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Report on Etna (Italy) — September 2013


Etna

Bulletin of the Global Volcanism Network, vol. 38, no. 9 (September 2013)
Managing Editor: Richard Wunderman.

Etna (Italy) 46 paroxysms and birth of the New Southeast Crater (NSEC)

Please cite this report as:

Global Volcanism Program, 2013. Report on Etna (Italy) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 38:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN201309-211060



Etna

Italy

37.748°N, 14.999°E; summit elev. 3357 m

All times are local (unless otherwise noted)


Since our last report on Etna (BGVN 36:05), which covered activity through 29 December 2010, intervals of vigorous activity (paroxysms) have continued, with 18 paroxysms in 2011, 7 in 2012, and 21 in 2013. During this reporting interval, 30 December 2010-31 December 2013, the activity can be viewed as a series of paroxysms detailed in a chronology shown below. Activity at the Northeast Crater (NEC) remained minor during the reporting interval. The Bocca Nuova produced activity in July and December 2011, and then in January 2013 where two episodes of intense Strombolian activity occurred on the evenings of 16 and 18 January.

In addition, during this reporting interval, there emerged a "New" Southeast crater (NSEC). The "old" SEC was last active in May 2007. NSEC formed at a large pyroclastic cone that grew alongside the SEC's active crater. The cone's early growth took place during seven paroxysmal episodes between January and July 2011, and continued to grow though the end of 2013.

Paroxysms at Etna. The term paroxysm, and its use in the phrase 'paroxysmal episode,' has become common in describing Etna's eruptive outbursts, particularly in the past few decades. INGV's Boris Behncke has described the behavior associated with these terms, employing both photos and videos widely available online. Paroxysm is a short-hand for Etna's often intense Strombolian discharges that frequently include lava fountaining, lava flow emission, and tephra columns, which erupted at the summit craters.

Behncke notes that Etna's typical paroxysm consists of three main phases: (1) prelude and waxing, (2) climax, and (3) waning and cessation. The climactic phase 2 part of the behavior represents the true paroxysm. To describe a collective set of all three phases at Etna, Behncke prefers that they be called "paroxysmal episode," "paroxysmal eruptive episode" or "eruptive episode."

Summary and chronology. Table 10 contains a 2011-2013 chronology of Etna's paroxysmal episodes at the NSEC as reported by INGV. There were 46 such episodes during the interval shown in the table. There are clear cases where the description of a single paroxysm glosses over complexities of the eruptive process (see, for example, the 30 July discussion in the next section).

Table 10. A list of NSEC paroxysmal episodes from Etna's New Southeast Crater and their numbering for 2011- 2013. The column at far right contains occasional notations of interesting or extraordinary events taken from INGV reporting. In some cases there are minor variations in dates and numbering.

