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Cool lava in Africas Great Rift Valley
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Cool lava in Africa’s Great Rift Valley

July 14, 2010
This Envisat image captures volcanoes dotted across the landscape in Tanzania, including the distinctive Ol Doinyo Lengai, in the Great Rift Valley of East Africa.

The Gelai Volcano (2942 m) is visible at the top, and the Kitumbeine Volcano (1770 m) is southeast of Gelai. Both volcanoes are considered to be extinct - there has been no eruption for at least 10 000 years and they are not expected to erupt again.

The volcanoes are found in the Crater Highlands, a region along the East African Rift in Tanzania. Located at the intersection of the African and Somali tectonic plates, the Crater Highlands rise up from the floors of the Rift Valley and form a lush chain of mountains and volcanoes.

Ol Doinyo Lengai (2886 m), at lower left, is Tanzania's only active volcano. Uniquely, it is the world's only active volcano that produces carbonatites - unusual igneous rocks that contain more than 50% carbonate minerals. Furthermore, the type of carbonatite it produces, natrocarbonatite, is particularly rich in sodium.

This type of lava is characterised by a low temperature. Erupting at less than 600°C, Ol Doinyo Lengai is believed to have the coolest lava of any active volcano. For comparison, temperatures as high as 1200°C are known to occur in pyroclastic flows of hot gas and rock.

Several eruptions occurred between September 2007 and April 2008.

Radar images represent surface backscatter rather than reflected light, so there is no colour in a standard radar image. This image was created by combining three Envisat Advanced Synthetic Aperture Radar acquisitions (3 February 2010, 30 December 2009 and 25 November 2009) of the same area. The colours result from changes in the surface between acquisitions.

Published as Image of the Week on the 30th of April 2010.