Cumbre Vieja volcano eruption seen by ISS. Credit: NASA

Cumbre Vieja volcano eruption

19 September 2021 12:00 UTC-4 October 15:00 UTC

Photo credit: ISS

Cumbre Vieja volcano eruption seen by ISS. Credit: NASA
Cumbre Vieja volcano eruption seen by ISS. Credit: NASA

The Cumbre Vieja volcano on the Canary Island of La Palma erupted on 19 September 2021, causing thousands to be evacuated.

Last Updated

10 June 2022

Published on

20 September 2021

By Ivan Smiljanic and Alen Berta (CGI), Sancha Lancaster (Pactum), HansPeter Roesli (Switzerland), Jochen Kerkmann (Germany) and Miguel-Angel Martinez Rubio (AEMET)

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.

Figure 1: Meteosat-11 Ash RGB, 19 September 12:00 UTC-20 September 05:30 UTC.

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.

Figure 2: GOES-16 24-hour Microphysics RGB, 20 September 00:00-07:30 UTC

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)

GOES-16 VISO.6 Band v Ash RGB imagery

GOES-16 Ash RGB compare1

Figure 3: Comparison of GOES-16 VISO.6 Band (left) and Ash RGB (right) imagery, 20 September 07:20 UTC.

GOES-16 Visible 20 Sept 2021
Figure 4: GOES-16 VIS0.6 band, 20 September 07:00-07:30 UTC.

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. 500–1500m.

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.

GOES-16 Natural Colour 20 Sept 2021
Figure 5: GOES-16 Natural Color RGB, 20 September 07:30 UTC.

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.

Figure 6: Sentinel-3B SLSTR FRP, 19 September.

Notable events

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.

Aqua MODIS Natural Colour RGB 1 October 2021
Figure 7: Gravity waves capture by the concentric cloud formation, Aqua MODIS Natural Colour RGB, 1 October 14:41 UTC

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.

Terra MODIS True Colour RGB 4 Oct 2021
Figure 8: Ash ejection into lower tropospheric layers, Terra MODIS True Color RGB (enhanced), 4 October 11:55 UTC.

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 500 hPa 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.

Terra MODIS True Colour RGB at 11:55 UTC, with pasted Meteosat 11 Ash RGB at 11:55 over similar domain, 4 October 2021
Figure 9: Terra MODIS True Color RGB at 11:55 UTC, with pasted Meteosat 11 Ash RGB at 11:55 UTC over similar domain, 4 October. Red arrow indicate ash plume, green arrow SO2 plume.
Figure 10: Meteosat-11 Ash RGB, 4 October 03:00-15:00 UTC
Figure 11: Meteosat-11 Airmass RGB, 4 October 03:00-15:00 UTC

A similar episode of low level ejection occurred on 9 October. This time ash and SO2 plumes were constrained to even lower levels, at around 3km according to a nearby radiosounding (Guimar, Tenerife).

2 October — La Palma land extension

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).

Sentinel-1 false colour rgb
Figure 12: False-Color RGB from the combination of Sentinel-1 VH polarizations (GRD product) on dates 14 September (Blue RGB band) and 2 October (Red end Green RGB band), 2021. Yellow signal over water is where previously there was no signal, purple over the land where there was signal but it changed, and in grey shades no change at all before/after.

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.


Additional content

Thousands flee as lava spewing from volcano on Spain's La Palma island destroys houses (Reuters)
La Palma, Canary Islands: seismic crisis Sep 2021 - updates (Volcano Discovery)
Video of the eruption (Iván López/Twitter)