As reported by Sistema Poseidon, activity at Etna (figure 85) during December 2000-8 April 2001 was characterized by episodic Strombolian blasts, steam and ash emissions, and lava flows.

Figure 85. Aerial photograph of Etna looking E towards the Bocca Nuova vent within the central crater on 6 December 2000. Northeast Crater is also partially visible (in the left background), as well as Southeast Crater (right). Courtesy of Sistema Poseidon.

Minor activity during December 2000 through mid-January 2001. Low-intensity gas emissions dominated activity during this period. Observations on 6 December revealed three distinct cavities in the interior of the Bocca Nuova (BN) vent. The two near the center of the crater trended NW, were deep and full of material, and were delineated by pit-craters. The smaller cavity to the SE was encircled by a high wall of scoria; it weakly emitted light brown ash, possibly due to internal collapse. White steam emissions from BN in early January were visible during the early morning hours, and became more evident as each day progressed due to increased humidity. Sporadic ash ejections also occurred.

At the end of December, adverse atmospheric conditions prevented detailed observations, but during rare periods of visibility observers saw snow covering the W flanks of the central crater and Southeast Crater (SEC). A weak intermittent fumarolic emission emerged from the base of the fracture that runs from the SEC to the lava cairn at its base. The SEC also produced weak fumarolic emissions in early January from the W edge of the crater's summit. On the evening of 14 January a weak, diffused illumination was observed at SEC, likely coming from the E edge of the crater, where during recent months there was visible night incandescence.

Increased activity during mid-late January 2001. The BN vent produced abundant steam during the middle of January. Brown ash was weakly emitted on 16 and 19 January; darker ash ejections occurred on the 18th and 21st. Ash fell on the E flank of the volcano for five hours during the morning of the 18th, and weak illumination was visible for 30 minutes that night coming from BN. Ash-and-gas emissions increased toward the end of January. Isolated night glow suggested weak explosive Strombolian activity confined to inside the central crater. Activity alternated between visible degassing and intense phases of ash emission; one particularly acute phase occurred on 31 January.

New activity initiated from SEC on the evening of 15 January. Low-energy Strombolian eruptions were seen at night by distant observers. Activity increased in frequency during 16-17 January, reaching a maximum on 18 January when explosions occurred every 3-4 minutes, interspersed with high-energy episodes that repeated at variable intervals of ~1-2 hours. Ejected material from these events reached ~50 m high on the edge of the SEC, falling back into the crater. Strombolian activity continued through 19 January. Lava began to flow from the radial fracture cutting the N flank of the SEC beginning during the day on 21 January and persisting discontinuously until the end of the month. Intermittent flows formed several finger-like fronts. The flow reached down to ~2,800 m elevation, and remained confined to the Valle del Leone.

Strombolian explosions at Bocca Nuova during February-April 2001. During the nights of 1 and 4 February, frequent illumination was observed in the BN vent. Strombolian activity continued from BN throughout February. As during January, strong degassing and dark gray ash emissions were sporadic. High ambient humidity during morning hours made gas plumes distinct, especially on 10 February; activity was particularly consistent during 20-22 February. The fixed Montagnola camera captured images of frequent flashes from the crater interior, but activity did not extend beyond the crater area.

The BN vent produced increased explosive activity during March from two vents (W and E) inside the depression. The W vent exhibited Strombolian explosions; during some periods these were continuous and sent incandescent material just above the crater rim. A small number of lava fragments fell outside of the crater and rolled down its flanks. Explosive activity at the E vent did not eject material above the crater rim. Alternating degassing and dark gray ash emission continued as in February. Fine-grained material blown by wind fell as far as 2 km from the summit. Activity was more intense on 6 and 28 March when BN emitted copious amounts of ash from the NW and SE sectors of the crater. The Montagnola camera detected almost continuous night illumination of the crater, suggesting Strombolian activity from multiple vents. Strombolian activity also occurred from Northeast Crater, although it was rarely visible.

Strombolian activity and ash emission from BN continued throughout April. On the evening of 4 April an intense phase at the S zone of the central crater included ejection of some incandescent material above the crater rim. During 7-8 April, a slight increase in the frequency of ash emissions was observed, while night-time incandescence was sporadic.

Lava flows from Southeast Crater during February-April 2001. Early in February lava emission from the N-flank of SEC diminished; it produced modest regular lava flows for the rest of the month. On 4 February observers saw intense flashes that indicated explosive lava ejection from the fracture. Flashes and illumination visible in camera footage evidenced erratic SEC effusive activity throughout February. One early February lava flow from a vent at 3,100 m continued for several days. Bubbles frequently burst from the lava, indicating high gas content within the magma. The lava flow was ~2 m wide near the source, grew to 5 m wide toward the base, and reached an elevation of 2,900 m. During mid-February a vent at 3,150 m elevation produced a flow down a 2-m-wide canal. The flow ran N initially, but ~100 m downslope it headed E and formed a lava tube about 20-25 m wide. The flow moved toward the Valle del Bove, in the direction of Monte Sinome; it continued through the end of the month and reached 2,600 m elevation.

Through mid-March lava continued to flow from the fracture at 3,080 m elevation on the SEC's N flank. Near the vent the flow was ~1 m wide and ~80 cm deep. After having flowed less than 2 m it divided into two forks that ran roughly parallel to each other. The principal flow retained a width of ~1 m and headed N for ~100 m before deviating toward the NE and reaching an elevation of ~2,800 m. The secondary flow was about half a meter in width; it traveled at ~4 m/s near the fork and ~2 m/hour near the flow front where it spread to ~5 m across at an elevation of about 2,970 m. Effusive activity appeared to diminish on 23 March. The vent observed three days before was no longer active. A single flow was fed by a new vent about 5 m below the previous vent. A steep slope at the vent's mouth produced flow velocities of ~6 m/minute. This flow reached down to an elevation of 2,950 m, where it traveled at 1 m/hour over the flows of three days before. The flow front measured 5 m wide and 1 m high. On 30 March conspicuous white vapor issued from the SEC.

A 4 April survey of the flows revealed a moderate flow from the N flank of SEC. The vent had built up a small cone ~6 m tall at 3,095 m elevation. Two flows, each ~1 m wide and 1-2 m deep, traveled away from the cone and joined together 20-25 m away, flowing E. The flows in the two channels moved at a speed of ~0.1 m/s and an estimated 0.2-0.4 m³ of molten material emerged each second. The maximum length of the overall flow was ~350 m. During the evening of 8 April strong, persistent illumination from the E base of SEC probably indicated a new lava flow. The incandescence was distinctly visible as it reflected off of a steam plume from the summit crater.

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.

Information Contacts: Sistema Poseidon, a cooperative project supported by both the Italian and the Sicilian regional governments, and operated by several scientific institutions (URL: http://www.ct.ingv.it/en/chi-siamo/la-sezione.html).