• journal_title：Geology
• Contributor：Martin Reich ; Alejandro Zúñiga ; Álvaro Amigo ; Gabriel Vargas ; Diego Morata ; Carlos Palacios ; Miguel Ángel Parada ; René D. Garreaud
• Publisher：Geological Society of America
• Date：2009-
• Format：text/html
• Language：en
• Identifier：10.1130/G25457A.1
• journal_abbrev：Geology
• issn：0091-7613
• volume：37
• issue：5
• firstpage：435
• section：Articles

High-resolution transmission electron microscopy (HRTEM) observations of unaltered volcanic air-fall deposits from the ongoing lava dome explosive eruption at Chaitén Volcano, Chilean Patagonia, revealed the presence of highly crystalline silica nanofibers in the respirable fraction of the volcanic ash (<4 μm). The nanofibers are identified as the high-temperature (>240 °C), beta form of cristobalite, with average lengths of hundreds of nanometers and widths on the order of tens of nanometers. We propose that the beta-cristobalite nanofibers are formed during explosive eruptions by the reduction of amorphous silica by carbon monoxide to its reactive suboxide SiO, which is later oxidized to form one-dimensional crystalline silica nanostructures. Nucleation and growth of the nanofibers are enhanced by the high surface area of the micrometer- to nanometer-sized fragments of silica glass in the volcanic column. The formation of nanocrystalline cristobalite fibers during explosive lava dome eruptions poses new challenges for the assessment of the short- and long-term health hazards associated with the respirable nanofibrous components of volcanic ash.