jump to navigation

A look at Nabro’s history 19 June 2011

Posted by admin in Africa, Dubbi, Eritrea, Erta Ale, eruptions, Ethiopia, Nabro, volcanoes.
comments closed

Nabro is a little-known volcano. Its remote and inhospitable location has meant that very limited fieldwork has been carried out, and much of what we do know comes from remote sensing. Pierre Wiart and Clive Oppenheimer have analysed much of what is known about Nabro in a very useful paper published in the Bulletin of Volcanology in 2005: ‘Large magnitude silicic volcanism in north Afar: the Nabro Volcanic Range and Ma’alalta volcano’. The article is based upon remote sensing data and very limited fieldwork: thus eruptive sequences are established with reasonable clarity, but there is little dating information.

The authors note that much research on north Afar has focused on Quaternary basaltic volcanism, but that silicic volcanism in the region has been little considered, although ‘comparable volumes of silicic magma [compared with basaltic] have been erupted in the region’ (99). The Nabro Volcanic Range (NVR), which the authors identify as a single volcanic massif covering approximately 110 km and trending SSW-NNE from the Afar Depression to the Red Sea, is one significant but little-studied focus of silicic activity. The NVR encompasses the Edd Islands off the Red Sea coast, Dubbi volcano and the Edd lava field, Mabda volcano and the Bidu volcanic complex (Nabro and Mallahle calderas, and Bara Ale and Sork Ale volcanoes). The paired calderas of Nabro/Mallahle are described as follows:

Nabro has an 8 km diameter horseshoe-shaped caldera breached to the SW, and facing the 6 km diameter caldera of Mallahle. Nabro’s caldera contains a young volcanic centre, topped by two additional collapse craters. The flanks of the volcano are strongly dissected by gullies, whereas the inner walls of the caldera form 400-m high cliffs. The older of the two craters inside Nabro’s main caldera is also horseshoe-shaped and similarly open towards the SW. The walls of the innermost crater are 200 m high. (102)

Nabro and Mallahle are described as very similar in geomorphology and lithology, both being predominantly composed of trachytic lava flows. ‘On Nabro, geochemical and spectral evidence highlight at least two main periods of eruption of these flows’ (103). Both basaltic and silicic products are evident: ‘Whereas the main periods of edifice growth, collapse, and post-collapse volcanism have been characterized by silicic products, later volcanics of the Bidu Volcanic Complex include NNW-SSE basaltic lava flows, which streamed from vents or fissures located between the two calderas’. The authors suggest that these flows probably tapped separate source regions to those that fed the silicic volcanism, and note that ‘their superimposition on the boundary between the two calderas and orientation (i.e., perpendicular to the NVR axis), are enigmatic, but clearly not coincidental’ (103).

A very large eruption or eruptions in the past is evidenced by the presence of extensive ignimbrites, which the authors believe are ‘associated with collapses of both Nabro and Mallahle that formed the present day calderas’ (103). The age of these ignimbrites is unknown, but their spectral characteristics and state of preservation suggest their creation in a single eruptive sequence. The present-day ignimbrites cover an area of ~600 square kilometres, with a bulk volume tentatively estimated at 20 cubic kilometres. Prior to erosion of course a much greater bulk must have been present: the combined ignimbrite outcrop today lies within a 30 km radius of Mallahle, and the authors propose that if there was originally a single ignimbrite sheet extending this distance with a mean thickness of 40 m, the eruption magnitude may have exceeded 100 cubic kilometres (bulk volume):

These speculative upper and lower bounds on the ignimbrite volume [20-100 cubic kilometres] suggest an eruption (or eruptions) comparable in magnitude to the largest known historic eruption, that of Tambora in Indonesia in 1815, which expelled around 50 km3 of (dense rock equivalent) magma. This inference is compatible with the comparable caldera dimensions of Tambora (6 km), Nabro (8 km) and Mallahle (6 km). (107)

The total volume of the NVR is estimated by Wiart and Oppenheimer to be ~550 cubic kilometres, broadly comparable to that of Erta Ale. Overall they conclude that ‘the Erta’Ale range and NVR are, therefore, of broadly comparable area, volume, and age (Quaternary)’ but differ markedly in their composition and eruptive nature, with the Erta Ale range being composed of 91.4% basalt, 8.1% dark trachyte and 0.5% rhyolite, while the NVR is estimated as being 50% composed of trachyte and rhyolite (109). The authors suggest that the nature of the basement is responsible for this difference in composition, with the presence of continental crust on the margin of the Danakil region promoting the evolution of volatile-rich and ultimately explosive magmas.

