In July 2000 I organized an expedition to Ol Doinyo Lengai for four people.  We camped inside the crater for 7 nights, from July 23-30.  The region near the volcano was safer from the Somali bandits than in 1999 due to new military posts in the area, but was still not considered totally secure.  However, we experienced no problems and heard of no other groups that did.

Activity occurred at T49B, T51, T37N1, and from a small vent just below T37E.  The most interesting observations were as follows:

1. The number of deep fissures in the crater floor has increased dramatically since August 1999. Some of the fissures continue into the crater rim, suggesting that the crater is becoming more unstable.

2. We found a very large flow of aa lava that had covered much of the southern part of the crater floor.  The flow was still black and hot, suggesting it had been erupted lees than 48 hours prior to our arrival.  The aa was much thicker than is typically erupted, and a part of the flow east of the T37 cone complex was deeply covered in lapilli.

3. A new, highly active spatter cone (T51)  now exists in the western part of the crater. Photos made by Burra Gadiye indicate it began forming in January 2000.

4. Since August 1999, T49 collapsed and partially reformed.  A new cone (T49B) grew up adjacent to it, to the SW. T49B was almost continuously active during our visit.

5. During the period from July 1999-July 2000 very little lava flowed through the crater rim breaches and down the flanks of Ol Doinyo Lengai, and no new rim breaches were formed.

6. At 1300 on July 23 huge lava splashes occurred in T37N1.  The activity lasted for only about two minutes but created a large lava flow that nearly reached the eastern crater rim.

Looking SE from near the NW rim overflow late on July 29, 2000.  The black spatter cone on the left, T49B, erupted almost continuously from July 23 - July 30. The black cone on the right, T51, erupted on July 23 and July 28 - 30.  Neither of these cones existed in early August of 1999.  T51 was first seen around Dec 1999.  The light colored cone to the far right is T47.

We were amazed to find this spectacular feature on July 23.  It consisted of a huge thick aa flow covering much of the south part of the crater and this thick layer of lapilli covering the east part of the flow.   In the section shown above, the lapilli was up 7.5 cm deep and still very hot.  We later saw aerial photos taken on July 21 in which the flow did not exist, making July 22 the most probable date of its eruption.  It was obviously a very large and unusual eruption and we deeply regretted missing it. Although we were not certain, the aa  flow seems to have been discharged by a small vent called numbered T37E on the eastern  flank of T37N near the former site of T5T9.  (It is  possible that T37E and T5T9 are actually the same vent.)  To see what this lapilli looked like one year later, click here.

This photo was taken by Richard Roscoe at 1:04 pm on July 23.  It shows a powerful fountain from T37N1 that lasted for no more than one minute but produced a flow that reached nearly to the east crater rim.  The lava fountain reached a height of at least 25 meters.

Celia Nyamweru (left) and her daughter Wanjiru in front of T49B.  Could this be the first mother/daughter team on Lengai?
 

The level of the lava pond inside T51 increased throughout July 28, as did the vigor of its degassing.

From front to rear, Richard Roscoe, Paul Mongi, and Roger Mitchell observe a lava flow from T51.
 

At 4:45 pm on July 28 lava began spilling down the N slope of T51.

New lava flows across older weathered lava near the base of T51.

Tiny lava channels and breakouts form an intricate pattern below T51. The blackest lava has very low gas content.  The foamy gray lava is saturated with gas.

This is an unusual little lava fountain that broke out in the flow field below T51 and existed for several minutes.  It is only a few centimeters high and has formed a thin transparent fan of lava in the air.  It has built a little ridge from which small parallel flows have formed (lower right).

Here the volume of lava flowing out of T51 is the greatest that we observed.  This very black lava reflects the sun as it cascades down the cone's NW flank.  It is highly fluid and flows like water.  It contains relatively little gas compared to the "foamy" flows that occurred later in the eruption.  I did not stand here long due to discomfort from high temperature and occasional spatter from the vent.  Lengai's peak is to the upper left.  Photo by Roger Mitchell.
 

A slender lava channel coming from the erupting cone T51.

After erupting through the night of July 28,  the lava dropped to a lower level inside T51 by 8 am on July 29. A climb to the top revealed beautiful lava stalactites.
 

This eruption took place during the afternoon of July 29.  The cone had grown well over one meter taller than it was on July 28 when the eruption began.
 

The eruption of T51 continued through the night of July 29.   Lava is not visible on the upper part of the cone because it is enclosed in tubes there.
 

Repeated lava flows have built up a complex of tubes, little hornitos and lobes of pahoehoe.  Notice the slight void space between the freshly hardened lava on the edges and the older white lava below it.

I'm enjoying the warmth of the foamy lava erupting between my feet.  Actually the intensity of the heat made it impossible to remain here for very long.  It is relatively safe to stand on a structure composed of tiny active flows provided hiking boots and glasses are worn.  However, I do not encourage anyone to try this.

A fumarole in the western part of the crater floor

Looking back up at Lengai on the way down. The notch just right of the apparant summit is the passage between two buttes called the Pearly Gates. (I unofficially named the buttes after learning that the Masai have no name for them.)  Lava flowed through them in 1993, making the route impossible to climb for a while. Then it was necessary for climbers to go to the other side of Lengai and approach via the "Dorobo Route."

Richard and Roger recover from the descent as the porters prepare for the drive back to Engare Sero village.  Behind, Ol Doinyo Lengai towers nearly 1800 m above the valley floor.