Publié le 4 Février 2018 par Bernard Duyck

Can we stop a lava flow - 4 - Etna in 1983

In the early days of the 1983 eruption, the lava flows reaching the tourist complex around the Rifugio Sapienza and destroy the Casa Cantoniera restaurant - photo 28.03.1983 / courtesy of Pippo Scarpinati.

On March 26, 1983, a seismic crisis is triggered at Etna and a rotten egg smell hangs over around Monti Silvestri.

On March 27 around 8 am, a NNE-SSO-oriented fissure, 750 meters long, opens between 2,450 and 2,250 meters, 4 km south of the central crater. Several lava flows are emitted and a small explosive activity marks the crack, edifying about thirty hornitos.

On the evening of March 28, the lava flows cut a road and engulfed many buildings.

On April 1, vigorous gas and ash emissions created two craters of explsion upstream of the crack, around 2,700 meters of altitude.

On April 3, the main flow reaches the 1.450 mark. In the same alignment, upstream, fissures open go up to the central crater; one of them almost cut the Piccolo Rifugio in half.

At the end of April, the main stream extends over 6,000 meters, with a front located at 1,100 meters altitude. The lava flooded 4 km², partially destroyed a cable car, threatened the Rifugio Sapienza, engulfed the restaurants of the Cantoniera, hotels and many houses.

Etna - 28.03.1983 - The lava flow destroys the restaurant Casa Cantoniera - photo courtesy of Pippo Scarpinati.

Lava Field Map 1983 / Etna: A yellow asterisk marks the location where the lava flow was blown up to deflect it; the barriers built parallel to the flows are in blue. In dotted line, the plot of the underground dyke leaving near the southeastern crater, according to the deformation data of the soil, leading to the eruption under the Piccolo Rifugio. - Doc. INGV

Map of Etna with the different cities threatened on the southern flank

As Haroun Tazieff recounts in his book "On Etna": "The problem was as follows: However the source continued to pour several tens of thousands of cubic meters a day, the multilobed front, after having exceeded the lower edge of the forest, was now progressing in open ground and very soon in cultivated land, Nicolosi and Belpasso's anxiety was swelling, as well as the desire to do something, not to remain passive, even if the authorities did not dare to intervene to try to oppose the progress of the lavas, exactly as did in 1669, Diego Pappalardo and his Catan, until the hunt for those of Paterno "

The custom, more respected than a law, forbade altering the flow of the Etna flows ... interfering with the lava meant bearing the responsibility for everything that would subsequently be destroyed by the eruption.

Franco Barberi has convinced the new Minister of Civil Protection and the prefect that blocking the road of the lava flow is possible and is worth trying ... to the chagrin of protesters of all kinds, motivated by various motivations.

Destructive lava flow of Etna on 28.03.1983 - photo J. Lockwood / USGS

Three sites are open: the first two between 2,200 and 2,100 meters above sea level, the third near 1,800 meters.

The first site, the active phase of the intervention, prepared the blasting of the right bank of the lava flow.

The other two, below, must serve, passively, to channel the lavas once deviated, and to confine them behind a dam of slags and ashes, to protect Serra la Nave, the weather observatory, the Grand'Albergo Etna and many second homes. More than 750,000 cubic meters of materials are moved in 50 days.

After several outflows of the casting forcing the temporary stop of work, on May 14 at 4:09, the artificers explode 390 kilos of TNT, opening a breach on the side of the casting.

On the night of May 13 to 14, 1983, the fireworks work under the light of a DCA projector, and put the explosives at the bottom of the 48 jacketed tubes leaving the boreholes and cooled by water pipes - photo Haroun Tazieff / in his book "On Etna"

The construction site of barriers: To the left of the red jackhammer, the wall with the lining of the mine holes; the yellow bull consolidates the dike of the artificial bed; 400 m. below, the tourist complex and one of the Monti Silvestri - photo F.Le Guern / in the book of Tazieff "On Etna"

The lava flow and the Sapienza barrier, the 31.05.1983 - the aerial view of the flow along the Sapienza barrier on 01.06.1983 - photo J.Lockwood USGS

After the operation, Tazieff told to reporters that "the result achieved is excellent compared to what we feared, but below what we had hoped for".

At first, 20% of the total flow of lava is diverted, but thanks to the large blocks torn off by the explosion, the lava tube will clog, causing an overflow. Finally, about 80% of the flow (15 m³ / s on average) is diverted to the artificial bed at the foot of Mount Castellazzo, and 20% to the east.

The slow effusion continues for several months, but the techniques used have prevented many more destructions.

After 131 days of activity, the eruption stops on the morning of August 6th.

The balance sheet : 6 km² were covered with lava, which accumulated 80 meters thick east of the refuge Sapienza. Their volume is estimated between 80 and 100 million m³ ... and an effusive casting diversion technique duly tested.

Sources:

- Diversion of lava during the 1983 eruption of Mount Etna