STROMBOLI
Aeolian Islands, Italy (38.79°N, 15.21°E)
(This report covers the period October 2000 - February 2001; all times are local)
During the last three months of 2000 the seismic activity recorded by the summit station of University of Udine (Figure 1) remained in the low to moderate range, comparable to the previous months. Short periods were again characterized by a very low number of events. In particular during the period 29 October - 16 November, several days showed less than 50 recorded events.
The transition between the second and the third millennium was characterized by a slightly increased activity, with more than 250 events/day and a tremor intensity occasionally exceeding the value of 5 V.s.
A drop in the seismic activity at the end of January was followed by a growth of all parameter during the month of February, with the number of events again exceeding 250 per day on 20 and 21 February, sand aturating events concentrating in the period 17-22 February, with a peak of 44 and 48 saturating events on the same days 20 and 21 February. The tremor intensity showed a slower but more steady grow, starting from values slightly above 2 V.s at the beginning of the month, and ending with values near 6 V.s at the end.
Juerg Alean visited Stromboli in Mid October 2000, when the eruptive activity at Stromboli was quite variable.
On 10 October 2000, Alean observed roughly 6 eruptions occurring per hour at SW crater, with very much ash, sometimes almost totally hiding the glowing spatters which were also ejected to moderate heights. Vent 3B glowed intensively but never ejected any lava. The NE Crater had grown substantially since Alean last crater sketches (see Figure 2) and was clearly separated into two pits. Both were glowing at night, the back one (1/1) more strongly than the front one (1/2). Only two eruptions were observed within 2 hours from 1/1, and only a single very small one from 1/2 during the same time.
On 13 October 2000, another visit made by Alean revealed that SW Crater clearly had more eruptions, roughly 10 per hour. Also the kind of activity was very different, with a total absence of ash and a much longer duration of individual eruptions (up to more than 30 seconds). Spatters reached around 100m above the crater rim. Activity had also increased at NE crater: 1/1 delivered several eruptions per hour, mostly at an oblique angle towards Pizzo, 1/2 erupted only weakly about once per hour.
On 15 October 2000, Alean had another confirmation of the variability of the eruptive activity during this week. The sudden occurrence of very noisy degassing events was heard at Stromboli village (e.g. 11h06, 11h25, 11h45 and 12h45 local time). No similar noises were heard later on that day.
Roberto Carniel made a short visit to Stromboli summit crateric area on 29 November 2000.
Since Alean's visit there were significant changes.The hornito, located where the Central Crater
(formerly called Crater 2) was located, was showing more intense degassing,
and a new vent had opened between the hornito itself and Vent 3B (see Figure 2), thus
suggesting a renewal of the activity in this sector of the crateric area.
This new vent, which we will call 3C (although it could well be ascribed to Crater 2 rather than Crater 3),
showed continuous puffing degassing, similar to Vent 3B. Both were incandescent after darkness.
After darkness continuous moderate spattering was also observed at vent 3C, with small sized spatters sometimes managing to
reach the vent rim and land on the crater terrace. Vent 3C also showed strombolian eruptions, with vertically
ejected moltern material up to more than 50 m above the rim. At least 3 such eruptions were observed during the
afternoon of 29 November.
Figure caption
Figure 1. Seismicity detected at the summit of Stromboli during the period October 2000 - February 2001.
open bars = number of recorded events per day
solid bars = saturating events, i.e. with ground velocity exceeding 100 µm/s
line = daily average of tremor intensity on hourly 60-seconds samples.
The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.
Figure 2. Different sketch maps of Stromboli's Crater Terrace drawn on the base of terrestrial stereo photos in 1993, 1996, 2000. These highlight the changes in the morphology of the crater area during these seven years. Other maps and sketches can be found on Stromboli online website.
Information contacts:
Roberto Carniel
Dipartimento di Georisorse e Territorio, Università di Udine, via Cotonificio 114, I-33100 Udine, Italy. Email: carniel@stromboli.net
Jüerg Alean
Rheinstrasse 6, CH-8193 Eglisau (Switzerland) Email: alean@stromboli.net
Website: STROMBOLI ON-LINE, http://stromboli.net
