Calbuco volcano eruption – Expert reaction

The eruption of the Calbuco volcano in Chile – for the first time in over 40 years –  is causing headlines around world.

New Zealand coverage includes, reporting in the New Zealand Herald, and TVNZ News. MetService has stated that the  Wellington Volcanic Ash Advisory Centre, in collaboration with international partners will monitor the resulting ash cloud and its potential impact on air travel.

Our colleagues at the UK SMC collected the following expert commentary. Feel free to use these quotes in your reporting. If you would like to contact a New Zealand expert, please contact the SMC (04 499 5476;

Prof David A Rothery, Professor of Planetary Geosciences at The Open University, said:

“Calbuco volcano has erupted apparently without warning, though the eruption itself was of course recorded by local seismometers.

“Calbuco had been quiet since a 4-hour long eruption on 26 August 1972, except for an episode of fumarolic gas emission on 12 August 1996. One of the largest historical eruptions in Chile took place here in 1893-4, throwing  30 cm bombs as far as 8 km from the summit crater (for more see here). I understand that there have been two big eruptions so far in the past 24 hours, and that more are possible. Pictures show a 15 km high column of ash rising from the volcano and then spreading downwind.

“The current activity has the potential to produce pyroclastic flows, which are fast-moving ground-hugging currents of ash and hot air. These are deadly, and the 20 km radius evacuation zone that has been declared is a wise precaution.  After the eruption has ceased, ash that has settled to the ground will pose a risk of lahars (volcanic mudflows) that can choke water-courses and destroy bridges.

“Volcanic ash is dangerous to aircraft and the Buenos Aires Volcanic Ash Advisory Centre (VAAC) has issued a warning of ash up to 40,000 ft across Chile and Argentina. I expect the hazard to decline unless the eruption reinvigorates and continues.

“Calbuco is about  90 km south of the Puyehue-Cordon Caulle volcano whose eruption in June 2011 spread airborne ash round the globe, leading to airspace closures in Australia.

“These and other volcanoes in the Andes are present as a result of plate tectonic processes, which also cause earthquakes in the region. The floor of the Pacific ocean (actually the Nazca Plate) is being pushed (subducted) below South America. This leads to melting at depth and hence the magma that rises to feed the volcanoes. Because seawater has been transported into the melting zone, the magma contains gases such as water vapour and carbon dioxide , and violent expansion  of gas bubbles is what makes eruptions at these volcanoes so explosive.

“Calbuco’s summit is 2003 m above sea level, and it lies less than 30 km northeast of Puerto Montt, which has a population of nearly 200 thousand.”