14 December 1998

It took SE Crater more than 14 days to arrive at its fourteenth eruptive episode in three months, last night (13-14 December), confirming the trend of ever increasing quiet intervals between eruptive episodes. As usually before the paroxysmal phase of the episode, Strombolian activity began some 24 hours or so earlier. Carmelo Monaco of IGGCT was at Montagnola for skiing during the day, and heard explosion sounds from the direction of SE Crater, but clouds over the summit prevented visual observations. However, at about 1930 h (local time=GMT+1) the summit became visible from Catania, and by this time Strombolian bursts from SE Crater occurred every few seconds. Between 2000 and 2030 a growing incandescent spot became visible below the fountain, this was a slowly-moving lava flow at the "spillover" at the southern crater rim. During the next two hours, lava spilled down the southern (and possibly also the southwestern) flank of the cone, and pyroclastic ejections became gradually stronger. The culminating phase began at about 0430 h this morning, and it was marked by strong seismic activity (information from G. Patanè, IGGCT and Osservatorio Sismologico di Acireale). The exact duration of this phase is not yet known but it probably was similar to those of previous eruptive episodes, that is, between one and two hours. Tephra was carried by a northerly wind towards south, leaving a dark streak on the snow fallen during the days before.
This morning, clear weather is permitting perfect views of the volcano from Catania. The cone of SE Crater is covered almost all over with new pyroclastics and appears to have grown somewhat, although it is still lower than the rim of the former central crater (at 3300 m elevation). The extent of new lava flows cannot be ascertained, but it is probably similar to that of earlier flows. Activity has returned to low levels, possibly there is still minor Strombolian activity that may continue for another few days before complete quiet returns.
The previous eruptive episode, on 29 November, was not observed visually due to bad weather, but its effects were studied four days later, during a visit to the crater on the afternoon of 3 December by Boris Behncke and two geologists from the United States. That visit was made while much fresh snow covered the summit region, and it was only possible to reach the rim of SE Crater while the other summit craters could not be visited.

 

Two photos taken during the 3 December 1998 visit to Etna's summit area. Note thick snow cover and near complete absence of gas emissions from the craters. The cone of the SE Crater is visible to the right of the main summit cone in the first photo, part of its summit area being snow-free, but although the most recent eruptive episode prior to the visit had occurred only four days earlier, most of its product have chilled enough to be covered with snow. Second photograph shows the cone of SE Crater seen from its southwestern base (note half buried 1971 cone at left base) before we climbed to its summit.

Lava flows of the 29 November eruptive episodes may have been less voluminous than earlier flows, but we did not see if lava had flowed down the northern sector of the cone; however, the crater rims on that side did not appear to have another "spillover" point like that on the southern side. Lava had spilled through the breach in the southern crater rim and reached down to the base of the cone. Fresh snow covered much of the recent lava, and possibly also some of the 29 November lava. We climbed to the summit of the newly formed cone at SE Crater and observed the vent that had produced all activity in the past months; there was no eruptive activity, and only weak gas emissions occurred from time to time. The summit crater was found to be about 50-80 m wide, its rim being highest on the southeastern side while there were low points on the western, southern and northeastern sides. The crater floor was relatively flat and had a central pit about 15 m wide in its center; this was the vent from which the most recent activity had originated. While staying on the crater rim it was possible to see that the summit of SE Crater was only a few tens of meters lower than the rim of the former summit crater (elevation 3300 m), and thus SE Crater has grown at least 60-80 m since mid-1997.