The second eruption of the Italian volcano Stromboli occurred on 28 August - just a few weeks after a previous eruption.
By HansPeter Roesli (Switzerland)
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 1) 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.
Figure 1: Meteosat-10 HRV animation, 28 Aug 10:00–13:30 UTC
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 600 hPa. 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 2), 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 (600 hPa) 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 3), reveals that there was already a weak release of material after 07:30 UTC.
Figure 3: Meteosat-8 HRV (left panel) and Volcanic Ash RGB (right panel) animation, 28 Aug 07:30–12:30 UTC
On the HRV and Ash RGB image at 08:15 UTC (Figure 4) 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 5) 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 375 m spatial resolution from NOAA-20 (Figure 6), lava flow on the flanks of the volcano show as red areas.