Jan 2006: Bernhard Donth reported, that at the time of arrival (1100 on 4 January) lava escaped from T49B. Spatter and little flows went in all directions with an eruptive culmination of 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 on 06 January when B. Donth left the crater no more flows were observed.
Jan 2006: Christian Mann and his family sent me several photos from their climb of 10 Jan. They reported no activity except some degassing from T47. Their photo from the summit shows a white and brown crater with no indication of recent activity. However, it appears that during the previous weeks lava has filled up the large open vent of T56B and has flowed from there and possibly other locations onto the NE part of the crater floor.
Feb 2006: 2 - 7 Feb crater visit. 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 at 2830 m. No recent eruption had occured at T49B, but strong noisy degassing took place sometimes. Just east of T49B, the T56B hornito had convecting lava deep inside it’s cone and some lava flows only days old 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 2875 m altitude on 02 Feb.) has nearly grown up again to its former shape and altitude. Also from T58C and the collapsed T58B hornito some lava flows only days old were found on the eastern slopes passing the old and weathered T37, T37B and T45. The caldera shaped collapsed T58B hornito had it’s flat flour at ~2865m altitude with four active vents inside. Lava convection was close to the surface of T58B and depp inside the tall T58C at arrival (1100 hours) on 02 February.
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 caldera and up to ~150 m towards the east. Lava spattering and little flows at T58B occured as well the following 3 days. From 0500 until 0730 on 06 February higher activity occured with lava outflow at T58C. T58B showed also a higher activity level from than on until C. Weber and team left the crater on 07 February morning. Lava temperature was measured with 519°C (see Table 1.) at an Aa lava flow with cooled surface and not in motion any more. Fumarol temperatures were measured as well (see Table 2.). 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 meters):
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)
Feb 2006: Chris DeVries and a group of students from Mcgill University visited Lengai from Feb 25-26. He reports: "We arrived at the north crater at approximately 10:40 AM, February 25, after having ascended approximately via the northwest, starting at around 5:30 AM. We only had direct sun for the last 1.5 hours of the climb, making it quite bearable. There had also been some rain during the night, wetting the sand and making it hold better when stepped on. Many summit hornitos were intermittently visibly degassing, including but not limited to T37B, T45, T46, T47, and T51. Upon arrival at the centre collection of hornitos, intermittent (every 5 minutes or so), loud bangs were heard from within the volcano. T58B was spattering a bit when we got there, and you could hear the magma sloshing around, but nobody dared go close enough to look inside due to the spatter. A small flow had erupted from this vent earlier in the day, it was still very black and hot. It appeared that the flow had not erupted too violently, perhaps it just overflowed a bit. It proceeded for maybe 10 metres, so it must have been relatively short-lived too. T57B had a large opening to its northwest, but it did not appear that any recent flow had come out of this opening (at least not within a few days). It was possible to essentially walk right up to this opening and stare into the cone, where lava was visible sloshing around. It was quite noisy as well, a bubbling/sloshing noise. This lava was sampled using a simple soup ladle on a metal wire. About 30-35 minutes after the lava was sampled, the base at the south-southeast ruptured, and the lava inside drained out quickly and violently, with much spurting and bubbling. The flow proceeded to the east overflow, and we left after about 10 minutes witnessing this eruption, due to concerns that another cone (perhaps one we were standing on or near), could experience the same style of eruption, or even collapse, due to the partial emptying of the magma chamber.
We camped in the north crater at the advice of our guides, who said it was quite safe. During the night, some rare rumbling noises were heard and felt (quite easily distinguishable from the thunder we heard…a Serengeti storm hit us hard and fast, but our camp held fast, though people got wet). We left in the mid-morning (9:00 or thereabouts), after having sampled the previous day’s flow. Vents were again visibly degassing.
