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O. LENGAI (Archiv)
View from the summit down to the crater Reports (published) for the GVN, Smithsonian

Lengai Report Aug. 1996
Lengai Report Aug. 1998
Lengai Report Aug. 1999
Lengai Report Okt. 2000
Lengai Report Okt. 2002
Map of the crater 2002
Lengai Reports 2003
Lengai Reports 2004
Lengai Reports 2005
Lengai Reports 2006
Latest Reports 2007
Latest map of the crater

Filmteam at the summit of Lengai Back to the O. LENGAI main page!

Lengai Report Aug. 1996


Figure A. Sketch of the Ol Doinyo Lengai crater looking S from the N rim, 17 August 1996. Courtesy of Christoph Weber, revised by C.Nyamweru.


Figure B. Sketch map of the Ol Doinyo Lengai crater, 17 August 1996. Courtesy of Christoph Weber, revised by C. Nyamweru.

Christoph Weber reported that on 17 August the crater floor had been covered with new black aa and pahoehoe lava flows. Weber had met another traveler, however, who had observed no eruptice activity about 14 days earlier. When Weber visited, he estimated the thickness of the fresh flows as typically ~20-30 cm. Fresh flows were easy to distinguish because they change from black to grayish white as they cool. They were often stacked, particularly on flow field F37, the one most active at that time, forming a composite of new flow material perhaps a meter thick overall. The area covered by these new flows was ~30,000 m2. Thus, in the first half of August, the volume of erupted lava was on the order of 30,000 m3. Because of the rough irregular surfaces on some flows, their contacts with successive flows often contained considerable void space. Many of the flows were tube-fed, the tubes typically being 10- to 150-m long. When Weber left on 17 August lavas still poured out. He also observed a lava fountain ~3-m-high on T37. On 24 September some students from St. Lawrence University observed continuous bubbling and spattering of lavas from several vents.

Lengai Report Aug. 1998

Ol Doinyo Lengai
northern Tanzania 2.751S, 35.902E; summit elev. 2,890 m

Observation of the crater from 6 August 1998, 0800 until 7 August 0800 by Chris Weber. On 6 August at 0800 an eruption started at hornito T37N1. This hornito has a platform about 5 m above the surrounding area while it is highest peak at the northern flank is about 8 m high. A little splatter cone had build up on this platform where foaming white to pale grey carbonatite lava splashed out and fed short lava flows with a few meters length down the west-slope of T37N1. Most of the lava went into older lava tubes west of this hornito. The vasiculation of the gas rich lava was high. The activity stopped around 1100 with a 4 m drop of the lava level in T37N1. On the same day at 1400 lava splashed out of two openings close to it is peak of hornito T48. The black degassed very liquid lava fed little lava flows reaching 8 m of length down the east-slope. The activity stopped shortly after 1600.
On 7 August at 0408 a loud explosion blew of the top and northside of hornito T49 after several earthquakes during the night. The earthquakes seamed to have shallow and deeper hypocenter in the volcano. Rocks of this hornito up to 1 m3 were thrown or rolled a few meters to the north by this explosion. Right after the explosion a lava fountain (fire curtain) approximately 15 m high continued until 0413 with a loud turbojet-noise. Pahoehoe lava with little viscosity (1-5 Pa s) which splashed down north of the hornito traveled fast to the north and west . The 10-20 cm thin flow stopped moving shortly after the end of the eruption. The amount of erupted lava was about 70-100 m3. Lava pearls up to 4 mm diameter and fine ash were transported at least over 200 m by the wind in northwest direction. The fountain had a dark red glow. The hornito lost less than one meter of the 6 m elevation., whish it had before the explosion. At 0615 on 7 August hornito T44 started activity for an unknown time. Black liquid lava splashed out of it is 6 m high peak and splattered on the flanks of the cone. No lava flow was observed until 0815. T23 continued with fumarolic activity, T40 degassed with mild turbojet-noise.

Part of the crater 1999
Map of the center part of the crater (c)C. Weber 1998

The lowest point of the crater-rim over the crater-floor in northwest was 20 cm. Activity at the crater-rim to the outside of the caldera seamed to have occurred in recent months, because of white and fresh looking carbonatite lava on the outer northern flanks of Lengai. Destroyed or burned vegetation inside and outside the crater was not observed.

Lengai Report Aug. 1999

The following report resulted from a visit to the crater of Ol Doinyo Lengai during 23 July-7 August.

11/99 (BGVN 24:11) Very active hornito in the N part of the crater Prior to the visit and according to a local source (Burra Ami Gadiye), lava breaching the NW crater rim on 18 July flowed down the flank of the volcano and was visible at night from Ngare Sero village, ~10 km N. When the visitor's crater observations began at 1100 on 23 July, this lava flow from the NW crater rim breach had cooled and was becoming white from weathering, but it was clearly the most recent lava in the crater. Its source was hornito T40 based on comparisons of 1998 and 1999 photographs by C. Weber.

From 2 to 6 August, an intermittent lava lake 3 m in diameter also existed inside T37N1 at a depth of 20 m. The conical part of T40 was 85 m around at its base and 12 m tall. The N side of the hornito's cone was walled by a low overhanging rim and its S side was covered by a high half-dome. The hornito also included a large, 6-m-deep crater. A small lava pond at the N end of the crater ejected 16-20 spatters per minute through 24-25 July. Twice on 26 July parts of the half-dome and the cone's summit collapsed into the crater.

During 27-28 July lava gradually rose inside the crater of T40 and formed a 4 x 6 m lake and several ponds. By 29 July the lake was ~12 m long and 7 m wide. In a pattern repeating every 15-20 minutes a surge of fresh lava boiled up from the NE corner of the lake, raising the level by 0.5 m. Lava flowed out of the lake to the NW through a subterranean tunnel but did not escape onto the main crater floor. Although this pattern persisted for some time, at 1400 on 30 July an abrupt increase in activity produced high lava spatters that fell on the N flank of T40. Fresh lava swept into the lake from the N like breaking ocean waves and strong ground tremor shook the N flank of the cone. This activity continued through 31 July, when the lake rose to ~60 cm below the lowest point along the vent rim. Spatter gradually built up the N wall of the crater by more than 1 m and formed a large hood overhanging the area of most intense degassing.

