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.