Living in the shadow of a volcano
In 79AD the writer Pliny the Younger described the eruption of Mount Vesuvius, in a letter to his friend, the Roman historian Tacitus. The eruption devastated the towns of Pompeii and Herculaneum, and killed Pliny the Elder, who was Pliny the Younger's Uncle. The letter is the earliest existing account of a volcanic eruption. Almost 2,000 years and over 30 eruptions later, Vesuvius has the dubious distinction of being the highest risk volcano in the world, on the grounds of its highly explosive eruptions and the large numbers of people living in its surroundings. The man charged with analysing the risk posed by Vesuvius and protecting those at threat from eruptions is Franco Barberi, one of the world's leading volcanologists who from 1995 to 2001 was Italy's Secretary for Civil Defence. In a lecture at the Euroscience Open Forum in Munich, he outlined the threat posed by Vesuvius to those living around it, and explained what the Italian authorities are doing to protect them. The first task of the civil protection authorities was to determine the types of eruption they could expect from Vesuvius, and to do this they looked to history. Written records, including Pliny's letter, and other evidence show that Vesuvius alternates between periods of frequent, low level eruptions and periods of repose which are characterised by very low levels of activity interrupted by extremely violent, explosive eruptions. The longer the period of inactivity, the higher the energy of the eruption that interrupts it. Vesuvius has been quiet since its last eruption in 1944, and according to Prof Barberi, this means the next eruption, whenever it comes, will be a big one. So what kind of hazards can the local people expect, and how can they cope with them? The most dangerous volcanic phenomenon is the pyroclastic flow, in which a cloud of gas, ash and rock rush down the side of the volcano and across the landscape at speeds of over 100 km/h. The high pressure of the flow means they lay waste to anything and anyone in their path. Models from the EU-funded EXPLORIS project suggest that it would take just five or six minutes for a pyroclastic flow from Vesuvius to reach the sea, some seven kilometres away. Another serious threat to people living around Vesuvius is the lahar, a type of mudflow. Lahars are caused when heavy rainfall, which often accompanies volcanoes, loosens ash deposits on steep slopes, causing them to flow downhill at high speeds. Over half a million people in the vicinity of Vesuvius are at threat from pyroclastic flows and lahars. This area is classified in the Vesuvius Emergency Plan as the Red Zone, and people living in it will have to be evacuated before the eruption starts. According to Barberi, an orderly evacuation of the area will take seven days, due to the large numbers of people involved and the weak transport and communications infrastructure. Each Italian region is twinned with a municipality in the Red Zone, and on evacuation each district will move to its twinned region en masse. This means that people will keep their local administrations, schools and doctors in exile. The authorities regularly run exercises to build relations between the local municipalities and their host regions. Beyond the Red Zone, buildings and people will still be at risk from fallout of ash and rocks that have been ejected by the volcano. The location and extent of this damage will depend largely on the wind speed and direction, and people in this zone will be evacuated immediately after the eruption starts. In the longer term, the authorities are trying to move people out of the red zone permanently. The problem is that the volcano was ignored for many years, and illegal building in the area continued unchecked for too long. In 2003 a programme was established to reduce the population living in the Red Zone, under which all new building is forbidden, and illegally constructed buildings are destroyed. Families are given financial incentives to leave, and new houses built outside the zone are reserved for families from the Red Zone. So far 35,000 people have left. The authorities have started educational programmes in the Red Zone to increase awareness of the risks posed by the volcano. Engineers are also investigating whether the buildings in the area will reduce the pyroclastic flow, although this work is being done cautiously as they do not want people to think they can stay in their homes during an eruption. Meanwhile, Prof Barberi and other volcanologists continue to study Vesuvius, to refine their models of what the next eruption might look like. The challenge for the local authorities is to convince people living near the volcano of the risks to their lives and homes.
Countries
Italy