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Lothar Fritsch: Vulkane erleben! Vulkan-Survial Hier klicken! |
Lothar Fritsch, Jan. 2003
From November, 23 to December 15, an expedition group led by VEI Expeditions (1) traveled the Danakil desert in norteastern Ethiopia. The goal was to reach and explore the Erta Ale volcano and surrounding volcanic structures of the Danakil. This report summarizes findings of the expedition, including lava lake observations, recent changes at the crater, earthquakes, temperatures and a newly observed hazard to volcanologists at Erta Ale.
All photographs are linked to larger images when you click on them. This
also holds for the graphs of the caldera.
Footnotes are of the format (x)
where x is a number, hyperlinked to the footnote text. The footnote text is at
the end of the document,
References to GPS coordinates are noted like
(ERTFUM), where the characters refer to the coordinates in table
1.
All photographs and other materials are (c) Lothar Fritsch,
2002,2004, unless explicitly stated otherwise.
Measurements of landmarks and the shapes of the caldera and crater rims were made using a 12-channel GPS receiver. GPS receiption was excellent due to the exposed nature of Erta Ale, where signals are shaded only when the receiver is close to the caldera wall inside the caldera. Figure 1 depicts the caldera shape as measured. Table 1 lists the coordinates of several points of interest inside the caldera.
Please note that the measurement error of the rims is about 15m, shifting the lines to the outside of the caldera and the craters due to the necessary safety distance to be held towards the rims. The points of interest are precise coordinates.
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| Image 1: Aerial caldera view from East. | Image 2: Aerial caldera view from South. | Image 3: Aerial view of northern caldera end with crater pits. | Image 4: Aerial view of eastern caldera wall. |
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| Image 5: Pélée's Hair is found next to Erta Ale south pit crater. |
We found serveal volcanic minerals. First, the basaltic lava flows that proceed from the craters to the southern caldera end provide large varieties of flow patterns and lava tunnels. At the southern end, lava seems to have cooled off enough to brek into large tiles and create a lava field that was nearly impassible.
On the norteastern slope of the central honito (ERTHTO), crystalline sulphur was found. This was also the case at the western rim of the north crater pit, close to the place where the crater rim and the caldera rim join. More sulphur was found in the soil at the emergency exit location (ERTAEX) and in the caldera wall just north of the camp (ERTACMP).
Around the south pit, in particular near its northern and northwestern rim, the ground is widely covered with Pélées Hair. Gas eruptions and rock fall into the lava lake constantly caused this mineral to be ejected from the pit by hot air circulation.
On the outside of the caldera rim, strictly northwest from the fumarole
field position (ERTFUM), fumaroles are found. Grass lives off the water vapors,
while eggshell-like gypsum structures grow in a large field around the fumarole
openings.
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| Figure 1: Erta Ale Caldera Sketch according to GPS
measurements. Blue: Crater and Caldera Rims; Black: Point of Interest. Coordinates can be found in Table 1. |
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| Image 6: South crater with terrace. |
The south crater was of ellipsoid shape of about 160m in east-west orientation and about 130m in north-south orientation. Inside the crater, about 1/2 of the area were covered by basalt rock which built a terrace about 45 meters below the crater rim. The terrace was located on the eastern crater rim, while the remaining 1/2 of the area was taken up by a lava lake. The lava lake surface was about 90m below the western rim of the south pit.
Almost no talus was found on the terrace. In comparison with the crater described in (2) and (3), the lava lake must have risen up to the present terrace altitude since early 2002, when the last report found the terrace at about 70m below the rim, and widely covered with talus.
The surface near the crater rim was broken by cracks of different width that ran in concentric circles around the crater pit. Many parts of the edge were hanging over empty space.
When descending into the pit, the crater walls were found to be very instable material from small gravel up to large boulders. material fell out of the wall by itself, or by simply being touched by a rope. A climber set off large boulders with his feet.
We considered a prolonged stay near the pit's edge a considerable risk and thus recommend serious safety measures.
Activity, gas bubbles, patterns...
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| Image 7: Erta Ale lava lake. | Image 8: Erta Ale lava lake closeup. | Image 9: Erta Ale lava lake at night. | Image 10: Erta Ale lava lake pattern with gas eruption. |
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| Image 11: An avalanche of
rocks penetrates the lava lake at nighttime (click image to see animated image series). |
Rockfall was observed on all days. Generally, material fell out of the south crater pit wall in two ways:
Particularly the avalances seemed to destabilize the crater rim. We observed an increasing frequency of avalanches towards the end of our stay. On Dec. 6, a series of three large avalanches detached from the northwestern wall at about 8:00 local time while two team members were in the crater to retrieve a lava sample. They were evacuated from the pit with no harm, but also with no lava sample.
Three observations were made after avalanches hit the lava lake:
Measurements were made to assess the temperatures of the funaroles in the fumarole field (ERTFUM).
Several earthquakes were noticed during the stay. No seismic equipment was present, but nontheless five seismic events were well observed. On Dec. 4, 2002, a short trembling was noticed by group members in the early evening hours. The following day, on Dec. 5, at 12:40 and 13:12 local time, at both times a series of two seismic events of each 1-2 second of duration and a several-second break was noticed through ground trembling and noise. No rapid change on the lava lake was noticed at that time.
Clear sky, Dec. 3 clouds, temp.
SE winds up the caldera, N at Dec. 3
During our stay, several species of animals were encountered, some of which we did not expect in an hostile environment as the Erta Ale Caldera. We observed:
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Lothar Fritsch: Vulkane erleben! Vulkan-Survial Hier klicken! |