Oldoinyo Lengai Web Site

Nyamweru, Celia

Book ID 764

external link

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 01
Extract Date: -370000

Oldoinyo Lengai is young

Oldoinyo Lengai is less than 0.37 million (370,000) years old, and is the youngest big volcano in this part of the Rift Valley

Extract ID: 4499

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Extract Author: -150000
Page Number: 02
Extract Date: 1960

J.B. Dawson mapped the volcano

J.B. Dawson mapped the volcano in 1960 (Dawson 1962) and established the following sequence, from oldest to youngest:

Yellow tuffs and agglomerates with interbedded lavas. These make up the main bulk of the volcano, the result of many episodes of explosive activity. The tuffs are made of crystals of nepheline and pyroxene, set in a fine-grained yellow matrix of zeolite, limonite and carbonate. The lava flows within the pyroclasts are composed of nephelinite and phonolite. These rocks have been correlated with rocks exposed in the Olduvai Gorge succession which range in age from about 0.15 to 0.4 Ma (Dawson et. al 1995).

Extract ID: 4500

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 03
Extract Date: -100000?

Parasitic cones and craters

Grey tuffs and agglomerates make up parasitic cones and craters on the outer slopes of Oldoinyo Lengai. They contain blocks of the older yellow agglomerates. Some are lithic tuffs, composed of small lapilli of nephelinite lava; others are crystal tuffs composed mainly of mica, pyroxene, nepheline and olivine crystals.

Extract ID: 4501

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 04
Extract Date: 1250

Black tuffs

Black tuffs and agglomerates were laid down on a deeply eroded surface of the yellow pyroclasts. They occur on the lower slopes of the mountain and high on its western and north-western slopes. They include crystal tuffs (nepheline, pyroxene and mica), lithic tuffs (lapilli of nephelinite, ijolite and fenite) and agglomerates, with blocks of nephelinite, phonolite, urtite, ijolite and other alkaline rocks. These tuffs correlate with an ash in the Olduvai succession which is dated at about 1250 years. The earliest evidence for natrocarbonatite lava is found within these tuffs.

Extract ID: 4502

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 06
Extract Date: 1940/41

Grey semi-indurated tuffs

Grey semi-indurated tuffs, up to about one metre thick, consisting of nephelinite lapilli and mica plates cemented by carbonate. These tuffs overlie the stunted remains of trees and are tentatively assigned to the eruption in 1917 that killed off most of the forest on the outer slopes of Oldoinyo Lengai. Poorly consolidated black ash overlies the grey tuffs on the north, west and south slopes, and has also been observed at Olduvai Gorge, 45 miles to the west-southwest. The ash has formed spectacular barchan dunes; .... This was probably formed during the eruption in 1940/41.

Extract ID: 4504

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 07
Extract Date: 1954/55

deposits of soda ash

Variegated (light green, pale yellow, pink and white) deposits of soda ash, up to 20 feet thick on the southern wall of the summit crater. These may have formed in 1954/55.

Extract ID: 4505

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 08
Extract Date: 1883

G.A. Fischer

The first scientific description of Oldoinyo Lengai was by G.A. Fischer in 1883. He observed "smoke" rising from the summit and recorded reports by local people of rumbling noises within the mountain (Fischer 1885, quoted in Dawson et al. 1995).

Extract ID: 4506

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 08a
Extract Date: 1904

First scientist to climb Ol Doinyo Lengai

The first scientist to climb to the summit crater was F. Jaeger in 1904.

Extract ID: 4518

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 09
Extract Date: June 1917

Major explosive eruption

A major explosive eruption took place from January to about June 1917. Ash was deposited as much as 25 - 30 miles away, and killed the formerly luxuriant vegetation on the lower slopes of the mountain. The flat lava platform was replaced by a deep summit crater. Another eruption may have occurred for several months in 1926.

Extract ID: 4507

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 10
Extract Date: July 1940

First eruption with fairly complete record

The first eruption of which there is a fairly complete record took place between July and December 1940.

J. Richard's account of this eruption identifies three major phases

(1) a preliminary stage of small explosions that discharged old material from the vent,

(2) a phase during which great quantities of gas were discharged, preceded by violent explosions that ejected blocks and bombs,

(3) a phase during which mainly ash was ejected, but not to such great heights as during phase 2 (Richard 1942).

