Updates January 1999
The most recent updates
Etna news archive
23 January 1999
This morning SE Cone was the site of yet another eruptive episode, the 21st since the current series of paroxysmal eruptions began. The episode began at about 0630 h local time (GMT+1) and probably lasted less than one hour. Due to the absence of any wind, an eruption column rose several km above the summit; it then drifted slowly southeastwards, dropping ash on Catania and other towns in the southeastern sector of the volcano. In Catania, the ash rain was not dense at all, but people walking in the streets felt particles entering in the eyes; these particles were less than one millimeter in diameter and left a thin, discontinuous film on the ground. More serious effects were caused by the fallout in the upper southern parts of the mountain where any skiing activity was rendered impossible by the scoria cover on the snow, thus increasing the problems already caused by the unusually mild and snow-poor winter. The repose period between this and the previous eruptive episode from the SE Cone was two days and 18 hours, somewhat longer than the previous interval. It appears as though the volcano retains this rhythm of eruptive episodes every two to four days.
|Two views of Etna in eruption on early 23 January 1999 during a late stage of the eruptive episode at SE Crater. A tephra plume is rising 2-3 km above the summit, and ash fallout occurs to the south (seen to the left of the eruption column). Photos were taken from Sant'Agata li Battiati, north of Catania, by Giovanni Sturiale.
22 January 1999
SE Crater erupted again after only two days and four hours of inactivity,
shortly after noon on 20 January. Incereased gas emission began at about 1215
h, and by 1240 a lava fountain appeared at the vent of the SE Crater cone. This
fountain rapidly rose to a height of several hundred meters, and the column
which rose above it became more and more ash-rich. Less than 15 minutes after
the onset of the eruption there occurred the first slides of hot pyroclastics
from the upper part of the cone, and five minutes later the whole cone and part
of Etna's main summit cone were veiled by a black curtain of backfalling bombs
and scoriae. By 1300, the vertical eruption column had risen to a height of
several kilometers above Etna's summit. Ten minutes later the activity began
to decline rapidly, and by 1315 the eruptive episode was essentially over, with
only a few ash puffs being emitted during the following 30 minutes.
There seems to be a clear correlation between the length of an eruptive episode and the preceding repose period; both are becoming shorter with time. At the time of writing (22 January, 1530 h), though, two days and two hours have already passed since the end of the latest episode.
SUMMIT VISIT, 21 JANUARY 1999. On the day after this event, Giovanni
Sturiale and Boris Behncke of the Istituto di Geologia e Geofisica of Catania
University (IGGUC) climbed to Etna's summit during perfect weather conditions
to observe the effects of the recent activity and possibly ongoing activity.
The visit to the area of the SE Crater was overwhelming; the crater itself merits
to be no longer called "SE Crater" but rather "SE Cone"
(this naming will be maintained in future updates). This cone now stands almost
300 m above the elevation of the spot where it formed in 1971. Growth of its
new summit has completely obliterated any trace of the ~150 m-wide crater formed
in early 1990 which has been the site where a small intracrater cone grew in
1997-1998 (some readers will remember this from previous updates).
Thick pyroclastic deposits have mantled much of the nearby main summit cone and other areas adjacent to the SE Cone. While pyroclastics erupted up to the 29 December 1998 episode are buried under snow that fell at the turn of the year (most recently on 1 January), the five episodes that have occurred so far in 1999 have deposited scoriae and bombs that form several fans radiating away from the SE Cone on top of the snow. Near the southern base of the main summit cone, the deposits are up to 20 cm thick and contain abundant porous scoriae up to 10 cm in diameter. Larger dense bombs have created numerous impact craters in this area and in the area between the base of the SE Cone and the 1971 "Observatory" cone. Continuous scoria deposits also cover the terrace in the southeastern part of the former Central Crater and extend into the Voragine and to the southern rim of Bocca Nuova. The Central Crater platform near the SE Cone is littered with bombs some of which are several meters long, there are also many impact craters up to 3 m in diameter.
