Ol Doinyo Lengai

Volcano number:222120
Region:Africa and Red Sea
Country:Tanzania
Geodetic measurements?Yes
Deformation observation?Yes
Measurement method(s):InSAR
Duration of observation:April - August 2007
Inferred cause of deformation:Magmatic, Faulting/tectonics
Characteristics of deformation:

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.

Reference:Biggs, J., Amelung, F., Gourmelen, N., Dixon, T. H., & Kim, S. W. (2009). InSAR observations of 2007 Tanzania rifting episode reveal mixed fault and dyke extension in an immature continental rift. Geophysical Journal International, 179(1), 549-558.
Reference:Baer, G., Hamiel, Y., Shamir, G., & Nof, R. (2008). Evolution of a magma-driven earthquake swarm and triggering of the nearby Oldoinyo Lengai eruption, as resolved by InSAR, ground observations and elastic modeling, East African Rift, 2007. Earth and Planetary Science Letters, 272(1), 339-352.
Reference:http://volcano.si.edu/volcano.cfm?vn=222120
Location:35.914, -2.764

Photo of Ol Doinyo Lengai from March 2008, seen from the NNE. Ash can be seen erupting from near the main crater. Photo by Benoît Wilhelmi, 2008.