At 0045 on 1 August, a hole developed in the hornito's new crater wall. Lava escaped and moved N as short aa flows up to 60 cm thick. Lava ceased to escape by 0600 but similar eruptions recurred through 1300 on 2 August. Intense degassing later destroyed the hood covering the N part of the lake, but splashing built a thick covering of spatter on the N flank of the cone and reconstructed the hood. Around 0300 on 3 August a new vent opened low on the NW flank of T40 where the strongest tremor had been during the previous few days. An aa lava flow 20 cm thick moved 73 m NW. By 0800 the eruption had ended and the lake level dropped by 2 m. By 0600 on 4 August the lake temporarily disappeared, leaving a solid crater floor 2.5 m below the rim. Lava reappeared about noon but only occupied a 2 m2 area at the crater's N end; the lava frequently overflowed from the pond and produced many small lava flows that covered most of the hornito's crater floor. At 2345 solid lava covering the new vent on the NW flank of T40 blew off; explosions occurred at a rate of 18-20/minute and constructed a new spatter cone. During repose periods, the activity shifted to the lava lake, creating high spatters that reached the summit of T40. After explosions ended at 0800 on 5 August, the new cone was 3 m tall with a circular summit vent 60 cm in diameter. Lava was bubbling in the vent at a depth of 1 m.

At 2000 on 5 August pahoehoe lava flowed rapidly across the NE rim of T40 and moved E for 55 m. At 0645 the next morning, more lava escaped the lake through a hole in the NE rim of T40 and covered much of the previous night's flow. Beginning at 1800 on 6 August the lake repeatedly overflowed the hornito's NE rim, later overflowing the NW rim. Around 0400 on 7 August a hole that opened 1 m below the NE rim of T40 gradually enlarged and drained ~60 m3 of lava from the lake forming an open NE-directed lava channel 60 cm wide. By 0800 on 7 August the hole was 1 m high and 0.5 m wide. When observations ended at 0815, lava was nearing the NE crater wall and subsequent reporting noted that lava never reached the breach in the E crater rim, stopping short by 70 m. It was later learned from Guillaume Delpech, a French geology student, that during his visit to T40 on 9 August, the lava lake level inside the hornito varied between 3 and 4 m below its rim. No lava flowed outside of T40 and the spatter cone was inactive.

Christoph Weber made temperature measurements using a digital thermometer (TM 914C with a stab feeler standard K-type) during the crater visit. The instrument was used in the 0-1200 Celsius mode, taking readings by inserting the feeler 15 cm into the lava. Calibration was made by the Delta-T method: values are 6C in the 0-750C range. Most values shown were maxima recorded from a series of at least five repeat measurements.

Table. Temperature estimates from 60 measurements at Ol Doinyo Lengai made during 23 July-7 August 1999. See text for method used. Courtesy of Christoph Weber.


T40 lava lake
Pahoehoe flow in open channel
(3 m below lava lake)
End of a 60-cm-thick aa flow
Fumarole near base of T49

28 Aug 1999
01 Sep 1999

01 Sep 1999
28 Aug 1999
temperature (C)


Lengai Report Oct. 2000

An common expedition was organized by Chris Weber from 3rd October to 11th October 2000. A film team and four scientists, led by Joerg Keller, were members of the expedition. Joerg Keller has studied O. Lengai since his first visit in 1988 and has published several papers about O. Lengai:

  • Carbonatite Volcanism, K. Bell & J. Keller, 1995, Springer Verlag
  • Effusive natroncarbonatite activity of O. Lengai, M. Krafft, J. Keller, 1990, Bull.     Volcanoes
  • Historic and Recent activity of Oldoinyo Lengai, Dawson, Keller & Nyamweru, 1995

    3rd October to 11th October 2000

    Nature of record: Observation by J. Keller, A. Zaytsev, D. Wiedenmann, J. Klaudius, D. Szczepanski, M. Szeglat, C. Weber.

    Geography: GPS-Data and barometrical instruments (series of data-measurements) gave new information about the altitudes of O.Lengai. The highest summit is approximatly 2955 m (2950-2960 m). The cone peak C on the northern crater rim is approximatly 2835 m. The crater floor was on October 2000 approximately 2825 m at the Overflow NW and E.
    Despite the known track up the WNW flank of Lengai, two other different descents were made during the visit.
    1) The track down the eastflank (named Dorobo-Route "the ascent route of Krafft-Keller expedition in 1988") was followed by J. Keller and 2 scientists of his team on 7th October 2000 for reconnaissence. This track is difficult and should not be attempted without a guide.
    2) One track starting half way between the western crater wall and the summit down the WSW flank passing the Kirurum crater (named Reck-Route) was followed by Keller/Weber including expediton members and local porters on 11th October to 12th October 2000. One overnight camp was made at the Kirurum crater along this track to give time for fieldwork.
    Different craters around O. Lengai were visited beside of the summit-crater expedition, such as Lalarasi and Loolmurwak. For further information about geography around Lengai please contact J. Keller.

    Renumbering: Some frequent visitors and scientists who work on Lengai have decided to change some numberings for the current cones. This is because of an easy understanding for the future and owing to changes of cones during the last years. The new cone numbers will follow a logical system as followed: a new eruption center gets always a new T-number (e.g. T49). New cones at the flank of an existing cone, and clearly fed by this, will be numbered with an "B" (T49B), following ones by "C", "D" and so on.
    This leads to the following renumbering:
    • T52 (former T52C)
    • T52B (former T52W)
    • T52C (former T52E)
    • T37 (former T37S)
    • T37B (former T37N1)
    • T37C (former T37N2)
    • T37D (former T37E) and also (former T5/9)

    Eruptive activity: On 3rd Oct. from 1200 until 1350 hours spattering occurred in the saddle between T49 and T49B out of a small vent. Two little lava flows were observed at the northern and southern flank of T49 during that time. At 1350 the west side of T49B collapsed and released out of an approximately 6 m wide and 5 m high gap a sudden flash flood of lava. Parts of the collapsed wall of T49B were washed towards the west as big blocks. Within a few seconds the flow had reached halfway between the cone and the NW Overflow. After 5 minutes the flow had reached its final extent about 40 m short of the NW Overflow (See map of flows: Flow 4A). The lava flow was up to 5 centimeter thick and later Aa flows were several decimeters thick.
    Until 8th Oct. lava spattering and many small lava flows (formed from overflowing the vent, as spatter fed flows or emitted from small new vents and fissures) had nearly closed the gap in the west wall of cone T49B. Only close to the top of T49B spattering occurred on the evening of 8th Oct. On the morning of 9th Oct. at 1035 hours nearly the same west flank of new lava collapsed in the same manner as on 3rd Oct., leaving a 7 m wide and 7 m high gap. Lava went in a flash flood within seconds towards the NW and stopped just 10 m before the NW Overflow. The flow covered the Flow 4A and is shown in the flow map as Flow 4B.
    During the afternoon of 9th Oct. T48 had strong degassing and for only 10 minutes ejection of tear-drop lapilli occured. After this event T48 went quiet for the rest of our visit. Right after sunset of 9th Oct. at 1810 hours a crack opened at the SSW base of T49C with a sudden noisy gas jet followed by a 10 minutes spraying of lava droplets and sperical lapilli up to approximately 10 m high. A small lava flows (Flow 4C) were emitted too and moved NW.
    From there on until our descent on 11th October no flows were observed, meanwhile the lava lake inside T49B was still in motion and heavily splashing and degassing.

