19-20 Sep, Canary Islands
By Alen Berta, Jochen Kerkmann, Sancha Lancaster, Miguel-Angel Martinez Rubio (AMET), HansPeter Roesli and Ivan Smiljanic
The Cumbre Vieja volcano on the Canary Island of La Palma erupted on 19 September 2021, resulting in thousands being evacuated.
The Meteosat-11 Ash RGB imagery from 19 and 20 September (Figure 1) shows higher concentration of SO2 emitting from the volcano in the hours after the eruption.
The GOES-16 24-hour Microphysics animation (Figure 2) shows the volcano mouth as a blue hotspot (higher temperatures), as well as the SO2 plume around it in cyan/green shades.
Comparing the GOES-16 VISO.6 Band (Figure 3, left) and 24h Microphysics RGB (Figure 3, right) imagery, highlights that GOES-16 'sees' ash more clearly in the visible channel (due to strong forward scattering in morning hours). Because of the low altitude of ejected ash (an indication of a not very violent eruption) the 24-hour Microphysics RGB product does not detect it. This is because the component of this RGB, responsible for ash detection, relies on the temperature difference between background (sea/land) and the observed ash cloud — which in case of low ash cloud is minimal. Also there are few stratocumulus clouds aloft, obscuring the view at times — ash cloud is visible as more static cloud in the animated GOES-16 visible imagery (Figure 4)
It is worth mentioning that the SO2 signal is also absent in Airmass RGBs (not shown here), because the SO2 cloud is not high enough. Due to water vapour absorption, only mid to high SO2 clouds can be detected in the Airmass RGB. An SO2 signal in an Airmass RGB can be seen in many other eruptions, for example, in this Etna eruption case from 2015, with its plumes higher than 3km, but for the Cumbre Vieja volcano eruption where the plume is at ca. 500–1,500m.
With time the lava flow around the crater became larger, detectable even with the near-infrared channel of the GOES ABI instrument — namely the NIR1.6 band which provides red contribution to the Natural Color RGB in Figure 5.
The hotspot could also be detected in the Optimized Fire Radiative power for Copernicus Sentinel-3 (OFRP-CS3) product in Near Real Time (Figure 6). This is based on Processing Baseline 1.2 released in May 2021. The key parameter here is the Standard MWIR detection with a high enough confidence score (40% clear-sky), so no false alarms are caused by ash plumes or clouds.
1 October — Gravity waves
This volcano exhibited quite unique gravity-wave oscillations, seen by several satellites. See the example from 1 October in Figure 7.
4 October — Strong (low level) ash ejection
The strongest ash ejection from the beginning of this volcanic activity, mostly likely happened on 4 October. As well as ground level time lapse videos, several satellites captured this event, including the Terra polar orbiting satellite in Figure 8.
Interestingly, when comparing the Ash and Airmass RGB animations (Figures 10 and 11), the plume of SO2 is visible in the Ash RGB (green), but not in Airmass RGB (typically red). This is due to an inversion at around 500hPa which constrained the plume height, so the component of Airmass RGB, normally sensitive to SO2 presence — the WV7.3 channel — did not see it due to its weighting function peaking higher up in troposphere (i.e. due to a water vapour absorption above the SO2, as well as the ash cloud). The Ash RGB could see it since it utilises the IR8.7 channel to detect SO2 (this channels has comparably much less H2O absorption, explained further in this EUMeTrain module). Ash is normally red in Ash RGB, pale green in Airmass RGB.
Lava flow towards the ocean changed the local landscape. A new peninsula was formed out of cooled magma, which, by the evening of 2 October (five days after the lava reached the sea), measured approximately 25 hectares (Figure 12).
Another Sentinel-1 RGB image (not shown here), created by combining the VH polarisation, confirmed that by 14 October the peninsula had grown another 2.5 hectares.
3 July and 28 August, Italy
By HansPeter Roesli and Ivan Smiljanic
The Italian volcano Stromboli erupted twice in the summer of 2019 - first in early July and then again in late August.
Mount Stromboli, on a small island in the Tyrrhenian Sea, has been in almost continuous eruption for the past 2,000 years. Its activity is almost exclusively explosive, but lava flows do occur at times, most recently in 2014.
Initially both ash and SO2 were detected (Figure 13). After few hours most of the volcanic ash settled down and only the SO2 plume continued to spread into the following day.
Looking at the animated SEVIRI Ash RGB product, 3 July, 14:00–23:45 UTC, (Figure 14), it is clear that the main eruption occurred some time between 14:30 and 14:45 UTC. There was one stronger episode of ash and SO2 ejection in the atmosphere, sensed by SEVIRI infrared channels, where the content spread in arch-like pattern that expanded and spread mainly in a south-easterly direction.