Paroxysm number Date Notes
2011
1 13 Jan 2011 1-7 correspond to strong growth of NSEC; At irregular intervals small landslides occurred within the crater depression
2 18 Feb 2011 --
3 10 Apr 2011 --
4 12 May 2011 --
5 09 Jul 2011 A dense eruptive plume rose several kilometers and drifted S and SE, causing ash-and-lapilli fall in populated areas and forcing the closure of the Fontanarossa international airport in Catania.
6 19 Jul 2011 --
7 25 Jul 2011 --
8 30/31 Jul 2011 See figure 142 (30 July 2011) The event was essentially a repetition of the previous paroxysms, with the emission of a lava flow W toward the Valle del Bove, lava fountains rising to maximum heights of 450-500 m, and an ash plume that was blown E by the wind.
9 08 Aug 2011 --
10 12 Aug 2011 --
11 20 Aug 2011 --
12 29 Aug 2011 --
13 08 Sep 2011 --
14 19 Sep 2011 This event, which occurred during rather poor weather conditions, produced lava fountains from various vents within the crater and on its southeastern flank, lava flows that descended the western slope of the Valle del Bove, and an ash cloud that was bent by the strong wind to the NE.
15 28 Sep 2011 --
16 08 Oct 2011 --
17 23 Oct 2011 --
18 15 Nov 2011 This episode has in nearly all details been a repetition of its predecessors, though with a few minor variations; the culminating phase lasted about one hour and terminated rather abruptly. Ash-and-lapilli falls affected the SE flank, including the towns of Zafferana, Etnea and Acireale.
2012
1 / 19 05 Jan 2012 --
2 / 20 09 Feb 2012 This event was less violent than its predecessors, but lasted more than 5 hours. A lava flow descended toward the Valle del Bove, stagnating before it reached the valley floor.
3 / 21 04 Mar 2012 --
4 / 22 18 Mar 2012 Tall lava fountains, a tephra and vapor column several kilometers high (leading to ash and lapilli falls over the E sector of the volcano), and lava flows that descended into the Valle del Bove, locally interacting explosively with thick snow cover on the ground.
5 / 23 01 Apr 2012 --
6 / 24 12 Apr 2012 --
7 / 25 24 Apr 2012 This event, which occurred after a relatively quiet interval of 11.5 days, repeated in virtually all details the preceding episodes, with lava fountains, copious emission of ash and lapilli, and lava flows that descended into the Valle del Bove.
2013
1 / 26 20 Jan 2013 The two episodes of Strombolian activity at the New Southeast Crater during 20 and 22-23 January represented the first emission of new magmatic products after a quiet interval of nearly nine months.
2 / 27 22-23 Jan 2013 --
3 / 28 19-20 Feb 2013 Starting the morning on 19 February, with 3 more paroxysms during the next 54 hours. Pronounced cone growth at NSEC. Lava flows emitted from base of NSEC ongoing between paroxysms.
4 / 29 21 Feb 2013 --
5 / 30 23 Feb 2013 Very active event. See figure 143 (23 Feb). Ash plume trending ESE, lava flows from the fissure cutting the SE crater rim and also from a new eruptive fissure, and small lahars. The second paroxysm of the day produced an ash cloud that drifted E; new lava flows descended toward the Valle del Bove, following the paths of their predecessors. The rapid succession of three paroxysmal eruptive episodes in less than 36 hours is quite notable; the only known historic precedent of three paroxysms occurring in such a short time interval at Etna was the series of eruptive episodes in 2000
6 / 31 28 Feb 2013 --
7 / 32 5/6 Mar 2013 --
8 / 33 16 Mar 2013 This event, one of the most intense of the current series of paroxysms, was preceded by a long "prelude" (Strombolian activity) that started on the afternoon of 15 March, and was followed by weak, discontinuous activity at the Voragine.
9 / 34 3 Apr 2013 --
10 / 35 12 April 2013 Lava fountaining; high column of pyroclastic material; The eruption formed a pyroclastic cloud directed to the SE, initially producing lapilli and ash, which fell mostly near the inhabited centers of Zafferana Etnea, Santa Venerina e Acireale; later including the communities of Giarre and Milo situated slightly to the N.
11 / 36 18 Apr 2013 --
12 / 37 20 Apr 2013 Very powerful episode: lava fountains reached heights of 800-1000 m above the crater, whereas the cloud of pyroclastic material expanded toward ESE, leading to heavy fall of ash and lapilli over the areas of Zafferana Etnea, Milo, Santa Venerina and further downslope, in the area of Giarre.
13 / 38 27 Apr 2013 --
14 / 39 26 Oct 2013 A gas plume laden with pyroclastic material rose several kilometers above the summit and drifted SW, affecting population centers as far as the Caltanissetta area. Activity caused the closure of airspace near Catania airport before dawn through the early morning.
15 / 40 11 Nov 2013 --
16 / 41 17 Nov 2013 --
17 / 42 23 November 2013 Very powerful episode: rapid evolution from Strombolian activity to lava fountains. The eruption column, several kilometers high, was charged with pyroclastic material that was dispersed by the wind to the NE.
18 / 43 28 Nov 2013
19 / 44 02 Dec 2013 See Figure 144 (2 December) This event produced tall lava fountains, lava flows, and an eruption column charged with pyroclastic material, which drifted NNW, causing ash and lapilli to fall in the area of Bronte. Several lava flows were emitted to the SSE, SE, NE and S. The flow traveled SE and reached the base of the W headwall of the Valle del Bove.
20 / 45 14-16 Dec 2013 Ash emissions caused the cancellation of more than 20 flights in and out of the Catania airport on 15 December.
21 / 46 29-31 Dec 2013 --
Figure (see Caption) Figure 142. A photo of NSEC in eruption during a paroxysm on the evening of 30 July 2011. The photo shows lava fountaining activity, ash plume, and lava flow from the new and actively growing cone on the E flank of Etna's old Southeast Crater (barely discernible at extreme left). The photo was taken from a point about 1 km to the SE of SEC but the height of the lava fountains were undisclosed. Photo taken by Marco Neri, INGV-Catania.

Regarding paroxysm number 8 (30-31 July 2011), INGV featured photos (e.g., figure 142) and made comments such as the following.

"About 19.00 h local time (= UTC-1), the mean amplitude of the volcanic tremor started to increase again, and so did the Strombolian activity. At around 19.30, a dilute gas and ash plume was again blown eastward by the wind. The Strombolian activity progressively gained in intensity, quite more rapidly than during the morning's activity, and the incandescent jets became continuous around 21.30 local time. At the same time, renewed lava overflow toward east showed a rapid increase in effusion rate, forming a multilobate flow down the western slope of the Valle del Bove, which traveled approximately 3 km down reaching about 2,000 m elevation by 2300 local time. The ash plume became denser and was blown eastward by the wind, generating ash falls in the Ionian sector of the volcano.

