Erta Ale volcano (Ethiopia): field report 19-21 Nov 2015 - lava lake at high levels

During our recent volcano expedition to the Danakil depression, we have observed the active lava lake of Erta Ale - which had been at very high level just a few meters before overflowing - for three continuous days (19-21 November 2015).
Upon our arrival on the morning of the 19th, the lava lake was only about 2-3 m below us. Our local guide explained that the lava lake had been very active in the past few weeks and risen so highly for the first time since its overflow in late 2010. Standing on the rim of the active vent within the large Erta Ale caldera, we observed a second terrace no more than 1 m below us. The fresh black pahoehoe lava of this level had been erupted and solidified a few days before.
Midday 19 November, the surface of the boiling lava lake was just 1.5 m below this second terrace. Throughout that day, however, the lava lake was rising steadily and had almost reached the height of the second terrace - but then stabilised at a mere 30 centimeters below the rim of the second terrace. A few active lava fountains at the edge of the lake periodically splashed fresh lava onto the second terrace,

with some droplets reaching the outer rim of the vent. Pele´s hair was continuously formed and blown around. Zigzag patterns broke up the lake´s black crust, pushing it to the lake´s edges where they were recycled into the molten lava. Degassing in the form of Strombolian activity and short-lived fountains was sometimes so intense that lava spattering could even be seen from the old caldera ridge where we had our camp.
Overflowing of the second terrace never occurred and by the morning of the 20th November the lava lake had actually dropped a few metres. Activity had thereby changed from Strombolian explosions and short-lived fountains from a few locations along the lava lake´s edge, to a seemingly quiet surface that once every 5-10 minutes would suddenly form a central depression before lava rose up in a large lava bubble that exploded, with recycling of the cooled crust in a series undulating lava waves (similar fluid dynamics as when one drops a pebble in a calm water body). During 20 and 21 November, the lava lake mainly showed this latter, large exploding bubble activity with only minor Strombolian activity or fountaining along the lakes edges. The level would rise and fall relatively quickly, between 5 m and 1 m below the edge of the second terrace. On the evening of the 21st, we witnessed how the lava lake rapidly rose about 3m, starting from 5 m below the second terrace. This
fast change in the lava lake´s surface level coincided with a different activity, namely fresh red-hot lava seeping up along the zigzag cracks and overflowing a large part of the thin crust in a matter of seconds.
The fumarole fields along the rim of Erta Ale´s second active vent continue to be active, with the centrally located tall hornito, built during the 2012 magmatic eruption there, also still degassing.