Some more details may be detected in animation in Figure 15, that compares the HRV band with the Volcanic Ash RGB from the rapid-scanning Meteosat-9. The first signs of an eruption plume appeared at 14:45 UTC in both panels, i.e. the eruption must have started between 14:40 UTC and 14:45 UTC. As clearly shown by the HRV images, the plume expanded in two opposite directions from the start. A bright plume expanding west and a darker plume going east. The west plume was loaded with SO2 (green-tinted pixels in the Volcanic Ash RGB). The east plume was more of an ash cloud with some SO2 included (brown-red-yellow tints).
Viewed from the rapidly scanning Meteosat-10 (5-minute repetition rate) it was only a short eruption, as was the previous eruption in July (see Eruption of Stromboli volcano).
The animation of the HRV channel between 10:00 UTC and 13:30 UTC on 28 August (Figure 16) shows two distinct plumes emerging simultaneously from the volcano top. A longer one heads north-eastwards over the Tyrrhenian Sea, while just a short puff goes east-south-east towards Sicily.
Checking with the nearest 12:00 UTC radiosounding at Trapani, it appears that the first plume must have reached levels above the green line, i.e. well above 600hPa. Meanwhile, the short puff must have travelled with winds in the maritime boundary layer, for which the Trapani sounding was not representative.
A comparison of the HRV channel (middle panel) with the Airmass RGB (left-hand panel) and the Volcanic Ash RGB (right-hand panel) at 11:40 UTC (Figure 17), reveals that on the Ash RGB the typical colours of green for SO2 and yellow for SO2/ash mix appeared. However, the colour intensity was very bland due to the bad spatial resolution of the rather small-scale plume.
Surprisingly, the Airmass RGB also gave an extremely weak signal of a neutral colour. If it identified SO2 (usually red tints), the plume must have risen above the green line (600hPa) on the Trapani sounding, where the airmass was relatively dry.
Meteosat-8 positioned at 41.5 °E saw the scene from an angle that enhances the scatter of sunlight. The sequence of the image pairs. HRV and Volcanic Ash RGB (Figure 18), reveals that there was already a weak release of material after 07:30 UTC.
On the HRV and Ash RGB image at 08:15 UTC (Figure 19) the green arrow goes along the volcanic plume, whereas the red arrow points to a temporary orographic cloud. Note that the Ash RGB did not show any sign of ash or SO2 at this time.
The higher spatial resolution of the Volcanic Ash RGB from the VIIRS instrument on NOAA-20 (Figure 20) that flew over the scene around 12:14 UTC, had more intense colours that make a differentiation between ash (red tints, in particular close to the Stromboli island), SO2 (green shades) and SO2/ash mix (yellow to orange shades) much clearer.
On the Natural Colour RGB at 375m spatial resolution from NOAA-20 (Figure 21), lava flow on the flanks of the volcano show as red areas.
28 Aug-20 Sep, Iceland
By Ruediger Lang and HansPeter Roesli
As part of the ongoing activity around Bárðarbunga volcano (Bardarbunga in English) a fissure eruption took place north of Dungfujökull, northeast of the volcano. According to the Icelandic Met Office the eruption started in Holuhraun, at around 24:00 UTC. It was a small fissure eruption and at 02:40 UTC the activity appears to have decreased.
Meteosat-10 3.9 micron imagery captured the hotspot at the area; dark shades indicated 3.9 micron signal of 300K or above.
During the morning of 31 August a new hot fissure developed in the Bardarbunga volcanic complex. On the colour infrared animation from Metetosat-10, 09:30–13:00 UTC, hot spots can be seen. The sensed temperature went beyond the saturation temperature of the detectors, i.e. ~335K.
The saturation is manifested by the 'ringing' of some pixels east of the hot pixel, best seen at 12:15 UTC on the black and white enhanced imagery, Meteosat-10, 09:30–13:00 UTC.
2 September activity
The Day-Night Band (DNB) and the Night Microphysics RGB give an overview of the fissure. The DNB signal from the fissure is very strong and made it difficult to get the weak reflection of lunar and aurora light from the clouds at the same time.
The Night Microphysics RGB shows two major cloud systems north and south of the fissure area and some low cloud in between. Note in particular the grey area just south of the Askja volcanic area. This is the thermal signal (band M13-IR4.05, aka SEVIRI IR3.9) from the fissure.
Band I4 (IR3.74) is hot-temperature sensitive. Like the SEVIRI channel it gets easily saturated with very hot features, at higher temperature values, ~360K instead of 335K. Perhaps the grey pixels are due to CO2 absorption or sensor saturation. The coloured area spans 11.6km SW-NE.
When the heated area is larger than the pixel size the IR window channels pick up the signal, as demonstrated in the band I5 (IR11.45) image.
3 September activity
On 3 September Meteosat-10 could see that a fissure eruption continued northeast of the Bardarbunga volcano. According to Icelandic Met Office the seismic activity had decreased in the area.
