New eruption of Mount Nyamuragira

By Jochen Kerkmann and Alexander Jacob (EUMETSAT)

The Nyamuragira volcano is the most active volcano in Africa. It is a 3056m high massive basaltic shildvolcano located within the Virunga National Park, north of Lake Kivu and north-west of Nyiragongo, a neighboring volcano. Lava from Nyamuragira covers 1500 km² of the East African Rift and has come as far as 30km from the volcano, even down to Lake Kivu.

May 2004

According to the Goma Volcano Observatory, the Nyamuragira volcano erupted on 8 May 2004 at 05:48 local time. The lava flows remained within the National Park boundaries and did not threaten populated areas.

Ash fell in several villages on the west and north flanks of the volcano. The volcano also emitted a large amount of sulfur dioxide (SO₂) into the atmosphere, which could be observed from satellites (e.g. AIRS on EOS/Aqua, TOMS and Meteosat-8). Like the Nyiragongo, the Nyamuragira volcano is well known for its high emission of SO₂.

The Meteosat-8 images below show the volcanic SO₂ plume on 10 May 2004, two days after the first eruption. Like in the case of the Nyiragongo eruption on 12 July 2004, the SO₂ plume is best visible in the IR10.8– IR8.7 brightness temperature difference image (with values of up to +8K).

As can be seen in the animation, large parts of Rwanda and Burundi are covered by the SO₂ cloud, which moves in a south-easterly direction towards lake Victoria. Later during the morning, with the clouds clearing and wind direction changing to north, the satellite is seeing more SO₂ in lower layers in the eastern region of the Democratic Republic of the Congo.

According to measurements from the Earth Probe Total Ozone Mapping Spectrometer (EP TOMS) the highest SO₂ concentrations were detected in a zone across Rwanda, which contained ~190000 tonnes of SO₂.

November 2006

Besides ash and possible lava, when the volcano erupted in November it released large amounts of sulphur dioxide (SO₂). The SEVIRI instrument on Meteosat-8 tracked the emission of SO₂ and the corresponding plume at 15 minute intervals. SEVIRI has two channels, the WV7.3 and the IR8.7 channels, that are principally sensitive to high SO₂ concentrations (see figure, courtesy CIMSS, University of Wisconsin and CSIRO).

The images below show the situation about 36 hours after the start of the eruption when the area was less cloud covered. In the left image, which presents the so-called 'Ash RGB', the sulphur dioxide cloud is shown in green colour. This RGB exploits the SO₂ absorption band at around 8.6 microns (SEVIRI IR8.7 channel).

Although not designed for SO₂ monitoring, the 'Airmass RGB' shown in the right image also shows the long SO₂ plume over the Democratic Republic of the Congo. It exploits the much stronger SO₂ absorption band at around 7.3 microns (SEVIRI WV7.3 channel), and as long as the SO₂ plume is above 3km height it is principally able to detect high SO₂ concentrations. Indeed. the cooling effect of the SO₂ cloud on the WV7.3 channel leads to small Brightness Temperature Differences between the WV6.2 and the WV7.3 channels, which is displayed on the red colour beam of the Airmass RGB. Thus, mid/high-level SO₂ clouds from volcanic eruptions appear with a red/orange colour in this RGB composite.

The movement of the SO₂ cloud can be easily followed in the animations, given in the links below the images and under additional content. Although the SO₂ concentration in the cloud gets lower and lower with increasing distance from the source, careful inspection of the animations shows that the SO₂ cloud moved westward and northward into the Central African Republic, Chad and Cameroon.

More information about the movement of the SO₂ cloud can be obtained from the data of specialised instruments like the Ozone Monitoring Instrument (OMI) on the Aura platform. The OMI data confirms that the SO₂ plume first travelled westward and then moved in a clockwise direction toward the northeast, eventually reaching India (see Aura/OMI average SO₂ concentration, source: S. Carn, UC).