Monitoring Mount Etna for more than 20 years
22 July 2001-11 March 2021
Here we take look back at cases since 2001, which have focused on Mount Etna.
Mount Etna, or Etna is an active stratovolcano on the east coast of Sicily. It is one of the world's most active volcanoes and is in an almost constant state of activity.
16-28 Feb, Sicily
On 16 February 2021, Etna started a series of very spectacular lava-fountaining eruptive episodes, known as paroxysms. The short, but violent paroxysms, produced spectacular fireworks of lava fountains and blanketed part of Sicily with black ash.
In total, eight short paroxysms (with durations of around 2-3 hours) were observed by Meteosat-11 in the period 16-28 February (Figures 1, 2 and 3), under perfect viewing conditions, ie no clouds obscuring the scene.
Each time the volcano sent lava hundreds of metres (or even more than 1000m) high in the sky creating beautiful sceneries (especially in the night), it also injected a fair amount of ash and sulphur dioxide (SO2) in the atmosphere.
In the Ash RGB (Figures 1 and 3) the ash and SO2 plumes are seen in red/green shades, respectively. In the Airmass RGB (Figure 2), SO2 clouds appear with red hues — ash is not different from water cloud in the Airmass RGB.
Note that, due to hot lava flowing down the mountain, Mount Etna is clearly visible as hot spot in all eight cases (dark magenta pixels in the Ash RGB, black spots in the Airmass RGB).
The first of eight eruptions occurred on 16 February at around 16:00 UTC (17:00 local time), producing a tall ash plume that rose to up to approximately 10km elevation (30,000ft) above sea level, according to Volcano Discovery reports. The plume quickly moved southward driven by very strong upper-level northerly winds (Figure 4).
Only 32 hours later, Etna produced another impressive eurption (see 17 February image in Figures 1 and 2). The volcanic plume rose again to about 10km height. This time strong winds carried the SO2 plume in a south-easterly direction towards Libya.
While creating the animation of the 2nd paroxysm, we observed, in real-time, the 3rd paroxysm, which started on 19 February at 08:30 UTC (day-time eruption), exactly 33 hours after the 2nd eruption. The impressive eruption column, with circular umbrella cloud, could be observed from many places in Sicily. The high-level SO2/ice plume travelled eastward towards Crete, where it arrived in the morning hours of 20 February. Sentinel-3A OLCI captured Etna at 09:12 UTC on 19 February, around 40 minutes into the eruption (Figure 5).
In the following days, Etna continued its regular activity, with a new paroxysm every 36-48 hours. Inhabitants of Sicily and experts around the world started to focus on the volcano and predictions started to be made about when would be the next eruption.
Eruptions four, five, six and seven were again spectacular night-time events, very similar to the previous paroxysms. Only paroxysm number six (image from 23 February, Figures 1 and 2) was a bit different: it occurred only five hours after paroxysm number five, and it released a pure ash plume. As the high-level winds had changed to easterly directions, all the plumes from these eruptions headed towards western Sicily and the Tyrrhenian Sea.
Figure 6 shows two instances of the volcano plume at 00:33 UTC and 01:25 UTC on 23 February, captured by the Day-Night-Band (DNB) of VIIRS on NOAA-20 and Suomi NPP, respectively.
The imagery is enhanced using Zinke’s method, which clearly highlights the Moon-lit plume (three-quarter waxing Moon). Note in particular the fine cellular structure of the plume at 01:25 UTC, a pattern found in Dust-Infused Baroclinic cyclone Storm (DIBS) clouds and a sign for interaction of the volcanic ash with water cloud.
The last lava fountain episode, or paroxysm, of February occurred in the morning of Sunday 28 February, after a longer interval than the previous seven. After roughly three and a half days, the awaited number eight episode of the series of paroxysms occurred Sunday morning around 9am local time.
Figure 7 shows close-up views of the ash/SO2 plume two hours after the start of the eruption. They show a higher-level ice/SO2 cloud (white in the True Color RGB, green in the Ash RGB) and a lower-level ash plume (brown in the True Color RGB, red in the Ash RGB). While the ash plume disintegrated quickly within a few hours, the SO2 plume travelled a long distance across the Mediterranean Sea towards Crete and further to the Middle East.
