Near-constant fountains of lava at Stromboli have served as a natural beacon in the Tyrrhenian Sea for at least 2,000 years. Eruptive activity at the summit consistently occurs from multiple vents at both a north crater area (N area) and a southern crater group (CS area) on the Terrazza Craterica at the head of the Sciara del Fuoco, a large scarp that runs from the summit down the NW side of the volcano-island (figure 168). Periodic lava flows emerge from the vents and flow down the scarp, sometimes reaching the sea; occasional large explosions produce ash plumes and pyroclastic flows. Thermal and visual cameras that monitor activity at the vents are located on the nearby Pizzo Sopra La Fossa, above the Terrazza Craterica, and at multiple locations on the flanks of the volcano. Detailed information for Stromboli is provided by Italy's Istituto Nazionale di Geofisica e Vulcanologia (INGV) as well as other satellite sources of data; September-December 2019 is covered in this report.

Figure 168. This shaded relief map of Stromboli’s crater area was created from images acquired by drone on 9 July 2019 (In collaboration with GEOMAR drone group, Helmholtz Center for Ocean Research, Kiel, Germany). Inset shows Stromboli Island, the black rectangle indicates the area of the larger image, the black curved and the red hatched lines indicate, respectively, the morphological escarpment and the crater edges. Courtesy of INGV (Rep. No. 50/2019, Stromboli, Bollettino Settimanale, 02/12/2019 - 08/12/2019, data emissione 10/12/2019).

Activity was very consistent throughout the period of September-December 2019. Explosion rates ranged from 2-36 per hour and were of low to medium-high intensity, producing material that rose from less than 80 to over 150 m above the vents on occasion (table 7). The Strombolian activity in both crater areas often sent ejecta outside the crater rim onto the Terrazza Craterica, and also down the Sciara del Fuoco towards the coast. After the explosions of early July and late August, thermal activity decreased to more moderate levels that persisted throughout the period as seen in the MIROVA Log Radiative Power data (figure 169). Sentinel-2 satellite imagery supported descriptions of the constant glow at the summit, revealing incandescence at both summit areas, each showing repeating bursts of activity throughout the period (figure 170).

Table 7. Monthly summary of activity levels at Stromboli, September-December 2019. Low-intensity activity indicates ejecta rising less than 80 m, medium-intensity is ejecta rising less than 150 m, and high-intensity is ejecta rising over 200 m above the vent. Data courtesy of INGV.

Figure 169. Thermal activity at Stromboli was high during July-August 2019, when two major explosions occurred. Activity continued at more moderate levels through December 2019 as seen in the MIROVA graph of Log Radiative Power from 8 June through December 2019. Courtesy of MIROVA.

Figure 170. Stromboli reliably produced strong thermal signals from both of the summit vents throughout September-December 2019 and has done so since long before Sentinel-2 satellite imagery was able to detect it. Image dates are (top, l to r) 5 September, 15 October, 20 October, (bottom l to r) 14 November, 14 December 2019, and 3 January 2020. Sentinel-2 imagery uses Atmospheric penetration rendering with bands 12, 11, and 8A, courtesy of Sentinel Hub Playground.

After a major explosion with a pyroclastic flow on 28 August 2019, followed by lava flows that reached the ocean in the following days (BGVN 44:09), activity diminished in early September to levels more typically seen in recent times. This included Strombolian activity from vents in both the N and CS areas that sent ejecta typically 80-150 m high. Ejecta from the N area generally consisted of lapilli and bombs, while the material from the CS area was often finer grained with significant amounts of lapilli and ash. The number of explosive events remained high in September, frequently reaching 25-30 events per hour. The ejecta periodically landed outside the craters on the Terrazza Craterica and even traveled partway down the Sciara del Fuoco. An inspection on 7 September by INGV revealed four eruptive vents in the N crater area and five in the S crater area (figure 171). The most active vents in the N area were N1 with mostly ash emissions and N2 with Strombolian explosions rich in incandescent coarse material that sometimes rose well above 150 m in height. In the S area, S1 and S2 produced jets of lava that often reached 100 m high. A small cone was observed around N2, having grown after the 28 August explosion. Between 11 and 13 September aerial surveys with drones produced detailed visual and thermal imagery of the summit (figure 172).

Figure 171. Video of the Stromboli summit taken with a thermal camera on 7 September 2019 from the Pizzo sopra la Fossa revealed four active vents in the N area and five active vents in the S area. Images prepared by Piergiorgio Scarlato, courtesy of INGV (Rep. No. 37.2/2019, Stromboli, Bollettino Giornaliero del 10/09/2019).

Figure 172. An aerial drone survey on 11 September 2019 at Stromboli produced a detailed view of the N and CS vent areas (left) and thermal images taken by a drone survey on 13 September (right) showed elevated temperatures down the Sciara del Fuoco in addition to the vents in the N and CS areas. Images by E. De Beni and M. Cantarero, courtesy of INGV (Rep. No. 37.5/2019, Stromboli, Bollettino Giornaliero del 13/09/2019).

Strombolian activity from the N crater on 28 September and 1 October 2019 produced blocks and debris that rolled down the Sciara del Fuoco and reached the ocean (figure 173). Explosive activity from the CS crater area sometimes produced ejecta over 150 m high (figure 174). A survey on 26 November revealed that a layer of ash 5-10 cm thick had covered the bombs and blocks that were deposited on the Pizzo Sopra la Fossa during the explosions of 3 July and 28 August (figure 175). On the morning of 27 December a lava flow emerged from the CS area and traveled a few hundred meters down the Sciara del Fuoco. The frequency of explosive events remained relatively constant from September through December 2019 after decreasing from higher levels during July and August (figure 176).

Figure 173. Strombolian activity from vents in the N crater area of Stromboli produced ejecta that traveled all the way to the bottom of the Sciara del Fuoco and entered the ocean. Top images taken 28 September 2019 from the 290 m elevation viewpoint by Rosanna Corsaro. Bottom images captured on 1 October from the webcam at 400 m elevation. Courtesy of INGV (Rep. No. 39.0/2019 and Rep. No. 40.3, Stromboli, Bollettino Giornaliero del 29/09/2019 and 02/10/2019).

Figure 174. Ejecta from Strombolian activity at the CS crater area of Stromboli rose over 150 m on multiple occasions. The webcam located at the 400 m elevation site captured this view of activity on 8 November 2019. Courtesy of INGV (Rep. No. 45.5/2019, Stromboli, Bollettino Giornaliero del 08/11/2019).

Figure 175. The Pizzo Sopra la Fossa area at Stromboli was covered with large blocks and pyroclastic debris on 6 September 2019, a week after the major explosion of 28 August (top). By 26 November, 5-10 cm of finer ash covered the surface; the restored webcam can be seen at the far right edge of the Pizzo (bottom). Courtesy of INGV (Rep. No. 49/2019, Stromboli, Bollettino Settimanale, 25/11/2019 - 01/12/2019, data emissione 03/12/2019).

Figure 176. The average hourly frequency of explosive events at Stromboli captured by surveillance cameras from 1 June 2019 through 5 January 2020 remained generally constant after the high levels seen during July and August. The Total value (blue) is the sum of the average daily hourly frequency of all explosive events produced by active vents.

Geological Summary. Spectacular incandescent nighttime explosions at Stromboli have long attracted visitors to the "Lighthouse of the Mediterranean" in the NE Aeolian Islands. This volcano has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent scarp that formed about 5,000 years ago due to a series of slope failures which extends to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy, (URL: http://www.ct.ingv.it/en/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).