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2001 Expedition

Page history last edited by Frederick Belton 13 years, 2 months ago

From July 21-30 I led an expedition of 5 clients on a week-long stay in the crater. From July 23-28 there was nearly constant activity, including a paranoxymal eruption from July 27-28, and then no activity from July 29-30.

 

The most interesting observations are as follows:

 

1. Very few changes had occurred in the southeastern two thirds of the crater since July 2000, in fact the aa flow and lapilli field of approximately July 21, 2000 was virtually unchanged except for weathering.

 

2. Five new features were named and are shown on the latest crater map. They include new hornitos T51B, T40C, T49D, and T53.  An open lava lake was designated T49E.

 

3. Hornito T51 grew in height by at least 100% since July 2000, as did the amount of the NW crater rim that is covered by new lava flows.

 

4. The eruption of July 27-28 lasted for approximately 36 hours.At the height of the eruption, lava was ejected from 4 sources that produced distinctively different types of activity:

 

T49B: Dome fountain

T49C: Strombolian spattering, incandescent gas jets

T49D: Angled lava spray at high pressure

T49E: Fountaining lava lake

 

Lava flowed east, northwest, and south in the crater. Lava channels more than one meter wide were formed. Twice during the eruption lava flowed down the east and northwest flanks of Lengai simultaneously. However, lava never actually crossed the east rim because it entered a fissure in the crater floor and disappeared, later breaking out of a hole several meters down on the E flank. For more details, see 2001 News.

 

5. After the large eruption, there was no activity for approximately 28 hours, the longest repose period I have experienced on Lengai. Unfortunately the total length of the repose period is unknown because we left the crater at 7:15 am on July 30.

Technical descriptions like those above do little to explain how extremely spectacular it was to be in the crater for such a large eruption.So much was happening during the first 10 hours that it was hard to decide where to go.  I was constantly running between the crater rim overflows, the T49 vents, and the camping area, and became increasingly thirsty and hungry because I didn’t want to take time for a break. It was difficult to cross the crater due to wide lava flows in three directions. (One expedition member, Roberto Carniel, set his blue jeans on fire while crossing a flow.)  Once the lava rivers were well established in channels it became possible jump across them at their more narrow points.  However, they were so powerful and fast that it was like leaping over an Alpine stream, and to fall in would have meant being washed down the flank of Lengai while being cremated. We became concerned that lava was getting too near our camp, and that lava flowing into the fissure might cause the internal structure of the crater to weaken.  We were simultaneously awed and a bit scared for a little while, because we knew that absolutely anything could happen.  Our guide Paulo summed it up best when he said  “God, he big people!”
 
At night, with two huge orange fountains, incandescent gas jetting from T49, an overflowing lava lake, and glowing lava channels in three directions, there was a distinct feeling of being in the midst of an animated science fiction film set in the most alien of landscapes. We wondered if maybe we had been teleported to Io, the volcanic moon of Jupiter.  By that time, nothing would have surprised us.

 

 

Lengai guide Burra Ami Gadiye (center) and porters wait to receive their wages after arriving with their loads at the North Crater. 

 

 

On July 23 there was an open lava lake in a new vent that has been named T49E.  Jeff Brown is observing a lava channel that is draining the lake toward the north. The cone behind him is also new and has been named T40C.  The large cone behind T40C is T40 and has existed since 1997. View is from the flank of T49C, looking NE.

 

 

The lava lake rapidly built up steep walls. Here I am waiting for the next overflow.

 

 

Expedition members Andrew Locock, Jeff Brown and Marco Fulle and local guide Paulo Mongi observe lava spilling down the north side of T49C on July 26.  View is approximately SW.
 

 

Roby photographs a flow while Paulo, Andrew and Kurt look on.

 

 

Kurt and Marco observe the lava flow from the lake.