    Lava and fumarole temperatures: Between 3rd Oct. and 9th Oct. 2000 temperature measurements were made by three different instruments and gave consistent values. The following table gives values from a digital thermometer (TM 914C with a stab feeler standard K-Type). the instrument was used in the 0-1200 Celsius mode, taking readings by inserting the feeler 10 cm into still moving and liquid lavas (10 times at various days) and as deep as possible into the fumaroles (5 times at various days). Calibration was by the Delta-T method: values are +/- 6C in the 0-750C range.
    All values shown were recorded by four repeat measurements at one spot.
    • Pahoehoe lava flow (15 m below outflow from lava pond (lake) inside T49B in an closed lava tube); 507C
    • Aa flow front in slow motion (shortly after escaping a closed lava tube near T49B, 25 cm thick); 496C
    • Fumarole 25 m NNW of T49C in a crater crack towards the rim (see map of cracks); 75C
    • Fumarole at the Overflow NW inside the old crater rim; 69C
    • Fumarole at the NW flank of T48; 95C
    No measurements close to the emitting lava pool inside T49B were obtained. The temperatures are close accord with the lower range ot temperatures of Krafft & Keller 1989 (Krafft, M. & Keller,J. 1989. Temperature measurements 245, 168-170). Dawson et al. 1990 had reported temperatures of 573-597C for the Nov. 1988 effusions. In Aug. 1999 Chris Weber determined max. Temperatures of 529C, this again in accord with temperature measurements by Joerg Keller in Oct. 1995, which gave 524C at the flow issued from a suddenly opened fissure at cone T37.
    According to the red glow of lava in the night of the recent visit and the visit of 1998 by Chris Weber, he has noticed, that the lava glow during a visit by Chris Weber in Aug. 1998 and Aug. 1996 was more intensive, therefore probably hotter than 530C.

    Appearance of crater: Flow 1 had still a brown appearance, but had continued to weather after the 30th July describtion. The younger Flow 2 was partly black to gray in the joints and cracks of the Aa flow field. Some smaller flows around T49 and T49B were slightly black, though probably only a few hours old. We learned from this visit and many other visits, that hydration of fresh lava flows (specially under high humidity) can cause a black surface turn into soda-white within 24 hours respectively overnight.
    NW of T49B another cone belonging to the T49 eruption cluster had appeared after 30th July and is named T49C (see map). T51 was surrounded by flat Pahoehoe flows and had grown since 30th July. There was a new cone in the collapsed T48 with some small light gray looking lava flows close to the cone.
    During this year many new cracks (in a maximum up to 1 m wide and 5 m deep) had opened all across the crater floor. The V-shape of cracks could lead to an expansion or doming theory of the crater floor. Most of the cracks point to the T52 and T49 eruption clusters, roughly the center of the major cone concentration. Some of the cracks break through the crater rim. Other cracks are filled up or covered by young lava flows. So the map of cracks may not show all actual cracks in the surface.

    Accident: On the evening of 3rd Oct. 2000 at 2010 hours, one of our scientists (Jurgis Klaudius) stepped by accident with his left foot in a fresh but already black and solid looking lava flow (about 25 cm thick) at the westslope of T49B. This can easily happens to everyone in the night if solid and fresh black flows are all around one site. In this case it caused a serious second degree burning to Klaudius around his ankle up to his lower leg. All light plastic and gorotex parts of his sport shoe were burned away owing to about 500C lava temperature. The leather parts and the sole were left as a framework.
    On 6th Oct. without any chance to get a helicopter for rescue, evacuation was necessary because of the risk of an infection. He managed to slide down the steep slopes of O. Lengai on his hands and right foot for most of the steep upper track, but was finally carried by a seat-construction and by four strong porters on their shoulders the rest of the way down. He was brought to hospital in Arusha right after the evacuation and flown out to Germany after further 24 hours. After a skin transplantation J. Klaudius is recovering very well and will not suffer lasting damage.

    Warning: O. Lengai is as dangerous as any other active volcano. We have experienced explosive eruptions, suddenly appearing lava fountains, several cone collapses, lava flash floods and flows with enormous quantity.
    Lava temperature of 500C is hot enough to burn someone seriously and because of the very low viscosity, this natrocarbonatite lava is extreme fluid and can flow very fast. But most difficult is the problem of rescue at Lengai like our example shows, though even the danger of the mountain itself and the weather should be taken very seriously. We do not recommend visits on Lengai without a guide or an experienced person.

    Information contact: Celia Nyamweru, Department of Anthropology, St. Lawrence University, Canton NY 13617 USA (Email:;
    Joerg Keller, IMPG, Albert-Ludwig-University Freiburg, Albertstrasse 23b, 79104 Freiburg, Germany (Email:;
    Christoph Weber, Volcano Expeditions International, Friesenstrasse 20, 42107 Wuppertal, Germany, Tel: 0049-202-4491897 (Email:;
    Frederick Belton, 3555 Philsdale Ave., Memphis, TN 38111 USA (Email:; URL:;
    for video-film clips contact: Marc Szeglat, Duelmenerstrasse 11, 46117 Oberhausen, Germany (eMail:, URL:

