Amorphous silica coating on flank deposits of the 1783 CE eruption at Asama volcano

Silica-rich coatings of up to 660 μm thickness were found on the juvenile volcanic lapilli and blocks of the 1783 CE pyroclastic flow deposits 1.9–3.6 km northeast of the Maekake crater of Asama volcano in Central Japan. These coatings are composed of fine-grained volcanic ash particles with silica-...

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Bibliographic Details
Published in:Journal of volcanology and geothermal research 2021-03, Vol.411, p.107149, Article 107149
Main Authors: Nakatani, Takayuki, Sugaya, Sarina, Yasui, Maya, Okumura, Satoshi, Nakamura, Michihiko
Format: Article
Language:English
Subjects:
Acid rain
Amorphous silica
Asama
Rock coating
Vog
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Summary:Silica-rich coatings of up to 660 μm thickness were found on the juvenile volcanic lapilli and blocks of the 1783 CE pyroclastic flow deposits 1.9–3.6 km northeast of the Maekake crater of Asama volcano in Central Japan. These coatings are composed of fine-grained volcanic ash particles with silica-rich cement. Raman spectroscopic measurements revealed that the interstitial silica-rich phase is hydrous amorphous silica and is considered to be a reaction product of ash particles with acidic volcanic rain and fog like volcanic smog (vog) as it has been recorded in Hawaii. The formation of amorphous silica without jarosite and the preferential alteration of plagioclase compared with pyroxene indicate that the reaction occurred with a sulfuric acid solution of pH 
ISSN:0377-0273
1872-6097
DOI:10.1016/j.jvolgeores.2020.107149