Erta Ale volcano (Ethiopia), activity summary 25-28 Nov 2010: lava lake overflows

Significant changes have occured recently at Erta Ale volcano, the lava lake having filled up the south crater and overflowed repeatedly into the N and NW section of the caldera floor adjacient to the crater.
During our latest expedition, we stayed on Erta Ale from early 25 Nov - 28 Nov. Upon our arrival, those changes very obvious. The lava lake had risen to the level of the former lower N section, the old terrace was gone, and the whole south crater was filled by overflows to the level of the lower old N-NW rim. Flows had indeed overflowed that section of the old crater circumference on a length of about 150m, or about 1 third of the old circumference. The still hot overflows had covered the outside caldera floor to about 50-100 distance, and one long flow, probably dated from 24 Nov (judging from its temperature) had almost reached the W caldera walls, as it followed the descending floor of the caldera in that direction.
The still active lake itself was circular, about 40 m in diameter (about 2 thirds to half its size observed in 2008 and 2009), contained within a low ring-shaped wall and extremely active. Degassing fountains kept the whole surface violently boiling most of the time.
At rythms of around 30 minutes, the lava level was rising and falling by ca. 2-4 meters. Fountaining often projected incandescent spatter to 30-70 m vertical height. During the 3 days observation, several more intense phases were observed, when the lava overflowed about 12 times and fed new flows emplacing themselves on top of the young flows already outside the former crater. The morphology of the ring wall constantly changed as more and more lava flowed outside, parts collapsing and rebuilding by fountaining activity. The overall average level rose an estimated 3-5 meters during this time and the lava lake looked like a small shield volcano of its own occupying the old south crater.
The deeper north crater had not changed too much since our last visit. In its center, a large hornito with a glowing vent was observed to sometimes spatter lava. In one occasion, an extremely bright glow from the N crater became visible. When we arrived, we saw a large fresh flow that had surged out from the hornito and covered most of the crater floor, but we were unable to observe repeated events like this.
Photos from the activity will be posted soon on our website.

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