Monday 13 June 2011

The Puyehue Eruption, Chile, 2011.

Puyehue is a stratocone volcano (i.e. a cone-shaped volcano of the kind seen in Hollywood movies) in central Chile. It forms part of the Puyehue-Cordón Caulle Volcanic Complex, along with the Cordón Caulle volcanic fissure and Cordillera Nevada caldera. Puyehue began erupting on June 3rd this year, the complex having been dormant since 1960, when, following an earthquake with a magnitude of 9.5 on the Richter scale (the largest earthquake ever recorded), the Cordón Caulle fissure erupted throwing ash eight kilometers into the air.

See The Puyehue-Cordón Caulle Volcanic Complex.

It is not clear what part of the volcanic complex the eruption occurred in - the complex is rather remote - it could be Puyehue itself or the Cordón-Caulle fissure. There has been an evacuation of the immediate area, although it is unclear what proportion of the population has actually left.

The ash cloud is proving to be far more disruptive than the volcano itself; this has caused heavy ash-falls in neighboring Argentina and Uruguay, leading to power failures as ash settles on power lines and brings them down, as well as the closure of airports in all three countries. The Argentine army has been dispensed to the area to help with the clean-up operation.

From South America the ash-cloud has spread east across the southern ocean (ash clouds entering the upper atmosphere always spread to the east, as this part of the atmosphere does not rotate as fast as the solid Earth; effectively the ash stays still while the planet moves beneath it), missing the tip of Africa then arriving in South East Australia and New Zealand, where it is causing considerable disruption to air traffic. Most airlines affected have agreed to follow guidelines and remain grounded while the crisis lasts, but worryingly Air New Zealand appear to be following the lead of British and Irish airlines and are proposing to fly during the crisis, hoping to dodge the ash clouds. Volcanic ash is particularly dangerous to jet aircraft as the fine ash can melt inside the hot engines, coating their innards with volcanic glass.

Satellite image showing the progress of ash from the Puyehue eruption (false coloured in yellow) around the southern hemisphere.

In addition to the ash cloud a pyroclastic flow (avalanche of hot volcanic material) has apparently reached the Nilahue River, raising the temperature from 10°C to 45°C and causing a mass die-off of salmon. Other rivers in the area are reported to be partially blocked by ash, leading to some flooding of farmland; there are no reports of any urban areas being threatened, nor have there been any reports of loss of life directly connected to the volcano.

The volcanic cloud has produced some spectacular lightning displays. These occur when convection currents in within the cloud carry particles with different charges apart; eventually the charge differential becomes to great and an electric discharge occurs.

See also The Grímsvöten Volcano and
Volcanos on Sciency Thoughts YouTube