The NE Crater in eruption under a starry sky, 31 May 1996. View is from the SW. Photo taken by Marco Fulle

The NE Crater from 1995 to 2001

Activity at the NE Crater from July 1995 to July 1998 can be divided in several distinct periods: the first, between late July and early November 1995, was characterized by deep-seated Strombolian activity at the bottom of the collapse pit formed in 1992; the second lasted from 9 November 1995 until 10 February 1996 and included eight episodes of vigorous fire-fountaining that produced major tephra columns; during the third period, between mid-February and late August 1996 the eruptive behavior changed to persistent Strombolian activity, punctuated by two more paroxysmal episodes of fire-fountaining in June 1996 and culminating in four weeks of lava effusion; the fourth period began in late August 1996 and brought about the return to conditions similar to the first period (except for an isolated episode of lava fountaining in late March 1998), with sporadic deep-seated Strombolian activity occurring on the floor of a newly-formed collapse pit in the central part of the crater floor. A fifth period in June-October 1999 included a brief interval of intense Strombolian activity.

During the 1995-1996 activity the NE Crater appeared to return to its characteristic behavior seen during the 1950's to 1980's, the period of most vigorous growth of its cone. The ten episodes of fire-fountaining and tephra emission resembled strikingly the series of paroxysmal eruptions produced by the same crater between July 1977 and March 1978 except in one respect: the 1995-1996 paroxysms lacked true effusive activity (only minor rootless lava flows caused by the rapid accumulation of still-fluid ejecta on steep slopes occurred during the 23 December 1995 event). Even when the activity switched to persistent Strombolian activity that continued for about 6 months, no lava effusion took place until the fifth month. When lava flows finally issued from the crater, this effusive activity differed markedly from that observed during the 1950's to 1970's at this crater. Lava had then issued from vents located on the flanks or at the base of the cone, and at times from vents located several kilometers downslope from the summit of the cone.

In 1996, lava effusion was first observed in mid-July within the crater, at the base of the growing scoria cones on its SW rim, this lava slowly spread across the crater floor and crusted over. By this time the crater was filled almost to the rim with scoriae produced by the latest two paroxysmal events of June 1996. The rising magma that erupted on the SW crater rim evidently bypassed the thick piston of agglutinated pyroclastics in the crater rather than breaking through right in its center. Lava eventually broke through the unstable crater rims on the NE and S side, being fed by large tubes. The feeder tube of the northeastern flow was later exposed as the center of the crater floor subsided; at this location it was some 30 m wide and about 10 m high, and the thickness of lava above its roof was about 10-15 m.

The 1995-1996 eruptions and subsequent collapse profoundly modified the morphology of NE Crater. The simple large pit truncating the cone before the activity was completely filled by pyroclastics, the SW crater rim collapsed, and in its place grew a cluster of overlapping scoria cones during the final phase of the activity. Volume estimates of the 1995-1996 activity give about 5 million m³ of pyroclastics and 1 million m³ of lava. No significant morphological changes occurred after the collapse of the central pit in October 1996, in spite of persistent weak Strombolian activity on the floor of the pit and the late March 1998 paroxysmal episode.

The overall growth of the NE Cone during the 1995-1996 activity does not appear to have been significant, contrasting with the vigorous growth until the early 1980's. In fact the cone failed to regain its position as the highest point on Etna, and in spite of its vigor the activity in 1995-1996 was relatively short-lived, underlining a profound change in the eruptive behavior of the crater since the early 1980's.

Between late 1996 and late 2001 the NE Crater showed increased activity on five occasions: in July-October 1997, in the summer of 1998, in September-October 1999,in May-June 2000, and in the spring of 2001. In all cases the activity consisted of Strombolian bursts that took place deep within its central pit, and at times incandescent ejecta were ejected above the rim of the pit. The most spectacular activity was that of September-October 1999 and May-June 2000 when bombs fell onto the outer flanks of the NE Cone, and in the earlier case it seemed as though the crater was about to resume a more persistent type of Strombolian activity. However, in the end the grand show was left over to the other summit craters; only in 1995-1996 did the NE Crater behave like in its best days.

Very little significant morphological change due to the eruptive activity of the NE Crater itself occurred after 1996, but the two paroxysmal eruptions from the Voragine on 22 July 1998 and 4 September 1999 had major effects on the morphology of the crater and its cone, which will be described in the Voragine section.

Copyright © Boris Behncke, "Italy's Volcanoes: The Cradle of Volcanology"