Somma-Vesuvius is a moderate size composite central volcano consisting of an older, repeatedly collapsed structure, presently forming the semi-circular Monte Somma caldera, and of a more recent cone, Vesuvius, built inside the caldera. The lowermost lavas encountered at a depth of 1125 m b.s.l. by an exploratory deep geothermal well drilled on the southern slopes of the volcano are not younger than 0.3-0.5 Ma: this age can be assumed as marking the onset of the volcanic activity in the area. The last eruption of Vesuvius occurred in 1944 and since that time the volcano has entered a quiescent state with only moderate fumarolic activity within the crater. However, Vesuvius must be regarded as one of the most dangerous volcanoes in the world with an elevated potential for territorial damage. Over the past half a century the settled areas surrounding the volcano were characterized by an impressive growth and the present urbanization of the area results in a situation of extremely high potential risk. More than 700,000 people live on the slopes of the volcano and within 10 km radius from the summit crater, and the outskirts of Naples itself are not more than 15 km from the vent. The volcanic risk is aggravated by congestion and urbanization. Herculaneum, Ottaviano, Torre Annunziata and Torre del Greco and other towns surrounding the volcano may require an evacuation of more than 600,000 people and 300 km^2 are exposed to ash loading which can produce roof collapses.

Detailed studies carried out during the past two decades suggest that over the last 25,000 years Vesuvius has been characterized by extremely variable kinds of activity ranging from quiet lava emission and moderate strombolian explosions to catastrophic explosive plinian eruptions. Three main categories of eruption have occurred:

• 1. Small magnitude (10^7 m^3), effusive or explosive-effusive eruptions. Eruptive phenomena for this type of event include lava effusion, lava fountain, strombolian explosions and phreatomagmatic ash explosions. Secondary mud flows are commonly produced in connection with these eruptions. The involvement of external fluids from shallow hydrothermal systems is invoked to explain the complex dynamics of the largest eruptions of this type (e.g. 1944, 1906).
• 2. Medium magnitude (10^8 m^3), subplinian (e.g.: A.D.472 and 1631) eruptions. This type of event is exclusively explosive. The fallout of tephra and the formation of pyroclastic flows and surges are the most common phenomena. Secondary lahars and floods are an important additional source of hazard.
  
• 3. Large magnitude (10^9 m^3), plinian (e.g.: A.D.79 "Pompei", 3,400 BP "Avellino") eruption. These eruptions are by far the most dangerous events of Vesuvius. They typically start with moderate phreatomagmatic explosions and ash fallout, followed by the paroxysmal ejection of large volumes of pumice and lithics; pumice and ash flows are common during the final stages of the eruption and produce extensive devastation all around the volcano. The emplacement of surges, ash flows and mud flows occur during the final stage of the eruption, generally accompanying caldera collapse.

As a result of this highly variable eruptive behaviour the forecasting of type and size of the future eruption is problematic. Recent views hypothize that the plumbing system of the volcano is characterized by the presence of magma resevoirs fed through the periodic arrival of relatively small mafic magma batches (e.g.: 5-10 x 10^9 kg during the 1906 eruption). Around the active reservoirs, hydrothermal systems gradually form and grow. When the conduit is open and the reservoir is full, the arrival of a new batch triggers an eruption. This consists of the emission of mafic magma through either: (1) summit or lateral lava effusion with weak explosive activity; or (2) polyphased eruption, whose climax is largely propelled by the flashing of the hydrothermal system. Type-1 eruptions (e.g. 1929, 1895-99, 1881-84, etc.) leave the magma high in the conduit with immediate resumption of persistent strombolian activity. Type-2 eruptions induce the substantial emptying of the reservoir, leaving conduit either open or obstructed. When the conduit is obstructed a magma chamber forms and grows until an explosive eruption of mildly to highly evolved magma is initiated. According to this model of operation, in the assumption that no magmatic residua remained in the Vesuvius subsurface after the 1944 eruption, the maximum expected eruption should consist of a mainly explosive event of subplinian size related to the emptying of a magma chamber which is possibly already under formation, at unknown depth, since 1944 (the original message had erronneously written "1994" in this place). This type of event was chosen as a maximum expected event for the formulation of the civil defence preparedness plans.

