by Boris Behncke; English translation by Chiara Montagna
20 years ago, in 2000, Etna went through an exceptional eruptive period: during 7 months, the youngest of its four summit craters, the Southeast Crater, produced an impressive series of 66 (sixty-six) paroxysmal eruptive episodes. Never in the documented history of Etna, or of any other volcano for that matter, has such a behavior been observed. Many of the paroxysms were recorded by a monitoring camera, run by the “Sistema Poseidon”, a seismic and volcanic monitoring organisation that was absorbed in the Istituto Nazionale di Geofisica e Vulcanologia (INGV) in 2001. We are making some of the unique video footage of that camera available for the first time in a special playlist on the YouTube channel of INGVvulcani.
When, in summer 1995, Etna awoke after two quiescent years, nobody could anticipate the frantic eruptive cycle that would follow in the coming years. All four central craters were to be involved in the forthcoming eruptions, beginning with the Bocca Nuova crater, followed shortly thereafter by the Northeast crater, then, in November 1996, by the Southeast Crater, the youngest among the summit craters at Etna, and finally, during the summer of 1997, by the Voragine crater.
Between 15 September 1998 and 4 February 1999, the Southeast Crater originated a long sequence of around 20 paroxysmal events. Then the eruptive activity moved to the base of this same crater, producing small-volume lava flows for the months to come, until mid-November 1999. Meanwhile, the Voragine (on 4 September 1999) and Bocca Nuova (in October-November 1999) craters produced spectacular eruptions that largely modified the shape of the summit area.
After the end of effusive activity at Bocca Nuova (5 November 1999) and Southeast (14 November 999) craters, Etna underwent a relatively quiet period, abruptly interrupted on the morning of 26 January 2000.
First paroxysm: 26 January 2000
The eruptive activity started shortly after midnight with Strombolian explosions at the Southeast Crater that gradually intensified (Figure 1a) to become lava fountains (Figure 1b). At the peak of the activity, the south flank of the Southeast Crater fractured, and lava started flowing on the snow-covered terrain at the cone base (Figure 1c). After a few relatively quiet hours, a second paroxysmal phase began (Figure 1d), which lasted until early afternoon.
After three days, on the morning of 29 January, the same pattern repeated, although with smaller intensity and duration: the paroxysmal phase lasted less than 30 minutes. Like in the previous event, at the apex of the activity the southern flank of the cone fractured, emitting a small lava flow. A third episode, substantially identical to the former, took place on 1 February, and another one on the day after. During the three weeks to follow, paroxysmal events followed each other frantically at a rate of one to three per day (Table 1, at the end of this article).
The Southeast Crater in a frenzy: February 2000
In a few days, a sort of “choreography” was established, that was faithfully reproduced with small variations during each event: (1) a reactivation phase, slowly intensifying, that usually consisted of lava effusion from a vent on the northeastern flank of the Southeast Crater (Figure 2a), sometimes associated with small Strombolian eruptions from the vent on top of the cone; (2) opening of a fracture from the effusive vent on the northeastern flank toward the top of the cone (Figure 2b), and rapid increase of the explosive activity, with tall lava fountains and eruptive columns heavily charged with pyroclastic material (Figure 2c,d); (3) at the peak of the paroxysm, fracture opening on the south flank of the cone, and lava emission from its lower end; (4) fast diminution and cessation of the explosive activity (Figure 2e,f), followed by slow exhaustion of lava effusion (Figure 2g). In most cases, the entire episode would not last more than 30 minutes, while the high fountaining phase would only last 10 to 15 minutes.
The “Sudestino” is born: March 2000
After 20 February 20, the rhythm of the paroxysmal activity slowed down, with successive episodes days apart (Table 2). The fracture on the south flank of the cone kept opening and extended beyond the base of the cone itself. A very active vent formed there, which became more and more the focus of the activity during paroxysmal episodes. Lava from that vent began forming a small shield (Figure 3 – see Glossary), nicknamed “Sudestino” (‘Little Southeast’).
During the first half of March, the activity shifted from the summit vents of the Southeast Crater to the “Sudestino”. During the episodes on 12, 14 and 19 March, the latter produced lava fountaining, while the summit vents of the cone mostly emitted ash and sporadic lava jets (Figure 4). Lava flows advanced toward “Torre del Filosofo” (“Philosopher’s Tower”), an edifice built at the end of the Sixties to serve as a hotel but never launched, at 2940 m elevation, 1 km south of the crater. On 14 March lava entirely engulfed the edifice and burned a volcanological guides’ wooden hut, while snow melting generated a small mudflow (lahar).
After the paroxysm on 19 March (Figure 4d), the activity focused again at the top vents of the Southeast Crater, and eruptive episodes on 22, 24 and 29 March once more followed the “choreography” that had been established in February. During some eruptive episodes at the beginning of April, the fracture on the southern flank of the cone did not open, and it looked like that the short life of the “Sudestino” had ended already. However, at the end of the 6 April paroxysm, slow lava emission began from this vent, lasting a few hours. Then, the Southeast Crater entered a 10-days hiatus in eruptive activity, the longest up to that point in the eruptive sequence. At that moment, the number of paroxysms had reached the remarkable quantity of 49 within slightly more than two months!
