Smithsonian Institution
Bulletin of the Global Volcanism Network, v. 20, no. 11/12, November-December 1995
Ol Doinyo Lengai (Tanzania)  Minor lava flows and projectile
     emission in December

Ol Doinyo Lengai
northern Tanzania
2.75 S, 35.90 E; summit elev. 2,890 m

Summit visits by members of the Societe de Volcanologie Geneve
during 15-19 December revealed low rates of intermittent effusive
activity and some small explosions. Five episodes of lava emission
were observed from hornito cluster T36 (Bulletin v. 20, no. 10),
each lasting <50 minutes. These very fluid carbonatitic flows
averaged only 5 cm thick, had a velocity estimated at ~4 m/second,
and a temperature measured at 508 degrees C. The flows mostly moved
W, to a maximum distance of ~50 m (figure 11). When emitted from
the top of the hornito, the lava had the appearance of brown
chocolate foam, but turned a dense black color downslope. After the
flow stopped, the color quickly changed back to brown and later
started turning white.

Almost continuous ejection of lava fragments occurred from a cinder
cone T37 (~15-25 m high), and with less intensity from a hornito in
a small collapse depression just W of T5/T9 (figure 11). A small
lava pond, observed for ~3 hours on 16 December, inside the
depression at the foot of the hornito exhibited splashing and small
bubbles. Two major flank collapses of T37 released large quantities
of very fast-moving (5-8 m/second) aa lava flows that were ~50 cm
thick. The first flank failure, on 16 December, was a progressive
event on the W side. However, the E-flank collapse on the 18th came
without warning, quickly sending a lava flow NE between T5/T9 and
F35, almost to the crater rim.

Fumarole temperature measurements were taken on the N crater rim,
inside new cracks on the crater floor, and at the tops of T8 and
T15. All temperatures were 70-80 degrees C.

Information Contacts: P. Vetsch, S. Haefli, and C. Peter, Societe
de Volcanologie Geneve, B.P. 298, CH-1225 Chene-bourg, Switzerland
(Email: pvetsch@iprolink.ch).

Figure 11. Sketch map of part of the Ol Doinyo Lengai crater
showing new features and lava flows, 15-19 December 1995. Modified
from the January 1994 map in Bulletin v. 19, no. 4.