March 2006: Rick Rosen and his wife, Heidi, flew over Lengai on 13 March and photographed the crater. Although there appeared to be no activity at the time, there were many lava flows which had recently turned white, with several still showing dark areas, indicating that they were not too many days old. Narrow flows extended in all directions from the central cone mound, and a small flow originating on the upper part of T49B extended across the NW crater rim overflow and a short distance down the flank of Lengai. Lava also appear to have reached the E crater rim overflow. Most of the flows appear to have been subject to the same amount of weathering, except for the flow down the NW flank, which looked more recent. This suggests than most of the flows may have resulted from a single period of activity several days prior to the observation.
March 2006: Serge and Sandrine Magnier of France climbed Lengai on 14 March and reported that there was fresh lava on the crater floor that had probably flowed during the night. Photos of the lava show thin, fine textured aa flows, very black, originating from an unidentifiable source in the central cone cluster. They reported that three days earlier, while they were trekking in an area near Lengai, they heard a rumbling noise and saw a puff of "smoke" come out of the crater.
NOTE: Information below on the March-April 2006 activity would be very limited without the help of Michael Dalton- Smith, Achmed Phillips of Basecamp Tanzania, Dean Polley, Matthieu Kervyn, Amos Bupunga, and Matt Jones. Their help is greatly appreciated.
March- April 2006: A large eruption of Lengai has been reported for 30 March. Several news sources, including CNN, have reported a major eruption at Lengai with evacuations of up to 3000 people from several villages, some quite distant from Lengai. As of April 5, there is a great deal of contradictory information about this eruption. It seems that news media and people distant from Lengai are reporting explosions of rock and ash, but that people living and working near Lengai have reported a smoke column followed by a very large lava flow down the W flank of Lengai to its base, but no explosions or ash. All evidence now indicates that there has been no explosive activity and that this is a very large eruption of lava only. The following are from emails I have received from Michael Dalton-Smith who has provided extremely useful and interesting observations.
On April 1 Matt Jones climbed and reported: "Speaking to people in Ngare Sero they were saying that activity started on the 27th, this was backed up by the Ngorongoro District Commisioner who we ran into on the lower slopes. He said that a new crater on top meant it wasn't safe to walk anti-clockwise round the crater, so I assume he had spoken to someone else who had been up between the new activity and the 1st. There is a fairly large lava flow down the western flank which is visible for almost all of the climb about 200 meters to your right on the way up. As we summited in the dark we didn't see any lava activity (nothing was glowing) Although what the DC had told us was true, the new eruption had made a big hole to the left of the climb up and was pouring out plenty of smoke so we walked across the floor of the main crater to avoid it. The next day there was lots of white smoke activity from the hornitos, there was also plenty of steam coming from fissures all around the rim. 2 central hornito's had been blown open relatively recently (according to my friend who has been up 6 times before)". A photo by Matt Jones appears below.
On April 4 M. Dalton-Smith wrote: "I actually just did a fly over lengai about an hour ago and have some photos of a very large lava flow down the climbing root. I am not sure if you can still climb.A bush pilot did observe the eruption on the 30th, justa fountain and flow, noash cloud.Report from local pilots are that the eruption has in fact stoped. We did not see steam or any evidence that this flow is still hot or flowing.The volume was considerable for l|}lengai. No report of any tourist on top at the time. The new lava flow runs down the length of the mountainand into a corrongo (gorge) It is over 1 km long. The majority of the flow was contained in the channel next to the climbing path. The crater was covered by cloud unfortunately!" And on April 5 he wrote: "I drove from Seronera last night to the crater, and had a great view of lengai without clouds. I noticed something that looked odd at the summit, and quickly looked at it through binoculars. It appeared to me that there was a huge fountain out of one of the hornitos, it was tough to tell though as we were really far away. I did see fluctuation in size and there was no drift due to wind. After a minute I preped my video camera with a huge lens (2600mm) and video the summit. THe fountain had stopped. I re checked with the binose, and notice what I had seen as fountain had stopped. The over all structure of the horinitos were there, but it looks like the new one that has been rebuilding lately (you should know the one I am talking about) is about half the size it was. All horintos had black smoke coming out of them. I will follow in 2 days time with pictures from my video showing the light smoke. It is hard to tell from the distance I was at what is going on, but it is clear there is still activity going on. There appears to be a lake up there about the size of the large hornito base on how the smoke was rising. I noticed the channel on the flow was shinny, possibly the flow in my picture was active at the time."