The overall picture of Nabro is of a complicated and fascinating volcanic complex with a violent but varied history involving both explosive and effusive activity, some of the latter being possibly relatively recent in date, and set apart from the more northerly Afar volcanoes by its greater involvement of silicic and explosive magmas. The current eruption involved some initial explosive activity, but appears to have subsequently settled down to an intermittent and relatively low-level effusive event. It is to be hoped that clear images from the satellites will soon show the extent of the lava flows, and their sources. Given the evidence of Nabro/Mallahle’s history, it could be that their sources lie between the two calderas, replicating the behaviour which seems to have characterized the most recent activity at this obscure and intriguing volcano.

N.B. Several people have been in touch or left comments here to say that the Wiart & Oppenheimer paper is freely available via ‘a well-known file hosting site’. However, the paper in question is copyright Springer-Verlag 2004, and this blog respects copyright. Accordingly I won’t be providing the link here, and I respectfully ask that no-one else does so via the comments.

Reference
Pierre Wiart and Clive Oppenheimer, ‘Large magnitude silicic volcanism in north Afar: the Nabro Volcanic Range and Ma’alalta volcano’, Bulletin of Volcanology, vol. 67, no. 2 (2005), pp. 99-115 [DOI: 10.1007/s00445-004-0362-x]

Information
Global Volcanism Program: Nabro – summary information for Nabro (0201-101)

The Volcanism Blog

Advertisements

Eritrea eruption update: Nabro volcano erupts (updated) 13 June 2011

Posted by admin in activity reports, Africa, Dubbi, Eritrea, eruptions, Nabro.
comments closed

Ever since news of the eruption in Eritrea began to seep out early today the identity of the volcano responsible has remained unclear. Dubbi was a prime candidate (and that’s the one Toulouse VAAC went for [UPDATE – Toulouse VAAC has now confirmed that the volcano is Nabro) but with the release of high definition MODIS satellite imagery from the Aqua satellite it is now pretty clear that the eruption originates at Nabro (as Mark Dunphy at Irish Weather Online and several commenters at Eruptions and Earthquake-Reports had suggested, so due acknowledgements to them for their insight). The image below comes from Aqua/MODIS, 10:45UTC 13 June 2011.

Eritrea eruption 13 June 2011, 10:45UTC (NASA Aqua/MODIS image)

Nabro is a stratovolcano reaching to 2,218 metres a.s.l., truncated by nested calderas of 5 km and 8 km diameter, the latter caldera having a wide breach to the SW. Although Nabro has no recorded Holocene eruptive activity, the GVP (from which this description comes) notes that ‘ Some very recent lava flows were erupted from NNW-trending fissures transverse to the trend of the Nabro volcanic range’, so if the current activity is from the Nabro complex it does not necessarily represent the surprise re-awakening of the volcano after millennia of dormancy. Wiart and Oppenheimer (2005) identify these ‘recent basaltic flows’ as originating from ‘Vents … located between Nabro and Mallahle calderas, and fed in part from fissures aligned perpendicularly to the NVR [Nabro Volcanic Complex] axis’ (p. 104), although, working with strictly limited data, they do not venture a date for these flows. Satellite imagery shows these flows as weathered, but fresher and distinctly darker than surrounding material.

Map of the Nabro Volcanic Complex from Google Earth, incorporating information from map in Wiart & Oppenheimer (2005), p. 106
Above. Map of the Nabro Volcanic Complex from Google Earth, incorporating information from map in Wiart & Oppenheimer (2005), p. 106. Yellow line is the Eritrea/Ethiopia border.

Toulouse VAAC has issued a new ash advisory at 1200UTC for the volcano it is still calling Dubbi, reporting ash at altitudes varying from FL200 (20,000 feet/6000 metres altitude) in the vicinity of the eruption to FL450 (45,000 feet/13,700 metres altitude) to the north, where the plume curves back around to the east (map in .png format) after spreading across Ethiopia to reach Israel, Jordan, northern Saudi Arabia and western Iraq. In Israel the Jerusalem Post is reporting that the ash may disrupt flights from Eilat in the south of the country.

Erik Klemetti has an update on the Eritrea event at Eruptions (just before he goes away on honeymoon too, so congratulations and all good wishes to the happy couple). And have a look at this video from Earthquake-Report.com at YouTube.

The International Big News Machine is now catching up with this eruption. BBC News and Associated Press have both published reports in which they confidently identify the volcano concerned as Dubbi, based on the information from Toulouse VAAC. Reuters says it’s Dubbi, mentions that some people think it might be Nabro, then goes right back to talking about Dubbi again. And U.S. Secretary of State Hilary Clinton, attending some international get-together or other in Addis Ababa, is flying out early because of the ash cloud blowing in from Eritrea.

UPDATE: Toulouse VAAC has confirmed that the volcano erupting is Nabro in its latest volcanic ash advisory (issued 18:00 UTC); and via Twitter comes this photograph of Nabro’s plume, taken from ~200 km away by Mark Haldane.