2-12 March, Sicily
Eruptions continued in March 2021, with very regular intervals. In the first two weeks of March there were a further four eruptions. The total number between 16 February and 11 March was 12, with very regular intervals between each of an average of 2.5 days.
After little more than two days after the eighth paroxysm, the ninth such episode of vigorous lava spewing from the volcano's SE crater occurred on the afternoon of 2 March (Figure 9) . It was remarkable for its long duration.
Less than two days later, the 10th paroxysm took place in the morning of 4 March (Figure 10).
Just another three days later, paroxysm number 11 was underway. According to the National Institute of Geophysics and Volcanology (INGV), the eruption column reached more than 10,000m (30,000ft) elevation (Figure 11).
On 9 March the 12th paroxysm started around 23:30 UTC and lasted more than three hours (Figure 12).
The Japan Meteorological Agency (JMA), reported that the Etna SO2 plume travelled a long way, across Asia to Japan. This can be clearly seen in animations of the Himawari-08 Airmass RGB images, where the SO2 appears in red shades. Figure 13 is the longer loop in three-hourly time steps and Figure 14 is a shorter loop in 1-hour time steps.
On 12 March 2021, the volcanic plume was still visible in Meteosat-11 Ash RGB imagery (Figure 15, top left) and also detected in CIMSS-derived products (ash height, ash efffective radius and ash loading).
12-21 Dec, Greece, Sicily, Turkey
In December 2020 there were several paroxysms from the volcano from 12 December onwards. The strongest paroxysm seen on satellite imagery was on 21 December, which started around 09:00 UTC. As is typical for a short Etna paroxysm, the event lasted less than two hours. The 15-minute Meteosat-11 24-hour Microphysics RGB animation, from 09:00-16:00 UTC (Figure 16), shows the initial movement of the volcanic (SO2) cloud.
The longer animation in Figure 17 shows the extended movement of the SO2 cloud, from initial paroxym to travelling from Greece towards Turkey in the early hours of 22 December.
Sporadic eruptions continued into January 2021, although with smaller paroxyms, so much weaker signals made it difficult for satellite products to pick up. On 18 January 2021, the weak volcanic plume was only faintly visible in Meteosat-11 Ash RGB imagery (Figure 18, top left) and not detected at all in CIMSS-derived products as signal was to weak for the algorithm (Figure 18).
A series of earthquakes, occurred from the afternoon of 31 December 2020 until the morning of 2 January, mainly under the southern flank of the volcano. Forty quakes of magnitudes of up to 3.8 were recorded. Later in the month, on 24 January, following more sporadic eruptions, at least 50 small quakes were recorded.
24-25 Dec, Mediterranean Sea, Sicily
By HansPeter Roesli
The Meteosat-11 Volcanic Ash RGB image (Figure 19) and animation (Figure 20) shows the first phase of the eruption, from 24–25 December.
In the following days Etna only released a quite strong SO2 plume (green), no red-to-yellow ash signal was detected in the plume any more. In the new year the activity appeared to have weakened considerably or stopped altogether.
In the animation the colours of red-gold-green show that ash and SO2 travelled eastwards across the central Mediterranean.
15 March, Sicily
By Djordje Gencic, Jochen Kerkmann, Jose Prieto and HansPeter Roesli
Etna woke up again in the evening of 15 March 2017, spewing ash and SO2, and forming a nice looking plume.
After a few hours the plume consisted of mixture of ash (seen as red) and SO2 (seen as green). This process of mixing continued in next few days as it can be seen in the Meteosat-10 Ash RGB, Figure 21 and animation.
On next day, the hot melted rocks from inside of Earth (lava) could be seen flowing onto the slopes of Mount Etna. This four panel image (Figure 22) which consists of VIIRS and SEVIRI data shows lava very well. Three of them are VIIRS images, and only the lower left is SEVIRI.