Amos Bupunga visited the crater on 7 or 8 April and wrote "The mountain is still throwing lava although it is not flowing outside of the new lake.The lava came out on 29th March flow was only 2km left to reach the Masai boma who live on the foot of the mountain. Since that day the volcano is still active up-to-date. Up to this moment no one has vacated the place as you had informed before. People are still there. The lava that came out had covered almost the Northwest to the southeast crater for the depth of 2m and made an outlet of 2.5m depth at the west where the lava flow out fro m the crater and the width is 3m."
Lava flow of March 30 on the west flank of Lengai. It passed across the West Crater Rim Overflow (as determined by photographic analysis by Joerg Keller and a second photo by M. Dalton-Smith. It appears that there may have been a subsequent flow, possibly earlier in the day of this photo (April 4) or April 3. The black lava appears to be covering an older gray lavaflow. Photo courtesy Michael Dalton-Smith.
Cell phone picture made by a driver of Basecamp Tanzania on March 30. This plume is either a sudden release of water vapor from a vent or from vegetation being covered by a lava flow. Vegetation could produce such a plume from vaporization of the moisture in the plants and also from combustion. A similar plume was formed on 15 July 2004 when a large area of vegetation was abruptly covered up by lava.
Remote thermal monotoring of Lengai by satellite (MODLEN data downloaded and analyzed by Matthieu Kervyn) suggest that there was an increase in activity around March 11 - 13. Aerial photos made by Cristine Mentzel and Rick Rosen on Mar 11 and 13, respectively, indicate numerous small lava flows extending in all directions in the crater from the central cone cluster. Thermal alerts on March 25, 27, and 29 indicate a small but intense area of activity possibly in the form of a large lava lake. This theory is supported by the photos made by Dean Polley showing that there has been a huge collapse of the upper parts T56B and T58B which probably contains or did contain a lava lake. (Such a lake was described by Amos Bupunga above during his visit on April 7 or 8 although he did not specify its location) A thermal alert at approximately 10:55 PM on March 29 probably indicates the lake again or the start of the large eruption that sent lava flows to the base of Lengai and prompted the news reports. A thermal alert covering pixels on a large area of the flank on April 3 probably indicates a second flow of lava to the base of Lengai (See the above April 4 photo by Michael Dalton-Smith showing fresh black lava covering the lighter-colored lava of March 30).
The following 2 images are cropped sections of high resolution pictures taken by Dean Polley during an April 1 overflight of the crater:
The photo above is of the central crater looking toward the south. There is a very recent large collapse of cones T56B and T58B which appear ro have merged together into one cone recently. The sharp edges make the collapse look quite recent, possibly around March 25 when MOLDEN indicated a thermal alert on one pixel of the crater floor. Photos by Rick Rosen show that the collapse had not occurred by March 13. The cone just behind the collapse pit is T58C. At its SE base appears to be a new vent with prominent lava channels leading away from it to the SE. It appears that lava from this vent filled up the low lying areas of the south part of the crater and then began to flow across the West Overflow and down the flank. A similar eruption probably occurred again on April 3. It is likely that a large amount of the lava was flowing through deeply buried tubes curving to the right and not visible in the photo, which would be typical during an eruption of long duration. The large cone on the right is T49B. The light color of the lava only two days after the eruption suggests that some rain might have fallen during the prior 48 hours. Image courtesy Dean Polley.
The photo above is a view of the West Overflow looking slightly SE. A large open lava channel is seen on the crater floor near the rim.The deep channel on the flank indicates a strong flow of long duration as there is very significant thermal erosion. The channel was estimated by Amos Bupunga to be 2.5m deep. Evidently lava again flowed through this channel on April 3. Image courtesy Dean Polley.
