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Survey AN506

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AN506 - Pozo de los Ninos


August 1998: let us forget about the first couple of days where we had to carry all gear up to 2170 m of altitude and set up our small camp (2 tents). Let's go straight to the AN506!

The AN506-team arrives at the top of the Anialarra after a 2 hour walk in terrible conditions: mist, strong cold wind and melting snow. Putting our caving clothes and gear on is awful; seeking some shelter against the elements behind a 1 by 2 metre boulder. Finally we arrive at the bottom of the entrance pitch (23 m deep). While the other two (Annette and Flip) sort out the gear and try to get a bit warmer, I put a couple of bolts on top of the second pitch (8 m.). We have the Hilti drill with us, and two battery packs, so rigging goes fast. We also have got 7 heavy kitbags for the three of us, but we hope to get rid of most of the weight (essentially ropes) during our descent. After the P8, a splendid freehanging P23 follows. The water showers down and I have to rig a traverse line that brings us out of the water. At the foot of this pitch, I have to climb up a ledge that dominates the enormous pitch that we found last year. We estimated this "Monster" at over 200 m deep!

I throw my first 100 m rope down, and with another 100m rope in a bag at my belt, and the hammer drill around the neck, I carefully go down the formidable shaft. Re-belay at -5m, another one at -20m. I deviate to the right, in order to get out of the water that is dripping down. Outside it must be raining hard!

Jos goes down the Monstre, 259m deep. The pitch is getting very wide (section 20 x 7 m) and I go down another 75m until I reach a tiny ledge, that was my terminus last year in 1997. Under me there's sheer blackness; unknown territory! The ledge is way too wet and I climb up again for about 15 m. I swing 4 m to the right again, drill a couple of bolts into the rock and rig my second 100 m of rope. I make a mess of my jammers when I'm switching from climbing to abseiling again and I have a few scary moments, untangling my gear whilst swinging above 100, 200 m? of frightening blackness. Every noise echoes for at least 10 seconds... ooh boy!
Annette and Flip wait patiently at their re-belays a hundred metres above me. I have to decide between rigging a fabulous free-drop (a 100 m or more), or staying close to the wall. I choose the second option, since we would loose a lot of time when prusiking up again later on those very long sections of rope. But following the wall means a lot of re-belays, since the rock is very sharp and we cannot accept the slightest rubbing with our 9 mm ropes. So this second rope costs me about 1 hour. I'm desperately seeking a small ledge to stand on for a few minutes, since both my legs are deeply asleep, but the giant pit stays very vertical all the time. Finally I see the bottom approaching.... but no, it's just an optical illusion. End of my rope, I have to switch to our last rope (84 m) and I'm hoping that it shall take us to the bottom of the pit! The first battery-pack of the Hilti is flat by now (after 20 10 mm bolts), and I have to make a risky manoeuvre to switch the batteries, while hanging on the rope.. Again the hammering of my drill echoes through this giant echo chamber of Mother Nature. And then, after a 2,5 hours descent of 260 m in one of the most impressive pitches I ever did, I reach a big platform, made out of some giant boulders that are stuck in the middle of the pitch. I don't have one metre of rope left! My wife Annette and Flip also arrive; Flip pulverises his record: his deepest pitch up to now only measured 28 metres!

But it isn't finished yet. Under the boulder platform, the pitch continues, a bit less wide and not so vertical anymore. I throw down a rock and it goes down a very long way; we guess at least another 100 m! I rig only the top of the pitch, the rest is for the second team that arrives tomorrow. We sort out all gear, warm some soup and hurry out of the cave, since we had agreed on a radiocontact with "base camp" at exactly 21.00 h. But prusiking up 300 metres on the first day of your holiday is quite tough, and breathless I arrive a few minutes late outside. But the others are listening, and soon I can report the great news to them: we have done one of the deepest pitches of the Pyrenees, we got to -310 m, the cave is still going, the underground river must be within reach! It is still raining and we seek shelter in the tent, where we prepare ourselves a hot meal. We didn't get a lot of sleep, though we're pretty tired, since the wind howled over the mountains and shook the small tent around all night.

The next days it is Jos' and Johan's turn to continue the exploration. If our estimation of 100 m for the new pitch is correct, they should arrive at the level of the underground rivers, that all flow at 400 m depth on an impenetrable layer of "schist". Horizontally viewed, we are less than 100 m away from the Anialarra river (System AN3-AN6-AN51). We have solid hopes for a junction with it.
Jos and Johan go down the new pitch. It is less vertical and they have to place a lot of bolts (by hand because of a battery problem). Then they arrive at the bottom: there is only a flat and sandy floor... no river! They are at -410 m, the pitch measured indeed 100 m. Probably the cave is blocked because of the schist layer just beneath. But at the way down, they have noticed some giant "windows" in the wall, and they are convinced that parallel pitches exist.

