not much but I have to admit but I was extremely pleased to participate a little bit to that famous institution, so big and diverse.
below is an extract of the bulletin. Just in case, to see the whole longer article, go to: http://www.volcano.si.edu/ Volume 34, Number 5, May 2009.
and for most of my volcano Lengai pictures, go to http://www.oldoinyolengai.org/. That is the most complete website on Lengai.
Ol Doinyo Lengai
Tanzania
2.764°S, 35.914°E; summit elev. 2,962 m
All times are local (= UTC + 3 hours)
Conditions during 2009 visits were
generally calm, although minor eruptions on the crater floor
continued. This is in contrast to explosive eruptions during September
2007-March 2008 (BGVN 32:11, 33:02, 33:06, 33:08, 34:02).
Most of the groups that arrived at Lengai in 2009 did not ascend to
the active crater and the SE route remained difficult.
Comments on aviation hazards during 2007-2008. Comparatively few
pictures or comments on aviation hazards have emerged from the recent
episode of Plinian eruptions during 2007-2008. Ben Wilhelmi took a
series of photos of the ground surface at distance from the volcano
during a week in November 2007. From the air he saw ash as far away as
70 km from the volcano, including in many cases, over Masai villages
that dot the landscape.
Wilhelmi's discussion and photos follows. "[During] 2007 and 2008 ...
smoke and ashes sometimes [rose] up to 50,000 ft, 15 km high. It
looked like a Hiroshima mushroom [cloud (figure 8)]. Here is ash
deposit on my aircraft [(figure 9)]. Often the ash was invisible in
the air though. [Three] turbine engines died in different companies
because of ash intakes. It happened one of these engines [died] on me.
Luckily I could finish the flight, but I didn't like the feeling to
see the engine temperature in the red and [flying] on reduced power.
Figure 8. A tall (roughly 15-17 km altitude) Ol Doinyo Lengai plume
from the 2007-2008 eruptive interval taken at unstated date and
directional bearing. Short burst of lightning were visible in the
plume but were not captured in this photo. Courtesy of Ben Wilhelmi.
Figure 9. Two photos of Ol Doinyo Lengai ash deposits on leading
surfaces of a small propeller-driven airplane from encounter with ash
while in flight. Photographer and pilot Ben Wilhelmi commented that
the ash was often invisible during the encounter.
"In other countries, such an activity [as seen in figure 8] would have
imposed the area to be closed within 200 miles [~ 320 km], that would
have included Arusha and all the Serengeti [and] Ngorongoro [park and
conservation areas]. "Competent" authorities were asleep, the regional
companies happily kept on flying ... and subsequently lost 3 engines
as I've said earlier. Costs could go up to $350,000 for a new turbine
engine ... I certainly didn't complain as I could shoot [photos at
will and] got to see incredible spectacles like this day with a 55,000
ft or 17 km high plume of smoke with an electric thunderstorm inside!"
Table 3. Summary of selected observations describing Ol Doinyo Lengai
during January-April 2009. Courtesy of Ben Wilhelmi and Frederick
Belton.18 Feb 2009 A.N. Zaitsev, S.V. Petrov, T.A. Golovina, E.O.
Zaitseva, G. Markl, and T. Wenzel (CV) See text above
25 Apr 2009 Ben Wilhelmi (A, figure 13) Photos showing numerous
hornitos with spatter widespread on the crater floor and in places on
the crater walls.
Figure 13. Aerial photo of Ol Doinyo Lengai's crater floor taken on 25
April 2009 with uncertain orientation with respect to N. The floor
contains numerous hornitos. According to the pilot and photographer,
Ben Wilhelmi, who often flies over for observations, these features
probably formed during the previous 4-5 months. Courtesy of Ben
Wilhelmi.
Geologic Summary. The symmetrical Ol Doinyo Lengai stratovolcano is
the only volcano known to have erupted carbonatite tephras and lavas
in historical time. The prominent volcano, 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 of the
volcano 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
eruptions 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.
Information Contacts: David Sherrod, Cascades Volcano Observatory,
USGS, Vancouver, WA, USA; Anatoly Zaitsev, St. Petersburg State
University, Saint Petersburg, Russia; Gregor Markl, Tuebingen,
Germany; Frederick Belton, Developmental Studies Department, PO Box
16, Middle Tennessee State University, Murfreesboro, TN 37132, USA
(URL: http://frank.mtsu.edu/~fbelton/lengai.html;
http://www.oldoinyolengai.org/); Ben Wilhelmi (URL:
http://www.benwilhelmi.com/;
http://benwilhelmi.typepad.com/benwilhelmi/).