The Karstic System of Cave Formale
(Carpineto Romano - Latium - Italy)
by Emanuele Cappa, Giulio Cappa, Alberta Felici

taken from:
Proceedings of the 12th International Congress
of Speleology, 1997, La Chaux-de-Fonds (Switzerland)
Volume 4, pages 79-82

    Abstract

   The entrance of cave Formale was known from time immemorial but a sump was blocking the access to the inside after only few metres. The speleo-divers of G.S.CAI-Foligno recently explored some hundred metres beyond three long sumps; in May-June 1996 the writers, together with other cavers of the region, got the sumps empty by means of submerged pumps: such operation allowed to explore and survey more than 3Km of passages, gently sloping with few short pitches, showing an alternation of phreatic and vadose tracts, each only few metres long. The galleries join few great fractures generating sets of vertical shafts, on the whole more than 100m deep.

   The description is followed by morphologic and hydrologic observations: the main feature of the cave are the rare but violent floods that follow several rainy days. The characteristics of the cave are related to those of already known neighbouring caves: these new explorations give more information for the understanding of the deep karstic network draining the Mounts Lepini, already outlined in former studies published by one of the present authors.

    Résumé

   Le système karstique de la grotte Formale: l’entrée de la grotte était connue depuis un temp immemorial mais un siphon en interdisait l'accès. Les plongeurs du G.S.CAI-Foligno avaient exploré quelques centaines de mètres au-delà de trois siphons; en mai-juin 1996 les auteurs, avec d’autres spéléos de la région, ont vidé le trois siphons au moyen de pompes submergées: cela a permis d'explorer et de topographier plus de 3Km de galeries, en pente douce et avec quelques petits puits, caractérisées par une alternance fréquente de passages phréatiques et vadoses longs seulement de quelques mètres. Les galeries interceptent de rares grandes fractures qui entraînent des successions de puits en série pour une profondeur de plus de 100 mètres.

   La déscription est suivie par des observations morphologiques et hydrologiques: les crues, rares mais puissantes, qui suivent plusieurs jours de pluie sont la particularité de la cavité. Les caractéristiques de la grotte sont comparées avec celles des cavitées voisines: les nouvelles explorations permettent une meilleure connaissance du réseau karstique profond des Monts Lepini décrit dans des précédentes études publiées par un des auteurs.

    1. Introduction and historical data

   The cave Formale opens in a small valley, tributary to the main valley of river Rio, in the central part of Mounts Lepini. Both flow towards NW and are divided by a fossil valley having the same orientation (FELICI, 1976, table 3). The general hydrologic pattern of this zone has already been treated (FELICI, 1973-1974-1994).

   The local farmers have used, since immemorial times, to penetrate in the cave during the hot season in order to draw water from its former pools; but the configuration of the entrance and the huge floods flowing out of it in highly rainy days gave rise to legends and, in the nineteenth century, to a poem (GESSI, 1843?) briefly imitating the Divina Commedia.

   The cave Formale has been registered in 1948 by Segre with the number 39 La RM in the file of natural caves of region Latium. At 25m from the entrance a first sump is met: only in extremely dry weather it opens giving access to a hundred metres of meandering passages, at the end of which can be seen on the right wall an inscription of August 1922. In 1971 the divers of ASR (Associazione Speleologica Romana) club went over a second sump, stopping at the beginning of a third one, and surveyed the first 245m of the cave. Only in 1990 the exploration was resumed, by another club (the caving Group of CAI-Foligno: BOLLATI, 1994): beyond the third sump a long gallery was discovered and surveyed up to 704m, with many lateral unexplored leads.

   In 1996 the writers together with other local colleagues decided to open the three sumps by drawing water with submerged electric pumps: the operations started on May the 9th and continued for 8 days before finding air even at the third sump. Then the explorations began, while pumping was protracting in order to reduce the water levels in the sumps and in the many lakes that follow them. The Spring and Summer 1996 were pretty rainy, so the pumps had to work at different times up to September; at the end of this month a lot of rain caused the infilling of the second sump.

   At that moment 3294.15m of passages were already surveyed but the total explored length was certainly above 4Km, including nearly 500m of 5 branches beyond a fourth sump on the main route inside; at least other four sumps were encountered together with a few lateral branches descending below -120m.

    2. Description of the cave Formale

   The "main route" starts with a sequence of three sumps, the 1st and 3rd being short and shallow, the 2nd 12m deep and 40m long. Both between the sumps and beyond them are narrow meanders which make the advancing laborious. The 3rd sump is followed by some pools that make the wearing of neoprene suit very advisable because they don’t get empty even when pumping out the sumps; also between these pools are tight meanders. At 526m from the entrance the "main route" falls suddenly down a 1st shaft, 8m deep, then it continues wider but generally lower, again with some short pool. On the right a low squeeze allows to "by-pass" (that’s just hits name) the 1st shaft, but very uncomfortably. At 711m the "main route" leads to a twin-shaft ("pozzi gemelli"): the former gives access to a small sump ("sifonetto"), the second one to a wider prosecution of the "main route" which arrives (about 1150m) to a 4th sump, 50m long, beyond which five tunnels branch out, at the moment explored for a few tens metres each.