The field workshop will focus on representative depositional sequences of eruptions of each different magnitude known from Vesuvius. Discussion will focus on emplacement of pyroclastic deposits, eruption dynamics, the role of external fluids in conditioning the eruptive style as well as the role and relevance of the sequence of melt extraction from stratified magma chambers. Participants are invited to contribute ideas on topics relevant to the Vesuvius volcanism and hazard assessment during daily evening sessions. Exchanges of information, data and ideas will provide the opportunity to discuss a number of volcanological problems of general relevance such as:

• the role and the nature (phreatic vs hydrothermal) of external fluids involved in most of Vesuvius eruptions;
• the time variability of the eruptive style
• the evolution of the caldera and shallow magma chamber(s)
• the deep magma alimentation and its variability with time;
• the modality of formation and evolution of layered magma chambers;
• the volcanic hazard assessment (based on classical approach and the modelling of the expected eruption).

Venue: Marad Hotel, Torre del Greco, Napoli.
Coordinators: Roberto Santacroce, Mauro Rosi, Alessandro Sbrana and Raffaello Cioni (Dipartimento di Scienze della Terra Universita di Pisa); Lucia Civetta (Osservatorio Vesuviano Napoli).

The date of the Vesuvius Workshop has beed scheduled to follow the Santorini Workshop (7-15 September).
Programme: Day 1 Opening programme, visit to the upper part of the volcano, the 1944 crater and products, the Mount Somma caldera; Day 2 The volcanic stratigraphy of the past 19,000 yr activity, Day 3 deposits of the plinian eruption of 19,000 ybp (Basal Pumice); Day 4 deposits of the the 79 AD plinian eruption;Day 5 visit to the archaeological areas devastated by the 79 eruption; Day 6 deposits of the 1631 eruption.

Participants should plan to arrive to Naples on September 16. Transportation from Naples airport and railway station will be arranged in both the morning and afternoon of September 16. Participants will be returned to the airport or railway station on the evening of September 23 or the morning of September 24.

Application: Due to logistical limitation, the number of partecipants is 30. To apply fill in the form at the end of this announcement and mail to Mauro Rosi Dipartimento di Scienze della Terra Via S. Maria 53, 56126 Pisa Italy (Fax 50-500675 ; Email rosi@dst.unipi.it) before April 31 1996.

Registration costs: An amount of US$ 400 for participants will cover all workshop and field trip costs (based on double room occupancy) and meals at Marad Hotel. A deposit of US$ 100 will be required at the time of registration.

We are currently exploring the possibility of accomodating a limited number of people who cannot afford to pay the regular fee (students) by the Osservatorio Vesuviano. Those who are interested are invited to contact M. Rosi before April 31 1996.

Name            ______________________________________________

Affiliation     ______________________________________________

Address         ______________________________________________

Phone    _____________________    Fax ________________________

e-mail    ____________________________________________________


Check if you wish to have a single room (cost of registration will increase
by US$ 150)       Yes ____;   No _____


Please indicate if you wish to make an oral presentation; give the
approximate title

___________________________________________________________

___________________________________________________________

___________________________________________________________



Please return these form before 31 April 1996. A deposit of US$ 100 is required.
Payment must be in the form of US$ or Italian Lire by bank transfer to:

CASSA DI RISPARMIO DI PISA - Ag. 1
Account no.1111-64605 - Co: Mauro Rosi
cod CAB 1401; cod ABI 06255

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Raffaello Cioni
Dipartimento Scienze della Terra                     fax 39 50 500675
V. S. Maria 53                                       phone 39 50 874214
56126 PISA                                           e-mail:cioni@dst.unipi.it
Italy

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