Table 1 Table summarising information from reports of basaltic lava flow events at Mt. Etna that have threatened inhabited areas since 1950

1971 (1, 2, 3)

Two lava flows emerged from a vent at 3000 m asl on Etna’s southern flank. Flows destroyed the volcano observatory, cable car network, agricultural land, 350 m of road, and bridges and ignited forest fires. Tourist facilities and two towns on the southeastern flank were threatened but not inundated. (9.5 weeks)

Parallel practice was common, i.e. increased religious practice in conjunction with practical measures such as preparing to evacuate.

Huntington 1972) An lamented that nothing could be done because it was illegal to alter the course of a lava flow.

1981 (4, 20, 21)

A lava flow emanated from a vent at 1200 m asl on Etna’s northern flank. Lava inundated train tracks and agricultural land. The only town threatened was not inundated. (1 week)

Parallel practice was observed again.

Numerical software packages were developed and calibrated to predict Etnean lava flow footprints. The science teams that implemented the diversion barriers and channels in each of these eruptions were composed of many of the same people who maintained institutional knowledge of actions during previous eruptions.

1983 (5, 6, 22, 24)

A fracture system opened on Etna’s southern flank at approximately 2300 m; resulting lava flows advanced south. A road and building were inundated within a day. A compound flow field was formed within three days. The flow field reached its full run-out length within five weeks of the eruption onset. Agricultural land was inundated. A town was threatened but not reached. (4.5 months)

Public pressure led to government approval to attempt a lava flow redirection project. An international explosives expert was contracted to create a hole in the lava tube. The hole did not divert a significant portion of the flow and self-healed quickly.

1991–1993 (7, 8, 9, 10, 20)

Two fissures opened on Etna’s SE flank, producing lava flows that advanced east. In five months, the lava flow had advanced > 8.5 km and was < 1 km from Zafferana Etnea. Although the eruption continued for many more months, the effusion rate slowed, and the lava flow did not continue to threaten inhabited areas. (1.25 years)

Lava flow modelling was carried out within the first week of the eruption and indicated that the town Zafferana Etnea could eventually be inundated. US military were asked to assist by dropping objects into a skylight in the lava tube. Earthen barriers were built to slow the flow’s advance (Fig. 2). Diversion channels were used to redirect the flow. Eventually, the entire lava flow was successfully diverted into the artificial lava channel that had been dug to redirect the lava flow.

2001 (11, 12, 13, 15, 18, 17, 19, 20)

Fissures on Etna’s SE cone produced seven vents, four of which effused lava flows that eventually threatened tourist facilities and two villages. A local highway was inundated within 24 h of the eruption onset. Within two weeks, ski lines and part of the tourist facilities’ car parks had also been inundated. (3.5 weeks)

A preliminary version of DOWNFLOW was used to model the lava flows during this eruption; the resulting maps were shared on the news (S. Tarquini, pers. comm.) Tourist facilities and a monitoring station were closed. Thirteen earthen barriers and a diversion project (similar to the 1991–1993 eruption) were implemented. Some structures were saved. A detailed evacuation plan was also drafted although not enacted.

Post-eruption lava flow modelling was undertaken to analyse how well the earthen barriers performed (i.e. examine if the barriers were built in optimal orientations).

2002–2003 (14, 16, 20, 21, 23)

This eruption involved activity on both the northeastern and southeastern rifts. A vent at 2500 m on Etna’s southeastern flank created a lava flow that advanced 1 km. A second vent at 2200 m effused a lava flow that inundated tourist facilities and two roads and ignited forest fires. A month later, a third lava flow again threatened the tourist facilities. A final lava flow inundated a government building three months after the eruption onset. (3 months)

DOWNFLOW lava flow modelling was undertaken to determine potential inundation sites. Six earthen barriers were constructed. The flow front did not reach the barrier on the northern flank, which was subsequently removed. The barriers on the southern flank successfully protected the tourist facilities.

Lessons learned about precursory monitoring methods have been implemented including augmenting ground-based networks and improving remote sensing techniques.