The spatial resolution difference (375m for VIIRS and 3km for SEVIRI) is very obvious. Lava can be seen in two right-hand side images (IR 3.74µm for top and 11.45µm for the lower one) as a yellow/orange area, which in this colour table represent very high temperatures.
Top left image is the S-NPP Natural Color RGB. On it, the side slopes of Mount Etna which were still covered with snow appear as cyan, while the lava is red/brown.
The lower left image shows more or less the same as the top right, just from the Meteosat-10 SEVIRI instrument.
The Meteosat-10 Near-Infrared Channel 3 (1.6µm) animation shows the evolution during the night, in synchrony with fresh lava eruptions. In the 1.6µm imagery the lowest meaningful counts were enhanced, less than 3% equivalent reflectivity, if compared with the Sun. But the source is emitted energy, and not reflection, still well detectable at this solar wavelength.
The Meteosat-10 Infrared Channel 4 (3.9µm) animation shows a similar evolution during the night, with values frequently saturating the Meteosat sensor at 336K, and highly correlated to the values at channel 3.
As discussed in this Portuguese fire case from 2006, in SEVIRI imagery the saturation of the IR3.9 channel causes some kind of ring structures (ripples) around the hot lava spot, as is very clearly seen in the Night Microphysics RGB (Figure 23). The users of MSG data should be aware that these ring structures are artefacts coming from the digital filter that is applied to the data. For lower wavelengths (0.8µm or 0.6µm), Meteosat is not sensitive to lava.
17-18 May, Egypt, Sicily, Mediterranean Sea
By Jochen Kerkmann, Ian Mills, Fred Prata (NILU) and HansPeter Roesli
A paroxysm from Mount Etna sent huge plumes of ash and smoke hundreds of metres into the skies above Sicily on 17/18 May (Figure 24).
Activity began at the 3350m high volcano on 17 May, with emissions from its north-east crater.
While ash and lava settled locally, plumes of SO2 were driven by high-level winds east-southeastward.
A sequence of Ash and SO2 RGB composites from Meteosat-10, 17 May 03:00 UTC–18 May 18:30 UTC shows the SO2 emissions in green. The emissions varied in intensity over time, culminating with a final larger one on 18 May at around 11:00 UTC (Figure 26). Suomi-NPP's VIIRS imaging radiometer happened to fly over Etna just over an hour after this last paroxysm. The Ash and SO2 RGB at 750m spatial resolution (Figure 25) shows the high-level exhaust plume in various colours: green for SO2, red for ash, and yellow for a mixture of SO2 and ash.
The Suomi-NPP VIIRS Natural Colour RGB at 375m spatial resolution (Figure 27) shows two red pixels just west of the erupting crater, most probably coming from the hot fiery lava flowing down the western flanks of Etna.
The initial evolution of this plume can be followed on five-minute imagery from Meteosat-9. The sequence of Meteosat-9 Ash and SO2 RGBs, 18 May 10:25 UTC–15:00 UTC demonstrates that the ash was falling out early and only SO2 was left in the plume.
On the SEVIRI SO2 retrievals from Meteosat-10 (Figure 28, animated gif, Credit: Fred Prata) the plume can be followed as it moved east-southeast, driven by winds at a height of around 7km (as confirmed by HYSPLIT trajectories.
These winds pushed the plume further south east and it crossed the south-eastern corner of the Mediterranean late on 19 May, as can be seen on the Meteosat-10 animation, 18 May 10:00 UTC–19 May 21:00 UTC.
This is confirmed by the AIRS granule of 19 May at 11:29 UTC (Credit: Fred Prata), where the SO2 plume was detected just north of Egypt.
3-10 Dec, Canada, Crete, Iraq, Japan, Sicily, USA
By Jochen Kerkmann and Martin Setvak
On 3 December 2015, for the first time in two years Mount Etna, erupted. Following an earlier 'pre-eruption' emission, at around 02:00 UTC Mount Etna, an active stratovolcano on the east coast of Sicily, Italy, erupted. It was a short, but spectacular paroxysm, which could be clearly seen in satellite imagery.