  • Lengai Report Jun. 2002

    Observation on Oldoinyo Lengai, Tansania, 18th June until 22th June 2002

    During the morning of 18th June 2002 Chris Weber from Volcano Expeditions International with a travel groupe, Jurgis Klaudius from the Institut for Mineralogy, Petrology and Geochemics of the University of Freiburg and the volcano filmers Marc Szeglat and Daniela Szczepanski reached the crater of Oldoinyo Lengai with several local guides including Burra Gadiye. Chris Weber left the crater with his groupe in the morning of 21th June while Mr. Klaudius and the filmers finished there observation and work at the morning of 22th June. The observation included:
    By the arrival 18th June the fresh looking and still black lava flows were visible from T49B on a length of 120 meters towards western directions. From T46 black lava flows streched towards NW, W, SW, and South on a length of 20 to 80 meters. The hornito T37B was covered with still black lava and propably had erupted recently. The flanks of T48 as far as to T44 were covered with black lava lapilli also propably from recent activity. The diameter of the T49 base (eruption center) increased strongly compared to august 2001.
    A new eruptioncenter was clearly visible half way between T46 and the West overflow an could be numbered as T54. The eruption site of T54 was an open lava pond with an overflow of about 40 meters towards the west. Black lava had covered older lava flows who had left the crater on his west side in Febuary 2002. A lava lake bubeling deep inside T48 was clearly heard during the days of our observation. The fumarolic activity and its temperature (> 125C) increased also from summer 2001 until summer 2002. Three recognizable relativly deep released single vibrations occured during our visit
    Activity and small lava flows were observed from T49B. On 18th June lava spattering from the top of T49B went on in intervals of intensitiy from 14:00 until 19:00 hours. The maximum height of the lava fountains of was arround 3 meters. A litle lava flow went from the top towards the norh east for about 50 meters. During the day of 19th June spattering occurred with a duration everedge of 30 minutes followed by one and a half our breaks of now activity until 04:15 hours in the afternoon. No more activity outside hornito T49B and other hornitos was observed until 22nd June. On 22nd June arround 10 m3 collapsed from the wall below the summit of T49B into the crater.

    NE part of the crater
    Picture of the NE part of the crater with T54 (c)C. Weber 2002
    Central part of the crater
    Image provided by C. Nyamweru(c), central area of Lengai crater 26 September 2002

    Lengai: map of the crater 2002

    Map of Lengai

    Lengai Reports 2003

    Around February 2003, the frequent visitor of Langai, Bernahrd Donth, has reported, that activity of T58B was very high. Overflows of this hornito occured and Bernhard estimated the lava pond inside the T58B (he looked inside) was about 30 meters width, so extended also under the T58 complex. He thinks, that the area T58 increased in size and altitude.

    Central part of the crater
    Image provided by B. Donth(c), central area of Lengai crater February 2003

    Short report about June/July 2003 Oloinyo Lengai observations by Chris Weber, VEI

    The crater of Lengai
    View from the top of Lengai towards the crater, June 30th, 2003 (c)VEI

    Fumarol temperatures at the NW rim overflow were 86 degrees celsius and inside a fracture at the base of T49C about 76 degrees celsius.

    From 29 June through 3 July 2003, a visit by Chris Weber revealed, that since the report from Bernhard Donth and others by visits Febuary 2003, most activity had occurred in the center part of the crater. Lava flows and hornitos out of the center part were strongly weathered. C. Weber noticed a new formed hornito NW of T56 and because of an open connection to T56 this hornito could be numbered as T56B. Lava penetrated once through the underground from T56B into T56. This T56B was on 29 June a collapsed hornito located at the north end and inside (integrated) of the huge T58B, T58 pont. This pre June hornito T56B erupted with strombolian typ during the visit of C.Weber. Observations by Burra Gadiye established this kind of eruptions of T56B also some days before 29 June.

    Only in averege the following facts discribe the activity of T56B. One third of the time of observations, a lava lake inside T56B spattered in common kinds with a strong, but non explosive release of gas.
    Another third of the time of observation the lava lake seemed calm (forced back or secluded), but a huge quantity of gas released outside the hornito T56B, simular in sound and power like a Boing 747 jet engine on full thrust. The period of this events lasted from 1 to 2 hours.
    Another third of the time strombolian eruptions accoured with very explosive lava spattering more than 40 meters in altitude. The strombolian intervals were between one and 30 seconds. The period of this events lasted from 10 minutes to 2 hours.

    Center part of the crater
    Central area of the crater with the black T56B, June 30th, 2003 (c) VEI

    Center part of the crater
    Sketch map of the central area, Aug. 08th, 2003 (c) Fred Belton

    Report from Fred Belton Aug. 1st until 8th, 2003.

    Just down from Lengai, camped in the South crater from 1-8 Aug. Heres some preliminary info on the visit. There were two active cones, T56B and T58B. T56B on several days produced strong strombolian eruptions with bombs reaching 50m high. Explosions were sometimes audible in the South crater. During other periods eruptions consisted of a narrow ash column ejected at times to 100m. Light ashfalls occured all over the crater and the rim, depending on the wind. There were two collapses of the upper fourth of T56B which resulted in particularly violent eruptions. T56 and T58 were no longer visible. There were no lava flows on the crater floor, just a very short one in the T58 "caldera".
    After spitting lava clots for a day, T58B began steaming heavily from a crack in its side and from other locations and then abruptly collapsed. Violent strombolian explosions blew blocks and bombs up to 50m high during a 15 minute eruption following the collapse. Later T58B produced ash puffs that were nowhere near as strong as T56B. A couple days later a lava lake in T58B overflowed slightly and then strongly bursting lava bubbles built a new section of cone toward the NE, in the direction of T56C.

    Dramatic activity and summary of 2003 (by C. Weber)

    Activity has continued intermittently since October 2002 (Bulletin v. 27,no 10). The summary report of 2003 is based on the observation made by Joerg Keller, Jurgis Klaudius, Fred Belton and Christoph Weber, as well as other information of visitors, collected by Celia Nyamweru. C. Weber visited Lengai latest in Febuary 2004. GPS-Data was collected again to provide a new and precise crater map. All altitudes are approximatly. C. Weber also measured temperature of fumaroles and lava flows. Lava samples were taken and are provided to research departments.
    During the first half of 2003, two new hornitos appeared in the center of the active crater at Oldoinyo Lengai at the T49 and T48 locations. A huge lava pond appeared at this locations and caused several lava flows in all directions. By midd of June (according to information by Burra Gadiye, a local Lengai observer), an unusual typ of dramatic activity started at both new hornitos. Strong degassing and rythmic explosive eruptions caused lapilli, ash and lava spatter being thrown up to 100 m above the hornito (F. Belton Aug, 2003 and others). Those eruptions can be best described as "strombolian activity". It continued until January 2004, accompanied by several lava flows, and had finally built up the tall strato typed hornitos at the T49 location (described as T49 or T56B) and at the T48 location (described as T48B or T58B). Note, that the summit of T48B is now just above the former T44 hornito, which is not visible anymore.

