During 14-20 May 2000, lava emission continued from the N fissure of the Southeast Crater (SEC). At about 1900 on 17 May there was an increase in the intensity of Strombolian activity and lava began to flow in several directions, forming two sub-parallel tongues toward the E. On 18 May observers noted that the lava flow emerged from a single vent at 3,156 m elevation, with an effusion rate of 2.5-4.5 m³/s. A short distance below the effusive vent, the flow divided into three branches: one to the NE, whose front flowed at about 2,700 m and reached a distance of about 1 km from the vent; the central branch flowing to the E, widest of the three with some points wider than 20 m; and one to the S, flowing below 3,000 m elevation at about 700 m from the vent. The farthest lava front was estimated to reach ~2,700 m elevation, 1.2 km from the vent. During this period, the Bocca Nuova (BN) crater continued to degas, accompanied by occasional emissions of brown ash. Also noted were a further deepening and widening of the internal crater in the BN's SE quadrant.

During 21-27 May, lava flows from the N fissure of SEC continued intermittent and variably intense Strombolian activity. Sporadic emissions of brownish-reddish ash came from the N crater of BN. Problems with surveillance cameras precluded continuous observation of the summit craters; however, on the morning of 24 May, renewed explosive activity was seen. Observations from Belevedere showed three hornitos on the N flank of the SEC, which emitted pulsing pressurized gas. The lava flow was active and well fed, with branches of ~1.5-2 km in length.

Activity at SEC increased considerably during 28 May-3 June. On 28 May, the presence of a small cinder cone, possibly having formed slowly over recent months, was discovered at the base of Northeast Crater (NEC), occupying about 2/3 of the crater floor and at least 20 m high.

At SEC, evidence of Strombolian activity was masked by discrete flows of gas and steam. The active lava field on the N flank, emerged from a main vent at about 3155 m elevation, which fed two principal flows, one to the E and one to the NE (then turning E). The latter flow formed a lava tube and then re-emerged ~100 m downstream from a small tumulus from which spewed other lava flows, the longest of which extended more than 1.5 km. The S-most branch also initially flowed partly inside a lava tube.

During the evening of 28 May, between 2222 and 2242, Strombolian activity at SEC rose sharply, with ejecta reaching as high as 50 m above the crater rim and with materials occasionally falling on other flanks of the cone. Lava flow rates on 29 and 30 May were estimated at 6-8 m³/s. Temperatures measured using a K-type (Cr/Al) thermocouple showed a maximum temperature on the inside of an expansion bulb to be of 1,065°C at 5 cm depth. Intense degassing continued at SEC for the next several days.

On the evening of 3 June two sub-parallel lava flows descended to the E, of which the northernmost was the longest and reached at least 2,600 m elevation. A few hundred meters ahead of its front, a small branch flowed N but stopped soon after. The other flow was directed toward the Valle del Bove and its advances were discontinuous. Further deepening of the two interior Voragine vents was observed. Eruptive activity was not continuous.

The W rim of BN had a very warm fissure that ran to the N. The N vent was much widened, but it was not possible to observe the base. During observations, gas explosions occurred about every 15 minutes, but it was not possible to observe the fall of ejecta. The S vent had also widened and deepened. On its SE flank, a small semi-circular vent emitted rumbling explosions every 3-10 minutes, accompanied by mostly blue-colored gas mixed with brown ash.

Although intense degassing did not permit views of the interior of the NEC, an apparently recent fissure on the N side of the cone was very warm.

During 4-10 June, two episodes of lava fountaining occurred at the SEC. The first began during the night of 5-6 June, with modest Strombolian activity at the SEC's secondary vent. At 2136 on 6 June, Strombolian activity at the secondary vent reached a frequency of about one explosion per minute, which in successive hours included the main vent as well. The activity eventually climaxed at 0145 on 7 June, when the secondary vent produced a lava fountain whose altitude reached 50 m. Falling to the ground, the stream of lava formed a primary lava flow, which immediately divided into three branches and stopped at about 3,000 m elevation. A second stream flowed to the N before turning E, reaching 2,600 m and superimposing in part on earlier lava flows. The eruptive episode concluded about 0340, with copious ash emissions from the SEC and the BN.

On the night of 8-9 June, a new eruptive episode occurred at the SEC, also beginning with Strombolian activity at 2011 at the principal and secondary vents. The activity evolved into lava fountains which reached a maximum altitude of about 200 m at the principal vent and about 80 m at the secondary vent. The strong activity continued until about 0322 and was accompanied by sustained lava emissions from the secondary vent, which gave rise to two flows which spread to the E and N respectively, superimposing themselves over preceding lava flows.

Activity at the other craters during this period was characterized by continuous degassing at the Voragine and NEC, accompanied, as in the case of the BN, by frequent ash emissions in the SE sector of the 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).