   On the left of the "main route" it is possible to descend through a network of smaller meanders, showing many restrictions and ducks: "vermiciattolo" (small worm) followed by "via condotti" (the name of a famous street in Rome) is the main way which continues beyond the surveyed part, down to a couple of sumps; on its left "via dei laghi" (the lakes’ road) followed by "via dei pozzi" (the shafts’ road) reaches a sequence of drops ending, at -123m, with another sump; on the right the branch "D" comes back to the "main route" and its sub-branch "L" has been explored up to nearly 10m from the back side of the "sifonetto". On the map (see Fig. 1) it is possible to see a few other passages, but in this whole area there is a lot of unexplored leads: the smallest holes can give access to the largest branches! The second part of the "main route" yields two important branches on the right: "fangolandia" (mud-land) is a very muddy upward meander, the branch "G" soon gets to a bifurcation: forward it continues towards the end of "fangolandia", downwards it gets -112m ("pozzo dei conetti" i.e. the way followed by some small SPIT cones that fell down during the first exploration) with some shafts and meanders, ending just beneath the "main route", in a large chamber with a lot of mud and big boulders: among them a small stream sinks down.

   There are also, in unexpected places, a few ascending shafts, not all surveyed, approaching the external surface but only one of them shows a real chance of opening a new access, which could avoid to pump out the sumps every year.

    3. Morphologic and hydrologic observations

   The cave opens in limestones of upper Cretaceous, mainly rudist mounds . The local dip is 21° towards NNE, with an alternation of thick strata, up to 1-1,5m, and 10-20cm thin ones.

   The deposition of limestones ended during Palaeocene following an upward movement without appreciable folding or faulting; it started again at the beginning of Miocene when limestones were soon followed by marly mudstones, then marls and clays (pelitic turbidites), all deposited nearly with the same orientation of former limestones: only scarce traces of epi-karstic erosion at the interface. The uplift of the massif became considerable during the middle and late Miocene and the whole Pliocene. The area in these periods have been dissected by faults, thrust faults and a lot of minor rifts; according to GALLO et al. (1986) it was possible to reconstruct a sequence of at least five deformational phases, including tear faults nearly horizontal or parallel to the strata dip.

   The "main route" is prevalently developed along two thick strata (one up to the "twin-shaft", the second, about 7m below, further on), very rich with Rudist fossils. The general trend shows a sequence of sinusoids both in plan and in vertical developed sections: the ratio of their heights just corresponds to the tangent of the dip (21°). In the details it is noticeable that short rounded phreatic sections are frequently alternated to vadose trenches (showing smaller phreatic tubes near their ceiling): the homogeneity of the passage shape is never longer than 10-15m.

   The other branches are generally smaller and only in some parts follow the thick strata with rudists; they form a very complex network prevalently guided by small phreatic tubes, with consistent vadose meandering trenches rarely wider than 50cm. They are cut by a number of vertical rifts: along them developed sets of chimneys (one only has been ascended) and shafts (mainly descended: at a certain moment more than 400m of ropes were in place though the total difference of level within the cave is lower than 150m).

   Now it is possible to imagine that the first development of the cave was along a network of small phreatic tubes nearly all included in the thick rigid rudists strata: at the beginning of the uplift the faults were all compressive but a gentle folding, connected with nearly horizontal thrusts, made the thick strata (nearly 1000 times more rigid to flexural deformations than the decimetric strata) break while the thinner ones only slipped along the clayey interstrata. Consequently we suppose that the origin of the cave is certainly very ancient: probably it started in Middle-Upper Miocene. The relaxing faulting which generated the vertical rifts began very later: mainly at the end of the 4th tectonic phase and during the last one, i.e. from the late Pliocene to the lower Pleistocene.

   During this last period started the Glaciations, meaning in the Mounts Lepini (never covered by a permanent ice cap) very rainy periods; in Pleistocene a great thrust fault had dissected the area into two pieces and probably cut the way down to the deep phreatic tubes developed during the "crisis of salinity" of the Mediterranean (5,5 to 4,5 My before present): so the cave, and especially the "main route", was subjected to great and prolonged floods that widened the passages, creating not only scallops but also excavations typical of strong water flows (pot-holes on the walls and ceilings, vertical cylindrical holes on the ceilings). In Pliocene and the earlier Pleistocene the western coast of the massif, that was in contact with the Mediterranean sea, was covered with hundred metres of marine deposits (sands, clays, etc.) which created a barrier to the water flow from the karstic system developed formerly: this is another possible factor for the re-activation of the upper karst drainage (FORTI, 1992). The shape of the "main route" confirms that from that period on this one has been the way through which the water flowed outside; the other branches probably were subjected to development later. Then the eruptions of Latial volcanoes covered the region with ashes and consequently stopped the floods: inside the cave we observe many thick speleothems (mainly stalagmites) that could not have developed when water was prevailingly flowing.