    Visit on Lengai by C. Weber February 2004:

    The crater of Lengai
    Pictures show the crater at Lengai after heavy rain and 4 days later dryed up by the sun (Feb. 2004, (c) C. Weber). The crater of Lengai

    Observations during Febuary 2004. On 10 February 2004, Chris Weber, Frank Lehmann and Rainer Albiez visited Lengai for 5 days. The summit of the tallest hornito in the center area of the active crater at Oldoinyo Lengai was at approximately 2886 m altitude (GPS), standing about 33 m above the surrounding crater floor to the north. This tallest hornito at the T49 location (T56B) was not active anymore, while T48B (T58B) had a lava lake deep inside it's hornito, clearly indicated by noises and tremor. The activity had changed to the common effusive and lava lake activity. This occured at the old T49 eruption center, also indicated by the activity of T49B during observation and an active new vent (numbered T49G by C. Weber) at the north flank of T49 (T56B), about half way up from its base to the north side.
    This new activity propably caused two collapses (depression) in the north flank of T49 (T56B), already visible since January 2004 (first described by B. Donth). The T49G vent, hosted at the upper collaps, had a steady degassing lava lake with many overflows during the visit of C. Weber. Lava penetrated the lower collaps at T49 and lava flows reached as far as to the NW overflow. On 12 and 13 February T49B spattered lava for some hours, feeding lava flows to the west (T51), finally escaped into a lava tube system. The lava temperature very close to the lava lake was measured at 588C. Aa lava flows not in motion anymore at flat terrain were measured between 480C and 500C. On 7 February C. Weber and R. Albiez heard a 30 seconds lasting paroxysm of T48B (T58B) as they were staying at the north slope of the neigbouring Karimassi volcano. During the visit on 10 February the results of this paroxysm were indicated by fresh lava spatters all around T58B (radius of 100 m) and the fact, that lava crusted bombs were found all around T58B.

    T56B and T49B
    View from the north rim towards the tallest hornito T56B and T49B (left of it), person gives scale. Courtesy by C. Weber.
    Lava lake at T49G
    R. Albiez standing on the slope of T56B, looking into the the vent T49G towards the west. Courtesy by C. Weber.

    Temperatures recorded by C. Weber.
    T40 lava lake28/08/1999529
    Pahoehoe flow near T4001/09/1999519
    Aa flow in motion01/09/1999516
    Pahoehoe flow near T49B03/10/2000507
    Aa flow in motion03/10/2000496
    Pahoehoe flow near T49G11/02/2004588
    Pahoehoe flow near T49G12/02/2004579
    Aa flow not in motion13/02/2004490
    Table 1. Lava temperature measured by a digital thermometer (TM 914C with a stab feeler standard K-Type). The instrument was used in the 0-1200 Celsius mode. Calibration was by the Delta-T method: values are +/- 6C in the 0-750C range, with at least 4 different measurements at one spot. Courtesy of Christoph Weber.
    Near T4928/08/199982
    Near T49C03/10/200075
    Hottest crack in the crater floor20/10/2002124
    Near T49C30/06/200376
    Table 2. Fumarol temperature at cracks in the crater floor, measured by a digital thermometer TM 914C (for modification see table 1.) Courtesy of C. Weber.

    Reports on O. Lengai (June/July/August 2004):
    (c) Weber, VEI

    (c) Weber VEI

    Report by Chris Weber:

    A group of VEI spent 6 days on Lengai from June 24th, until June 30th. No big change was found at the hornitos since Feb. 04. Half of the upper 10 m of hornito T56B had collapsed on it's east side. An active lava lake was inside this hornito and pured over several times throug the collapsed opening to it's east. The lava flows reached about 200 m to the east. The lava was rich on gas and at Aa'flows with an temperature of 560 degrees celsius. The hornito T58B spattert lava most of this day and some lava flows from this hornito reached about 150 m towards the south. The fumaroles at F1 had a temperture of 78 degrees celsius, at T46 hornito 150 degrees celsius. No significant change of distance was found at CR1-3. An Egyptian Cobra was seen at the track to the south carter.

    (c) Fred Belton

    Report by Fred Belton:

    After meeting Chris at Lengai on June 29th/30th, Fred has spent all together 4 weeks at the summit crater of Lengai.

    Crater rim overflow measurements (width in meter):

    NW overflow: 2 Aug 03 (135m); 29 June 04 (135m); 29 July 04 (135m)
    E overflow: 2 Aug 03 (44m); 29 June 04 (44m); 29 July 04 (47m)
    W overflow: 2 Aug 03 (17m); 29 June 04 (18m); 29 July 04 (18m)

    The 3m increase of the E overflow occurred during the eruption of T58C on 15 July, 2004.

    Description of activity:

    I arrived in the crater with 8 expedition members and approximately 30 local porters at around 0900 on 29 June in high winds, fog, and a dust storm. A group led by Christoph Weber was camped in the north crater. From that time through 1 July there was no activity except for a small bubbling lava lake located inside a hole at the rear of the lava platform in the half-collapsed cone T56B. Around 2000 on 1 July, ~ 30 square meters of the lava platform collapsed into a huge underlying lava lake. (I had walked with an expedition member across the platform about 40 minutes before it collapsed. Our discovery of the collapse such a short time afterward was a terrifying experience, and for several minutes we did not know if all of our group members were safe.) Over the next few days the strongly degassing lava lake formed a new platform similar to the original one. (Several times during the month, sections of T56B's overhanging NW flank collapsed onto the platform and lake, and near the end of July a large area of the platform collapsed again.)

    From 2-3 July T58B erupted repeatedly, showing strombolian activity and overflows. Lava flowed south, passing near the base of T47. The partially charred body of a mouse-size rodent was found on top of one flow, probably killed almost instantly as it tried to run across freshly erupted lava. 4 July saw some of the most intense activity of the month, with strong strombolian eruptions of T58B and several collapses of its vent area which released large cascades of lava onto the crater floor. Simultaneously, a tube-fed eruption of pahoehoe lava from T49G flowed across the NW crater rim overflow and down the flank of Lengai. Early on 5 July numerous eruptions of T58B sent lava flowing toward T47 at an estimated velocity of10 m/sec. After a mid-day pause, more flows and spatter came from T58B late on 5 July and before dawn on 6 July, with incandescent gas jets also coming from a second of T58B's vents. Around midnight on July 6 lava flowed out of the lake in T56B and onto the crater floor toward the east, entering the cave in T45 for a short distance.

