Report on Etna (Italy) — 17 February-23 February 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
17 February-23 February 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Etna (Italy). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 17 February-23 February 2021. 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 a series of paroxysmal events separated by relative calm periods at Etna began on 16 February and continued at least through 23 February. The first episode began late on 16 February, characterized by gradually increasing Strombolian activity at the E vents of the Southeast Crater (SEC). Overflows of lava from the crater at 1805 caused a partial collapse of the cone and a pyroclastic flow that traveled 1.5 km along the W wall of the Valle de Bove. Lava fountains afterwards rose 500-600 m high. An eruptive plume rose several kilometers and drifted S, causing ashfall in areas as far as Syracuse, 60-80 km SSE. Lava flows advanced into the Valle de Bove and the Valle del Leone, and produced explosions in areas where they interacted with snow cover. Activity ended around 1900.
After a 30-hour pause the second paroxysmal episode began at 2330 on 17 February with overflows of lava from the eastern SEC vents. Lava fountaining began just after 0100 the next morning. Lava flows traveled towards the Valle de Bove, NE, SE, and SW. The eruption plume drifted SE, causing ashfall in Zafferana Etnea and Acireale. The lava fountains reached maximum heights of 600-700 m then ceased around 0140.
After another pause lasting about 32 hours, lava overflowed the SEC at around 0855 on 19 February. A rapid increase in explosive activity followed and lava fountaining began during 0945-0950. At 0953 lava fountains emerged from the S, or saddle, vent. At this time there were “fan-shaped” lava fountains rising from 4-5 vents orientated E-W. The eruption plume rose 10 km (32,800 ft) a.s.l. and drifted SE, again causing ashfall in downwind municipalities. Lava flowed S and towards the Valle de Bove causing explosions where they interacted with snow. Explosive activity ceased at 1110. Lab analysis of lava samples collected during 16-19 February eruptions showed that the magma was the most primitive over the past 20 years, meaning that the composition had changed little from its formation at depth and that it ascended quickly.
Weak Strombolian activity was visible in the late afternoon of 20 February. At 2230 a small lava flow descended a deep notch at the E end of the SEC and traveled towards the Valle de Bove. By 2300 the Strombolian activity had shifted to pulsating lava fountaining. Beginning at 0100 on 21 February more western vents became active and the E vents jetted lava 600-800 m high. Activity intensified at 0128 with jets of lava that rose more than 1 km high and were sustained for about 10 minutes. An eruption plume again rose to 10 km (32,800 ft) a.s.l. Beginning at 0200 the lava fountain became smaller, and at 0220 explosive activity ceased. Lava flowed SW and into the Valle de Bove.
Periodic ash emissions rose from both the S and E vents later than evening. Lava overflowed the SE crater just after 2230 and advanced 1 km towards the Valle de Bove. Lava fountains and Strombolian explosions occurred at multiple vents. Activity intensified at 0128 on 21 February and lava fountains rose 800-1,000 m above the SEC. Lava flowed from the S vent and an eruption plume rose several kilometers, but activity rapidly ceased at 0220. Lava flows continued to advance in the Valle de Bove; the longest flows were 3.5-4 km from the crater, between elevations of 1,700 and 1,800 m. During 0430-0515 very intense explosions from multiple SEC vents ejected incandescent bombs that fell as far as the base of the cone.
Weak Strombolian explosions at the SEC crater were visible late on 22 February. The frequency and intensity of the explosions increased and by 2210 material was ejected onto the flanks. By 2305 jets of lava were 300 m high, and by 2327 lava fountains rose from a second vent. Lava overflowed the crater at 2328 and headed towards the Valle de Bove. Within the first hour on 23 February lava fountains rose more than 1.5 km high and a sub-Plinian eruption plume had risen several kilometers above the summit, making this episode the most powerful and intense compared to the previous four. Lava overflowed the S vent and descended SW. Lava fountaining suddenly decreased at 0115 on 23 February, though lava flows continued to be fed. Strombolian activity again intensified at 0450, accompanied by ash emissions. Two lava flows formed and traveled SW and SE, the latter was longest and reached 1,700-1,800 m elevation. The activity ended at 1000.
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.