resort.

Cueva de Las cascadas

Richard Carey in the Meanders, Cueva de Las cascadas

This was found on day two of the trip and I think it's the best cave in the province of Malargüe. And it really is a classic. After the end of our tour of the hills around Cueva de la Nieve we stomped all the way up the head of the side valley and peered over the lip to the continuation of the main valley. On the far side just before the end of the gypsum we could see a large resurgence that chucked out a large proportion of the river. Clearly this was going to be a primary target of the trip and we returned the following day. It takes on average about three hours to reach the entrance so days spent up at cascadas were long ones. Indeed on the last surveying trip Peat and I were almost benighted despite clocking up record breaking walk-in and walk-out times. The cave is so-named because of a fine crashing cascade at the end of the cave. This is the only large streamway and waterfall that we've come across in Argentina. The cave's length is around 400m.

The cave starts as a very low crawl in ice-cold meltwater. Thank God we'd brought Mendip kit. Our friends from INAE really felt the pain in this section. Luckily it soon popped out into large stomping passage. To the right closes down but to the left is a fine stream passage, something that it is highly unusual in the gypsums of Argentina. We got some excellent shots in this section.

Another junction was met. Straight ahead runs for 50m or so until it closes down at a dry choke. The passage smelled heavily of sulphur, hence the name. It does draught though and we know from the survey that it lies close to the cascades at the end of the cave. The main streamway twists off to the left into a Yorkshire-style series of meanders. The gypsum is extremely hard here so the water has scoured a delightful series of twists and turns. This section of meanders emerges, via a chossy choke into a very large boulder slope with a streamway crashing down from above. This was really exciting stuff. At the top of the slope it all closes down in the inevitable boulder choke. I pushed this along the solid left wall as far as I felt was prudent but it does continue. That's one for someone of a less nervous disposition I can tell you. Above the meanders is a second, but smaller, series of passages we named The Tubes. These phreatic wriggles meet up with the meanders at the choke at the base of the cascade which makes for a pleasant, if cold, round trip. They are also unusual in that there is a small grotto of straws. You don't tend to see much active stal at this altitude.

Side valley rambles

As well as looking at the main valley we wanted to look around the back of the gypsum ridge to see if there were caves on the side and round the back. There is a tributary valley that starts a little bit closer to Las Leñas with a broad flat floor at its mouth. We had looked at the lower levels of this valley briefly in 2004 and found Cueva Langosta and another flood prone looking crack. We knew that there wouldn't be much gypsum to traverse as in flood the river runs orange rather than grey. So we walked up the valley one day, hugging the gypsum on our left and checking out ever nook and cranny. For a laugh we climbed up over 3000m to peer over into the main valley and onwards to cascadas in the distance. It was no surprise that all the depressions at this height were filled with snow. Peat and Rubèn, our mountain goat duo, climbed up even higher for some fantastic views of the Andes all around.

Cueva de Las Flores

One reasonably-sized resurgence was spotted but the water runs out of a too-tight crack. Elsewhere all the depressions in the gypsum are blind apart from one small, and very pretty, cave. It is only 25m in length, but very pretty at the back. There does seem to be very little potential on this side of the mountain. A longer-term plan would be to walk / ride in to the mountains to get to the gypsum right around the back. This would be quite an epic in this terrain and definitely involve camping.

Back to Cueva Miranda, Poti Malal


Yes, despite our good intentions we did end up back at Miranda after all. However there was a good reason for this. There had been some pretty serious floods a few months before and Carlos was keen to check out the effects. San Agustin had really taken a battering with several large boulders crashing down the entrance slope. There is now a large trench in the scree slope.

Top sink, Cueva Miranda

Tim Francis and Ruben Cepeda at the Flood sink, Cueva Miranda

Of more interest was what has happened to the streamway in the side valley above Miranda. In the many years we have been visiting this has changed the position at which it sinks. This year we were astounded to see that a completely new sink had opened up on the right hand side of the valley. Even more astounding was that we were able to dig our way into the cave. It only went for a few metres but is definitely diggable. I've said this many times but if someone puts in the effort here you could have a cracking through-trip and create the longest gypsum cave in Argentina.

Malargüe Hills and Valenciana

Round the back of Malargüe are some low scrubby gypsum hills, Barda Blanca. We spent a frustrating and extremely hot afternoon looking for caves here. But there is nothing. Also in the foothills off the main road at El Chacey we had heard about an abandoned gypsum quarry. We were stopped by some farmers at a gate who said that we would need to speak to the landowner. So something to set up for the future perhaps? Finally we had an idea about trying to get onto the gypsum on the horizon beyond Valenciana. We'd seen and photographed this many years ago but never visited the area. It is of interest because it forms the northerly end of the limestone / gypsum ridge that you see at Brujas further to the south. Unfortunately they've re-opened the gypsum quarries in the area so everything was fenced off and strictly off limits to itinerant cavers. That's one for the future.

Outstanding projects

After six trips to Malargüe we have now exhausted all the obvious caving areas in the area. There are of course pockets of gypsum scattered about in the Andean foothills between Brujas and Las Leñas. But without any tarmac roads or public access these will be extremely tricky to explore. On several occasions we have come across verbal references, spoken to local farmers, hearsay and notes on maps that indicate the potential for cave. But these will require considerable effort to follow up without any guarantee of new cave, and would be best recced first by our friends in INAE. Our remaining medium term leads, without resorting to bang, are as follows:

        Las Leñas
  • Cueva de las cascadas - pushing the boulder choke upstream of the cascades, and digging through the drafting choke at the end of Sulphur Passage with a potential connection to the cascades.
  • Cueva del Colibri - confirming that the stream crawl doesn't go. A thick wetsuit and low water will be required for this. Digging the upstream choke on the left.
  • Colibri Muerto - climbing up the tufa wall above the resurgence.
  • Cueva Langosta - digs at the far end of the main chamber and right hand passage.
         Poti Malal
  • Cueva Miranda - dig top sink to connect to the main cave.

If we return again we will be looking to explore a completely new region but we have no firm plans yet.


Peat Bennett, Ariel Benedetto, Carlos Benedetto, Richard Carey, Rubèn Cepeda, Ricardo Fernández, Gaston, Tim Francis


A Colibri is a small brightly coloured bird, indigenous to this area. I think it's a type of finch.

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Mendip Caving Group. UK Charity Number 270088. The object of the Group is, for the benefit of the public, the furtherance of all aspects of the exploration, scientific study and conservation of caves and related features. Membership shall be open to anyone over the age of 18 years with an interest in the objects of the Group.