At the close of this eruption there was a deep funnel-like hole in the summit crater, the slopes of the volcano were blanketed with white ash, and ash had fallen as far west as Loliondo, about 100 kilometres away.

Extract ID: 4508

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 11
Extract Date: 1954

Minor eruptions

Minor eruptions of lava were observed in 1954, 1955 and 1958; a small eruption of ash may have occurred in early 1955.

Extract ID: 4509

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 12
Extract Date: 1960's

Minor lava eruptions

Similar minor lava eruptions were recorded from several dates in the early 1960s; see the photographs [on the web site].

Extract ID: 4510

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 13
Extract Date: 14 August 1966

Eruption observed by airline pilots

This eruption was first observed by airline pilots on 14th August 1966, and two geologists, J.B. Dawson and G.C. Clark, visited the volcano six days later and climbed to the active crater rim on 21st August.

The following description of the eruption is drawn from the account by Dawson, Bowden and Clark published in 1968. They first sighted the volcano at 2.30 p.m. on 20th August 1966, when "a Vulcanian-type eruption was in progress. A thick column of black ash was rising for approximately three thousand feet above the volcano and, due to the dominantly southerly wind, was drifting away northwards towards lake Natron; the ash fall was very heavy on the upper northern slopes of the volcano" (page 868).

Extract ID: 4511

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 14
Extract Date: August 1966

Major Acticity

During the climb on 21st August, the lower slopes were covered with about half an inch of new, snow white ash which reached a thickness of about 2 inches closer to the summit. The active crater was full of swirling ash and dust. In it was a new ash cone in whose summit was a shallow bowl-shaped pit about 100 yards in diameter. In the centre of this pit was a small double vent from which there was a continuous discharge of gas and whitish-grey ash and dust. There was a continuous roaring noise and a strong smell of sulphur. Ash was scattered all over most of the inside of the crater and there was about 6 inches of new black ash on the outer slopes of the east rim. The crater was observed from 10.30 a.m. to 1.50 p.m., during which period no lava extrusion was seen, and the ejected material was not larger than ash size.

The photograph [see web site] (taken by Gordon Davies) shows the active crater in August 1966.

At 2.45 p.m. on 21st August there was a violent harsh explosion and a dense column of black ash rose vertically above the crater. A series of loud explosions occurred at intervals of less than 15 seconds, each one accompanied by the expulsion of more ash. This continued until about 4.0 p.m., when the explosions ceased, though the ejection of ash continued all that day and throughout the night.

At 11.30 a.m. on 22nd August, when these observations ended, the pine-tree shaped cloud of a Plinian-type eruption was towering above the volcano.

On the morning of 23rd August activity had almost ceased; only a small amount of ash was rising to a few hundred feet above the volcano. The ash cone within the northern crater had grown higher.

On 1st September another violent ash eruption was reported.

On 3rd and 4th September activity continued; a column of ash rose above the volcano and drifted away to the north. The summit crater was almost infilled with ash, though there was still a deep pit in its centre. On 11th October the volcano was still active; the local Maasai pastoralists and the wild game animals had moved out of the area, probably because the water and grazing supplies were contaminated by the ash. The photograph [see web site] , taken by Joan Westenberg in August 1966, shows the thickness of ash on the lower slopes of the volcano.

Ash fall was reported as far as Seronera (130 km west), Loliondo (70 km north-west) and Shombole (70 km north).

On 28th October the volcano was seen to be covered with white ash, and was still active, with a light plume of ash blowing away to the north-west.

Observations in late December 1966 and on 1st January 1967 established that there was no activity.

A major explosive eruption was reported on 8 - 9th July 1967. Ash fell at Arusha (110 km southeast) and at Wilson Aerodrome in Nairobi, 190 km to the northeast. After this the volcano seems to have remained dormant for several years. Click here to see what happened in 1983.

Extract ID: 4512

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 15
Extract Date: 28 October 1966

Covered with white ash

On 28th October the volcano was seen to be covered with white ash, and was still active, with a light plume of ash blowing away to the north-west.

