type to the 1631 VEI 4 eruption. In this scenario, the volcano's slopes, extending out to about from the vent, may be exposed to pyroclastic surges sweeping down them, whilst much of the surrounding area could suffer from tephra falls. Because of prevailing winds, towns and cities south and east of the volcano are most at risk from this. It is assumed that tephra accumulation exceeding —at which point people are at risk from collapsing roofs—may extend out as far as Avellino to the east or Salerno to the south-east. Near Naples, this tephra fall hazard is assumed to extend barely past the volcano's slopes to the northwest. The specific areas affected by the ash cloud depend upon the circumstances surrounding the eruption. The plan assumes between two weeks and 20 days notice of an eruption and foresees the emergency evacuation of 600,000 people, almost entirely comprising all those living in the zona rossa ("red zone"), i.e. at greatest risk from pyroclastic flows. The evacuation, by train, ferry, car, and bus, is planned to take about seven days, and the evacuees would mostly be sent to other parts of the country, rather than to safe areas in the local Campania region, and may have to stay away for several months. However, the dilemma that would face those implementing the plan is when to start this massive evacuation: If it starts too late, thousands could be killed, whereas if it is started too early, the indicators of an eruption may turn out to be a false alarm. In 1984, 40,000 people were evacuated from the Campi Flegrei area, another volcanic complex near Naples, but no eruption occurred. Ongoing efforts are being made by the government at various levels (especially of Campania) to reduce the population living in the red zone, by demolishing illegally constructed buildings, establishing a national park around the whole volcano to prevent the future construction of buildings and by offering sufficient financial incentives to people for moving away. One of the underlying goals is to reduce the time needed to evacuate the area, over the next twenty to thirty years, to two or three days. The volcano is closely monitored by the Osservatorio Vesuvio in Naples with extensive networks of seismic and gravimetric stations, a combination of a GPS-based geodetic array and satellite-based synthetic aperture radar to measure ground movement and by local surveys and chemical analyses of