Report on Etna (Italy) — 16 August-22 August 2023
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 16 August-22 August 2023
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2023. Report on Etna (Italy) (Sennert, S, ed.). Weekly Volcanic Activity Report, 16 August-22 August 2023. Smithsonian Institution and US Geological Survey.
37.748°N, 14.999°E; summit elev. 3357 m
All times are local (unless otherwise noted)
INGV reported that an eruption at Etna began on 13 August. Tremor amplitude suddenly increased at around 2000 on 13 August and reached high values within 20 minutes. Significant infrasonic activity coincided with the tremor increase. Strombolian activity at SE Crater began to gradually intensify starting at 2040. Seismic activity continued to increase. The Aviation Color Code was raised to Yellow (second lowest level on a four-color scale) at 2126 and then to Orange at 2129 due to above-background activity. By 2333 the Strombolian activity had evolved into lava fountaining and lava overflowed the S flank of SE Crater. Ash, gas, and steam plumes drifted S and caused ashfall in areas downwind, on the volcano’s flanks and beyond. The Aviation Color Code was raised to Red at 2241 based on strong explosive activity and ashfall in Rifugio Sapienza-Piano Vetore at 1,700 m elevation on the S flank.
Seismic and infrasonic activity continued to intensify, reached a peak at around 0320 on 14 August, then rapidly decreased to pre-eruptive levels between 0450 and 0530. Coincident with the decreasing seismicity, fountaining ceased at around 0520. The Aviation Color Code was lowered to Orange as volcanic ash was confined to the summit area. Sporadic, minor ash emissions continued throughout the day. At 1415 the Aviation Color Code was lowered to Yellow and then lowered to Green at 1417. According to a news source the ash emissions caused the closure of the Catania airport, about 50 km S, from 0238 until 2000; the airport averages about 200 flights a day. Though activity decreased at the beginning of the day, ashfall continued to impact the area. The mayor banned the use of motorcycles until 16 August and banned drivers from driving over 30 kilometers per hour.
At 2346 an explosion at SE Crater produced a volcanic cloud that rapidly dispersed. The Aviation Color Code was raised to Yellow at 2355 on 14 August due to increasing unrest and lowered back to Green at 0954 on 15 August. At 2030 on 15 August a report noted that during the day the amplitude of volcanic tremor fluctuated widely and was mostly centered beneath SE Crater and E of the central craters. By 1700 infrasonic activity increased and coincided with more intense periods of tremor; the signals indicated that the source of the activity was at Bocca Nuova Crater. Gas emissions rose from both the SE and Bocca Nuova craters. The Aviation Color Code was raised to Yellow at 1944. During 15-20 August gas emissions rose from Bocca Nuova Crater and from the SE Crater’s E vent and numerous fumaroles located along the crater rim.
An 18 August satellite image was used to estimate the extent of the flow field, though the analysis was difficult due to weather clouds obscuring features in the image. The image revealed that a fissure had opened on the SW flank of SE Crater, was about 350 m long, and oriented NNE-SSW. The lava flow reached 2,790 m elevation, W of Frumento Supino, and had an estimated volume of 900,000 cubic meters and an area of 300,000 square meters.
Geological Summary. Mount Etna, towering above Catania on the island of Sicily, has one of the world's longest documented records of volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.