    After very low activity from 7 July through 10 July, 11 July brought renewed flows and spatter from T58B and frequent but short (usually 2 minutes) episodes of loud degassing (incandescent gas at night) and spattering from the lava lake in T56B. This pattern continued until the morning of 14 July when eruptions at T58B became more explosive and small ash clouds were expelled. On the morning of 15 July a collapse in the vent area of T58B released large rapid lava flows toward the east. The episodes of degassing and spattering from T56B increased in frequency until 1500 on 15 July, when a small hole formed in the crater floor just E of T58B and began emitting visible gas puffs mixed with spatter. At this time the degassing episodes from T56B ceased. Activity of this new vent, T58C, rapidly intensified with strong degassing and an intermittent lava fountain that fed a large lava stream moving toward the south crater wall. By 1600 a paroxysm was in progress, with a 10-12m fountain and flash floods of lava that completely inundated the crater floor between T56B, T58B, T37, T37B, T45, and T57B. The new vent also ejected strong jets of ash and gas. Turbulent rivers of lava flowing at more than 10m/sec swept toward the S crater wall and the E rim overflow and completely surrounded T37B and T45. Flow rate from the vent was estimated to peak at 10 m3/sec. The momentum of the lava carried it nearly 3m up the W flank of T45 and obliterated the large cave within that cone. A surge of lava flooded over a 3m wide swath of vegetation as it poured over the E. crater rim and down the flank, instantly forming a huge cloud of steam and smoke that resembled a small pyroclastic flow. The smoke cloud was accompanied by a loud sizzling sound. A brush fire burned along the crater rim overflow as additional floods of lava arrived. These huge flows lasted for little more than 30 seconds and were separated by repose periods of 5 to 6 minutes. After sunset, incandescent gas could be seen flaming from the vent during the repose periods. Weak strombolian activity was seen in T56B. In the pitch darkness of the new moon, the orange glow of the lava was bright. Similar eruptions continued until after 2000.

    Early on 16 July the newly formed T58C was a circular pit ~2m in diameter with lava sloshing violently at a depth of ~2m. Two small sub-vents on the N and S edge of the pit were interconnected with the main vent. After virtually no activity on 16 and 17 July, early on 18 July lava built a small hornito over one of the sub-vents, and lava from it flowed halfway to the NW rim overflow. Bursting lava bubbles and small overflows began to slowly build a rim around T58C. By 19 July T58C was an open lava lake contained by a low crater rim. 20 July was an active day, with lava flows from T58C and strombolian activity in both T58B and T56B. T58B also produced moderate ash explosions. Slow growth of the new T58C cones continued on 21 July. The vent now consisted of two separate cones above an interior lava lake.

    From 1200-1600 on 21 July there was an exceptionally strong eruption of T58B with loud explosions, jetting of poor ash clouds, and spattering to great heights. Explosions blasted a new vent in the upper E side of T58B. At least four oval bombs ranging from 9-12 cm in length were ejected along with a great deal of lapilli and ash. Later examination of the bombs after breaking them open revealed that they all had a distinctive inner core and an outer layer ~1.5 - 2 cm thick. (A large natural arch that formed at the summit of T58B during this eruption collapsed at ~1700 on 24 July.) After 1600 on 21 July activity was low until the evening of July 22 when an area of the crater floor adjacent to the northern slope of T58C began to exhibit strong localized tremor and slight steaming. A small spatter cone later formed at that location, probably around 2330 (based on sounds heard by another visitor). At 0800 on 23 July, a sloping ~4 square-meter oval section of the crater floor immediately SW of the new spatter cone began to steam and vibrate. Tremor increased and ground movement was visible. The small section of crater floor was rapidly pushed outward and then sucked inward several cm like a vibrating membrane, juddering in time to the degassing sounds of lava in T58C just behind it. Abruptly it broke outward and a flood of lava ensued. Several explosions within the flowing lava may have been caused by pockets of dew on the crater floor. When looking into this new vent, which led horizontally into the sloping crater floor, sunlight shining down into the original T58C cones vas visible on the surface of the moving lava deep inside. The vent stopped erupting by noon and became sealed, but reopened at 1630, continuing its eruption. From 24 -25 July it produced a steady lava flow to the south that formed a well-developed tube/channel system extending to the T30 area. Many small hornitos erupting foamy lava had formed on top of the lava tubes near T58C by noon on 24 July. On the night of 24 July the two original cones of T58C grew in height; the E cone by successive overflows and the W cone by spatter accumulation. They were now both a little over 2m tall. On 25 July, extremely slow-moving clinkery aa lava flowed south. The eruption ended around 1600 on 25 July.

    There was little activity until 28 July when weak strombolian eruptions resumed in T58B. In the late afternoon T49G erupted for the first time since 4 July, but this eruption was much smaller and of shorter duration than the 4 July eruption. By this time I had been joined by Celia Nyamweru and two others, and while we were observing T49G a leopard on the W crater rim was observing us. During the night T58B became increasingly explosive and deposited spatter in all directions around the cone. At 0500 on 29 July activity decreased. Observations ended at 0700 when we left the crater

    Lengai: map of the crater February 2004 (C. Weber)

    Map of Lengai 2004

    Report on O. Lengai (February 2005):
    Areal view 14 February 2005 (c) T. Schulmeister
    Areal view 14 February 2005 (c) T. Schulmeister/ C. Weber (also 3 figures below)

    Report by Chris Weber:

    Observations during January/Febuary 2005. Bernhard Donth reported, that during his visit on 10 January 2005 hornito T49B erupted in many effusive lava flows escaping first time over the northern edge of the crater (see figure 1 - latest crater map). On 3 February 2005 Chris Weber and others spend 5 days on O. Lengai. The hornito T49B was as well active at that time with lava flows travelling to the north. Pahoehoe lava flows in motion (little Levées) at flat terrain were measured from 520 degrees celsius up to a maximum of 561 degrees celsius. The fumaroles at F1 had a temperature of 84 degrees celsius and at T46 hornito a maximum of 91 degrees celsius. No change in distance was measured at CR1-3 cracks cutting the upper crater walls. The hornito T58C had grown to approximately 2870 m altitude. A Spitting Cobra was seen close to the summit of O. Lengai. An overflight py plane on 14 February showed no change since then, but do give an excellent view of the crater ant it's central hornitos (see figure 2).

    Areal view 14 February 2005 (c) T. Schulmeister Areal view 14 February 2005 (c) T. Schulmeister Areal view 14 February 2005 (c) T. Schulmeister

    A table with the chemical analysis (by Frank Moeckel) of a lava sample 2005 - ENTER here!

    Report on O. Lengai (July 2005):

    Report on the activity of Ol Donyo Lengai, July 3-5, 2005 by Brnard Marty

    On July 3-5, 2005, a Tanzanian-French-American scientific team composed of Pete Burnard (CRPG-Nancy, France), Tobias Fisher (Univ. New Mexico, USA), Chamba Makene (Geological Survey of Tanzania), Fredrick Mangazini (Univ. Dar el Salaam), Bernard Marty and Fabien Palhol (both at CRPG-Nancy, France) visited the crater. The volcanic activity is described below following the maps and hornito designations published by Chris Weber (http://www.v-e

    At the time of arrival (08h00 local time, 03/07/2005), sporadic lava flow of the AA type was emitted from a vent situated at the base of T56B, which was itself disrupted by an explosion, leaving an open cavity of about 15 m in diameter. The lava was flowing eastward towards the eastern overflow but never reached the crater rim. On July 3rd, 2005, a survey of temperatures indicated that most of vents emitted gases at a temperature close to 84 C, close to the water boiling temperature at this altitude (=88 C), or lower. These included the F1 fumarolic area and a steaming area on the western flank of T37. A temperature of 124.6C was recorded near the base of T46 between T46 and T58B.

