S3 phases

Major eruption of La Soufrière volcano

9-12 April 2021

S3 phases
S3 phases

A major eruption of the volcano La Soufrière, on the Caribbean island of Saint Vincent, sent ash more than 15 km into the air in early April 2021.

Last Updated

15 April 2021

Published on

12 April 2021

By Federico Fierli  and Jochen Kerkmann (EUMETSAT)

La Soufrière iis an active volcano in the Caribbean (Lesser Antilles) with a series of major explosive events in the past from the 18th century to the 21st century. Precursor phenomena in early April warned of an imminent activity, and on 9-11 April there were multiple explosive eruptions: two eruptions on 9 April, followed by further major pulses on 10 and 11 April. This was the largest eruption from the volcano in more than a decade.

Intense volcanic eruptions as the explosive ones of La Soufrière have also an impact on the global environment. In fact, they have a key role in the Earth's climate due to the injection of particles and gases that can modify the radiative budget of the atmosphere. The effect and intensity depends greatly on the total amount of mass and the altitude the eruption reaches. More intense eruptions can inject both ash and, more importantly, gases, as sulfur dioxide and carbon dioxide, up to the stratosphere at around 20 km high, where they can reside for longer periods and be transported around the planet. In 1991 a major eruption from Mount Pinatubo, a stratovolcano in the Philippines, produced a persistent layer of small particles in the stratosphere that had a measurable impact on global temperatures.

It is, therefore, very important to monitor the extent, height and duration for a proper estimate of the impact of eruption at various spatial and temporal scales, using data from different instruments on different satellites.

The images from instruments detecting in the visible range of the spectra identify the presence of ashes. The OLCI instrument on-board the Copernicus Sentinel-3 satellite in Figures 1 shows a particularly explosive eruption on 11 April. Ash is visible as brown-yellow layers.

Sentinel-3 OLCI True Colour 11 April 13:38 UTC
Figure 1: Sentinel-3 OLCI True Colour RGB, 11 April 13:38 UTC. Source: EUMETView.

The image from 11 April which is more focused on St Vincent (Figure 2), is particularly interesting, showing the top-view of the mushroom cloud of the explosive event, also clearly seen in animated GOES-16 True Color imagery from NOAA (Figures 3 and 4).

Sentinel-3 OLCI True Colour 11 April 2021
Figure 2: Sentinel-3 OLCI True Colour, 11 April 13:59 UTC. Source: CODA
Figure 3: GOES-16 True Color 1-min rapid scans, 11 April 10:31-11-58 UTC. Credit: NOAA/CIRA
GOES-16 True Color NOAA
Figure 4: GOES-16 True Color, 11 April 13:20-13-50 UTC. Credit: NOAA/CIMSS

Another look at the volcanic plume comes from the aerosol absorbing index (AAI) measured by GOME-2 onboard the Metop satellites. AAI is a degree of the absorption of radiation in the UV and is representative of the amount of particles 'active' in this spectral region (unitless quantity). The Atmospheric Composition Satellite Application Facility (AC SAF) provided a series of maps from the GOME-2 onboard the Metop-B and C satellites in Figure 5, showing the progressive eastward extent of the plume.

GOME-2 AC SAF product
Figure 5: GOME-2 Absorbing Aerosol Index from Metop-B and C from 9-12 April.

The last data used to create a full picture, comes from the detection of sulfur dioxide (SO2) that is emitted by volcanic eruptions. SO2 is particularly important for climate since it can reach the stratosphere, where it can interact with water vapour and form small droplets of sulfuric acid that absorb and reflect solar light,  which, in turn, reduce incoming radiation, producing surface cooling.

La Soufrière emitted a substantial amount of SO2 up to the tropopause level, and higher, as shown by IASI instrument in Figure 6. The SO2 plume was likely transported by upper tropospheric/lower stratospheric westerly winds. The IASI instrument can also estimate the average height of the plume. Data on 10 April shows that SO2 reached 15-17 km high, across the tropopause region, with a raw estimate of a total burden in the order of 0.5 to 1 MTons of SO2 based on the preliminary analysis of Lieven Clarisse, Université Libre de Bruxelles (ULB).

IASI SO2 retrievals
Figure 6: SO2 total column (top) and plume height (bottom) from Metop-B IASI, 10 April. Credit: Lieven Clarisse, ULB

As well as the data above, Meteosat-11 Ash imagery could be used to spot the plume (Figure 7). The ash/SO2 plume is seen in three colours: red = ash, yellow = ash+SO2, green = SO2. The scene was quite complex as there were many low, mid- and high level clouds. Despite this complication, the massive triangular volcanic plume from La Soufrière is well visible in the imagery, especially in a fast animation.

Figure 7: Meteosat-11 Ash RGB, 9 April 18:00 UTC-10 April 17:00 UTC

The pronounced and widespread second eruption on 9 April at about 19:00 UTC could also be seen in GOES-16 True Color imagery (Figure 8).

Figure 8: GOES-16 True Color RGB, 9 April 19:00-21:30 UTC. Credit: NOAA/CIRA

The series of eruptions were visible on the GOES-16 ABI ash composite product (Figure 9. Credit: AERIS/ICARE) as abrupt green/ochre patterns from 9-11 April. Note also another smaller eruption on 13 April.

Figure 9: GOES-16 Ash composite, 9 April 12:00 UTC-13 April 12:30 UTC. Credit: AERIS/ICARE

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