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Journal Articles Bulletin of Volcanology Year : 2022

The anatomy of a channel-fed `a`ā lava flow system

Abstract

The stabilized channel is a crucial element of an `a`ā flow system, delivering lava to forward extending zones of dispersed flow. However, the term stable implies that channel geometries, lava properties, and dynamics are invariable. However, just how stable are these in space and time? To answer this question, we constrain the degree of variation for an extremely well-exposed stabilized channel on Kīlauea (Hawai'i), carrying out mapping, facies analyses, and sampling down the entire 5.5-km length of the channel-levee unit. Though active for only 3 days, flow and emplacement dynamics were highly unstable, experiencing both temporal and spatial variation. This resulted in a complex construction history and solidified channel form, where construction comprised three emplacement phases: initial, free-flowing, and late-stage ponded. These three emplacement phases were coupled with variation in underlying substrate, slope, and volume flux. These temporally and spatially varying conditions combined to result in four channel types and geometries (tubed, stable, ponded, and braided); five lava facies (smooth pāhoehoe, rough/spiney, slabby, transitional, and `a`ā); and four levee types (initial-rubble, surge-fed overflow, pond-fed overflow, and accretionary). Complexity in channel form was reflected in cooling rates that ranged from 6.6 °C km−1 for free-flowing conditions to 17.7 °C km−1 for ponded lava. Likewise, vesicularities ranged from gas-rich (as high as 74% vesicles) to outgassed (as low as 27%). Due to the high degree of variance at this system, we suggest that feeder channel is a better term for this component of a channel-fed `a`ā lava flow field. This term stresses the role of the channel in feeding zones of dispersed flow and is not a term that implies channel form and flow dynamics are unchanging. Although flow conditions can be complex, flow for some periods can be stable. If depths, widths, temperatures, and crystallinities during phases of below-bank stability can be identified, then the system can be modelled. We show this by fitting down-channel variation in flow properties for stable periods to output of the FLOWGO thermorheological model. In doing this, we provide a dataset that can guide and benchmark models aimed at simulating the dynamics and properties of channel-fed systems.
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Dates and versions

insu-03825083 , version 1 (09-07-2023)

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A. J. L. Harris, S. K. Rowland, Magdalena Oryaëlle Chevrel. The anatomy of a channel-fed `a`ā lava flow system. Bulletin of Volcanology, 2022, 84, ⟨10.1007/s00445-022-01578-0⟩. ⟨insu-03825083⟩
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