The Meteosat-10 1.6 micron imagery , 02:00–05:00 UTC, captured hot lava surfaces emitting radiation above the SEVIRI channel threshold for solar light. This can be seen as the grey and black blocks above the site of the volcano.
The Natural Colour RGB image from Meteosat, 10:55 UTC, showed lava, as well as a smoke cloud drifting to the northeast from the eruption site. The Metop satellite also detected sulphur dioxide in the area, which was confirmed by measurements on the ground.
Sulphur dioxide emissions
Sulphur dioxide (SO2) is emitted by volcanoes often, but not always, together with the ash. At the Bardarbunga volcano the magna had not yet hit the ice, and there was no explosive eruption triggering large ash clouds. Currently the volcano is, therefore, predominantly emitting SO2 from side riffs, which can be observed very well by instruments on Metop.
The animated GIF (right) shows elevated SO2 values measured by the GOME-2 instruments onboard the Metop-A and Metop-B satellites, from 1–11 September. The data has been processed by the AC SAF and is available via their website.
Since SO2 is a gas it can often reach higher altitudes than ash and, therefore, stay in the atmosphere for quite long time periods and be transported over long distances. In large quantities it can be hazardous and also affect air traffic, as happened during the Eyjafjallajökull eruption in 2010. Therefore, as well as being monitored as an indication of an eruption, SO2 is monitored by the Volcanic Ash Advisory Centres (VAAC) to help prevent air traffic incidents. The VAACs use GOME-2 SO2 data, along with IASI data from Metop, operationally to monitor and advise the relevant authorities and agencies.
SO2 can be measured very accurately, in terms of quantities from GOME-2, and the dual GOME-2 operations give very good coverage. However, GOME-2 can only measure once per day during Metop-A and -B daytime overpasses, but IASI can provide an additional view during the night. Operational SO2 products from GOME-2 are produced by the AC SAF and available from the SAF and the EUMETSAT Data Centre.
The Meteosat-10 24-hour microphysics imagery shows the SO2 plumes from the Holuhraun fissure on 3–5 September. On 3 September the plume (light green) headed towards the Barents Sea before dissipating. On 4 September a second plume formed, travelling in the opposite direction, over the North Atlantic.
The SO2 releases from the Holuhraun lava field weakened over the weekend on 6/7 September. There was also a large cloud shield covering the area for most of the time. The Meteosat-10 24-hour microphysics imagery shows the plume as it headed south on 4 September. It reached Ireland on 6 September when Meteosat-10 lost track of it because of dilution and cloudiness.
Ash was released for a relatively short amount of time (a few hours). The plume travelled northwards beyond the SEVIRI field of view. The plume did not reach high altitude levels. Since the plume was above the deck of low cloud (yellow-golden colour) but was hidden by higher (brickstone colour) clouds, this tells us that it probably did not go above 5000m, (an estimate would be around 3000m).
The Holuhraun lava field released a new SO2 plume in the evening of 19 September. Driven by northerly winds and after having been driven off from the mid- and high-level clouds (brickstone to black colour on the 24-hour Cloud Microphysics RGB) that covered the fissure in the lava, the SO2 patch became visible on the Meteosat-10 imagery (light-green colour).
In the following two days, passing between the Shetlands and northern Scotland, it entered the North Sea, where it joined the back of a cold front. While the cold front moved east-southeastward over Western and Central Europe on 21 September, traces of the SO2 patch got lost over northern Germany in the evening of the same day.
Aurora borealis over Bardarbunga
On the Suomi-NPP image from 19 September 03:52 UTC the hot lava from the Bardarbunga volcano shows as bright white areas (red arrows) and the veil of aurora borealis can be seen undulating below the areas of lava (cyan arrows). The blue arrows show where various types of cloud were visible.
In the image comparison below it can be clearly sees that on the enhanced M15 image the temperature signal from the clouds is not correlated with DNB image. Therefore, the wavy structure cannot be a cloud feature, but aurora activity.
Both hot lava from the Bardarbunga volcano and the aurora borealis were seen by NOAA's Suomi-NPP satellite on 19 September.
In April 2007, the Piton de la Fournaise volcano in eastern Reunion, a French overseas department, was erupting for more than a week.
The eruption resulted in the collapse of the volcano's summit, with magma at times being spewed as high as 200m into the air. Besides ash and lava, the volcano also released sulfur dioxide (SO2).
The GOME-2 instrument on Metop-A tracked the emission of SO2 from this volcano from 3 to 10 April, 2007. The image from 7 April shows the larger SO2 plume, transported by the wind to the north-east of the volcano (the greatest SO2 concentrations appear in red). Volcanic SO2 derived from GOME-2 is monitored regularly, in the framework of the Ozone SAF project, at the DLR Institute for Remote Sensing Technology (IMF) and the German Remote Sensing Data Center (DFD).