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2004 News

Page history last edited by Frederick Belton 9 years, 11 months ago

January 2004: Chris Weber forwarded me the following: Bernhard Donth has visited Lengai on January 2004 for two nights. T56B has grown up to 40 meters high and hosted two active lava lakes inside. A channel about 5-10 meters under the surface of the crater discharged the lava overflowing into T56B and escaped out of this channel 50 meters down the northwest overflow. The lava squeezed out of this channel on the crater floor once before going down the northwest overflow. T58B was also active with a lava lake but impossible to look inside. Young lava flows, but more than 2 weeks old, were visible in northern directions.

 

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 collapse, had a steady degassing lava lake with many overflows during the visit of C. Weber. Lava penetrated the lower collapse 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 588°C. Aa lava flows not in motion anymore at flat terrain were measured between 480°C and 500°C. 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. Numerous photos from the expedition can be seen at the website of Rainer Albiez.

 

June 2004: A group led by Chris Weber of  Vulkan Expeditionen International  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 spattered 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 crater.

June - July 2004: 
Fred Belton camped at the craters from 29 June to 29 July, 2004. For photos see 2004 Centennial Expedition.


Appearance of the crater on 29 June, 2004: During the preceding year all activity seems to have taken place in the T49/T56/T58 cone cluster. Both T56B and T58B have grown much broader and taller, with T56B still the tallest (~25m) and now also the broadest cone in the crater.  T56B is now easily visible from the Rift Valley floor. Sometime after Feb 2004, (based on C. Weber’s Feb visit) the upper 10m of the SE flank of T56B collapsed.  On 29 June the upper part of T56B was open to the SE and contained a large lava platform of ~40 square meters. A small lava lake was bubbling in a hole at the rear of the platform. The upper NW flank of T56B, including the summit, was overhanging and dangerously unstable. The adjacent cone T58B had three distinct vents and has grown toward the south. There was no trace of the small “caldera” that surrounded T58B in Aug 2003. A new cone, T49G (identified by C. Weber) had formed high on the NW flank of T49B. Other cones such as T37, T37B, T40, T46, T47, T51, T53, and T57B appeared much as they were in Aug 2003 except for having been increasingly covered around their bases by lava flows from the active vents. A large cave in T45, observed one year earlier, had been partially filled by lava flows originating from T56B and possibly other sources. The floor of the cave was about one meter below the crater floor. The cave contained stalactites up to 3m long. The summit vent of T45 formed a skylight into the cave. The cave’s floor, composed of recent pahoehoe lava, was littered with small blocks that have fallen from the ceiling.

 

Crater rim overflow measurements:

                            NW overflow                     W overflow                       E overflow

2 Aug 03                   135m                                 17m                                44m

29 June 04                135m                                 18m                                44m

29 July 04                 135m                                 18m                                47m


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.

 


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