In November 2014 Pico do Fogo, a stratovolcano on the Cape Verde Islands, erupted for the first time in 20 years.
05 November 2020
23 November 2014
by Fred Prata (NILU), Hans Peter Roesli (Switzerland) and Jochen Kerkmann (EUMETSAT)
After the eruption of 23 November the SO2 column was seen on satellite imagery for a number of days.
By coincidence the main volcanic activity stopped on the last day on November, as can be seen in the animation.
The eruption was unusual as the majority of SO2 emission remained in the atmospheric boundary layer. Usually with such a large and prolonged eruption the SO2 emission would be expected to extend to higher latitudes.
Download Volcanic Ash/SO2 RGB animation Meteosat-10, 23 November 10:00 UTC–30 November 23:45 UTC
When Pico do Fogo erupted on 23 November the first indication from a satellite came from SEVIRI on Meteosat-10 at 11:30 UTC. SO2 was detected from SEVIRI, and also AIRS on NASA's Aqua satellite, with an initial estimate of around 14 kilotonne (kt).
Although it appeared on the Dust RGB as though no ash was emitted, the yellow colour in the Volcanic Ash/SO2 RGB imagery is indicative of an ash/SO2 mixture.
The corresponding RGBs from S-NPP VIIRS 750m resolution) clearly show a yellow signal.
The VIIRS Natural Colour RGB (Figure 5) shows the hot spot as one reddish (IR1.6) and 3–4 whitish spots. There is also a faint greyish plume indicating there was some ash, but it was rapidly thinning/falling out in a relatively turbulent flow during the first day.
Airmass RGB animation, Meteosat-10, 23 November 10:00 UTC–25 November 08:00 UTC, showed a weak signal, hinting that the plume had not reached into the drier upper troposphere.
The wind cross-section for 24 Nov 18:00 UTC, GFS (Global Forecast System) analysis, shows southerly winds between 2.5 km and 5.5 km, with different wind direction above and below this layer, in line with the direction of the plume at that time, i.e. the plume did not rise above the middle troposphere.
The lack of height is also indicated by the Volcanic Ash/SO2 imagery from Met-10, 25 November 2014, 08:45 UTC (see above), which shows that part of the volcanic plume was hidden by the low/mid level clouds, so the height was probably relatively low, between 2 km and 3 km.
The presence of particulate matter (e.g. carbon (soot), tar, oils or ash) on 24 Nov afternoon could be seen on the imagery from the S-NPP VIIRS visible channels (Figures 6 and 7). On the Natural Colour RGB (Figure 7) there is a very faint veil that correlates well with the SO2 signal.
What is not clear is whether the particles are a small amount of ash which travelled with the SO2 or particulate matter from chemical reactions of the SO2 with the atmosphere (the clouds).
In Figure 8, over the volcano and to the north of it, there were two distinct yellowish patches in the SO2 plume. This can be interpreted as a signal produced by the SO2 and lower-level (reddish) cloud, as the SO2 passes over the clouds. The rest of the plume remained below the clouds, shown by the green areas.
When colleagues at KNMI studied data from the UV/VIS instruments GOME2/OMI/OMPS (Figures 9, 10 & 11) they noticed large quantities of SO2 and a much bigger and better signal than the infrared AIRS and IASI instruments and RGB images.
According to Jos de Laat, from KNMI, the weaker signal in AIRS and IASI was most likely related to the low altitude of the SO2 emissions.
Eruption at Fogo (NASA Earth Observatory)
Cape Verde Evacuations Ordered As Pico do Fogo Volcano Erupts (The Weather Channel)
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