   Probably the cave was subjected to repeated cycles of flooding and rest: the latter ones progressively increasing while the lower (and up to present unknown) conduits, obstructed by faults in Pliocene and/or the marine sediments, were taking again their function. At present the floods last only two-three days and require at least some days of continuous rain in November or December, but there is evidence that in recent periods, a little warmer and dryer than to-day (e.g. at the end of Wurm) the cave was devoided of floods for pretty long times.

   A thin coat of dark brown-black colour (Manganese and Iron oxides?) covers the walls and the ceiling, mainly in the "main route"; it has been found on a piece of Roman tile too: probably it was due to a crisis in the local vegetation (big wood fire ?) at the beginning of Middle Ages. The walls are deprived of that coat and appear of a shining white colour below the normal level of the pools and in the places where a film of water comes down when outside it is raining: this indicates that the dark coat can be easily removed where water covers the walls for long periods.

   It is noticeable that up to the last centuries should exist a few upper inlets (not said of human size) to the cave, that were filled with stones and debris when the surface was turned to farmed fields: some of them were probably closed in these last fifty years.

    4. Mutual relations among Formale and other neighbouring caves

   We have already mentioned that NE of Formale there are two other valleys, one is fossil and beyond it we find the main valley where Rio river flows: they both join, together with the Formale stream, 1Km North of the cave, at the Omo Morto (Dead Man) bridge. Close to it other four caves are known (FELICI, 1976; FELICI et al., 1994); they all start with vertical shafts: three have a mainly vertical development and their exploration ended with unexplored sumps (26 La Bocca Canalone, 40 La Ouso dell’Omo Morto) or mud choke (24 La Ouso dell’Isola). The fourth (832 La Grotta Ciaschi) sinks with seven shafts down to -113m (GIURA LONGO, 1994), then it develops with a few galleries for more than 1km, ending at three downwards sumps and a maze of ascending passages in the upper section: this part is approaching the "via dei pozzi" and "via condotti" branches of Formale but still without any sign of connections. The main part of the nearly horizontal galleries of Grotta Ciaschi are at the same height above sea level of the sump at the end of "via dei pozzi". A small permanent stream is flowing along the galleries of Grotta Ciaschi but it does not correspond to the main deep stream that all the cavers are still looking for in that place.

   During the prolonged rainy periods it happens that a strong flood comes out of Formale: one or two days later another important flood debouches from Bocca Canalone, the other three fill of water up to few meters below the entrance. Their entrances are all 20-50m lower than Formale, Bocca Canalone being the lowest one. On the contrary, when the flood is gently increasing, it happens that Bocca Canalone debouches the first, and Formale follows later, only if the rain continues during the following days. The area feeding all these caves ( the "Faggeta" large polje and the surrounding hills, with a lot of caves: FELICI, 1973) is supposed to be substantially the same: we should conclude that Formale has a more direct and wider connection to the main karstic collector; the fundamental aim of its exploration was to check this hypothesis but the goal has not yet been achieved.

    5. Perspectives for future work

   Inside the cave Formale some tens of leads still wait to be pushed: of the highest interest is the upward prosecution of the "main route" beyond the 4th sump where we expect it will be possible to reach some active gallery drawing the main water flow. Also very interesting will be the prosecution along the descending passages of "via Condotti" and its lateral routes: will they join the cave Ciaschi or continue to descend to greater depth? Generally speaking will some caves of the Omo Morto area be reached, even if through very complex and long passages? Unfortunately the exploration in cave Formale requires to pump out again the three former sumps and, of course, to wait for a new dry season, but in the meanwhile we are going to explore the sumps at the bottom of the other neighbouring caves.

    References

BOLLATI, M. 1994. Il Formale a Carpineto Romano. Notiziario Speleo Club Roma n. 11: 33-35.

FELICI, A. 1973. L’idrologia carsica nel territorio di Carpineto Romano. Proc. 6th Int. Congr. Spel. Olomouc: IV, 63-72

FELICI, A. 1974. Considerazioni sull’evoluzione del carsismo nei Monti Lepini. Atti XII Congr. Naz. Spel., S. Pellegrino T.: 293-302

FELICI, A. 1976. Il carsismo nei Monti Lepini (Lazio): il territorio di Carpineto Romano. Notiziario del Circolo Spel. Romano XXI-XXII: 3-230

FELICI, A. , GIURA LONGO, A., GRASSI, L. & TRIOLO, I. 1994. L’esplorazione della Grotta Ciaschi apre la porta alla scoperta del drenaggio profondo dei Monti Lepini. Atti XVII Congr. Naz. Spel. Castelnuovo G.(in press)

FORTI, P. 1992. Inverse evolution of some Italian karst systems. Proc. Int. Congr. on Alpine Caves Asiago: 215-221

GALLO, F., RABITO, G.L. & SALVINI, F. 1986. Analisi strutturale dei Monti Lepini. Mem. Soc. Geol. It. 35:603-610

GESSI, G. 1843? (manuscript) Il Formale, canto unico ed inedito. Comune di Carpineto Romano (1995): 1-68

GIURA LONGO, A. 1994. Grotta Amedeo Ciaschi. Notiziario Speleo Club Roma n. 11: 39-42


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