In particular, the eruption and the resulting plume can be tracked using Meteosat's Airmass and Dust RGB imagery.
The Dust RGB loop starts at 02:00 UTC. In this RGB combination the SO2 plume, that the volcano has pumped all the way to the tropopause, appears in green shades. The origin of this colour can be easily depicted by the 'RGB Colour Interpretation Tool ', developed by the EUMeTrain project (Figure 29). The 'X' sign on this figure shows the sampling position of this tool.
The main contribution here comes naturally from the green beam which reveals relatively big differences between signals from SEVIRI channels IR10.8 and IR8.7, while the the other two contributions are rather small.
The Airmass RGB loop also starts at the 02:00 UTC and in the beginning of the eruption gives the strong white signal over the wider volcano area.
Normally with this RGB combination, high-reaching thick clouds appear in white shades, but only very high clouds give such a bright signal. In later moments, when the clouds gets thinner and made of only SO2, the colour changes to specific 'peach'
The initial phase of the main eruption was not captured by polar orbiting satellite instruments due to a mismatch between the timing of the satellite passes and the onset of the eruption.
However, there was a Suomi-NPP overpass at 1:21 UTC that captured the precursor-initial (low level) plume, see the yellow-green plume on the VIIRS Ash RGB image (Figure 31).
This low level, initial plume can also be seen on the Meteoesat-9 rapid scan loops of the 24-hour Microphysics RGB, 3 December 00:00–12:50 UTC and the zoomed-in 24-hour Microphysics loop, 3 December 00:00–13:20 UTC.
The SEVIRI data suggests that in the early phase of the eruption the ice cloud masked the SO2 signature, either because the radiative effects of the ice particles prohibited to see the SO2 or because much of the SO2 gas was absorbed onto the ice particles, only to sublimate at a later stage as the ice evaporated.
The change of the character of the volcanic cloud, from ice cloud (masking the SO2) in the initial phase to a more pure SO2 cloud at a later stage (from 04:00 UTC onwards), can be seen by the change in the colour of the cloud.
In the Dust RGB imagery (Figure 29 animation), initially the volcanic cloud appears with a red colour (indicating a thick ice cloud) with dark blue borders (indicating a thin ice cloud). Later, at about 06:00 UTC on 3 December, the volcanic cloud appears like a mixed cloud: thin ice (black) and SO2 (green) mixed. After about 09:00 UTC the entire cloud becomes green (SO2), and the cloud is split into a northern branch (high level, around 10km height) and a southern branch, travelling at a lower level (about 6.5km).
Later analysis revealed there were least two clouds at different levels, drifting into two slightly different directions. By 4 December the leading edge of the higher plume was over Iraq.
According to the forward trajectories from the Met Office this cloud was travelling at a height of around 10km. The other (main) part of the plume had reached Crete and was estimated to be travelling at a height of 6.5km.
On 4 December, Terra MODIS perfectly captured a second major paroxysm of Etna (see Figure 33). Some local airports are plotted on the image. A guess from the plume shadow of this MODIS image gives 12km as height of the volcanic cloud.
Later on the same day, between 20:00 and 24:00 UTC, Meteosat-10 observed yet another eruption of Mt Etna that sent a volcanic cloud to the upper troposphere (see animated GIF, source: Dan Lindsey, CIRA).
Over the next few days ever weakening volcanic ash signals could be detected over the Pacific towards Japan, over Canada and parts of North America, including Wisconsin. Further detailed analysis can be found in the presentation 'Comparison of observations of SO2 from the eruption of Mount Etna on 3 December 2015 with a model simulation ' by Dov Bensimon and Philippe Barnéoud, from the Montréal VAAC.
Figure 35 is the summary plot of AIRS SO2 detections for 3–10 December 2015. About 280 AIRS granules have been processed and the data has been smoothed a little. Note that the narrow AIRS swath and the Aqua polar orbit conspire to give an incomplete picture of the ‘true’ spread of the SO2 plume, but you do get a good idea.
