Wednesday, June 29, 2011

Nabro Volcano, Eritrea

Shortly after midnight local time, on June 13, Nabro volcano in Eritrea began erupting after a series of earthquakes in the region.  Eritrea, for those unfamiliar with the name, is a country in the Horn of Africa bordered primarily by the Sudan to the northwest, Ethiopia to the southwest, and a long coastline with the Red Sea to the east.

Nabro volcano is located next to the border with Ethiopia in the Danakil depression, shown on the map at right.  This area is also known as the Afar triangle.  It's basically the northern end of the East African Rift Valley which extends down through Ethiopia into Kenya and Tanzania (a western arm of the rift also runs down through Uganda and into Lake Tanganyika between Tanzania and the Democratic (hah) Republic of Congo.

The East African Rift system is where the Horn of Africa (Somalian subplate) is trying to pull apart from the rest of the African continent (Nubian subplate) due to tensile forces in the lithosphere.

These tensile forces lead to faulting which acts to accomodate stretching of the crust by the formation of deep rift valleys.  Periodic movement on these faults results in numerous regional earthquakes.  The thinner crust also leads to melting in the underlying mantle resulting in volcano formation in the rift valleys.

Red triangles on the map are volcanoes (Erta Ale is in Ethiopia near Nabro).

Here's what Nabro volcano looks like from Google Earth satellite imagery.  You're looking southwest over the volcano into Ethiopia (yellow line is border between Eritrea and Ethiopia).  There are no good surface photos of the volcano - it's located in a very arid, isolated, and dangerous region of Africa.

Nabro (13° 22' N, 041° 42' E) is, at 2,218 m (7,277 ft), the highest of the stratovolcanoes in the Danakil depression and belongs to a group of calderas called the Bidu volcanic complex.  Nabro itself consists of two nested calderas (8 and 5 km in diameter) breached on the southwestern side (as seen in the image above and at left).

While it's certainly erupted numerous times in the past, this is the first eruption in recorded history for the volcano.  Below is an image from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua satellite (supporting NASA has practical benefits - we can monitor volcanoes in obscure parts of the world in real-time).

Here's another great image from the Advanced Land Imager (ALI) on NASA's Earth Observing-1 satellite on June 24.

The image is actually false color with infrared.  The red and orange areas obviously indicate high temperatures and show a lava flow extending off to the northwest from the erupting volcano.  The blue white clouds are primarily water vapor and carbon dioxide gas mixed with ash.

This ash cloud has disrupted flights in East Africa and has caused problems for people in the area.

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