Reference
Pierre Wiart and Clive Oppenheimer, ‘Large magnitude silicic volcanism in north Afar: the Nabro Volcanic Range and Ma’alalta volcano’, Bulletin of Volcanology, vol. 67, no. 2 (2005), pp. 99-115 [DOI: 10.1007/s00445-004-0362-x]

News
Eritrean volcanic ash may affect some flights from EilatJerusalem Post, 13 June 2011
Nabro volcano in Eritrea erupts, ash cloud spreads – Irish Weather Online, 13 June 2011
VAAC: eruption underway at Dubbi volcano in Eritrea – Channel 6 News, 13 June 2011
Eritrea eruption: Lufthansa cancels flights due to ash – BBC News, 13 June 2011
Airlines watching East Africa volcanic ash cloud – Associated Press, 13 June 2011
Clinton cutting short Africa trip because of volcano eruption in EritreaWashington Post, 13 June 2011
Volcano erupts in Eritrea after earthquakes: VAAC – Reuters Africa, 13 June 2011

Information
Global Volcanism Program: Nabro – summary information for Nabro (0201-101)

The Volcanism Blog

Eruption in Eritrea: 1,000 km plume 13 June 2011

Posted by admin in activity reports, Africa, Dubbi, Eritrea, eruptions, Nabro.
comments closed

Infrared image of Eritrea eruption plume, 13 June 2011 07:30UTC (Sat24.com/Eumetsat/Met Office)

Infrared image of Eritrea eruption plume, 13 June 2011 07:30UTC (Sat24.com/Eumetsat/Met Office)

A significant eruption is evidently under way at Dubbi volcano (although there is still some doubt about the precise identity of the volcano involved [UPDATE – it’s Nabro, not Dubbi: see update here]) in Eritrea, north-east Africa. An earthquake swarm occurred during during the evening of 12 June, with moderate quakes followed by two strong quakes of magnitude 5.7, all around 10 km depth:

12 June 2011 15:37UTC: mag 5.1 Eritrea-Ethiopia region (USGS info)
12 June 2011 19:21UTC: mag 5.0 Ethiopia (USGS info)
12 June 2011 20:32UTC: mag 5.7 Eritrea-Ethiopia region (USGS info)
12 June 2011 21:03UTC: mag 5.7 Eritrea-Ethiopia region (USGS info)

A volcanic eruption appears to have begun around the time of the last 5.7M earthquake, at about 21:00 UTC. Toulouse VAAC identified the volcano as Dubbi and issued two Volcanic Ash Advisories so far for this eruption today: at 04:00 UTC the eruption was reported to have started at 23:00 UTC on 12 June 2011, and to have produced a plume between FL150/300 (15,000-30,000 feet/4,500-9,000 metres altitude), while at 06:00 UTC the volcano was described as being in ‘continuous emission’ with ash at FL300/450 (30,000-45,000 feet/9,000-13,500 metres altitude) and trending W/WNW.

Eumetsat image, Eritrea eruption 13 June 2011, 08:00UTC

Eumetsat image, 08:00UTC. Thanks to Eruptions commenter Shérine France for providing the link. Click on the image for the original.

Dubbi was responsible for the largest known volcanic eruption in Africa in historical time, in 1861: more than 100 people were killed, ash fell more than 300 km from the volcano and the lava flows travelled 22 km and reached the Red Sea. Other possible candidates for the current eruption include Nabro and Mallahle.

UPDATE. Via Oxford volcanologist David M. Pyle’s Twitter,here are MODIS images of the Eritrea volcanic ash plume. Thanks to Clive Oppenheimer of Cambridge University (via Earthquake-Reports) we have a useful news report from the Cambridge Geography Department site related to Clive’s Eruptions that Shook the World book: Eruption in Eritrea, 12 June 2011. ‘Loud explosions were heard in Afdera, across the border in Ethiopia, and ashfall is reported as far as Mekele in Tigray province’ … the identity of the volcano is still to be confirmed – Nabro or Dubbi? And more coverage can be found at the Simplement Géologie blog (in French), Séisme et éruption volcanique en Éritrea, Afrique, and at Volcano Blog, Eruption of Dubbi in Eritrea. The Irish Weather Online site has identified the volcano as Nabro rather than Dubbi, on the grounds that satellite images show plume is originating at a point too far south to be the latter. Nabro has no recorded Holocene eruptive activity, so its awakening would be an interesting development. Confirmation one way or the other is still awaited.

ACKNOWLEDGEMENTS. A major source of information on this eruption has been the comment thread at this post over at Dr Erik Klemetti’s Eruptions blog. And excellent ongoing coverage is available at Earthquake-Report.

News
Eritrea volcano eruption: ash plume length exceeds 1,000 km (630 miles) – Earthquake-Report, 13 June 2011 (title changes as the post is updated)
Quake storm hits Ethiopia-Eritrea – Stuff.co.nz, 13 June 2011

Information
Global Volcanism Program: Dubbi – summary information from the GVP for Dubbi (0201-10=)

The Volcanism Blog