Observations in late December 1966 and on 1st January 1967 established that there was no activity.

Extract ID: 4513

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 16
Extract Date: 8 July 1967

Major explosive eruption

A major explosive eruption was reported on 8 - 9th July 1967. Ash fell at Arusha (110 km southeast) and at Wilson Aerodrome in Nairobi, 190 km to the northeast.

After this the volcano seems to have remained dormant for several years.

Extract ID: 4514

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 17
Extract Date: 1983

Small ash eruptions

From January to March 1983 a number of small ash eruptions occurred; in mid-February there was a slight fall of fine grey ash at Olduvai Gorge, 65 km to the west.

John Fanshawe and Harvey Croze took photographs from the air in early April 1983; [see web site] There was a lava flow reaching about two thirds across the floor of the pit crater and two small black cones with open vents at the base of the north wall.

Extract ID: 4515

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 18
Extract Date: July 1988

Lava flow

Between July and October 1988 lava began to flow southwards across the Saddle into the Southern Depression.

The photograph [on the web site] was taken from the southern summit by Martin Smith in October 1988 and shows how lava (already white when this photograph [on the web site] was taken in October 1988) has spilled over the Saddle and begun to fill the floor of the Southern Depression. The photograph to the right [on the web site] was taken by Celia Nyamweru about a month later and looks almost due east along the Saddle. A large vent (T11) has opened just north of the saddle and during our visit to the crater we observed lava flowing southwards from this vent on several occasions. At times when the hot lava came into contact with vegetation on the slopes around the Southern Depression it started small brush fires.

Activity continued within the crater in the early 1990s. Lava cones built up at different locations on the crater floor. The photograph to the left below [on the web site] , taken by Celia Nyamweru in August 1990, shows T14 which was active in August 1990; note the contrast between the white side of the cone which is several months old and the fresh black material that was being erupted as the photograph was taken. Lava flows continued to build up the level of the crater floor and to flood across the former line of the Saddle, creating a single oval crater in place of the former northern pit crater and southern depression.

Extract ID: 4516

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 18b
Extract Date: 4 August 1910

A horse-shoe-shaped southern rim

C. Uhlig and F. Muller climbed the volcano on 4 August 1910 and observed that "the northern crater had only a horse-shoe-shaped southern rim immediately below the summit, and lacked a crater rim to the north, west and east. The crater was more like a platform on which there was a central cone from which gas was being emitted".

Lava flows and pinnacles formed on this platform between 1904 - 1910 and again between 1913 - 1915.

Extract ID: 4519

See also

Nyamweru, Celia Oldoinyo Lengai Web Site,
Page Number: 19
Extract Date: jun 1993

Maasai move their livestock

We do not have a detailed eyewitness account of the events in May-June 1993, but from interviews with people who were near the volcano at the time, and photographs by Martin Kuper of Zurich it is possible to put together a reasonable picture of what happened.

Minor activity occurred through April 1993, and there are reports of a loud explosion near the summit on about 22 May.

During an ascent on 8 June 1993 Burra Gadiye observed that T20, a cone in the centre of the crater floor, had grown considerably. Also a large amount of steam was escaping from a crack on the west slope of the volcano, a few hundred metres below the west rim. Burra reported feeling an earthquake on 14 June and dark, dense plumes from the crater could be seen from Ngare Sero, the village about 10 kilometres north of Oldoinyo Lengai.

Maasai herdsmen moved their livestock out of the area. On 15 June Burra climbed the west slope but was unable to reach the rim, being stopped by flowing lava in the approximate vicinity of the steam on 8 July. Dark ash was being erupted from within the summit crater on 15 June, and again on 18, 21 and 25 June.

When a party from St. Lawrence University climbed the west slope on 27 June, we observed no ash clouds from the crater, though there was a strong smell of sulfur detectable from far below the crater rim. There was a light dusting (maximum about 2 mm thick) of fine gray ash on the outer slopes, and a lot of dead vegetation on the upper slopes. Steep rock slabs a few hundred metres below the rim were covered with several centimetres of loose ash, making climbing very difficult. It was not possible to proceed up the path to the rim, as it was blocked by slabs of lava, by now cold and solid.

Extract ID: 4517
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