15 Apr, Sicily
By HansPeter Roesli
The first spring full moon of this year, on 15 April, produced this scene of Etna in the VIIRS day-night band (DNB). The DNB scene has been slightly enhanced (@750m spatial resolution) with the IR11.45 band (I5, @375m spatial resolution) in bluish hues (cooler - white, warmer - bright blue). The cone of Etna stands out from the city lights of the surrounding urbanised area, in particular Catania in the SE — but there is a white blotch slightly off-centre of the dark cone — possibly a cap cloud or a volcanic plume? The Natural Colour RGB (@375m) from the VIIRS daytime overflight almost 12 hours later proves this to be wrong - the blotch is there again, but cyan-coloured, indicating snow that still covers the northern flanks of Etna.
26 Oct, Sicily
By Zanita Avotniece and Jochen Kerkmann
Preceded by a series of underground tremors, the most recent paroxysm of Etna took place on Saturday, 26 October 2013.
The plumes of Etna’s eruption moved south-westwards, producing a sulphur dioxide (SO2) cloud with periodic mixture of volcanic ash.
According to the BBC, the plume of ash rising from Mount Etna could be seen across much of eastern Sicily.
The nearest airport and airspace were forced to close temporarily, but the eruption did not require any mountain villages to be evacuated. Etna’s eruptions are frequent, but the last major one occurred in 1992.
The evolution of the paroxysm is shown in the sequences of Ash and Airmass RGB images (Figures 37 and 38). In Ash RGB images green colours represent the extent of the SO2 cloud, the pink colours show the ash plume, but the hotspot from the lava is a dark violet colour. However, in the Airmass RGB the SO2 cloud appears in more red colours, with the volcanic ash in light yellow.
The volcanic cloud could also be seen in the IR10.8 image, 24-h Microphysics RGB, the Natural Colours RGB and Convection RGB.
The plume of volcanic ash/SO2 was optically thick, and reached a great height. According to the retrieved cloud physical properties (Credit: KNMI, see Figure 39), the maximum height of the ash cloud at 07:00 UTC was 8690m, with a temperature of 241.1K or -32.05°C. However, the 12:00 UTC sounding from Trapani weather station in Sicily suggested that the height of the plume could be around 8km.
5 Jan, Sicily
The column of ash rose up to 5,000m above sea level and lava was seen flowing from a new crater on the southeast side of the summit. (Credit: NILU).
12-13 Aug, Libya, Sicily
On 12 August 2011, Etna had its tenth paroxysm of the year, captured in the Meteosat-9 Ash RGB product.
Etna spewed first an SO2 cloud (green colour) followed by an ash cloud (red colour).
The plumes moved south-eastwards and only rising a few hundred metres above the craters. In rapid succession Etna spewed some SO2; a thick white plume; a plume of black ash and SO2 and, finally, ash only. These details may be gleaned from a sequence of Meteosat-9 SEVIRI images (Figure 42) that shows: a) the HRV channel (top images), b) the Ash RGB product (central images) and c) the Dust RGB product blended with HRV and IR3.9 (the hottest pixels).
|Time (UTC)||HRV Channel||Ash RGB Product|
|08:30||light-green smudge (SO2 cloud)|
|09:00||white smudge (water cloud)||light-green plume (more SO2)|
|10:00||short dark plume (ash)||pale-yellow smudge (SO2 and ash)|
|10:45||longer dark plume (more ash)||reddish-yellowish-green plume (ash, SO2 and ash, SO2)|
The temporary westward extension of the hot spot at top of Etna is an artefact of the IR3.9 detectors that go in saturation when the sensed temperature goes above ~336K. By the day after the brief eruption the SO2 cloud has travelled as far as the eastern coast of Libya (Figure 42).
MODIS on Terra overflew the paroxysm just after 09:40 UTC. A comparison with the SEVIRI images (Figure 45) shows more details of the complexity of the plume in this instance. The bottom row shows SEVIRI images with the Ash RGB product, the VIS0.6 channel and a combination of them. The top row is from MODIS and shows the same using proxy channels.
