Puy de Dome, France

Mysterious antiquity

The summit of the Puy de Dôme bears the ruins of a great Gallo-Roman temple dedicated to Mercury. As can be seen from the ex-voto found on the site, its influence extended way beyond the frontiers of Arvenie. It was discovered in 1873, during building work on the Observatory. The Temple of Mercury was built in the first two centuries A.D., on the site of a more ancient Gallic sanctuary. Its plan follows that of the traditional Gallic temples, with a cella, ambulatory and opening facing the East.

According to Pliny the Elder, a fabulous statue of the God Mercury, some 18 metres high, was made by the Greek sculptor Zenodore around 60 A.D. No vestiges of this statue have yet been unearthed.

We know nothing of the downfall of the sanctuary in the IIIrd or IVth century, or even later. Was it abandoned at the arrival of Christianity or razed by the barbarian hosts? Objects discovered around the ruins, dating back to the Vth century, provide us with precious little information. No traces of any human presence on the site during the next seven centuries have been revealed, no mention in the writings of the time of any sacred place!

In the XIIth celltury, we now know of the existence of a romanesque chapel, inhabited by a hermit monk, but one century later, there was only mention of an annual pilgrimage, on June 11, for the feast of Saint Barnabas. The scribes make increasingly rare mention of the place and the divine presence seems to have totally forsaken the site, overrun by witchcraft in the XVIth century for - so the legend has it - satanic rites. The chapel was abandoned in the XVIIIth century and fell rapidly to ruin. Vestiges found there less than forty years ago seem, however, to reflect the presence of a somewhat less ancien monument.

Child of the Earth

The Romans probably recognized the volcanic nature of the site on which they built the temple of Mercury. This knowledge became lost in the centuries darkness which followed and it was not until the middle of the XVIIIth century that the mountain's volcanic genesis was reaffirmed.

The formation of the Puy de Dôme was still a mystery for vulcanologists. They were unable to identify it in relation to the known eruptive types (Hawaiian, Strombolian, Vulcanian). The eruption of Mount Pelée in 1902 enabled them to assimilate the Puy de Dôme to a Pelean type edifice.

The constitution of the Dôme as we know it is the result of several periods marked by different eruptive types. The first eruptions, which occured some 12,000 years ago were "Strombolian", generating flows of basalt. Then followed the edification of a cone of scoria caused by "Vulcanian" explosions. This cone was finally infiltrated by an extrusion of extremely viscous lava (clear trachyte called domite), some 8300 years ago.

This was the origin of the volcano's current outline. The last phenomenon was a sprinkling of domite from an adjacent puy and the formation of the little Puy de Dôme, in an ulti mate series of Strombolian type explosions.

The giant of the puys peaks at 1465 m, but the dome itself stands on a crystalline plateau nearly 1000 m high. It seems to be quite deeply dormant, but in theory it could awaken at any time. Fortunately, a warning is more than probable!

The volcano and science and communication

Blaise Pascal's childhood in Clermont was dominated by the familiar presence of the Puy de Dôme. In 1648, he quite naturally chose this symbolic summit as the theatre and witness of his famous experience into the gravity of air.

He showed that the level of mercury in the barometer gradually fell the greater the altitude. To do this, he measured the difference between the device he had left in Clermont and the one he installed at the peak of the Puy de Dôme.

Two centuries later, in 1875, a physics laboratory was built at the peak of the Puy. Its role was to study the atmosphere, paying particular attention to the clouds. Its work was extended to cover vulcanology, seismology, geothermics and geomagnetism.

In 1925, the laboratory became the "Physics Institute and Observatory of the Globe of the Puy de Dôme".

With the installation of the television transmitter in 1956, the first laboratory was demolished and a new building was built as a base for the tower. It now houses the inter-ministerial centre for Communications (TV,radio), the Interior (highway transmissions for the Police), Defence (air force radiogoniometric services), Education (observatory) and Roads and Highways (meteorology and civil aviation navigation).

Taken from a leaflet entitled "Once Upon a Time A Volcano" obtained at Le Puy de Dôme circa 1997.