Ash plumes from the eruption of the Indonesian volcano Sinabung could be seen in satellite imagery on 19 February 2018.
By HansPeter Roesli (Switzerland)
According to the Global Volcanism Program Weekly Volcanic Activity Report, the PVMBG (Pusat Vulkanologi dan Mitigasi Bencana Geologi), the Indonesian Center for Volcanology and Geological Hazard Mitigation, reported that at 08:53 (01:53 UTC) on 19 February a large, explosive event at Sinabung generated a dark, grey plume with a high volume of ash that rose to at least 16.8 km.
The Darwin Volcanic Ash Advisory Centre reported that ash plumes that were identified in satellite images, recorded by webcams, and reported by PVMBG, continued to rise throughout the day to 13.7 km and drift 320 km NNW. The plume heights are similar to those given in the report on the eruption in the CIMSS Satellite Blog.
Parts of the ash plumes drifted in multiple directions at lower altitudes, and ash and tephra as large as pebbles fell in areas downwind. The event was considered to be possibly the largest since the beginning of the current eruption, which began in September 2013.
These before/after photos by PVMBG shows the lava dome missing from the volcano’s summit during the blast.
The timing of the eruption and the plume colour reported, agree with the animated sequence of enhanced Himawari-8 ABI True Color RGBs (Figure 1), which starts around 20 minutes before the blast. The video also illustrates the diverging drift of the plumes as described in the report.
Figure 1: Himawari-8 ABI True Color RGB, 19 February 01:30–10:30 UTC. Download animation
Around five hours after the initial outbreak there was an overflight by TROPOMI on Sentinel-5P.
The SO2 column extracted from TROPOMI (Figure 2) compares well with the SO2 traces found in the Himawari-8 Volcanic Ash RGB (light green to yellow) and Airmass RGB (pink) at about the same time (Figure 3).
Note on the Airmass RGB the inverted-comma like swath in electric blue at the upper right of the volcano plumes, which identifies an ice cloud, most probably with the ash working as cloud nuclei.
The entire evolution of the plumes can be followed in the animated sequences of both the Volcanic Ash RGB, 19 Feb 00:00–19:00 UTC (MP4, 20 MB) and the Airmass RGB, 19 Feb 00:00–19:00 UTC (MP4, 10 MB), which last until midnight local time.
Even though a lot of cloud covered the scene the majority of the time, SO2 could still be seen to have continued to stream off the volcano top (white dot on animations) for many hours after the initial blast of a mixture of SO2 and ash (in particular see green signal in the Volcanic Ash video).
The RGB scheme used for the Airmass RGB was tuned to tropical conditions, i.e. the blue beam is rescaled to take account of the colder tropical tropopause.
The clear pink SO2 signal in places is due to the fact that the upper troposphere was relatively dry, as shown by the nearby radiosonde Medan launched a couple of hours before the eruption. The low density of water vapour at higher levels uncovered the SO2 absorption lines in one of the water vapour bands used in the Airmass RGB scheme.
The radiosonde diagram also gives the tropopause at around 70 hPa, i.e. initially the plumes might have reached the 19 km level. The wind profile only has organised winds between 500 and 300 hPa, blowing at moderate speeds from the eastern to south-eastern sector and confirming the drift of the plumes shown in the videos.
Just 15 minutes earlier than TROPOMI, Suomi-NPP flew over the scene. The VIIRS Natural Color RGB at 375 m spatial resolution (Figure 4, left) reveals the dense ash cloud expanding west and north-west of the volcano, whereas the Volcanic Ash RGB at 750m spatial resolution (Figure 4, right) gives an even sharper view of the complex distribution of SO2, ash and cloud than the already excellent Himawari-8 imagery (2 km spatial resolution).
Schoolchildren in Tiga Pancur village in North Sumatrawatch as the volcano erupts. Credit: AFP/Getty Images