More details including various photos on this paroxysm are given in a report by the Istituto Nazionale di Geosfisica e Vulcanologia (INGV) in Catania, only in Italian though.
10-14 May, Iran, Greece, Sicily, Turkmenistan
On 10 May 2008, an eruption of the Etna volcano on the Italian island of Sicily was measured by the Global Ozone Monitoring Experiment (GOME-2) on EUMETSAT's Metop-A polar-orbiting satellite. The data were evaluated by scientists at the Deutsche Zentrum für Luft- und Raumfahrt (DLR), the German Aerospace Center, in Oberpfaffenhofen, a member of EUMETSAT's Ozone Monitoring and Atmospheric Chemistry Satellite Application Facility.
Etna began erupting on 10 May, belching sulphur dioxide up to 12km into the atmosphere. GOME-2 measured the sulphur dioxide cloud as it moved over Greece on 11 May, Iran on 13 May and Turkmenistan on 14 May (see three-day composite SO2 product, 11–14 May, source: DLR, Applied Remote Sensing Cluster).
The movement of the SO2 cloud over the Mediterranean Sea towards the Middle East and up to Iran can also be followed in Meteosat-9 Ash RGB products (see greenish cloud patch in the Ash RGB animation, 10 May 13:00 UTC–12 May 06:00 UTC).
A second eruption of Etna took place on 13 May from an 800m crack which opened north-east of Etna's south-eastern crater, emitting large amounts of sulphur dioxide which were measured by GOME-2 and MSG SEVIRI over southern Italy (see images below).
While GOME-2 detected the SO2 cloud in the morning of 14 May, Meteosat-9 'saw' the eruption immediately, i.e within 15 minutes, at around 09:30 UTC on 13 May. The eruptions were some of the heaviest since 2002 and volcanic ash forced the closure of the nearby Catania airport.
29 March, Greece, Sicily
On 29 March 2007, Mount Etna was active once again. According to Volcanodiscovery, following a rapid increase in tremors starting at 07:24 (local time) in the morning, the south-east crater began to emit lava fountains and ash/SO2 plumes until around 9am.
Meteosat-8 captured the ash/SO2 cloud and its movement/expansion towards the north-east. In the beginning, the ash signal dominated the RGB composite (see Ash RGB at 05:45 UTC), but later, as the volcanic cloud moved towards Greece, the SO2 signal became more and more visible (the sulfur dioxide cloud is shown in green colour, see Ash RGB at 11:45 UTC). Luckily, at 11:47 UTC the AIRS instrument on the Aqua platform also captured the SO2 plume over western Greece (see AIRS retrieval, source: F. Prata). A comparison with MSG shows a very good agreement of the position and the size of the SO2 cloud (see comparison).
13 Oct, Catania, Sicily, Valle del Bove
On 13 October 2006 a new lava flow started, flowing from the south east crater into the Valle del Bove. There was no associated eruption at the summit. The lava flow, i.e. the heat emitted from it, is clearly visible in the Meteosat-8 image (Figure 51) by the dark magenta spot (see link to Interpretation below the image). In the animation it actually looks to be blinking, which is mainly due to artifacts coming from the saturation of the IR3.9 sensor and the digital filter that is applied to the data. Another example of these artifiacts is given in the case study Fires raging in Galicia (7 August 2006).
A new eruption of the Mount Etna volcano took place on 24 November. In the early morning the south east crater started spouting lava and ash emissions, accompanied by new lava flows from a fracture on the upper southern slope the crater, as well as from the 3050m vent on the flank of Bocca Nuova.
According to Volcano Discovery, the ash plume reached a height of 5km and travelled to the south-east. Volcanic ash fell on Catania, forcing authorities to close the Catania airport overnight. The last time volcanic ash forced the closure of the airport was in 2002 (see Satellite images of the volcanic eruptions in October 2002).
Both, Metop-A and Meteosat-8 captured the thin ash cloud and its movement/expansion towards the south-east. They also captured the new lava flows, ie the heat emitted from them (see e.g. Metop-A AVHRR RGB composite IR3.7, VIS0.8, VIS0.6 from 09:30 UTC).
