Eruption of the Raikoke volcano

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A powerful, rare eruption from Raikoke volcano in the Kuril Islands on 21 June 2019, could be clearly seen on satellite imagery.

Date & Time
21 June 2019 17:50 UTC–5 July 23:00 UTC
Himawari-8, GOES-17, Metop-A & B
Volcanic Ash RGB, Airmass RGB, Sulphur Dioxide (SO 2)

By Hans-Peter Roesli (Switzerland), Anu-Maija Sundström (FMI/AC SAF) and Sancha Lancaster (Pactum)

On 21 June, just before 18:00 UTC, volcano Raikoke in the Kuril Islands, started a sequence of spectacular eruptions. It is reported that the last big eruptions dated from 1924.

Himawari-8 detected the first signs at local daybreak, between 17:50 UTC and 18:00 UTC. Both, the Himawari-8 visible band VIS0.64 and the Volcanic Ash RGB captured the first emerging plume of SO2 and ash from the eruption (Figure 1).

Figure 1
Figure 1: Himawari-8 visible band VIS0.64 (top panels) and the Volcanic Ash RGB (bottom panels), 21 June 17:50 UTC and 18:00 UTC

The red arrows on the top left panel (VIS0.64 at 17:50 UTC, 500 m spatial resolution at subsatellite point (SSP), enhanced) point to the very feeble shadow of the emerging plume. Ten minutes later shadow and plume were evident (top right panel).

On the Volcanic Ash RGB (lower left panel, four times lower spatial resolution than the VIS0.64) a red arrow points to a dark spot, which turns into a rising plume of SO2 (green pixel) and ash (brown pixels) ten minutes later.

All four panels are in native projection in order to get a 3D-impression. Checking band IR3.9 for a hot spot (not shown) did not reveal any sign either before or after the first eruption, probably due to an inadequate spatial resolution or the oblique view not reaching the hot lava sources.

Also in native projection the animation of the same image couple (Figure 2) documents the evolution of the eruptions during the local daytime of 21 June (21 June 18:00 UTC to 22 June 09:00 UTC).

Figure 2: Himawari-8 Visible and Volcanic Ash RGB animation, 21 June 18:00 UTC–22 June 09:00 UTC
Figure 3
Figure 3: GFS analyses of the wind and relative humidity cross section from the position of Raikoke eastwards, on 21 June 18:00 UTC

During this initial phase of the volcanic activity a sequence of large eruptions spewed considerable amounts of ash and SO2 into the atmosphere, that spread, at low level westward, then, after reaching five km height, eastward, accompanied by some overshooting tops consisting of ash (red tints) and sometimes mixed with SO2 (yellow).

At the same time, although at a slower pace, ash moved in the opposite direction. This outflow appears to be confined to lower levels, as confirmed by the GFS analysis of the wind cross section from Raikoke on 21 June 18:00 UTC, see red barbs in wind cross section on Figure 3. Close to Raikoke the winds in the maritime boundary layer, i.e. up to some 2–3 km, were rather weak and from the east, whereas from 3 km to 16 km stronger westerlies were blowing from Raikoke, beyond a distance of 800 km.

The animation in polar-stereographic projection of Volcanic Ash and Airmass RGBs, from the start of the eruption to its end at about 16:00 UTC on 23 June (Figure 4), not only shows the very clear ash and SO2 signals in the Volcanic Ash RGBs (red, yellow and green) on the left panel, but also an extraordinary SO2 signal in the Airmass RGB (red) in the right panel.

Figure 4: Himawari-8 Volcanic Ash (left) and Airmass (right) RGBs animation, 21 June 18:00 UTC–23 June 16:00 UTC
Figure 5
Figure 5: Skew-T profile extracted from the GFS analysis at 18:00 UTC on 21 June (click to see details)

The deep red colour suggests that the standard temperature range of the WV6.2–WV7.3 difference, which colours the red beam, was saturated due to a large amount of SO2 under a slant viewing angle, reducing brightness temperature at 7.3 µm through an intense absorption line.

The position of the tropopause and lower stratosphere can be gathered around 150 HPa from the skew-T profile extracted from the GFS analysis at 18:00 UTC on 21 June (Figure 5).

Therefore, it is assumed that most of the long-distance SO2 transport happened in the westerly winds in the drier higher troposphere and lower stratosphere up to around 16 km high.

After having travelled eastward for a few hours and shedding most of the ash, the high-level SO2 swath was taken up by a big deep cyclonic whirl over the Aleutian.

Figure 6
Figure 6: Himawari-8 Volcanic Ash and Airmass RGBs, 23 June 09:00 UTC

Figure 6 shows the situation at 09:00 UTC on 23 June, again in the Volcanic Ash and Airmass RGBs, when the cyclonic path had already made much progress. At the same time, a first break-up of the streamer, due to a deformation zone, had set in (white arrows). Subsequently, above Siberia, the SO2 streamers broke down into ever smaller whirls and streaks. The SO2 distribution became quite chaotic, it even flowed back over the Kuril Islands.

The GOME-2 instruments on Metop-A & B also detected the large sulphur dioxide plume. The AC SAF SO2 products (Figure 7 and 8) show the very small expulsion of SO2 on 21 June and the swirling mass of SO2 by 27 June.

Figure 7: Met-A/B GOME-2 SO2, 21 June
Credit: AC SAF
Figure 8: Met-A/B GOME-2 SO2, 27 June
Credit: AC SAF

The combined view from Himawari-8 and GOES-E (GOES-17) gives an idea of the situation on 28 June at 00:00 UTC (Figure 9).

Figure 9
Figure 9: Himawari-8 and GOES-17 Volcanic Ash and Airmass RGBs, 28 June 00:00 UTC

The SO2 was still detectable on the Himawari-8 RGBs for a few days beyond that date. The animation in native projections of hourly Volcanic Ash and Airmass RGBs gives an overview from the start of the eruption on 21 June to 5 July (Figure 10).

Figure 10: Himawari-8 Volcanic Ash (top) and Airmass (bottom) RGBs animation, 21 June 18:00 UTC–05 July 23:00 UTC

Note: In other volcanic eruptions that were documented with Airmass RGBs, this RGB never showed such a strong (deep red) SO2 signal. Compared to this event, these cases (see Previous Case Studies below) were observed at smaller viewing angles and in a very dry upper troposphere. In this case of Raikoke the airmass was variably humid through almost the whole troposphere, as shown by the blue to green colouring in Figure 3 and only really dry (yellow) only from close to the top of the troposphere upward.

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