According to Frederick Belton's Ol Doinyo Lengai website, a visitor reported a large plume accompanied by a "bang" during 26-27 February. The Toulouse VAAC reported that a pilot observed an ash plume that rose to an altitude of 10.7 km (35,000 ft) a.s.l. on 27 February. Another possible ash plume rose to the same altitude on 28 February and drifted SW. Based on a SIGMET, pilot reports, and observations of satellite imagery, the VAAC reported that eruption plumes possibly containing ash rose to altitudes of 10.7-13.7 km (35,000-45,000 ft) a.s.l. during 29 February and 3-4 March.

Geological Summary. The symmetrical Ol Doinyo Lengai is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent stratovolcano, known to the Maasai as "The Mountain of God," rises abruptly above the broad plain south of Lake Natron in the Gregory Rift Valley. The cone-building stage ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.

Sources: Ol Doinyo Lengai (Fred Belton), Toulouse Volcanic Ash Advisory Centre (VAAC)