Ol Doinyo Lengai is an unusual volcano given its eruptive product are natrocarbonatitic. Ol Doinyo Lengai is often erupting, and has done so since 1983. Most eruptions are small lava flows, pools and spatter cones (hornitos) confined to the summit crater.
In 2007 (July – August) a larger eruption, described as a rifting episode, occurred. This event was studied using InSAR by Biggs et al. (2009). The eruption began with subsidence that was attributed to ∼40 cm of normal motion on a NE striking fault to the south of the volcano. However, from 17th July deformation was dominated by the intrusion of ∼7-km-long dyke. Dyke opening increased gradually to a total of ∼2.4 m. From July 21, the collapse of a shallow graben above the fault dominated the near-field displacements.
A similar study by Baer et al. (2008) concluded the same sequence of events: attributing deformation to normal faulting in the first week of the event, followed by intermittent episodes of dike propagation, oblique dike opening and dike-induced faulting. They report a gradual decline in the intensity of deformation occurred over the final weeks.