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ASTER imagery of Ethiopia eruption 18 November 2008

Posted by admin in activity reports, Africa, Alu, Dalaffilla, eruptions, Ethiopia.
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Alu and Dalaffilla, before and after the November 2008 eruption (NASA ASTER imagery)

On 16 November the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) equipment aboard NASA’s Terra satellite acquired the area of north-east Ethiopia where the volcanic eruption took place on 3 November 2008. The ASTER data provides the clearest imagery made available to date. On the evidence of these images it is a fissure vent zone between Alu and Dalaffilla, rather than Dalaffilla volcano, which is responsible for the current eruption.

Our thanks to Rob Simmon of NASA for these images. For more NASA satellite imagery, visit the NASA Earth Observatory.

ASTER image of Dalaffilla and Alu, 5 Feb 2006, reduced (NASA)
Figure 1. The Alu/Dalaffilla area captured on 5 February 2006, before the current eruption. To see a larger version in a new window, click here.

ASTER image of Dalaffilla and Alu, 16 Nov 2008, reduced (NASA)
Figure 2. The Alu/Dalaffilla area captured on 16 November 2008, after the current eruption began. A new, large dark lava flow is evident, covering a large area and extending about 12km to the east and north. The main cone of Dalaffilla, in the lower centre of the image, shows no signs of activity. To see a larger version of this image in a new window, click here.

ASTER image of Dalaffilla and Alu, 5 Feb 2006, detail (NASA)
Figure 3. Close-up of the Alu/Dalaffilla volcanic zone from the 2 February 2006 image.

ASTER image of Dalaffilla and Alu, 11 Nov 2008, detail (NASA)
Figure 4. Close-up of the Alu/Dalaffilla volcanic zone from the 16 November 2008 image.

The lava flow produced by this eruption covers a large area and overlies previously-deposited flows. The Global Volcanism Program summary for Alu describes ‘voluminous youthful basaltic lava flows to the east’, so the current event is clearly the latest in a long line of similar effusive eruptions.

The source of this eruption may well fall between Alu and Dalaffilla and represent the type of basaltic, effusive eruption associated with the former, but the question arises of how far Alu and Dalaffilla are interrelated, perhaps even forming part of the same volcanic complex (this image from Stromboli Online shows how the two features, which are only about 3km apart, relate to one another). Dalaffilla is silicic rather than basaltic, but Alu, which is a complex of fissure vents, also appears to produce silicic lava flows, which emerge from vents on the west of the horst, while basaltic flows originate from vents on the east and to the south. It’s all very interesting.

The latest MODIS imagery and hotspot data for the area indicates that all is quiet at the moment.

[N.B. The first version of this post located Alu closer to Dalaffilla than is actually the case, and as a result was rather more definitive in attributing the eruption to Alu than was justified. Alu is a volcanic horst and can be identified as the rounded shape on the left edge of the ASTER images – a comparison with this picture at the Global Volcanism Program confirms the identification. However, the style and location of this eruption suggests that Alu’s southern fissures (‘fissures to the south have produced voluminous youthful basaltic lava flows’, says the GVP caption) have more to do with it than any flank activity originating at Dalaffilla.]

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

Information
Global Volcanism Program: Dalaffilla – information about Dalaffilla (0201-07=)
Global Volcanism Program: Alu – information about Alu (0201-06=)
Global Volcanism Program: volcanoes of Africa (northeastern) and the Red Sea – regional list of volcanoes from the Global Volcanism Program

The Volcanism Blog

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Comments

1. Boris Behncke - 19 November 2008

Finally we’re getting a better image of this eruption! So what we have here is truly new lava, not pyroclastic flows as I suggested in an earlier comment. But I did think of pyroclastic flows only when those crazy numers of 300 square kilometers began to circulate in the news, which is an area that lava flows can hardly cover in one single day unless the eruption is GIGANTIC. What we se here is not that big an eruption; the Earth Observatory web site in its update

http://earthobservatory.nasa.gov/IOTD/view.php?id=35926

luckily provides a scale, which indicates that the longest lobes of the new lava flow are less than 5 km long. This would then be indeed a rather modest-sized lava flow, similar to many lava flows we see on Etna and much inferior to Kilauea’s recent lava fields. If we are really, really generous and say the new lava field is 5 km long and 5 km wide (I don’t know whether the full extent of new lava is shown in those satellite images), then we get an area of 25 square kilometers. It should be admitted, though, that this new lava appears to have been emplaced quite rapidly. The most important feature of this eruption, however, seems to be the large quantity of SO2 emitted.


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