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2003 Expedition

Page history last edited by Frederick Belton 9 years, 6 months ago

Four clients (Marco Fulle, Stephane Granier, Tom Pfeiffer, and Martin Rietze) joined me in the crater from 1 - 8 August to witness some exciting and unexpected activity.  We were accompanied by Othman and Paulo, expert Lengai cook and guide, victims of the 2002 Kitchen accident.  We slept and ate in the inactive south crater, a much safer and more comfortable camp than the active north crater.  With regard to safety in the active crater this year, the main problem was the threat of bombs and liquid lava that sometimes fell on the summit of T57B, where we all frequently stood to photograph the nearby eruptions. We had to run up and down T57B many times to avoid bombardment from T56B, which was only 20m away.  The greatest danger came when T56B collapsed.  Fortunately there were no hits that caused injuries.  Lava landed on Martin's head and burned a hole through his wool cap, and a small bomb landed in Tom's  jacket pocket and burned the headband of his flashlight.

 

During the visit we experienced hot sunny days, a cold foggy day with strong wind, cold clear nights, and cold foggy nights. On some nights the temperature dipped to freezing, leaving frost on a backpack beside my tent. One evening we were near the erupting T56B cone when thick fog arrived.  It was a strange experience to be in a dark pea-soup fog while bombs from the unseen eruption smacked into the ground nearby!

 

Highlights of the crater changes and activity are as follows:

 

1. Activity was limited to two cones in the central part of the crater, T56B (a new cone identified by Chris Weber in early July)  and T58B.  T39, T46, T37C, T52, T52B, T40C, T55, and T58 have disappeared. The size of the NW Rim overflow was unchanged from 2002 and the two other overflows increased in width by only a few meters. It appears that during the previous year there were many lava flows from the central crater but that a relatively small number of them reached the crater rim.  They covered up old cones and further increased the height of the central crater.

 

2. Nearly all of the activity was Strombolian (periodic gas discharge with explosive bursts of lava bombs).  With one brief exception, there were no lava flows. T56B at times ejected bombs up to 50m high and ash up to100m.  We were surprised by the amount of explosive activity and wondered if it signals an overall change in Lengai's behavior.

 

3. During our visit we witnessed 3 structural failures of the active cones. One collapse of T56B's upper slopes was simply due to the cone's inability to support its oversteepened peak.  A second collapse of T56B's upper section was caused by internal lava pressure.  Most surprising was the collapse of T58B which was caused by internal gas pressure.  All of the cone collapses were followed by strong eruptions which covered the remaining part of the cone and its immediate surroundings by a thick coating of spatter.

 

For a more detailed description of the crater and activity, see 2003 News.
 

Two of our 21 porters, Marios and Thomas, have a rest after delivering their loads to the south crater camp.  Without these hard working porters, long stays on Lengai would be impossible.

 

 

Our expedition camp in the inactive south crater.  Here we could sleep well and not worry about danger from the eruptions.

 

 

During our observations from Aug 1-8, 2003, this cone, designated T56B, was highly active. We unofficially named it "Little Etna" because its appearance and activity closely resembled much larger cones we had seen at Etna eruptions.  This view is to the SW, taken from near the base of T40.  As a result of earlier observations by Johan Smith, Chris Weber, and Paul Hloben, I believe T56B may have formed sometime during the second half of June, 2003.  Its eruptions have deposited a thick layer of ash which appears as low white sand dunes in front of the cone.  Due to the prevailing southerly winds, most of the ash has accumulated here on the north side of T56B. The layer of ash extended all the way to the north crater rim, decreasing in depth as distance from the cone increased.

 

 

This cone, T58B, was puffing a little steam when we arrived on Aug 1. After a day of silence, it began ejecting lava and finally collapsed late on Aug 3. After occasional Strombolian activity and ash emissions from 3-6 Aug, part of the rebuilt cone collapsed, and a new vent was formed near the top of the cone with a vigorius lava lake inside. Finally the new vent merged with the old one to form one long narrow vent. This cone sits in a former lava lake that we have been calling a "caldera" since a cone has grown inside it.  The "caldera" rim is clearly visible on the left and between T58B and the black slope of T56B. View is from the top of T57B, looking SW.

 

 

"Little Etna" T56B in eruption, viewed from the top of T57B on Aug 2.  It is showing Strombolian activity, which means that lava is violently ejected as a result of periodic explosive gas discharge.The lower two-thirds of the cone is composed of scoria andthe upper third is composed of spatter that has stuck together and solidified to form a steep unstable peak. Early on Aug 3 the upper part of the cone collapsed silently and fell straight into its interior. Strong lava spattering began a few seconds after the collapse. Incandescent material fell amid the observers on T57B and burned a large hole in Martin's hat.

 

 

A strong bomb and ash eruption from T56B. This photo of "Little Etna" was taken around 1030 on Aug 3.  The top of the collapsed cone is already being rebuilt by new spatter.  Activity during the first half of Aug 3 was powerful, with bombs ejected to 50 meters and ash clouds to 100 meters.  Light ashfall occurred in varying parts of the crater, depending on wind direction.  At night, each ash eruption appeared as a long sharp orange knife stabbing upward from the vent.  The ridge in the foreground is the rim of the "caldera," which is oriented SW to NE. The tallest part of the rim, at right, may be the old flank of T56.  The photo is taken toward the NW from the base of T37B.

 

 

Tom takes a risk of being hit by bombs as he makes a photo of T56B.

 

 

A relatively weak ash eruption from "Little Etna", seen from the north. Clearly visible in the foreground is a layer of white ash covering older lava flows.

 

 

Around 1630 on Aug 4, cone T58B, which had earlier ejected spatter, began steaming heavily from several locations on its  flank and from its vent, especially from a vertical crack on its southern (left) flank. 

 

 

After about 30 minutes of strong steaming T58B abruptly collapsed. After a short pause it began to violently eject blocks and bombs. It became the site of Strombolian activity that partially rebulit the cone over the next 24 hours.

 

 

T58B continued its post-collapse eruption into the evening of Aug 4. View is from T57B.

 

 

Looking west from the top of T57B, as T56B erupts after sunset on Aug 4.

 

 

Martin Rietze films T56B from the top of the inactive cone T57B on Aug 4.

 

 

"Little Etna" as seen through the saddle between T37B and T45. The white cone on the right is T57B.

 

 

A closeup of the beautiful cone of T56B prior to its collapse, showing the layer of spatter over cinders.

 

 

Around 1900 on Aug 5, T56B (Little Etna) abruptly collapsed. Tom, Marco, and Martin were only 20m away on T56B and were in considerable danger since large amounts of lava were being ejected after the collapse. They immediately ran from their exposed position and joined me on the crater floor just SE of the cone. Here the broken cone is covered with a thick layer of spatter. The spatter exploded out of the cone but wascaptured by the time exposure as an orange glow above the cone rather than discrete blobs of spatter.

 

 

 Shortly afterward another section of the cone collapsed.

 

 

On Aug 7 in the early morning, T58B (at left)  formed a new vent which eventually merged with its original vent. At first a small lava flow broke out but was not sustained. Spatter from a lava lake inside the cone rebuilt the small breach and a second T58B vent formed, not visible in this photo. The two vents merged to form one long narrow opening into the cone.  At right, T56B begins to turn white due to inactivity. It has grown back into a steep cone since its Aug 5 collapse.


 

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