Report on Vesuvius (Italy) — August 1996
Bulletin of the Global Volcanism Network, vol. 21, no. 8 (August 1996)
Managing Editor: Richard Wunderman.
Vesuvius (Italy) Ongoing sub-crater seismic activity
Please cite this report as:
Global Volcanism Program, 1996. Report on Vesuvius (Italy). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 21:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199608-211020.
40.821°N, 14.426°E; summit elev. 1281 m
All times are local (unless otherwise noted)
Non-eruptive activity at the Mt. Somma-Vesuvius volcanic complex is characterized by low seismicity both in terms of energy and numbers of events; very few episodes of intense seismicity occurred during the last twenty years.
In the last three years, however, hundreds of earthquakes have been detected with magnitudes ranging from -0.4 up to 3.4. The plot of monthly seismic events (figure 2) shows the usual fluctuating pattern observed at Vesuvius. The energy release distribution (figure 2) has a sharp peak coinciding with the 1995-96 earthquakes; the strain release curve also recorded two clear steps at these times.
|Figure 2. Monthly seismicity at Vesuvius during 1 Oct 1994-31 Aug 1996. The lower part of the figure shows the energy release histogram and the strain release curve. Courtesy of the Osservatorio Vesuviano.|
After the seismic crisis of March-April 1996 (BGVN 21:06), seismic activity decreased. During May-August 1996, the permanent seismic network of the Osservatorio Vesuviano recorded 266 microearthquakes, the strongest one had M 2.7. The events belonging to this sequence affected an extremely reduced volume below the crater area at shallow depth, with hypocenters rarely exceeding 6 kilometers below the sea. No changes in ground deformation or fumarolic gas composition were reported in the last field measurements.
Geologic Background. One of the world's most noted volcanoes, Vesuvius (Vesuvio) forms a dramatic backdrop to the Bay of Naples. The historically active cone of Vesuvius was constructed within a large caldera of the ancestral Monte Somma volcano, thought to have formed incrementally beginning about 17,000 years ago. The Monte Somma caldera wall has channeled lava flows and pyroclastic flows primarily to the south and west. Eight major explosive eruptions have taken place in the last 17,000 years, often accompanied by large pyroclastic flows and surges, such as during the well-known 79 CE Pompeii eruption. Intermittent eruptions since 79 CE were followed by a period of frequent long-term explosive and effusive eruptions beginning in 1631 and lasting until 1944. The 1631 eruption was the largest since 79 CE and produced devastating pyroclastic flows that reached as far as the coast and caused great destruction. Many towns are located on the volcano's flanks, and several million people live within areas potentially affected by eruptions of Vesuvius.
Information Contacts: Lucia Civetta, Francesca Bianco, Giuseppe Vilardo, and Mario Castellano, Osservatorio Vesuviano, Via Manzoni 249, 80123 Napoli, Italy.