Editing Mount Vesuvius (section)

===Future===
Large Vesuvian eruptions which emit volcanic material in quantities of about {{convert|1|km3}}, the most recent of which overwhelmed Pompeii and Herculaneum, have happened after periods of inactivity of a few thousand years. Sub-Plinian eruptions producing about {{convert|0.1|km3}}, such as those of 472 and 1631, have been more frequent with a few hundred years between them. From the 1631 eruption until 1944, there was a comparatively small eruption every few years, emitting 0.001–0.01&nbsp;km<sup>3</sup> of magma. For Vesuvius, the amount of magma expelled in an eruption increases roughly linearly with the interval since the previous one, and at a rate of around {{convert|0.001|km3}} for each year.<ref name="Italian Volcanoes">{{cite book| title=Italian Volcanoes| publisher=Terra Publishing| year=2001 |author1=Kilburn, Chris  |author2=McGuire, Bill |name-list-style=amp | isbn=978-1-903544-04-4}}</ref> This gives an approximate figure of {{convert|0.08|km3}} for an eruption after 80&nbsp;years of inactivity.

Magma sitting in an underground [[magma chamber|chamber]] for many years will start to see higher melting point constituents such as [[olivine]] crystallizing out. The effect is to increase the concentration of dissolved gases (mostly [[sulfur dioxide]] and [[carbon dioxide]]) in the remaining liquid magma, making the subsequent eruption more violent. As gas-rich magma approaches the surface during an [[eruption]], the huge drop in [[internal pressure]] caused by the reduction in weight of the overlying rock (which drops to zero at the surface) causes the gases to come out of solution, the volume of gas increasing explosively from nothing to perhaps many times that of the accompanying magma. Additionally, the removal of the higher melting point material will raise the concentration of [[felsic]] components such as [[silicate]]s, potentially making the magma more [[viscous]], adding to the explosive nature of the eruption.

[[File:Naplesbay01.jpg|thumb|left|The area around the volcano is now densely populated.]]
The government emergency plan for an eruption therefore assumes that the worst case will be an eruption of similar size and type to the 1631 [[VEI]] 4<ref>{{cite web | url= http://vulcan.fis.uniroma3.it/vesuvio/VESUVIO_1631-1944.html | title= Activity of Vesuvio between 1631 and 1799 | work= Esplora i Vulcani Italiani | date= 1996–2009 | author= Giacomelli, L. | author2= Scandone, R. | publisher= Dipartimento di Fisica E. Amaldi, Università Roma Tre | access-date= 9 May 2010 | archive-url= https://web.archive.org/web/20110119185809/http://vulcan.fis.uniroma3.it/vesuvio/VESUVIO_1631-1944.html | archive-date= 19 January 2011 | url-status= dead }}</ref> eruption. In this scenario, the volcano's slopes, extending out to about {{convert|7|km}} 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 {{convert|100|kg/m²}}—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.<ref name = "Italian Volcanoes"/> 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&nbsp;people, almost entirely comprising all those living in the ''[[Vesuvius red zone|zona rossa]]'' ("red zone"), i.e. at greatest risk from pyroclastic flows.<ref name=mcguire2003/><ref name = "USA today 21-10-03"/> 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&nbsp;people were evacuated from the [[Campi Flegrei]] area, another volcanic complex near Naples, but no eruption occurred.<ref name = "USA today 21-10-03"/>

[[File:The crater of Vesuvius in 2012 (composite photograph).jpg|thumb|The crater of Vesuvius in 2012]]

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<ref name="USA today 21-10-03">{{cite news | url= https://www.usatoday.com/news/world/2003-10-20-vesuvius-usat_x.htm | title= Italians trying to prevent a modern Pompeii | first = Ellen | last = Hale | newspaper = [[USA Today]] | date = 21 October 2003 |access-date = 8 May 2010 | publisher = Gannett Co. Inc.}}</ref> and by offering sufficient financial incentives to people for moving away.<ref>{{cite news|url=https://www.theguardian.com/international/story/0,3604,970446,00.html |title=Italy ready to pay to clear slopes of volcano|first=Sophie|last=Arie|date=5 June 2003|newspaper=The Guardian |location=London |access-date=12 May 2010}}</ref> One of the underlying goals is to reduce the time needed to evacuate the area, over the following twenty to thirty years (i.e. by 2023–2033), to two or three days.<ref>{{cite conference| url = http://www.ewc2.org/upload/downloads/Gasparini2003AbstractEWC2.pdf| archive-url = https://web.archive.org/web/20090927120148/http://www.ewc2.org/upload/downloads/Gasparini2003AbstractEWC2.pdf| archive-date = 27 September 2009| title = Early Warning of Volcanic eruptions and Earthquakes in the Neapolitan area, Campania Region, South Italy (Submitted Abstract)| first = Paolo| last = Gasparini| author2 = Barberi, Franco |author3= Belli, Attilio| date = 16–18 October 2003| conference = Second International Conference on Early Warning (EWCII)| conference-url = https://web.archive.org/web/20081009131249/http://www.ewc2.org/pg000001.htm| location = Bonn, Germany| access-date = 8 May 2010| url-status=dead}}</ref>

The volcano is closely monitored by the [[Osservatorio Vesuvio]] in Ercolano 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 [[geophysical survey|surveys]] and chemical analyses of gases emitted from [[fumarole]]s. All of this is intended to track magma rising underneath the volcano.

The official INGV monitoring bulletin from the Vesuvius Observatory, as of July 2024, classifies Mount Vesuvius at a '''Green Alert Level'''. This indicates a state of low volcanic activity. The surveillance system has not detected any significant changes in Vesuvius' activity state. The low-energy earthquakes are attributable to gravitational [[subsidence]] activity of rocks inside the crater.<ref>{{cite web | url= https://www.ov.ingv.it/index.php/stato-attuale | title= Official INGV monitoring bulletin of Mount Vesuvius| location=Naples|publisher = Osservatorio Vesuviano, Italian National Institute of Geophysics and Volcanology | access-date =31 August 2024}}</ref>