At the southwestern base of the SE Cone we observed what appeared to be a debris flow, or lahar, deposit, probably formed during the 5 January episode when the fallout extended to the SW on thick snow fallen a few days earlier. Some of the snow apparently melted by the rain of hot pyroclastics, mobilizing freshly fallen and older material to form a small lahar. This lahar originated on the upper southwestern flank of a half-buried cone formed in 1971 ("Western vents") and extended some 300-500 m southwest, passing about 150 m to the west of the 1971 "Observatory" cone. At its front it split into at least five lobes which extended beyond the scoria sheet of 5 January on top of show littered with large scoria clasts. In the upper and central part of the deposit two distinct flow channels were visible, each about 1,5 m wide and 1 m deep. Lahars are not common on Etna, and their occurrence during the recent and ongoing activity of the SE Cone is therefore notable.
No distinct deposits related to the pyroclastic avalanches or slides observed during the two most recent eruptive episodes were found, but we did not approach close to the base of the cone for good reasons.
The SE Cone itself has grown in a striking manner. Being a rather broad cone truncated by a large crater after the early 1990 activity, it remained so until mid 1997 when the intracrater cone grew higher than the crater rim and lava began to spill onto its outer flanks. Now it has become a tall and steep cone whose summit stands more than 100 m above the former highest point on the crater rim. Although still a few meters lower than the terrace of the former Central Crater, it has now grown to an elevation of 3300 m, or nearly so, that is only 20-30 m below Etna's highest point.
The crater at the summit of the SE Cone is about 50-60 m wide, with irregular rims which are highest in the SE and W, and a deep notch in its NE rim through which lava hasspilled repeatedly onto the flank during recent eruptive episodes. A multilobate lava flow field has developed at the NE base of the cone, with some of the flows extending up to 500-800 m from their source vent. There are also numerous meter-sized blocks that have accumulated at the eastern base of the cone. Still another lava flow, certainly emitted during the most recent (20 January) episode, extends from a small notch in the southern crater rim almost down to the southern base of the cone.
Activity at the crater of the SE Cone was all but absent during the 3 hours of our visit, only a few weak fumaroles at the crater rims and at the sources of the northeastern and southern lava flows emitted bluish gas plumes.
Bocca Nuova was much more vigorously active. Like during previous visits, spattering and Strombolian activity occurred deep within two vents in the large crater in the southeastern part of Bocca Nuova, accompanied by dense gas emission. No significant morphological changes have occurred in this area since months.
The cone in the northwestern part of Bocca Nuova produced violent and noisy explosions every few minutes which ejected fountains of bombs high above the crater rim, and frequently ejecta fell outside the crater, mostly to the west but in a few cases also to the southwest and south. Between the explosions, deep-seated minor activity occurred within the 50-80 m wide crater of the cone. No effusive activity has taken place in Bocca Nuova since it was invaded by lava from nearby Voragine on 22 July 1998.
Very little activity except profuse steaming was observed within the Voragine, and we decided to descend into this crater; one of us arrived at the "diaframma", the septum that separates the Voragine from the Bocca Nuova. The floor of the crater is very flat in its eastern part, while a cluster of four craters with low cones occupies its central-western portion. The central crater, about 50 m wide and about 30 m deep, was completely quiet; on its western side a much shallower, about 20 m-wide crater contained a 2 m-wide degassing hole with overhanging walls on whose floor numerous incandescent spots could be seen. A small crater with a diameter of less than 20 m, and about 10 m deep, lies on the southeastern side of the central crater. The largest crater in the Voragine is what I called "diaframma vent" in last summer's updates; this lies in the southwestern part of the Voragine and is between 70 and 100 m wide and more than 50 m deep with very steep and unstable walls, so that its floor cannot be seen. Eruptive activity occurs at depth; as can be judged from the noises this must be similar to the activity observed in the southeastern Bocca Nuova vents. A fifth vent that was active in August and early September 1998 on the crest of the "diaframma" appears to have collapsed into the large southwestern vent, and only a part of its cone remains standing.
The "diaframma" itself is surprisingly smooth and stands only 5 m above the floor of the Voragine. Numerous fumaroles emitting sulfur dioxide render the sojourn in this area highly unpleasant and prevent one from obtaining good views into the Bocca Nuova. The view from this place of the Voragine, however, was beyond belief, and this impression mixed with the clear perception that this crater had been an inferno during the last summer. We can now curiously wait for the day when the Voragine reawakens and begins to experience another period of reshaping...