The image shows the central cones on April 1. T58C appears to have been split in half, with its southeastern half now missing. An old conduit to its former summit can be seen in cross section. This was evidently the source of the lava passing over the West Overflow on March 30. The rim of the large new collapse pit can be seen just beyond. Image courtesy Matt Jones.
May 2006: Jean Perrin and 4 others from Reunion Island visited Lengai from 6 – 11 May. He reports: “Unfortunately, during our stay on the top of Lengaï (4 days and 3 nights) we did not see any active lava flow but only little gas and smoke activity at some hornitos and some rare explosions (unless it was the sound of rocks collapsing). A very large collapse occurred during this last eruption and we can say that hornitos T56B, T58B, T58C and T57B do not exist any longer! We did not observe or hear any lava lake activity at all in the collapsed area neither in the hornitos .The crater floor is covered with a thick ash layer and does not look like before at all. The lava flow almost reached the boma in the low slopes: you will see that on our photos. Fortunately, we have discovered very beautiful white stalactites (ice like) formed by rains and infiltration/dissolution of minerals elements from carbonatite lava, located under the edges of this recent (march/april) lava flow channel near the T37 hornito and also near the west overflow.”
May 2006: Tobias Fischer reports: "We were there on May 12 and 13, 2006. We did not see any activity but the crater was filled with old lava, much higher than what we saw the previous year. We noticed the very large collapsed come with sharp rugged edges (The T58B area). We measured the SO2 flux using mini DOAS but emissions were low, same as last year. We sampled lavas and what seemed lto be carbonatite tephra, the composition is basically identical to last year's lavas. What we did notice, however, was discrete rumbling deep inside the volcano. The rumbling would occur for several seconds (up to 10) and up to 15 times per hour. We also felt very slight shaking of the ground associated with the rumbling."
May 2006: Matthieu Kervyn reports: “During our stay up the volcano (May 21- May 28), there has been no eruptive activity at all except for fumaroles from cracks in the rim and from most of the hornitos (especially in the afternoons). The collapse pit in the middle was enlarging through rim collapse. Visual inspection show that the collapse pit might soon cause instability of the very high T49B cone. Masai guides were also expecting T49B to collapse soon. For the rest, there was some deep some and tremors felt several times per hourswithin the North crater, as if rocks were collapsing beneath the crater. This is not clear what these sounds are but they are frightening and they must result from some rock movement within the upper part of the edifice."
June 2006: Matthieu Kervyn later reported that on June 20 remote sensing using the MODIS algorithm indicated a strong thermal anomaly in the crater of Lengai. This is likely to correspond to the new lava in the SE part of the crater and the two lava lakes that observers in July and August have reported below.
