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2001 News

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

January 2001: Paul Hloben of South Africa wrote, “We visited Lengai 15-17 Jan 2001. The place was very wet, and most soda coating of the crater floor and cones was washed away or in solution within the mass of the crater floor and cones. So the entire crater was sandy brown and muddy (except recent lava flows, which were brown or gray which were of course rocky-hard). Older cones were just soil-brown like gigantic termite mounds (I guess a very different to normal Lengai, which seems very white from the published photos and documentaries).Only two cones were active, first one which was the nearest position to camp site at the path leading down the volcano.” (This is T51)  "The cone was too high for lava flows or for viewing what was happening inside, but we heard continuous blows every 10-20 seconds. Further on there was twin-partially collapsed cones” (These are NEW FEATURES located between T49 and T48) “that harboured two active ponds (the lava level was about 1.5 metres below the collapsed crust-the view point). The ponds were interconnected, with lava and gas surges approximately occurring every 20-30 seconds independently in each pond.  The smaller pond (north) was about 1-2 metres in diameter depending on the crust that built up and collapsed numerous times, the larger pond was about 4-5 metres in diameter, not easy to see due to heat blows that forced us to escape, we could observe it best during the night as it was glowing.”   These features are shown on the following map sent to me by Paul Hloben based on a previous map by Christoph Weber.
 


NOTE: In July 2001 the two active ponds (NEW FEATURES) described above had disappeared.  They were never given a T-designation.

 

June 2001:  We climbed "The Mountain of God" on 28 June 2001 and spent  from about 0800 to 1245 in the active southern crater. The crater floor is covered  with about 20 steep-sided spatter cones and countless pahoehoe flows (some of  the longer flows are aa-like near their toes). Radial cracks on theyoung  surface of the crater floor penetrate the older rocks of the crater rim. Spatter cone T40B (Photos at the website below indicate that this cone was actually T49C)  had been active on 27 June, sending thin (about 10 cm thick) pahoehoe flows  about 10 m from the vent; moisture was turning the edges of the still  warm black natrocarbonatite flows white. Later a slightly explosive eruption had spewed tephra of tiny (1-2 mm in diameter] glassy spheres onto the surface of the 27 June pahoehoe flows. Spatter cone T40B (T49C) sounded like a steam engine for the entire time we were near the volcano's summit. From about 1130 to 1200 on 28 June this cone erupted spatter, throwing  blobs oftar-looking lava about 2 m into the air; the blobs landed on the side of the spatter cone making lava stalactites and short pahoehoe flows so that the cone looked like a giant sand castle.  Information Contacts: Bob Carson, Department of Geology, Whitman College, Walla Walla, Washington 99362 USA (Email: carsonrj@whitman.edu); Burra Ami Gadiye, c/o Sengo Safari Tours, P. O. Box 207, Arusha, Tanzania.

 

July 2001: Michael Lyvers reported:  "My wife and I climbed Lengai on July 3 and arrived at the crater to find a large fresh lava field that was still hot and oozing forward from the vent you call T49C. The flow almost reached the northwest rim overflow area. The vent was spattering and small watery black flows coursed across the fresh lava field.  The lava flows and spattering stopped a few hours later but the vent continued to roar and rumble as it spewed high-pressure gas jets all day. No other vents were active during our one-day visit."

 

July 2001: An expedition led by Fred Belton observed Ol Doinyo Lengai from 23-30 July 2001.  Members included Jeff Brown, Roberto Carniel, Marco Fulle, Andrew Locock, and Kurt Winter.  For photos see 2001 Expedition. Little change was noted in he SE two-thirds of the crater.  The large aa flow and lapilli field that was erupted about 22 July 2000 had been weathered to light brown powder but was otherwise unchanged. None of it had been covered by subsequent lava flows. Recent activity was confined to the NW third of the crater.  T51 was ~12m tall, an increase in height of at least 100%. It was a large pointed cone, inactive, and weathered to soft powder of varying shades of brown. A new hornito lying just SE was designated T51B.  It had a low  rim open to the SE and a deep overhung pit on the NW end, and was weathered to the same extent as T51.  T53 is a new hornito ~ 40m NW of T40, and is now the northernmost vent on the crater floor.  It was a rounded cone ~ 4m tall and contained a hooded cave that opened to the N into a shallow 12m x 6m basin, which fed lava channels to the north.  Its slight weathering indicated recent activity, during which a lava lake overflowed to the N and NW and formed a meter-thick flow of jumbled blocks and plates that accumulated against the N crater rim.  T48 showed little change.  T40 had grown several meters towards the W and a new vent was seen in its upper SW flank. Puffs of air and sloshing liquid sounds were heard from that vent early in the visit, but T40 never became active. A new cone, designated T40C, lay just SW of T40. It was ~5m tall and weathered to white and gray powder.  (A cone called T40B existed in 1998 but merged with T40 during the following year.)