    The following day (July 4th, 2005), gas sampling began at T46, while no lava nor explosions were active. At approx. 11h30, lava was observed spilling out violently of the eastern, fractured lip-edge of T58B and flowing towards the eastern overflow. Sampling had to be interrupted at T46 due to the risk of a sudden lava flood in the sampling area, a real possibility if the thin western wall of T58B fractured following thermal erosion of the wall by molten lava in the lava lake. One hundred meters south of T46, close to the base of T47, a deep hole approx. 1.5 m dia, boarded by lava splashes and piercing a pahoehoe lava flow was emitting high temperature gases with no visible steam. A thermocouple with a wire of 4 m was inserted into the hole (it did not reach the bottom) and indicated a temperature of 168C at this depth. Gases were sampled through a funnel attached to the end of a 4m-long pole and connected by several m of Tygon tubing to the gas sampling equipment (the several m of tygon tubing for the comfort and safety of the team). Each "Giggenbach" bottle required nearly one hour to fill, indicative of limited atmospheric contamination (low N2 concentration) of the gases. After 4 hrs sampling, the funnel was lost in the hole presumably because the temperature was higher than the melting point of the nylon funnel.

    A lava pond, not directly observed but for which bubble explosions were clearly visible, was discharging surges of lavas towards the eastern rim, while the adjacent T58C cone, now higher than T58B, was discharging high velocity gases which from time to time splashed lava. The eruption lasted the whole day and the following night, with variations from steady state outpouring with lower degassing to burstles of large bubbles with enhanced lava emission. By the afternoon the lava, which was now overflowing the eastern slope of the volcano, ignited a bush fire. The lava outflow was estimated to be approx. 0.3 m3/s, with a speed of approx. 2 m/s in the flat area towards the volcano flank.

    The camp originally proposed by the Masai porters was to be close to T58B, S-SE of the active vents at the foot of the southern wall; this part of the crater was protected from the wind by a some rockfalls and the cook wanted to avoid sand blowing into the meals. However, the emplacement was evaluated to be risky by the team and the tents were instead placed on the S-SW side of the crater; here, the camp was much further away from the active vents, was in the opposite direction to the lavas, was shielded from any potential lava flows by some rockfalls and also permitted direct access to the crater rim. However, the cook established the "kitchen" in the original S-SE camp. On the evening of July 4th, a small lava flow went close to the natural entrance of the "kitchen". The Scientific Team moved the scientific equipment out of the "kitchen" and urged the 5 Masai remaining in the crater to move to the tent area, without success. At 5 AM in the morning of July 5th, lava flows suddenly invaded the "kitchen" area to a depth of over 1m; fortunately the Masai sleeping there escaped safely, and even removed the food to safety. Breakfast was finally prepared directly on the 1 m thick lava that had just invaded the area that was proposed first as a camp. This episode which could have had dramatic consequences illustrates well the fact that there is no safe area within the southern crater. Camping should be limited to the northern crater or, as a bivouac, in elevated areas in the southern crater as far as possible from vents and directions of lava flows.

    contact: Bernard Marty, CRPG-CNRS, BP 20, 54501 Vandoeuvre Cedex France;

    Report on O. Lengai (Aug 2005):

    Lengai 2005 (10 Aug) initial report by Fred Belton:

    Dear friends,
    This is an initial report about Lengai I'm sending out to people who may be interested. I will get back to all of you with a more personal message as soon as I reach home next week.
    Came down from Lengai Aug 9 after 21 nights on top. The visit was extremely different from all my previous visits because after 3 eruptions from T58C on July 20 and 21, one of which lasted for 20 hours, there was no further activity through our departure on Aug 9. According to Burra, the most recent eruption prior to 20 July was on 9 July when large flows completely covered the campsite in the E part of the crater used by some menbers of my 2004 expedition. Large areas of vegetation on the E flank were burned by resultant brush fires.

    Burra is going to report to me on the date of the next eruption to come.
    Photos indicate that there may have been infrequent activity at Lengai at least back to May 15. No new cones have formed since JUly 15 of last year when T58C was born.

    For more details visit the website of Fred Belton (see link below).

    central area (c) Marko Schmiedel (c)Marko Schmiedel
    Figures form the left (c) Marko Schmiedel: central area of hornitos looking W from a plane, lava from T58C during the night, Feb. 2006.
    Lengai reports from December 2005 until February 2006:

    The local Masai and O. Lengai guide William reported of an flank eruption at hornito T49B during a visit on 20 December 2005.

    Bernhard Donth reported, that at the time of arrival (1100 on 04 January) lava escaped from T49B. Spatter and little flows went in all directions with an eruptive culmination every 30 minutes until activity decreased at 1500 that day. One bigger lava flow had reached as far as the NW overflow. Until the morning of 06 January when B. Donth left the crater no more flows were observed.

    Christoph Weber arrived with a film team at the crater of O. Lengai 1100 on 02 February. C. Weber took scale of the the tallest hornito T49B with approximately 2890 m altitude (GPS) standing ~60 m above the crater floor at the NW overflow. No recent eruption had accured at T49B, but strong noisy degassing took place sometimes. Just east of T49B the hornito T56B had convecting lava deep inside and some only days old lava flows streched from three different vents at T56B towards the east as far as the E overflow. After the major collaps of T56B in 2004, this hornito (standing at approximately 2875m altitude on 02 Feb.) has nearly grown up again to its former shape and altitude. Also from T58C and the collapsed T58B hornito some days old lava flows were found on the eastern slopes passing the old and weathered T37, T37B and T45. The caldera shaped collapsed T58B had it's flat flour at ~2865m altitude with four active vents inside. Lava convection was close to the surface of T58B and inside the tall T58C.
    At 1300 on 02 February a sudden increase of activity took place with two lava fountains at T58B lasting only some seconds. At the same time lava spilled out at all T58B vents, a T58C flank vent to the east and at a T56B vent. A lava flow went from T58B ~50 m towards the east. Lava spatter with lava flows inside T58B and up to ~150m towards the east occurred as well the following 3 days. From 0500 until 0730 on 06 February higher activity occurred with lava outflow at T58C. T58B showed also higher activity level from than on until C. Weber left the crater on 07 February morning.

