A globe-circling eruption
On June 4, 2011, after a half-century of quiet, the Puyehue-Cordón Caulle Volcanic Complex awoke with a powerful Plinian eruption. A fissure in the Cordón Caulle rift zone opened, sending a column of ash and gas soaring to an altitude of 10 to 12 kilometers. The initial explosion was intense, releasing energy equivalent to 70 Hiroshima atomic bombs and ejecting an estimated 100 million tons of ash, sand, and pumice. This ranked as a 5 on the Volcanic Explosivity Index (VEI), making it one of the largest eruptions of the 21st century.
The fine, glassy ash, primarily rhyolitic in composition, entered high-altitude jet streams. These powerful winds transported the plume eastward across Argentina and out over the Atlantic Ocean. In a matter of days, the ash cloud reached Australia and New Zealand, thousands of kilometers away. The plume completed its first circumnavigation of the Southern Hemisphere in about two weeks. The global spread of the ash created significant disruption. Hundreds of flights were canceled in Australia and New Zealand, stranding tens of thousands of passengers. Volcanic ash is a serious threat to aviation; its fine particles can melt in the heat of a jet engine, solidifying into glass and causing engine failure. The disruption continued for weeks as the main cloud circled the globe a second time and winds stirred up previously deposited ash in Patagonia.
A landscape transformed
Although the ash cloud made international headlines, the local and regional impacts were immediate and severe. Enormous quantities of porous, lightweight pumice rained down on the surrounding landscape. This pumice washed into nearby lakes, such as Lake Nahuel Huapi, forming vast floating "rafts" that were visible from space. These rafts covered large sections of the lakes, disrupting boat transport.
The region's rivers were also dramatically affected. The Nilahue and Golgol rivers became choked with tephra, the collective term for all airborne volcanic material. This influx of hot material raised the water temperature of the Nilahue River to 45°C (113°F), killing an estimated 4.5 million fish and impacting local aquaculture. The ashfall blanketed millions of hectares of Patagonian steppe, causing serious problems for livestock. Sheep that ingested the ash-covered vegetation suffered from dental abrasion and fluoride poisoning. In some nearby Argentinean towns, ash fell to a depth of 15 centimeters. The cleanup was a massive undertaking, and in the arid steppes, the fine ash remained loose on the surface for months, frequently remobilized by strong winds, causing persistent air quality problems.