July 2006: Beginning 13th July 2006 Steve Beresford, Michelle Carey, and Mark and Rene Tait, spent two nights on Oldoinyo Lengai. Here are some excerpts from their report: " Activity over the two observed days was limited to abundant fumarolic activity from the crater rim and central hornitos. They noted a recent major lava flow in the south-eastern part of the North Crater. The excellent preservation (grey colouration) suggested a very recent eruption. Guides confirmed the lava flow was two days old. (Ed. note: This date as reported by guides may not be correct). This lava flow emanated from the southern end of the lava lake and crater that now dominates the centre of North Crater.” Much of the central hornito cluster that dominated the pre-March morphology of the north crater has been destroyed. The dominant feature of the North Crater on July 13th is a wide (120 m x 120m) crater and a recently active lava lake. Clear evidence of south/southeastern lateral withdrawal is present in the form of two southern drained lava tubes at the base of the current lava lake level. The southern margin of the lava lake is very unstable and periodic collapse of the crater walls was common over the two days. The northern margin of the crater is marked by a steep collapse scarp in the impressive hornito T49B. Talus breccia from this scarp is present partially infilling the northern part of the lava lake. Numerous scarp collapses (associated with abundant seismic activity) was a constant reminder of the ephemeral nature of the current crater/lava lake outline. Tide marks within the lava lake record former lava high stands during the recent months. Two southeasterly and southerly training tubes are present. Both record the lateral draining of lava during the July (?) lava eruption. The southern tubes that emanate from the central lava lake appear to connect to the hornito T37B. The majority of the lava flow of July (?) eruption appears to have come from this hornito. The reduction in lava lake level and southerly flow direction suggests the lava lake dramatically drained to the south and was the cause of the T37B eruption. Clastogenic products surround the T37B suggesting early mild Strombolian/Hawaiian style activity preceded/accompanied effusion as is typical of recent north crater volcanism. The lava flow itself is dominantly slabby to spiny pahoehoe with many aa and frothy pahoehoe breakouts along the eastern margin. This flow has all the characteristics of an inflated slabby pahoehoe flow field. Very small toothpaste pahoehoe flows emanate from the slabby pahoehoe flow front. "
Aug 2006: Daniela Szczepanski, Andreas Ramsler, and Norbert Fischer camped on Lengai from 31 July – 5 Aug and saw no activity other than smoking cones and rockfalls in the collapse zone.
Aug 2006: Fred Belton, Peter Elliston, and Jennifer Elliston camped on Lengai from 4- 8 Aug. Report follows:
(For photos see 2006 Expedition.)
Central Crater Collapse: Since March 2006, ~ 8000 m2 of the central crater floor has collapsed. Photographs by several observers indicate that the collapse began just prior to or during the eruption of late March through early April 2006 and is an ongoing process. As of 8 Aug, the collapse zone consists of two collapse pits, designated CP1 and CP2, plus a fractured area between the two pits and south of CP1, where large sections of terrain have broken away from the crater floor proper and subsided by 1-3m. The displaced sections have also tilted at various angles and are separated from one another and the crater floor by 1-2m wide fissures. The fissures contain numerous large lava boulders composed of lavas that were altered by weathering and then lithified.
Cones T58C, T56B, and T58B have collapsed into CP1 and are completely gone. Further enlargement of CP1 has also claimed the SW half of T57B, the SE base of T49B, and the E half of T46. The SW half of T37B has collapsed into CP2. The magnificent cone T49B, visible from the Rift Valley floor, appears likely to collapse in the near future. Failure of its SE base has resulted in a talus slope that spills out onto the floor of CP1.
CP1 and CP2 are each ~10m deep with respect to the lowest point on their rims. CP2’s floor and E side is talus-covered, but CP1 has a bi-level floor of slabby pahoehoe lava, the surface of a frozen lava lake. Horizontal “high lava marks” are evidence that the lake existed at several levels before draining. A wide lava channel exits CP2 to the SE, near the base of T37B, indicating that it contained a lava lake which overflowed onto the crater floor (flow F1) during Lengai’s most recent eruption. From the lowest point of CP2 a subterranean tunnel slopes upward to CP1, interconnecting the two pits. The floor of the tunnel is entirely covered by talus from its unstable walls and roof.
March – April 2006 lava flow: A prominent open lava channel, with a smaller channel diverging from it, leads SSE from CP1 past T37 and then winds W and NW to the W overflow. This was the route of the lava that flowed from T58C to the base of Lengai during the exceptionally strong activity that occurred from approximately March 25 – April5, 2006. Near CP1 the channel is deeply thermally eroded to a depth of ~3m and is nearly closed at the top. A large overhanging ledge contains an impressive array of dead stalactites. The channel becomes indistinct in the S part of the crater but again becomes prominent near the W overflow where in places it attains a width of ~5m and depth of ~2.5m. Just below the W overflow there is a large chasm in Lengai’s flank carved by thermal erosion to a depth of 5m. The chasm extends about 20m down the flank of Lengai and has a width of ~12m. Its sides appear unstable and prone to collapse. Immediately downslope of the chasm, the lava entered an existing gully and cannot be easily seen again until the slope moderates near the base of Lengai. Here the lava lies only a few m from the climbing track and continues to an aa field at its terminus about 3km from the summit. The terminus of the flow lies within 1km of a Maasai boma, which was the only habitation evacuated as a result of the eruption. The lava channel near the climbing track is ~3m high and at one point has formed a tumulus ~5m in height. A video of this part of the lava flow made during the eruption, from the escarpment W of Lengai, shows a rapid, turbulent flow with blobs of lava becoming airborne. The lava near the base of Lengai has a dark gray-black coloration and is less weathered than might be expected based on its age of 4 months.