    Lava temperatur was measured with 519C at an Aa lava flow with cooled surface and not in motion any more. Fumarol temperatures were measured as well. During an observation flight on 13 February C. Weber noticed new lava flows from T58B and T56B vents. Crater rim overflow measurements on 2 February 06 indicate no change since last reported in Bulletin v. 30, no. 4 by Fred Belton (width in meter):
    NW overflow: 3 February 06 (135m)
    E overflow: 3 February 06 (72m)
    W overflow: 3 February 06 (20m)
    N overflows: 3 February 06 (1m at each of three locations)

    central area central area
    Figures form the left: central area of hornitos looking NW (person at arrow gives scale), Looking N from the summit at 2960m

    Various attachments for others:

    Visitors on Lengai:

    02 February, Chris Weber and 4 participants (until 07 Feb.) plus 2 german day visitors
    03 February, non
    04 February, 2 germans camping one night
    05 February, 2 dutch, one german day visitors
    06 February, 2 russian, 2 german dayvisitors
    07 February, non

    Lava samples: Taken at 1330 on 02 February from gasrich Pahoehoe flow at T58B shortly after cooling off.
    Wind directions (over 5000m altitude) and climat on Lengai 02/2006:

    02 February, wind NE, closed high clouds, dry
    03 February, wind NE, clear, dry
    04 February, wind SE, clear, very hot, dry
    05 February, wind NE, some fog at the summit only, dry
    06 February, wind NE, clear, dry
    07 February, wind SE, clouds from midday on, dry

    Measurements of cracks:

    CR3, 4,63m -0,01m
    CR2, 4,79m -0,01m
    CR1, distroyed

    NEWS: Villagers flee as volcano erupts

    (SOURCE: Guardian (c)ippmedia ,Date: 2006-04-01 10:44:07)
    By (c)Adam Ihucha, Arusha
    Hundreds of villagers living around Mount Oldonyo Lengai in Ngorongoro District have been forced to flee their homes after the volcano erupted on Thursday, 30th. Eyewitnesses said they heard a rumbling noise before the volcano began discharging ash and lava, prompting local residents to flee the area in their hundreds. District officials estimated that about 3,000 people from Nayobi, Magadini, Engaruka, Malambo, Ngaresero, Gelai Bomba and Kitumbeine villages left their homes within a few hours of the eruption, adding that most of them trekked to villages in neighbouring districts. Ngaresero resident Ibrahim ole Sakay said alarm bells were sounded after smoke was seen coming from the peak of the mountain, adding that people panicked after lava began pouring out of the volcano. 'People had to flee their homes in order to save their lives?it was the only sensible thing to do because a volcano eruption can easily obliterate whole villages and communities,' he said. He added that the eruption destroyed vegetation and polluted water sources, but no casualties were reported. 'Thank God, nobody was injured although smoke is still visible at the top of the mountain,' he said, adding that it was unlikely that those who fled their homes would return while smoke was still bellowing from the peak. Ngorongoro District Commissioner Assey Msangi told The Guardian by telephone that it was not unusual for minor eruptions to occur at the mountain. 'I have not yet received an official report, but eruptions are a common phenomenon at Mount Oldonyo Lengai because they occur almost every year,' he said. Mt Oldonyo Lengai is located in the Rift Valley, about 120 kilometres northwest of Arusha. It is the only volcanic mountain in the world that discharges the highly fluid natrocarbonatite lava that usually contains almost no silicon. Natrocarbonatite lava is also much cooler than other lavas; averaging only about 950 degrees F (510 degrees C) compared to temperatures of over 2,000 degrees F (1,100 degrees C)?for basaltic lavas. At about 370,000 years old, Oldonyo Lengai is the youngest big volcano in this part of the Rift Valley.

    Summary: "Paroxysm" late March 2006 (C. Weber) ... so it has cooled down ...!?

    (based on information sources from Celia Nyamweru, Fred Belton, and others)
    ...The eyewitness David Peterson reported to Celia Nyamweru, that a smoke column was visible on 28 March 2006, which propably marks the start of a bigger eruption on Oldoinyo Lengai. This ash column could have been triggered by a violent degassing (lava fountain up to strombolian and explosive eruption) or a mayor collapse of the hornitos T56B and T58B because of flank uplift by lava. Both phenomena occurred during recent years and were described for example by F. Belton (Bulletin v. 30, no. 4) and C. Weber (Bulletin v. 29, no. 2) and may come together in one single event. This type of eruption is not comparable with the last big explosive eruption period of 1966/67.
    On 30 March a lava flow on the lower slopes of O. Lengai was observed. Aerial views on O. Lengai indicated that a large lava flow had traveled from T58C (and T58B?) to the southeast and clockwise over the south part of the crater. At the west overflow the lava escaped on the outer flank of O. Lengai running down mainly inside a gorge (deep erosion gully/korongo) until approximately 1000 meters altitude. Some vegetation at the crater rim and along the gully was ignited by this lava, but because of rainy season the fire was not very severe or prolonged. During the first days of April no activity was observed on the outer flanks of O. Lengai. Reports of evacuations of the Maasai communities around O. Lengai during the first days of April were not confirmed, though the Tanzanian government's recommendation to evacuate was reported by the local media (e.g. Guardian, Arusha, by Adam Ihucha, 1 April).
    Michael Dalton-Smith flew over O. Lengai on April 4 and reported to F. Belton that fresh looking black lava covered the already grey lava flows from 30 March inside the gully on the western slope. Visitors who climbed Lengai later on reported about a big lava channel, 5 meters wide and 2,5 meters deep, starting from the hornito T58C, following the flow field to the south west and then continuing outside the crater at the west overflow where there was a channel 8 meters wide and 3 meters, probably deepened by thermal erosion. The collapsed hornito area at T56B and T58B measured about 30 meters north to south and 15 meters east to west with an active lava lake inside. The tall hornitos T58C (partly collapsed to the southeast) , T49B and T57B were mostly not affected by the collapse, and as wll the west part of T56B remained standing.

    Lengai: Map of the crater February 2006 (C. Weber)

    map of Lengai 2006 (c) C. Weber

    WARNING by the frequent visitors of Oldoinyo Lengai (Keller, Nyamweru, Belton, Klaudius, Weber): Lengai is not a gentle "toy volcano". Do not climb hornitos and avoid getting close (min. 100 m) to any erupting hornito, unless you know this volcano very well. The red Spitting Cobra, the Egyptian Cobra and Pythons were all seen at the top of Lengai (2900 m) and on the slopes. A leopard may stand infront of you as well on the top of Lengai and watch carefully the baboons and craws. If you think of camping up there, do it in the south crater and NOT in the active crater. Accidents have nearly caused death to victims camping in the active crater.

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