The
occasion is rather rare: it has the possibility to visit
the caves of Villanova reaching features not opened to the
public. The meeting happened near the locality of Villanova
of the Caves, one small fraction of Tarcento. It was a cold
clear day, the temperature surely under zero. As soon as
we parked the cars, the first stage is the bar Panorama.
The name is clear, because in front of us there are a series
of mounts that generated the more energetic forces of the
zone; talking about external Adriatic fault. In this zone
the pressures generated from the meeting of African continent
towards Europe seemed to have worked overtime. Michela explains
to us the phenomenon, crushed the one against the others,
the several mountainous formations, created from the overflowing
and the folding of the fault. After the coffee, the friends
of the Circle Speleologico Idrologico Friulano, have accepted
our demand to visit the caves, showed us the equipment that
we will have to use, and explained quickly how we will have
to use it; talking about helmets, equipped with a headlight
working with the gas provided from carbide and lasks of
water, hung around the belts. Other than carbide, for every
convenience, the helmets are supplied with electrical head-lamps
and battery. The intense cold makes the movement difficult,
but in short time we succeeded to fill up the flasks with
carbide, the tanks with the water, and to connect it all
together with the rubber hose. At last we put on with a
few awkward movements belts and helmets. The flame to carbide
works by dripping of water-drops, controlled from a tap,
over the carbide, provoking therefore a reaction that generates
the emission of a flammable and luminous gas. The ignition
happens thanks to one spark obtained from a piezoelectric
quartz lighter. Thanks to the experience of our companions,
after a while we are all ready for the departure, with the
head-light ignited. The entrance is close to the bar Panorama,
well locked with a metal gate, Inside is warmer then outside:
there is approximately 10 degrees difference and the humidity
is around 90%. Both ground and shoes are frozen, and the
path in sloping down makes the march very difficult for
who is not accustomed to this type of distance, but slowly
we reached the interesting zones.
The helmets reveals suddenly essential, the ceiling is often
low, and small peaks bump hard against them. Fortunately
soon we adjust and the attention is shifted to where we
lay our feet. The small flames of gas are suitable to illuminate
the cliff and the distance, so the torchs that we have carried
with us in order to facilitate the photographic resumptions
and video, though we might not use them, except in order
to evidence particular zones. The conformation of the cave
is truly interesting. The friends speleologist point out
the several conformations of faults that we cross in length,
and explain the particular mechanisms of creation of the
caves. It consists of a mixed phenomenon of chemical aggression
and physical flowing of the water. With the first one, the
limestone is melted in the water thanks to the presence
of carbonic acid, created with combination of water and
carbon dioxide.
It's an unstable acid , but it succeeds in time to generate
important eroded phenomena. The second is a well-known phenomenon,
but that in this case has created unusual conditions that
are characterizing these formations. Usually in fact, the
carsic phenomenon, is limited to the dissolution of the
limestone and the formation of caves, over stalactite and
stalagmite as a result of the depot of the limestone melted.
In the coves of Villanova, over the carsic phenomenon, we
can find the phenomenon of the erosion, in emphasized measure,
also.
The wide corridors in which it is possible to remark it,
are the strong pressures and the fast currents of water,
that have generated these cubicles. Some of cliffs so called
"flysh" constituted from thin limestone layers and marnal,
and often present in the zone, are present also in the conglomerate,
formed from round pebbles cemented together. While the ceiling
often is formed from rubble of clutch, formed from the cementation
of little pieces derived from the disintegration of the
cliffs, as a result of the movements of the fault. The fragments
that form the rubble, with the exception of the conglomerate,
are very shaped and much younger then the pebbles, whose
have rolled inside current waters like streams and rivers.
Inside the cove it is possible to observe various plans
of active faults that testify with their micro-movements,
the existence of generated pushes still perfectly active,
from which it is called neo-tectonic, phenomenon that has
collaborated to the generation of the Alps and still nowadays
shows its effects with the mountain and land raisings. Still
coming down we meet inside a small lake well delimited with
stones; and Lucia, the official caretaker of the caves,
explains us in that part of the water the passage flooded
integrally, as often happens inside of similar caves, and
because of some maintenance works, in order to make the
path viable, it has been generated the small lake. Immediately
after the reconstruction the life of a beautiful black bear,
the story leaves us astonished by us. The bear is of course
one of the first inhabitants of the coves generally, in
other coves in fact, it has been possible to recover also
remains of meal and ancient bones.
