By Mark Dunphy,
Satellite imagery has confirmed that the Nabro volcano in Eritrea has once again started emitting ash, just 24 hours after the Toulouse-based Volcanic Ash Advisory Centre (VAAC) reported activity at the north east African stratovolcano had ceased.
With the exception of Thursday, the volcano has been spewing ash continuously since it erupted for the time in its recorded history on June 12 last. During the 17-day period much of northern Ethiopia and parts of neighbouring Djibouti and Sudan have been affected by the ash cloud, which also disrupted air traffic in the region.
Image from Modis, captured at 11am (GMT) Friday reveals that eruption activity has restarted after a brief 24-hour lull. Ash is seen drifting west from the site over the Eritrean border into Ethiopia and toward the eastern Sudan border.
Since the beginning of the recent eruption, a dense plume of water vapor, gas, and ash has concealed the summit of the Nabro volcano. New images from June 29 finally provided a nearly unimpeded view of the summit, where lava flowed out of the erupting vent and down the slope of the volcano.
Nabro began its eruption explosively on June 12, 2011. The powerful eruption sent plumes of ash streaming over North Africa and the Middle East, and pumped vast quantities of sulfur dioxide into the atmosphere. The ash halted flights in East Africa for a time. The eruption killed seven people, said the Eritrean government, and other reports indicate that thousands were affected in both Eritrea and Ethiopia, though news from the region is sparse.
More recently, the volcano has eased into a quieter, lava-oozing phase, as shown in these images from the Advanced Land Imager (ALI) on the Earth Observing-1 (EO-1) satellite. The top image shows the volcano in visible and infrared light (shortwave infrared, near infrared, and green). The hot lava glows orange-red, fading to black as it cools. The long flow on the west side of the volcano is mottled with black, a sign that the surface is cooling. The lava to the east and south of the vent appears to be newer, since little of it has cooled. It is possible that the cooling lava in the western flow diverted the fresh lava to the south and east.
Throughout the eruption, satellite images have been nearly the only source of new information about activity at the volcano. Detailed images like this one provide insight into how erupting lava is behaving. For example, volcanologist Erik Klemetti used previous images from ALI to estimate how quickly the lava is moving and to guess at how thick (viscous) the lava is.
The Nabro volcano has not erupted in recorded human history, but lava flows near the volcano are relatively recent geologically. Nabro is part of the very active East African Rift, where three tectonic plates are pulling away from each other. As the Earth’s crust thins in the region, volcanoes rise in weak spots.
NASA Earth Observatory image by Robert Simmon, using EO-1 ALI data. Caption by Holli Riebeek. Instrument: EO-1 – ALI
Irish Weather Online was one of the foremost reporters of the eruption when many mainstream news agencies ignored one of the most geologically and historically significant eruptions in modern African History.