 

 

An eruption of foamy gas-rich lava

 

 

This is the year-old weathered remains of the last year's aa and lapilli eruption as it appeared on July 28, 2001.  To see the same flow as it was on July 25, 2000, about three days after it was erupted, click here. The SE crater rim is in the background.

 

 

This tiny little volcano is only about 2 inches (5cm) tall!  It is erupting foamy lava at its vent. It and the tiny light tan flows around it are typical of "squeeze-ups" which are of great interest to mineralogists.  Squeeze-ups usually erupt through tiny cracks that form in larger flows that have stopped moving and are beginning to cool.  This little cone was erupting from a flow near T49E.

 

 

A little flow of "intestinal lava" formed at the base of T49E.

 

 

From left to right, Kurt, Roberto, Jeff, and Andrew observe small lava breakouts on the solidified lava lake in T49E.  On July 25 the lake was periodically becoming engorged with lava and then suddenly draining through cracks in its west (left) side.  Behind the lake are spatter cones T40C (left) and T40.  In the background at left is the Rim Cone (C).  View is to the NE.

 

 

Lava of very low viscosity bursts from cracks in the base of T49E.

 

 

This little lava rapid shows that the viscosity of the lava is near that of water.

 

 

Here at the end of the flow, the lava is much less fluid.

 

 


 

 

 

The above photos show a lava flash flood in progress.  In the first photo Roberto is filming an outbreak of lava from the engorged lava lake.  In the next picture the left side of the lake is disintegrating and being pushed to the left by the pressure of the lava within.   By now we were shouting at Roby to run!   .  In the last picture the lava has flowed 30m (100ft) toward cone T53 and carried with it many large blocks from of the disintegrated rim  View is toward the NNW.
 

 

On the afternoon of July 27, after continuous steady flows from T49E and T49C had been established, T49B and T49D suddenly began to fountain.

 

 

Closeup of the fountain at T49B.  Some small blobs of spatter hit me when I took this shot.

 

 

Suddenly the dry T49E lava lake burst into life with 1 - 2 meter  (3 - 6 foot) fountains over its whole surface. 

 

 

Looking SW at the line-up of three erupting vents. From left to right, T49E, T49B, and T49D.  In the right foreground is the flank of T49C.

 

 

Lava flowed down the NW rim overflow in wild rapids.  By dusk on July 27, fresh lava was visible hundreds of meters below.

 

 

Lava that flowed toward the east did not reach the E rim overflow because it entered this fissure in the crater floor and later burst out of the E flank about 12 meters down slope.  The existence of the fissure helped to save some seismic equipment that had been installed about 3 meters east of the fissure.  At right Roberto, who helped remove the equipment, films the fissure.

 

 

At mid-afternoon on July 28 lava was still entering the fissure.  Just beyond is the east crater rim overflow. Notice how the lava channel has become much deeper through the process of "thermal erosion", a very rapid process compared to erosion by water.  Thermal erosion also carves some erupting hornitos into new shapes.  Is it possible that thermal erosion helps to form new lava conduits under the crater, resulting in new eruptive vents?

 

 


 

In the two photos above, Andrew observes the lava channel flowing east toward the fissure entry from the base of T49D.  By Lengai standards, these channels are quite large.  Some of their depth is due to the effects of thermal erosion.

 

 

What is a perfectly formed sea shell doing on Ol Doinyo Lengai?  This is just another amazing formation of erupting natrocarbonatite.  The "shell" only existed for a few minutes.  The lava was erupting from a vent near the base of T49D around 11 am on July 28.

 

 

 

Paulo probes a fast moving lava flow with his walking stick.

 

 

Closeup of lava flowing in a small channel.  A little covering has formed over the channel on the right side.

 

 

Andrew stands on hornito T53, a new cone that is located very far north in the crater. The cone to the left is T40C, to the right is T49C.  Directly behind T53 is T49B. View is toward the south.

 

 

On July 30 we left the crater with 8 porters and began the tedious descent through the Pearly Gates, on powdery lava.

 

 

 

 



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