Etna plays Ping-Pong and makes pyroclastic flows: 16 April 2000
Paroxysm #50 took place on 16 April, and it was a particularly spectacular event – and a dangerous one indeed. Many people had climbed to Torre del Filosofo on that fine spring Sunday to take a look at the mild lava fountaining that had resumed from the “Sudestino” during the night (Figure 5a). For the whole morning eruptive activity shifted back and forth between the summit vents of the Southeast Crater and the “Sudestino” – until a large explosion from the summit at 14:35 (local time) generated a dense, oblique, bomb-rich jet (Figure 5b).
The abundant fall-out on the flanks of the cone generated a pyroclastic flow that travelled south-east for around 1 km (Figure 5c), just shy of Torre del Filosofo, where many people were observing the eruption. Many of them rushed down the smooth slope below the edifice – where a couple of years later, during the 2002-2003 eruption, a large new cone would form, Monte Barbagallo. Had the pyroclastic flow taken an only slightly more southern direction, it would have wiped out Torre del Filosofo and the people there.
The 16 April 2000 paroxysm marked the Grand Finale of the “Sudestino”, which never came back to life again and was completely buried by lavas from the New Southeast Crater in 2013.
Dangerous encounter in the sky: 26 April 2000
After another quiet 10 days, the next paroxysm from the Southeast Crater on the morning of 26 April was characterised by the same old “choreography”: lava flows from the vent on the northeastern flank of the cone, propagation of eruptive vents towards the summit and opening of the fracture along the southern flank. This episode made history because an airplane flying from Catania to Milan flew right into the eruptive plume at the peak of the paroxysm. The plane was showered with lapilli, which eventually cracked the cockpit windscreen and windows, luckily without completely breaking them. The pilot was forced to carry an emergency landing back in Catania.
Paroxysms into spring and summer: April-June 2000
Different from those of February, paroxysms in April, May and June lasted longer – up to an hour – and were more violent, producing a lot of pyroclastic material (ash and lapilli) and abundant fallout in inhabited areas around the volcano. Intervals between episodes were also usually longer than in February-March, ranging between 1 and 10 days; excluding 15 May and 1 June, characterised by two paroxysms in the same day (Figure 7). Among the two fractures opening on the south and northeast side of the cone, the latter was now emitting larger lava volumes, and at the main vent at its lower end, a small cone was forming, nicknamed “Levantino” (“Little East”). Lava emission from this fracture always began some hours before fountaining; the southern fracture would open only at the climax of the activity, and only in its upper part.
The last paroxysm, number 64 of this extraordinary sequence, started in the evening of 24 June 2000 (Figure 8). As almost every previous event, it was preceded by long-lasting lava emission from the vent on the north-east flank of the cone, and the lava flow reached a length of 3.7 km, the longest in the whole eruptive sequence.
Two more eruptive episodes took place on 28 and 29 August, less intense than those of May-June and characterised by lava emission mostly from the northeastern fracture. Then, the Southeast Crater entered a several months long hiatus that was to end in Spring 2001, but this is a different story.
At the end of the January-August 2000 activity, the cone of the Southeast Crater was at least 40 m taller than before, and it was much wider, especially due to the two lava fans built up at the fractures on the south and northeast flanks. The aerial photo in Figure 9a shows the cone “cut” by the fracture system. The total emitted volume has been estimated at 47 million cubic meters, of which 37 million as lava flows. Figure 9b shows a map of the lava-covered area from 2000 eruptions.
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Table 1. Paroxysmal eruptive episodes at the Southeast Crater of Etna in the year 2000
01: 26 January
02: 29 January
03: 01 February
04: 02 February
05: 03 February
06: 04 February
07: 05 February (morning)
08: 05 February (afternoon)
09: 06 February (morning)
10: 06 February (evening)
11: 07 February
12: 08 February (forenoon)
13: 08 February (evening)
14: 09 February
15: 10 February (morning)
16: 10 February (afternoon)
17: 10 February (evening)
18: 11 February (morning)
19: 11 February (evening)
20: 12 February (night)
21: 12 February (forenoon)
22: 13 February (night)
23: 13 February (afternoon)
24: 14 February (morning)
25: 14 February (afternoon)
26: 15 February
27: 16 February (morning)
28: 16 February (afternoon)
29: 17 February (morning)
30: 17 February (afternoon)
31: 17 February (evening)
32: 18 February (forenoon)
33: 18 February (afternoon)
34: 19 February
35: 20 February
36: 23 February
37: 27 February
38: 28 February
39: 04 March
40: 08 March
41: 12 March
42: 14 March
43: 19 March
44: 22 March
45: 24 March
46: 29 March
47: 01 April
48: 03 April
49: 06 April
50: 16 April
51: 26 April
52: 05 May
53: 15 May (forenoon)
54: 15 May (evening)
55: 18 May
56: 20 May
57: 23 May
58: 27 May
59: 01 June (forenoon)
60: 01 June (evening)
61: 05 June
62: 08 June
63: 14 June
64: 24 June
65: 28 August
66: 29 August