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A look at Nabro’s history 19 June 2011

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

BBC documentary probes the volcanoes of Danakil 19 March 2009

Posted by admin in Africa, Erta Ale, Ethiopia, volcanology.
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There’s only one thing that is more important than news on the BBC News website, and that’s self-promotion: hence the thinly-disguised plugs for BBC television and radio programmes that regularly infest the BBC News pages. Just occasionally, however, the BBC self-publicity machine throws up something worthwhile.

A new two-part documentary on the Danakil region of north-eastern Ethiopia, Hottest Place on Earth, will (among other things) look at the fascinating geology of the region. As part of the programme Dr Dougal Jerram of Durham University will be using 3D technology to provide high resolution maps of the interior of the Dabbahu fissure and the crater of Erta Ale volcano. BBC News has an interesting article by Dr Jerram in which he tells us all about it. The video extract showing his descent into Erta Ale is fascinating, and visually stunning.

The Danakil region was the setting for last November’s dramatic fissure eruption at Alu/Dalaffilla. It would be really nice if some enterprising scientific documentary maker went there and had a look around.

(The BBC likes to get its geologist-presenters to abseil into Erta Ale whenever possible. It’s not that long ago that Dr Iain Stewart was doing it for Earth: Power of the Planet. The video of that found its way onto the BBC News website as well.)

The Volcanism Blog

Ethiopian eruption – further coverage 10 November 2008

Posted by admin in Africa, Alu, Dalaffilla, Erta Ale, eruptions, Ethiopia, geoscience.
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NASA’s Earth Observatory has a feature today on one of the MODIS images of the eruption in the Afar region of north-east Ethiopia, captured by NASA’s Aqua satellite on 4 November, that have been discussed here in an earlier post: Activity on the Erta Ale Range.

This link came via Geology.com, who also have a very useful article on the wider geological context for all that’s going on in the Ethiopian Rift: East Africa’s Great Rift Valley: A Complex Rift System (by James Wood and Alex Guth). For further background reading, try this article from Spiegel Online, March 2006: Africa’s New Ocean: A Continent Splits Apart.

Viewing the Ethiopia category will bring up previous posts from The Volcanism Blog on this eruption.

The Volcanism Blog

Ethiopian eruption update 6 November 2008

Posted by admin in activity reports, Africa, Dalaffilla, Erta Ale, eruptions, Ethiopia.
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Just time to note that a new report from Bloomberg quotes an Addis Ababa University researcher as saying that the volcano responsible for Monday’s eruption was Dalla Filla (which the Global Volcanism Program calls Dalaffilla, so that’s the version of the name we will use here).

Also Erik Klemetti has two very useful and up-to-the-minute posts on the Ethiopian eruption at his highly-recommended Eruptions blog: ‘CORRECTED: Erta Ale(?) erupts … and more’, and the more recent ‘More details on the Ethiopian eruption’. Check the comments as well as the posts themselves.

There’ll be more on this intriguing Ethiopian event here later…

The Volcanism Blog

Eruption in Ethiopia – Erta Ale, or not? 6 November 2008

Posted by admin in activity reports, Africa, Erta Ale, eruptions, Ethiopia.
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The identification of Monday’s eruption in Ethiopia with Erta Ale may have been erroneous. An update on the eruption from Dr Simon Carn of Michigan Technological University via the VOLCANO listserv is circumspect:

Satellite instruments detected an eruption in northern Afar, Ethiopia on November 3. The eruption first manifested itself as a large sulfur dioxide (SO2) cloud drifting eastwards over the Arabian peninsula, detected by the Ozone Monitoring Instrument (OMI) and the Atmospheric Infrared Sounder (AIRS). MODIS data from the University of Hawaii’s MODVOLC hot-spot monitoring tool (http://modis.higp.hawaii.edu) confirmed an extensive hot-spot (presumably lava flows) near Alu volcano, in the northern part of the Erta ‘Ale range. Details are still sketchy and these observations are as yet unconfirmed from the ground.

Ethiopian news sources are also rather round-about in identifying the location of the eruption. The official Ethiopian News Agency describes the eruption as occurring ‘at Ertale volcanic area of Afar State, north-east Ethiopia’, while the EthioBlog also speaks of ‘a volcanic explosion in Ethiopia’s remote north-eastern Afar region’.

Wherever the plume came from, it was indeed extensive. The image of the plume below from 5 November, put together from data gathered by the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite, is from the NOAA’s currently experimental site displaying near real-time 24hr composite OMI SO2 information (thanks to Nickolay Krotkov for this link). The plume stretches across the Arabian Peninsula, the Gulf, and across Pakistan and northern India. The more red, the higher the concentration of sulphur dioxide.

SO2 plume

The Activolcans report on the eruption settles for Alu, on the basis of the SO2 monitoring information from OMI and the hotspot report from the University of Hawaii. More on this eruption as news comes in. Erik Klemetti also has detailed coverage at the Eruptions blog.

News
Volcano erupts in Ertale volcanic area of Afar Region – Ethiopia News Agency, 4 November 2008
Ethiopia volcano sets lava record – EthioBlog, 6 November 2008

Information
Global Volcanism Program: Erta Ale – information about Erta Ale (0201-08=)
Geophysical Observatory – Institute of Geophysics, Space Sciences and Astronomy at Addis Ababa University
L’Erta Alé, volcan actif dans le Danakil – a French page with many pictures of Erta Ale from an expedition to the volcano which took place in November 2006

The Volcanism Blog

Erta Ale eruption reported 5 November 2008

Posted by admin in activity reports, Erta Ale, eruptions, Ethiopia.
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Erta Ale, January 2007 (image by Flickr user filippo_jean, licensed under Creative Commons)

Erta Ale, Ethiopia’s most active volcano and one of the most active in Africa, has been busy with its current low-intensity eruptive phase since around 1967. A basaltic shield volcano, Erta Ale is well known for its remoteness, forbidding environment, and long-lasting lava lake (pictured above). A report today from the African Press Agency, quoting the Institute of Geophysics, Space Sciences and Astronomy at Addis Ababa University, says that a significant eruption took place late yesterday without ‘human or material damage’, but details are scarce. There is a fuller report at the South African business news site Moneybiz (also at the Independent Online) which talks of a 300 sq km lava flow and quotes expert opinion that the eruptions of Erta Ale are due to ‘the expansion of tectonic plates under the Great Rift Valley’. Hmm.

In August 2007 an eruption of Erta Ale caused some fatalities and forced local evacuations. UPDATE: Boris Behncke notes (see comments on this post, below) that this 2007 eruption was not at Erta Ale but at Manda Hararo volcano some distance to the south.

Image: lava lake at Erta Ale volcano, January 2007. Credit: Flickr user filippo_jean. Re-used here under a Creative Commons licence. [source]

News
Afar in Ethiopia rocked by volcano – African Press Agency, 5 November 2008
Record volcanic eruption in Ethiopia – Moneybiz, 5 November 2008
Volcano erupts in Ethiopia – Independent Online, 5 November 2008
Ethiopia volcano sets lava record – BBC News, 5 November 2008

Information
Global Volcanism Program: Erta Ale – information about Erta Ale (0201-08=)
Geophysical Observatory – Institute of Geophysics, Space Sciences and Astronomy at Addis Ababa University
L’Erta Alé, volcan actif dans le Danakil – a French page with many pictures of Erta Ale from an expedition to the volcano which took place in November 2006

The Volcanism Blog

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