DCO Project Summary

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Project Title
DECADE - Gas Composition of Oldoinyo Lengai, Tanzania
Start DateEnd Date
2014-06-01 2017-12-01
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Oldoinyo Lengai is the world's only currently active carbonatite volcano.  It is also a large emitter of CO2 and allows the access to pristine mantle derived gases in a continental rift setting.  Therefore, it is an extremely valuable geochemical window into Earth's interior and in particular into Earth's subcontinental mantle.  Oldoinyo Lengai usually erupts effusive carbonatite lava.  In 2007, an explosive eruption occurred producing several km high nephelinite ash columns.  A large pit crater formed as a result of the eruption.  Since then carbonatite has been erupting at the bottom of the pit crater.  CO2 emissions from Oldoinyo Lengai have not been quantified since 2009, but appear to remain significant.  Gas samples were collected on four occasions: in 2005, 2006, 2009, and 2014.  In 2014 soil gas emissions were measured in the crater.
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Reporting Year 2015 Click to expand

  • Update 2015: DECADE - Gas Composition of Oldoinyo Lengai, Tanzania - submitted on Oct 26, 2015

    Update Details:

    Update submitted by Tobias Fischer, October 2015

    As of July 2014, the top of Oldoinyo Lengai ash cone remains extremely steep and sloping at ~50° into the pit crater and ~60° to the other side. Only a very narrow (80 cm wide) path allows visitors to walk around the crater. The pit crater, formed in 2007, remains about 80 m deep with carbonatite erupting in the crater. The ash cone is made entirely of ash and bombs presumably from the 2007 and more recent (?) eruptions.

    The activity observed in July 2014 is characterized by violent carbonatite lava fountaining inside the pit crater. The carbonatite fountaining is focused on a cone located on the north-western side of the pit crater. The active carbonatite cone is approximately 30 meters high. Carbonatite lava was observed ponding inside the cone and violently fountaining out of the cone. Fountaining activity is sporadic and lasted approximately 15 minutes with 10 minute quiescence intervals. Fountains up to about 20 m high were observed. Importantly, the carbonatite activity is eroding or dissolving the pit crater wall, exactly below the area that is first reached by climbers.

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