 

The center of the most recent activity was the T49 hornito cluster.  T49 was a collapsed cone, unchanged except for weathering. T49B was a white cone with a rounded summit,  ~6m tall.  T49C was a broad hornito of about the same height, first noted by Christoph Weber in Oct 2000.  T49D was a new cone, slightly shorter than T49B, its vertical sides ringed with shallow grooves.  T49E, also new, was an oval (15m x 6m) low-rimmed open lava lake near the base of T49C. The north end of the lake was linked to the upper NE slope of T49C by a curved sloping ridge on which lay three small rounded spatter cones with sealed vents.

 

The E crater rim overflow was ~33m wide and appeared little changed. The NW crater rim overflow was ~105m wide, including a 2.5m section of rim remaining within.  That represents about a 75% increase in width of the overflow area, and about a 100% increase in the amount of NW rim covered by lava.  Radial fissures in the crater floor were not as numerous and were concentrated in the NE quarter of the crater, extending into the crater rim as before.

 

Activity: At 1000 on 23 July, T49E contained a frothy lava lake.  Short overflows occurred to the E about every 10 min. The lake also drained northward through a lava channel, feeding pahoehoe flows that extended between T40C and T53, nearly to the N crater rim. In the afternoon a section of the lake’s east rim collapsed. Around 1900 the N end of T49E crusted over and lava washed in waves into the south end from the direction of T49C. The lowest of the three small cones on the ridge above T49E began erupting 2-8m long flows of frothy lava every 5-10 min. There were occasional small spatters from T49C.

 

By 0630 on July 24 the lava lake in T49E was completely crusted over. Small fluid pahoehoe flows containing little gas frequently broke out on its surface.  A frothy lava lake was seen high in the summit vent of T49C.  The small cone above T49E continued to produce short flows until its vent became blocked around midday. Throughout the afternoon T49E inflated as lava entered and pushed up its solid surface. Small pahoehoe flows broke out through cracks in the base of T49E’s low NW and N rim, and also on its solid surface.  By 0630 on July 25 the solid surface of T49E was inflated to nearly 1m above its position of the previous evening. It made continuous cracking and popping noises and small rockfalls occurred from its 1m high rim as it became increasingly engorged with lava.  At 0720 a loud gurgling sound occurred and cracks opened in its NW base, releasing a torrent of very black, gas-poor lava. Its viscosity appeared to be near that of water as it flowed to the NW.  Just after the release, a section of the lake’s solid surface collapsed. After one hour the flow diminished to a trickle and then stopped. The lake began inflating again, and at 1205 a similar lava release occurred.  At 1710, after another period of inflation, a 3m long section of T49E’s NW rim collapsed, releasing a flash flood of lava that carried blocks weighing hundreds of kilos up to 9m from their original position in the rim.  Within seconds the flood extended 30m NW from T49E and covered a wide area with a thin coating of lava.

 

The filling and draining of T49E continued through several more cycles, occurring at least 3 times on July 26, but the period of the cycles became progressively shorter.  At 0917 a section of T49C’s summit collapsed. Around 1200 foamy lava cascaded down the N flank of T49C. At 1300 the filling/draining pattern of T49E ended when a continuous flow began from its NW base and continued unabated until at least 2000.  The lava stopped about 50m short of the NW crater rim overflow.

 

During July 27-28 an eruption occurred that was paroxysmal in that it far exceeded the vigor of average magmatic activity that is frequently observed on Lengai.  Estimates of lava output for this eruption were 5 cubic meters per second during the greatest outflow and no less than 1 cubic meter per second at anytime during the first 30 hours of the eruption.  At 0630 July 27, pencil-wide streams of very unusual lava were building up a small mound at the NW base of T49E. The lava was light gray and transparent while flowing, but became opaque immediately after solidifying.  The mound was soon covered by an outbreak of fluid black lava from a nearby crack. Activity was minimal until 1113 when flows broke out from the base of T49E and T49C began to spatter. By 1315 the flow from T49E was large and well established in a channel. At 1329 gassy lava began flowing out of T49C and joined the flow from T49E. At 1430 lava reached the NW crater rim overflow. Shortly afterwards T49C ceased erupting. T49D began to spatter from a small hole in its N side and T49B began to overflow from its summit vent.  T49B soon developed a large dome fountain and T49D began ejecting a narrow fan of spatter at a 30-degree angle.  At 1510 the previously solid surface of T49E was swept away and the lake began to fountain 1-2m high.  T49C began erupting clots of spatter every 10 seconds. Thus, 4 vents were erupting simultaneously. Fluid lava flowed in meter wide channels toward the NW, E and S.  Lava crossed the NW crater rim overflow and poured in wild rapids down the NW flank. Lava did not reach the E. overflow, but instead entered a fissure in the crater floor 25m E of the overflow.  The entry point steamed heavily and spattering occurred there several times.  After more than one hour of pouring into the fissure at  ~1m3/s, a vent opened in the E flank of Lengai, about 12m below the rim, within the weathered lava from previous overflows.  The released lava cascaded down the E flank of Lengai.  Smoke from burning vegetation could be seen far below.  Destruction of a seismic station established 4m E of the fissure by Joshua Jones of the University of Washington was narrowly averted thanks to the fissure’s absorption of the lava flow and the efforts of Roberto Carniel and Andrew Locock to move the equipment to the crater rim.  By 1800 T49D’s spraying vent had enlarged and was producing a powerful fountain equal in strength to T49B’s fountain.  New lava was visible hundreds of meters down the NW flank of Lengai.  Lava often spattered half a meter high as it raced down the flank through steep channels. After sunset, spectacular orange fountains played steadily from T49B and T49D.  Jets of incandescent gas appeared as flames 1-2m high above the vent of T49C.  At 1930 the lava lake emptied, ending the flow to the NW.  The lava flowing S from T40C produced a 0.5m thick clinkery aa flow that came to within 30m of the campsite by midnight.  Around 2100 T48 began expelling loud blasts of invisible gas from a small hole on its collapsed flank.