"During the phase of maximum intensity, fragments of fluid lava were violently thrown to heights of about 450-500 m above the crater rim, causing heavy fallout onto the external flanks of the pyroclastic cone to a distance of 200-300 m. Lava fountains were jetting from at least two vents located within the crater and on its upper east flank, roughly aligned west-northwest - east-southeast."

2013. There were two main phases of activity during 2013. The first occurred during January-April; the second, after a 6-month quiescence, began on 26 October (table 10).

Figure 143 shows a view of the paroxysmal event of 23 February 2013. Of the events listed during the first phase of 2013 (table 10), this was a particularly active one.

Figure (see Caption) Figure 143. View of the Pizzi Deneri area in the aftermath of incandescent bombs falling during the peak of the 23 February 2013 paroxysm at the NSEC. Photo taken from the Rifugio Citelli, on Etna's NE flank. Photo taken by Daniele Pennisi and taken from INGV report.

INGV reported that eight eruptive events occurred between 26 October and 31 December 2013. The largest of these events occurred on 23 November 2013 and stood out as a noteworthy event in terms of amplitude. Figure 144 shows a scene from the episode on 2 December 2013.

Figure (see Caption) Figure 144. Strong explosions at the end of the lava fountaining during the paroxysm of 2 December 2013 at Etna's New Southeast Crater, and lava flow directed toward the SE (at left). Note also the beginning of the formation of a small lava flow toward the NW, more to the right, forming a more luminous point on the cone's flank. Ballistics rose hundreds of meters. Photo taken from Macchia di Giarre by Walter Contarino, and INGV report.

Paroxysmal activity at Etna caused significant disruptions regionally during the reporting period; the Catania airport cancelled flights in and out of the airport several times. On 9 July 2011, Strombolian explosions turned into a continuous lava fountain; a dense eruptive plume rose several kilometers and drifted S and SE. Ash and lapilli from the plume fell in populated areas including Trecastagni, Viagrande, and Acireale (SE), and between Nicolosi and Catania (S), forcing the closure of the Fontanarossa international airport in Catania. In 2013, according to a news article, a representative from Catania airport noted activity at Etna prompted the closure of nearby airspace from before dawn through the early morning of 26 October 2013. According to another news article, the ash emissions caused the cancellation of more than 20 flights in and out of the Catania airport on 15 December 2013.

The New SEC (NSEC). The old SEC cone was last active in May 2007. The NSEC cone grew substantially between 12 January and 25 July 2011 (episodes 1-7) (table 10) and thereafter. Figure 145 shows a photo of the NSEC taken on 29 July 2011.

Figure (see Caption) Figure 145. A photo of Etna's Southeast Crater (SEC) taken on 29 July 2011 from 1 km S of the SEC. The photo shows the large pyroclastic cone that has grown around the active crater, located on the E flank of the old SEC cone, during the seven paroxysmal episodes between 12 January and 25 July 2011. Photo taken by Boris Behncke, INGV-Catania.

Since its emergence in 2011, the NSEC grew substantially, especially in 2013. The size of NSEC can be seen relative to the old SEC in figure 146. Smaller and farther left (E) is the low cone Sudestino ('little southeast'), which grew during several paroxysmal episodes during the spring of 2000 just beyond the SEC's S side (BGVN 25:03; 25:09). The right upper half of the image is dominated by the NSEC cone, which grew entirely during the previous 10 months. INGV noted that during 2013 the NSEC cone expanded both in height and width.

Figure (see Caption) Figure 146. A view of the Southeast Crater (SEC) complex at Etna as seen from the S on 14 December 2011. The "old" SEC cone is in the center and contains the conspicuous light colored area with wisps of fumarolic vapor and yellow sulfur deposits. The right half of the image shows the New SEC cone, which grew entirely during the previous 10 months. The large bombs and blocks in the foreground, with some clasts 3-5 m in diameter, were deposited during the paroxysmal episode of 15 November 2011. Mosaic composed of 3 photos taken by Boris Behncke, INGV-Osservatorio Etneo (Catania).

The October -December phase of Etna's 2013 activity is summarized in an INGV report from 22 January 2014 (B. Behncke & E. De Beni). Figure 147 shows a map of lava flows emanating from the NSEC during this phase of activity (26 October - 31 December 2013).

Figure (see Caption) Figure 147. Map of the lava flows emitted at the NSEC from 26 October to 31 December 2013 and morphology of the NSEC cone updated in January 2014 (base map, August 2007). BN=Bocca Nuova; SEC = Southeast Crater; NSEC = New South East Crater. Taken from UFGV Report of 22 January 2014, (INGV, by B. Behncke and E. De Beni).

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: Boris Behncke, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ct.ingv.it/).