Lava flows from the same eruption also covered much of the S part of the crater floor to a depth of at least 2m. Based on the indistinctness of the main lava channel in the south part of the crater, it is likely that the low areas of the southern part of the crater were filled by lava prior to spilling over the W crater rim overflow and down the flank of Lengai. T27 and T30, formed in 1993, were completely covered by this flow and can no longer be seen.
Activity: During 4-8 Aug there was no activity other than degassing of cones and fumaroles. No lava could be heard at depth. Occasional rockfall occurred in the collapse zone.
During the most recent activity lava flowed from T37B and CP2 and spread over the SE part of the crater floor. Remote sensing data (MODIS) analyzed by Matthieu Kervyn indicates that the eruption probably occurred on 20 June. An Aster image from June 29 shows new dark lava in the SE part of the crater. During the eruption lava lakes existed in CP1 and CP2 and lava flowed from CP2 and T37B and covered most of the crater floor lying between T45, T37B, T37 and the crater rim. Lava also flowed across the E overflow and down the flank of Lengai. The flow is composed of at least two distinct, differently weathered lavas that may have occurred with days or hours of one another. The first eruption phase produced a fine-textured aa no more than 0.4m thick and was the more extensive of the two flows, covering a greater area of the crater floor and crossing the E rim overflow. The second phase produced a less extensive but much thicker flow, nearly 2m deep in places, that stopped before reaching the crater rim or the E overflow. It consists of broken ropy pahoehoe slabs. Lava from this eruption and possibly from prior activity completely covered cone T24, which is no longer visible.
T46 cave: The collapse of the E half of T46 has revealed an interior cave containing long thin stalactites.
Crater overflow measurements:
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|
NW Overflow |
E Overflow |
W Overflow |
N Overflows |
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July 2000 |
60m |
38m |
|
|
|
23 July 2001 |
106m |
38m |
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5 Aug 2002 |
135m |
39m |
12m |
|
|
2 Aug 2003 |
135m |
44m |
17m |
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7 July 2004 |
135m |
44m |
17m |
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16 July 2004 |
135m |
47m |
17m |
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|
7 Aug 2005 |
135m |
72m |
20m |
~1m at 3 locations |
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7 Aug 2006 |
135m |
73m |
23m |
~1m at 3 locations |
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|
|
|
|
|
|
|
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Aug 2006: Ram Weinberger, member of a team from the geological survey of Israel, together with a Tanzanian geologist, Majura Songo, visited the crater on 20 Aug. Photos from their visit indicate that there have been no significant changes in the crater since 8 Aug. There are no fresh lava flows visible and there has been no growth of the collapse zone.
Aug 2006: Helene Frume of France climbed on 22 Aug and sent photos which showed no eruptive activity and no visible changes to the crater since the previous reported visit on 20 Aug.
Sept 2006: Magda Kozbial, a student at the University of Gadansk, climbed on 22 Sept and sent me a large number of crater photos. They suggest that there has been no activity since the previous reported visit. The only noticable change since early August is some additional collapse of CP1 on its western edge which appears to have destroyed all but a tiny remnant of T46. Magda reported, "We could only observe some smoke coming up from the cracks in the ground near the crater (CP1) behind the biggest cone, mostly where T46 is on your map. The smell of sulphate was quite strong."