 

By 0600 July 28 the lava flow to the south had ended 3m from the SW crater rim. The fountain from T49B was diminished but T49D continued to erupt a powerful “lava falls” into a pool at its base, which fed a very large and deep lava channel to the east. Width of the channel exceeded 1m and depth ranged from 0.5m-1m.  Lava flowed through the channel and into the fissure in the crater floor all day, although the vigor of T49D’s output gradually diminished and the lava in the channel became increasingly frothy. The fissure entry point had eroded considerably and appeared as a large deep cave entrance, large enough for a person to enter.  Around 1900 the T49E lava lake refilled and drained several times, then filled to its rim and degassed vigorously.  Lava exited the lake NW via a tunnel that led into the lava channel formed the previous day. Lava again flowed down the NW flank of Lengai.  However, after 1900 the flow to the east became sluggish, with very little lava entering the crack in the crater floor. At 2300 T49C began expelling incandescent gas, and lava spilled down its N and S slopes.  Sometime between 0100 and 0600 July 29 all activity ceased.  An orange glow was seen in the vent at the base of T49D on the night of July 29, but otherwise there was no further activity before observers left at 0715 July 30.

 


July 2001Joshua Jones of the University of Washington visited the crater on July 31 and reported seeing no flowing ava or fresh flows.

 

August 2001Joshua Jones again visited the crater on August 6 and reported no flowing lava or fresh flows, but heard lava sloshing inside an unidentified hornito.

 

August 2001: Thomas Kraft of Germany reported to Celia Nyamweru that he visited the crater on August 19.  There was no activity except for subsurface bubbling of lava.

 

September 2001: Joerg Keller reported, among other activity, a 10m horiziontal lava fountain. No details are  available yet.

 

November 2001: Steve Colliver reported from Kampala, Uganda: We climbed the mountain on friday 30th November night and got to the crater rim at about 9am.  We had a walk around and there was lots of sulphur coming out of the hornitos.  Then we came to a very large lava flow which we were about to walk over, until we noticed a lot of heat coming from it.  I hit it with my stick and suddenly heard a lot of creaking and bubbling noises.  The flow was about 40m long, 15 to 20m wide and about 30 to 40 cm thick. It had breached the crater rim and flowed down the side of the volcano. It was still obviosly molten in the centre.  We broke off a piece from the front edge of the flow and it was extremely hot to touch.  After a minute or two, it had cooled enough for me to touch and as I held it in my hand, it changed from black to a pale gray.  In my opinion, it couldn’t have been more than one hour old.  We decided to investigate the source of the flow and found that it had come from a small fissure about 30cm in diameter on the crater floor and not from one of the hornitos.  Suddenly, whilst stood next to the source, about 2m from where I was standing, a hole appeared in the crater floor to the side of the lava flow we had been studying.  Instantly, a sticky black lava poured from it.  It was amazing and the first eruption I have ever witnessed.  The flow lasted about 5 minutes, was about 15 cm thick and flowed for about 10m.  The viscosity of the magma was similar to engine oil and I believe it contained little or no gas as there was no bubbling or spitting.  We watched from less than a  metre away and had great fun playing with it, making shapes with our sticks and scooping it up to fill a tin can.  I think it had quite a low temperature because we placed a drinking bottle on top of the flow and the bottle remained there for quite some time before melting.  Almost as soon as the first flow had stopped, then another hole opened up in the crater  floor and again, lava poured out.  The fissure was about 10cm in diameter and the flow ended up being similar in size to the previous one. By the time we left, there were at least 10 fresh flows and they were all on the side of the summit.  There was no activity on the opposite side.  Another interesting point to note is that the samples I have collected have retained their black colour, and are producing a strange greasey/oily substance.  Wherever I place them, when I pick them up I find a small puddle of transparent oil.

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