After a day's rest we are present again: Paul, Annette and Jos. At the boulder platform at -310m Annette and me start surveying the fossil 100 m pitch. When we arrive at -410m, I notice a small climb, only 5 m high, but without a rope it is just too tricky... Meanwhile Jos has attacked one of the parallel pitches; a massive one with a section of at least 15 m. But we can hear his Hilti hammering very clearly, and after a descent of 60 m his pitch rejoins ours at -370 m. No luck for today. When we have regrouped at the platform at -310 m, we search around and find a small hole between the big boulders. A rock goes down at least 20 metres, so we rig it quickly. Jos goes down and yells "there's another big pitch here!". Annette and me go down also and indeed: a beautiful freehanging pitch awaits us! But we don't have anymore rope left, so Jos has to climb up the 20 m pitch again, to go and de-rig the fossil P100.
A long hour later he's back (in an over-heated state). Meanwhile I have already placed the bolts and 10 minutes later I go down a spacey 41 m-shaft. In the last 15 m. of it, the walls are not made of solid rock but of a bizarre sediment of mud and boulders. It looks like a giant man-made wall and it certainly doesn't look very stable to me. At the bottom, a narrow crack is the only evident continuation. I work for half an hour with my hammer to widen it up, until Annette can get through. But further on, only a too narrow (but ventilated!) meander goes on.

Back up then. Jos climbs out alone (rendez-vous at the CB at 2130 h.). Annette and me start surveying the Monster. It goes pretty good and we decide to go on until we're out. At 2300 h, after an 11 hour trip, we arrive at the surface, under a moonlit sky. It is a beautiful warm evening, and we spend a quit and peaceful night under the moonlit summits of the Anialarra.

In the following days, we made several other trips in the cave. At the bottom (-410 m), we made the 5m climb, but it ended in boulders. In the entrance zone, we started digging in a small gallery ("Galerie Pourrie") and explored about 100 m, featuring some small pitches and a 20 m. climb. In the big 259m pitch (we felt really comfortable in it after a couple of days), we explored some leads by making acrobatic traverses. During one marathon session (where Jos and I prusiked at least 600 m) we discovered another parallel pitch, Puits Paul, that unfortunately connected also with the fossil P100, and we surveyed everything that hadn't been surveyed yet.

Finally, after a photo-session (the picture was no good...) in the big pitch and a few very "pleasant" de-rigging trips to get the 700 m of rope out of the cave, we could call it a day (or better a week). No connection with the underground river had been made, but we had no reason to complain with our little "Monster"!


The Monster is 259 m deep. But it goes up for at least 15 m above the point of departure, and a simple traverse in the P23 just above would make you arrive exactly at the wanted point to make the big pitch a 274 metre drop. But, we didn't have time for it.

Geologically speaking, the pitch is 374m deep and the deepest of the PSM-massif. A look at the survey learns us that the P100 is the continuation of the P274 above it. But since the boulders that are stuck in the p?ch at -310 m. (real big ones: 10 m wide!) permitted us to leave the rope and walk for a couple of metres to the next rope, we thought it would be more correct to speak of two separated pitches. During the descent in the P259, there is not one single ledge that is big enough to have a comfortable foothold on it.

The pitch is absolutely a pleasure for the eye. The rock is black, with large veins of white calcite. Enormous deposits of yellow "moonmilch" flow down the walls. The wall are very eroded by the water, and at some places the wall has been dissolved into long sharp "knives", up to 20 m long.
The pitch constantly changes in size and shape and that's why it stays fascinating. Some other big pitches that I did ( P328m in Aphanic? P200 in Sima Cueto) are so regularly shaped that they become almost boring.

The acoustics are phenomenal. The shaft functions as a giant organ pipe and amplifies every sound. A scream echoes for 10 seconds. A rock, thrown down, makes a sound as a freight train going through a tunnel. During our photo-trip, the plastic lens cover (only 1 gram in weight??) fell down... the noise soon became a deep rumble. That was how we discovered that you only had to throw down a small pebble the size of a coin, to be rewarded with a mysterious hum of a giant didgeridoo. In other words: when you don't dare to go down a pitch this size, you can still amuse yourself in some other way.