2 Sep, Sicily
On 2 September, Meteosat-8 spotted a thin smoke plume coming from the top of Mount Etna. The plume was visible during the early morning hours when conditions are ideal for the observation of smoke and haze (strong forward scattering of solar radiation towards the satellite). The event was neither reported on the news nor mentioned on the standard volcano web pages, showing that the eruption must have been rather unspectacular and not worth mentioning in the news.
27 Oct-5 Nov, Catania, Sicily
Early in the morning of 27 October 2002, a new flank eruption began at Mount Etna (3315 m) after only a few hours of seismic activity.
This eruption was more violent and more devastating than the previous flank eruption in July–August 2001 and once more occurred from fissures on two sides of the volcano: at about 2,750m on the southern flank, and at elevations between 1,850 and 2,500m on the northeastern flank, in an area known as the Northeast Rift.
After its extremely vigorous start, the eruption generally declined until 5 November, and then continued in a more or less stable manner on the upper southern flank. The tourist complex and skiing areas of Piano Provenzana were all but devastated by the lava flows that issued from the NE Rift vents on the first day of the eruption. Heavy tephra falls caused by the activity on the southern flank occurred mostly in areas to the south of the volcano and nearly paralysed public life in Catania and nearby towns.
For more than two weeks the International Airport of Catania, Fontanarossa, had to be closed due to ash on the runways. Strong seismic activity and ground deformation accompanied the eruption; a particularly strong shock (magnitude 4.4 on the Richter scale) on 29 October destroyed and damaged numerous buildings on the lower southeastern flank, in the area of Santa Venerina.
In the Meteosat-6 visible image the ash plume is clearly visible as a bright band caused by the high reflectivity of ash particles when compared with the dark water surface. The wind direction on this day was from the north-west. The ash plume is also visible in the infrared images, as shown in the image below.
The animation in Figure 57 shows the start of the eruption when the prevailing winds at the height of 3000m were from the north. According to the satellite animation, the eruption started around 02:00 UTC.
17-24 July, Catania, Crete, Sicily
On 17 July, the latest in a series of violent eruptions from the south-east crater of Mount Etna (3315 m) led to a very spectacular eruption. This was the first since a large similar event in 1991–1993.
In the following days, ash frequently rained down on Catania, forcing repeated closures of the international airport. On 22 and 23 July, this flank eruption continued with great force, with a towering ash column rising from the explosive vent at about 2,600m elevation. The ash cloud drifted south-eastward, directly over Catania, dropping fine dark grey ash onto everything.
In the Meteosat-7 visible image (Figure 58) the ash plume is clearly visible as a bright band caused by the high reflectivity of ash particles when compared with the dark water surface.
While the wind direction was generally from the north-west (typical for the time of year), it varied in direction slightly during the day leading to an undulating structure of the plume. Furthermore, during the afternoon, the plume broadened slightly in the horizontal due to the onset of convection, which is also visible from the development of small cumulus clouds over Mount Etna. The ash cloud, which totally obscured the Sun over Catania, remained compact over a long distance until it dissipated and became invisible over the island of Crete (about 800km distance to the south-east).
The eruption of the Etna volcano and related atmospheric pollution was also closely monitored using data from the GOME (Global Ozone Monitoring Experiment) instrument on the ERS-2 platform. GOME is a nadir-viewing across-track scanning spectrometer that measures radiance back-scattered from the atmosphere and the surface of the earth in the ultraviolet and visible range allowing the retrieval of concentration of trace gases such as ozone (O3), sulphur dioxide (SO2) etc.
Figure 59 shows a three-day composite of the SO2 concentration derived from GOME data. The satellite data shows a region south-east of Sicily where the atmosphere is polluted with a concentration of SO2 up to ten times higher than normal.
The retrieval method for trace gases from GOME-2 data is currently being developed at DLR in the framework of the EUMETSAT Satellite Application Facility (SAF) on Ozone Monitoring.