Inflated pyroclasts in proximal fallout deposits reveal abrupt transitions in eruption behaviour

Jones, Thomas J. and Moigne, Yannick Le and Russell, James K. and Williams-Jones, Glyn and Giordano, Daniele and Dingwell, Donald B. (2022) Inflated pyroclasts in proximal fallout deposits reveal abrupt transitions in eruption behaviour. Nature Communications, 13. ISSN 2041-1723

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During explosive eruption of low viscosity magmas, pyroclasts are cooled predominantly by forced convection. Depending on the cooling efficiency relative to other timescales, a spectrum of deposits can be formed. Deposition of hot clasts, above their glass transition temperature, can form spatter mounds, ramparts and clastogenic lava flows. Clasts may also be deposited cold, producing tephra cones and blankets. Thus, the deposit and pyroclast type can provide information about eruption dynamics and magma properties. Here we examine pyroclasts from Tseax volcano, British Columbia, Canada. These newly identified inflated pyroclasts, are fluidal in form, have undergone post-depositional expansion, and are found juxtaposed with scoria. Detailed field, chemical and textural observations, coupled with high temperature rheometry and thermal modelling, reveal that abrupt transitions in eruptive behaviour — from lava fountaining to low-energy bubble bursts — created these pyroclastic deposits. These findings should help identify transitions in eruptive behaviour at other mafic volcanoes worldwide.

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Journal Article
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Nature Communications
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21 Sep 2022 11:10
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21 Sep 2022 11:10