In the list of "deep pitches" of the PSM-Massif, this pitch takes second place after the historical Puits L?ineux, the original entrance of the Pierre-St-Martin. Nowadays, no caver would dare to present this pitch as a P320, since it counts +/- 9 ledges, some of them big enough to put a regiment of cavers on. And in fact, when back in 1954, the body Marcel Loubens was hauled out of the pitch after his dramatic fall, fellow cavers were posted for hours onto these ledges. The longest vertical piece in the pitch measures 80 metres, and the pitch shifts 25 metres horizontally....

But, the Lepineux is a historical monument and we have to respect it! And so, it will remain "top of the bill" for a long time.


Over 50 pitches are known on the PSM Massif, that are deeper than 100 m. This is the top 10:

Cave Pitch Depth
1. Réseau de la P.S.M. Puits L?ineux 320 m
2. Pozo de los Ni?s (AN506) Le Monstre 259 m
3. Perte d'Eruso Puits des Dominiques 248 m
4. Réseau de la PSM (SL19-Gouffre Pascale) Puits d'Entr? 215 m
5. Trou de l'Ours (D10) Puits d'Entr? 206 m
6. Gouffre Sauveur Bouchet Puits d'Entr? 196 m
7. Gouffre du Pas de l'Osque Puits d'Entr? 170 m
8. Sima H (C108) x 167 m
9. C110 Puits du Citron Hallucinog?e 165 m
10. M213 x 160m


The small entrance (only 35x40 cm) is formed in lime-schist and aspires some cold air (when it is warm weather). The entrance pitch is a P23 with 3 re-belays: P-hangers that are glued into the soft lime-schist with epoxy resin. No bolt holds in lime-schist (best compared with cardboard!).
At the foot of the first pitch, we are already in good, black limestone; the "Calcaire des Canyons". We are in a chamber with an inclined floor that goes to a P8, in which one is always rewarded with a rain of small rocks that slide down the slope of the entrance chamber. A few metres further, begins the very aesthetic and cylindrical P23. You have to rig a traverse line at the left (4 bolts) since it could be pretty wet.

At the foot of this pit, you have to climb up for 3 m onto some boulders. Please use a rope for this, since on the other side of the boulders there is the yawning mouth of "the Monster". Rig a traverse line at the left. Then re-belay at -4 and at -20 m. Then a 65 m free-drop. The pitch is at it's widest here, very impressive. When you continue to go down, you'll reach a small ledge: you are too far down! Climb up again (15 m) and swing to the right (facing the wall). You'll find the bolts for the re-belay. The following 180 m are re-belayed often, never more than 30 m apart. It is not possible to describe the exact location of each re-belay, but 1) they are all at your right and 2) we have marked them all with a small circle in red paint. Most of the bolts are doubled.

At -310 m you reach the boulder platform, a good place to stop for a while and recover from the emotions in the "Monster". The logical continuation is the P100, with it's 10 m wide opening. It is re-belayed 5 times, because of it's big and sharp ledges, but these are all "exploration" re-belays so they are most of the time not doubled! At the bottom, everything is blocked by sand.
In this P100, you can make a "pendula" at -20m (North direction) to reach a platform. A gallery (1,5 m wide) starts here and after 10 metres you can go down Puits Paul, that rejoins the P100 after 68 m, near the bottom of the cave.
Back at the boulder platform at -310m, one sees in Southern direction a big hole: it is Puits Jos (15 m wide!) that also rejoins the P100, after 62 metres.
Finally, at the boulder platform one can go down a hole between the boulders (follow the water that drips down). A P18 and a P41 (Puits Maéénn? follow.

In the entrance chamber, a gallery leads off in the rotten lime-schist (Galerie Pourrie). A bit further, there is a P4+P7 at the right, or you can go straight on through some squeezes. At the end, it becomes too narrow. A 20m high chimney can be scaled easily.