18 January 1999
The latest eruptive episode of SE Crater
occurred this morning shortly after 0800 h local time (GMT+1) and lasted about
45 minutes. Minor Strombolian and effusive activity had occurred earlier during
the night, but no activity had been observed by myself at nightfall yesterday
evening. As in preceding episodes, the culminating phase was characterized by
initial strong lava fountaining which gradually became more and more ash-rich,
generating a dense eruption column. Due to the lack of strong wind in the summit
area, the column rose several km above the summit (3 km as estimated from Catania)
and attained a spectacular mushroom shape, this was perfectly visible in the
morning sky from all around the volcano (see the photo at left which was taken
by Giovanni Sturiale of IGGUC from the town of Sant'Agata li Battiati. At the
SE Crater cone itself, the heavy fallout and rapid accumulation of pyroclastics
led to frequent avalanches, especially on the steep eastern side. After 0830,
dull explosion sounds were audible to as far as Catania, accompanying the rhythmic
uprush of dark ash. The activity declined rapidly at 0845, but ash emissions
became again more forceful after 0900 and continued sporadically for several
hours, accompanied by near continuous sliding of hot pyroclastics from the steep
eastern side of the cone. No information is available about lava flows although
it is likely that they occurred, possibly on the northeastern side of SE Crater.
Some activity had been observed at SE Crater on Saturday (16 January) evening, but the details of this activity remain mysterious. While riding on a bus from Taormina to Catania between 1830 and 1900, at times incandescence was visible in the summit area, but this disappeared after a few moments. At 2045, Giovanni Sturiale observed what appeared to be a lava flow from SE Crater, but observation from Catania some fifteen minutes later revealed no incandescence at the summit. Giuseppe Scarpinati, a resident in Acireale and collaborator of the French "Association Volcanologique Europ�enne" (L.A.V.E.) reported "a very small incandescent spot at SE Crater and intense activity within Bocca Nuova".
14 January 1999
Since the most recent eruptive episode described on these pages, on 13-14 December
1998, SE Crater has produced four more eruptive episodes (Nos. 15, 16,
17 and 18), on 29 December, 5 January, 9-10 January, and 13 January. Little
detail is available about the 29 December episode: it occurred sometime during
the forenoon and produced a vertical eruption column during its culminating
phase that was visible from the northern ide of the mountain. The activity was
presumably similar to that of previous eruptive episodes, with mild Strombolian
activity followed by the emission of lava and vigorous spasmodic lava fountaining.
The next episode occurred shortly before noon on 5 January and was preceded by weak Strombolian activity that started around midnight (information from Sandro Privitera). The paroxysmal phase was characterized by vigorous fountaining, and lava flowed towards the northeast while tephra was driven southwest by the strong wind. Loud detonations were audible in towns on the flanks of Etna.
Episode #17 was equally preceded by mild Strombolian activity; the paroxysmal phase occurred shortly after midnight; lava presumably flowed northeast again and tephra fell towards northeast: Fiumefreddo, located some 8 km southwest of Taormina received a light showering of ash. Loud detonations during the final phase of the episode were audible over a wide area, and clear weather conditions permitted many night roamers in the Catania area to watch the spectacular display.
After the shortest repose interval observed since early in the current eruptive sequence in September, episode #18 took place on the morning of 13 January, between about 0630 and 0930. Visibiliby was hampered by clouds, but loud detonations were audible in a wide area around the volcano. Ash fell as far as Giarre, about 15 km to the east.
As a result of the recent activity, the cone of SE Crater has experienced further growth, and its shape is becoming more and more regular. Its present elevation is probably significantly higher than 3250 m, compared to its pre-1997 elevation of 3185 m. With the eruptive episodes becoming more frequent again, further growth is to be expected in the near future.
Again, the behavior of SE Crater is presenting interesting changes. During the period September-December 1998, the repose intervals between eruptive episodes increased progressively, from a few days to more than 15 days. Since the 29 December episode which occurred after the longest interval so far, the quiet intervals have shorteneddramatically, to seven days between episodes 15 and 16, 4.5 days between episodes 16 and 17, and 3 days and a few hours between the latest two episodes. So far there is no information available about a possible correlation of the length of the repose interval and the vigor and volume of the following eruptive episode. The summit eruptions that began in July 1995 are continuing, and they are doing so with new surprises and mysteries.