Continuing the visit, our attention is attracted to several
fractures of the fault, they make us feel like Jonah inside
the whale.
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Lucia tells us what happened during the seismic
tremor of Caporetto; last July, mean-time, some tourists,
present in the cave for a visit, were moved with emotion.
Staying inside a stable cove as that one of Villanova is probably
one of the safest places during a seismic movement of medium
intensity. There in fact the seismic waves of the surface
are attenuated from the depth and the conformation of the
arcades, in the majority of the cases, it offers a natural
protection from landslides or falling objects. Naturally the
landslides are possible also in cave, and the signals inside
are obvious, however these are more probably generated from
inside erosion than seismic events.
Numerous display windows and other fixed micrometric pointers
along the active faults supply us useful information about
several movements which the cave is subjected. It is possible
to detect them easily during the travel, while the emotion
comes up. Some hurdles are on the way. In order to reach one
of the most interesting part of the visit, we must cross a
small passage, hard to pass because the roughness. It was
necessary to sneak and avoid obstacles by unusual and laborious
movements, but after some moments of tension both physical
and emotional, we reach again an easy way, and after a while
the goal. The show is unique. The stalactites and the stalagmites
are more concentrated and the transparency is evidenced from
the light of the lamps. "The spaghetti (stalactites)" that
come down perfectly from the ceiling and "little pillars (stalagmites)"
perfectly shaped reward all the hard work in order to reach
the place. The most interesting is one stalagmite/stalactite
broken from the seismic of 1976. The fact that the other formations
have had no aftermath, we risk some hypotheses on the causes
of this phenomenon. The sliding of the fault generated from
a seismic is not a regular movement, talking about small movements,
followed at small blocks due to the friction. I point out
that a seismic event can be simulated by putting a brick over
a rough cliff plan and an elastic.
The elastic connected to the brick begins to carry itself
in tension, the tension increase until the friction that holds
brick to the cliff plan unties and therefore the brick is
moved ahead until the point in which the friction refrains
it and blocks it again. The width of the faults and the elasticity
of cliffs make it so that this type of movement, is reproduced
in discontinuous way during a seismic event, generating a
series of releases and blocks that can be represented in the
time and the space by one wave to a quadrant with variable
amplitudes. It's clear that all the quadrants waves, in their
propagation generate a series of almost infinite of harmonic
waves, a kind of sinusoidal waves, of multiple frequencies
from the fundamental one, and generating what it is called
noise. During one of the '76 phenomenons, these kind of various
waves, must have reached- up the stalagmite/stalactite, and
a particular frequency has probably succeeded to send in resonance
the concretion, generating inside some contrasting forces
that are particularly intense, so that they have broken it.
Other concretions present in the same area, subordinates to
various frequencies from the own resonance, have not experienced
the same effect, and remain therefore intact. The effect is
similar to two diapason that are equal and near, in which
when one of the two is shocked, it generates the vibrations
also in the other, while if the diapason are different, they
affect in different ways, they sound in various frequencies,
and the answer effect does not happen. For a better explanation,
imagine a tyre not perfectly balanced, on your car.
When a particular speed is reached, the car begins to vibrate
and if the vibration involves the entire vehicle, the forces
to which this is subordinate, are magnified to the point that
they could, in extreme cases, to cause the structure to yield.
On the way back we stop ourselves to resume a point in which
a partial landslide has occured after the formation of stalactites.
The divergent slanted positioning of these, testifies completely
of the theory of the instability of these two cliff layers.
At the exit, tired and sweaty, we try the emotion to change
our clothes in the winter cold. Fortunately it is only a moment
and the most reckless, almost nude, take it easy, testing
the fresh air on the skin. It has been a nice journey in the
heart of our earth and in the soul of the earth-quakes.
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