In 1986 the Belgian club of St. Nicolas (Liège) connected the AN6-Pozo de Frontenac with the AN3-Pozo Estella. In the rush, a third entrance was added to the system; de AN51-Pozo de los Acuarios. The resulting cave system measured 11 km and had a total depth of -711 m. However, when they tried to assemble their new surveys to the old surveys (dating from the 70ties) of the cave, it didn't fit at all. They found the solution in simply moving the entrances of the caves, for the AN6 more than 250 m South! The surveys were bended en twisted until they finally became something that could be called a "cave system". We (and probably nobody) were not aware of all this and we thought that we could quickly put our survey of the AN506 onto the map to know it's relation to the Anialarra System! But soon, in 1997 already, we came to the conclusion that the cave entrances just weren't where they were supposed to be!
In 1998 we spend a lot of time to determine the coordinates of each entrance repeatedly with a GPS (always averaging during at least 15 minutes). With a Suunto compass we also took readings on the 3 most important summits which gave us the possibility to verify (triangulation) the GPS-coordinates. Last but not least, we made surface surveys from the AN6 to the AN51 and to the AN506.
All this resulted in a new set of coordinates, with an estimated precision of 15 m. The differences with the old coordinates are enormous (up to 300 m). As a conclusion, we can only say that the existing survey of the Anialarra System is unusable and that we do not have an accurate idea of the distance that separates the bottom of the AN506 from the rest of the System.
We do know of course how far the entrances are apart, and this isn't much: the AN506 is about 110 m south-west of the AN6. The AN51 is 90m north-east of the AN6.

These are the coordinates we found: (Lambert 3):

AN3: X=348,082 Y=3076,580 Z=2070m
AN6: X=348,711 Y=3076,314 Z=2168m
AN51: X=348,800 Y=3076,354 Z=2153m
AN506: X=348,610 Y=3076,266 Z=2178m



Coordinates: Lambert 3: X = 348,610 Y = 3076,266 Z=2178 m

UTM (1950): X = 684,151 Y=4757,262 Z=2178m

Count on at least 2 hours, when starting in the PSM ski-station, and when you now the way! If you don't know the way, count on at least 3 or more hours. Start in the ki-station and follow the Pescamou track, until you arrive at the Gouffre de la T?e Sauvage (an upper entrance of the PSM-cave). This is a "jeepable" track but the last few years, the city of Arette has forbidden all traffic on the track! From the T?e Sauvage you have to follow a narrow footpath, marked with red paint, that climbs up steeply. After 10 minutes switch to the markings in white paint, that lead to the Col de Baticotch (metal shed, used by French cavers). Continue through the pastures, and stay on the same altitude. At your left is a big hill, the Murlong. In fact, you have to walk around it, staying on height. The path is marked with white/yellow paint, but not very well visible anymore. Half an hour after Baticotch, you reach the "Col Porteur", sort of a "pass" that dominates a beautiful lime-stone valley: the Faille X. Cross the valley, still following the white/yellow markings. On the other side of the valley, turn left direction of Pic d'Anie, and gradually climb up the right flank of the valley. In the distance you'll notice a very steep rock cliff, at least 50 m high: the aim is that you arrive above it!

You will arrive in small pastures again, where you abandon the yellow/white markings and follow through the grass, direction West. You arrive in a more or less horizontal pasture. At your left, the Faille X. At your right, a breath-taking view on Ukerdi, another valley similar to Faille X. Straight before you: a steep grassy hill, about 100 m high, that you have to climb. It leads to the summit of Anialarra, 2184 m high. At the left of the top there is big "cairn" (pile of rocks, made by man) just besides a big daylight shaft. Turn right before the cairn, follow a vague path between the rocks: 25 m further you'll find the entrance of the AN506.



Pitch Rope Re-belays Carabiners Remarks
P23-Ingang 30 -4m, -8m 4 3 P-hangers
P8 20 -3m 4 traverse line 4 m, right
P23 30   6 traverse line 2m left
E3 5   1  


100+100+90 -2m, -20m, -83m, -91m, -120m, -155m, -186m, -198m, -221m, -239m 24 traverse line 4 m left
P100 120 (of 2x60) -6m, -29m, -37m, -79m, -90m 9 must be bolted better

Puits Jos

85 -11m, -32m, -40m, 10 traverse line 3 m right

Puits Paul

85 -8m, -32m, -45m, -52m 6 must be bolted better
P18 20   2  
P41-Puits Maéénn?/td> 55 -2m, -7 m 6 traverse line 5m
Totaal 740 m   72  

NB: the last 4 pitches can all be rigged with the rope of the P100. Thus you can reduce the total length of rope to 495m, for 48 carabiners.


PARTICIPANTS Anialarra 1998

SC Avalon: Rudi Bollaert, Jos Beyens, Paul De Bie, Flip De Clerq, Herman Jorens, Mark Michiels, Frank Saenen, Chris Sinnaeve, Kris Vermeulen, Micha?a Van de Casteele, Annette Van Houtte
Krypta: Peter De Geest
Gopher-it: Johan Hovelynck

Many thanks to "Berghut" (Hamme) who provided us with useful gear.

Contacteer/contact us:  SC Avalon vzw
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