Pyroclastic density currents (PDCs) are a major volcanic hazard, whose variability of triggering and deposition mechanisms suggests highly complex and different initial states to be considered. Here, we describe block and ash flow deposits from the March 2019 eruption of Bezymianny volcano, Kamchatka. Ash clouds from this eruption extended into the Pacific Ocean, while block and ash flow deposits were found widely across the slopes of the edifice. We use satellite and drone-based photogrammetry to show material dispersal and accumulation during the eruption. We also use these photogrammetric data to obtain basic granulometry, suggesting dominantly 60 cm block dimensions, some exceeding 2 m in scale, embedded in a fine ash matrix. In addition, we sampled the deposit and herein demonstrate how distinct petrographical features can be used to distinguish the type of block and ash flow. Deposit characteristics, density, dimension, and petrography suggest that PDC initiation occurred during an eruptive episode conventionally considered as a "boiling over" event. This activity is characterized by rapid magma volume expansion due to intense gas exsolution which is driving a frothed mass out of the vent leading to the formation of large but highly vesicular juvenile blocks. Such an eruption style is transitional between effusive (lava dome forming) and explosive activity, and we suggest a new term "effervescent fountaining" to replace the term "boiling over" as a more appropriate description of such an eruption. Material dispersal, density of juvenile material, and Fe-Ti mineralogy are useful features to distinguish different types of block and ash flow deposits. These characteristics are also applicable to deposits from eruptions and deposits within the prehistoric geological record, improving our understanding of historic eruption patterns.
Auer, A., Walter, T., Ostorero, L., Belousov, A., Belousova, M., Balcone-Boissard, H., et al. (2025). Effervescent fountaining—a transition between explosive and lava-dome forming eruptions: evidence from “boiling-over” pyroclastic flows from the March 2019 eruption of Bezymianny volcano, Kamchatka. BULLETIN OF VOLCANOLOGY, 87(10) [10.1007/s00445-025-01868-3].
Effervescent fountaining—a transition between explosive and lava-dome forming eruptions: evidence from “boiling-over” pyroclastic flows from the March 2019 eruption of Bezymianny volcano, Kamchatka
Ostorero L.;
2025
Abstract
Pyroclastic density currents (PDCs) are a major volcanic hazard, whose variability of triggering and deposition mechanisms suggests highly complex and different initial states to be considered. Here, we describe block and ash flow deposits from the March 2019 eruption of Bezymianny volcano, Kamchatka. Ash clouds from this eruption extended into the Pacific Ocean, while block and ash flow deposits were found widely across the slopes of the edifice. We use satellite and drone-based photogrammetry to show material dispersal and accumulation during the eruption. We also use these photogrammetric data to obtain basic granulometry, suggesting dominantly 60 cm block dimensions, some exceeding 2 m in scale, embedded in a fine ash matrix. In addition, we sampled the deposit and herein demonstrate how distinct petrographical features can be used to distinguish the type of block and ash flow. Deposit characteristics, density, dimension, and petrography suggest that PDC initiation occurred during an eruptive episode conventionally considered as a "boiling over" event. This activity is characterized by rapid magma volume expansion due to intense gas exsolution which is driving a frothed mass out of the vent leading to the formation of large but highly vesicular juvenile blocks. Such an eruption style is transitional between effusive (lava dome forming) and explosive activity, and we suggest a new term "effervescent fountaining" to replace the term "boiling over" as a more appropriate description of such an eruption. Material dispersal, density of juvenile material, and Fe-Ti mineralogy are useful features to distinguish different types of block and ash flow deposits. These characteristics are also applicable to deposits from eruptions and deposits within the prehistoric geological record, improving our understanding of historic eruption patterns.
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