According to Frederick Belton's website, geologists that had climbed Ol Doinyo Lengai on 11 February saw periodic eruptions from a small fissure, and steam emissions from an area of the crater rim next to a part that had collapsed. Another group of geologists that visited during 14-15 February noted three new hornitos on the W part of the crater floor that were black and very fresh. They also noted a cone-shaped gray hornito on the middle of the floor and a new black lava flow to the S.

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.

Source: Ol Doinyo Lengai (Fred Belton)