High-speed lava flow infrasound from Kīlauea’s fissure 8 and its utility in monitoring effusion rate

Abstract

The 2018 eruption of Kīlauea Volcano produced large and destructive lava flows from the fissure 8 (Ahu 'aila 'au) vent with flow velocities up to 17 m s −1 , highly variable effusion rates over both short (minutes) and long (hours) time scales, and a proximal channel or spillway that displayed flow features similar to open channel flow in river systems. Monitoring such dynamic vent and lava flow systems is a challenge. Our results demonstrate that infrasound, combined with groundbased observations and imagery from unoccupied aircraft systems (UAS), can be used to distinguish vent degassing activity from high-speed lava flow activity. We use spectral characteristics and the infrasound frequency index (FI) to distinguish spillway infrasound from vent infrasound. Comparing FI with flow speeds derived from UAS videos reveals that spillway infrasound only occurs when flow speeds were sufficiently high to cause a supercritical flow state and breaking waves (Froude values > 1.7), and we propose that the spillway signals are produced primarily through the interaction of the turbulent lavafree surface with the atmosphere. We show that FI can also provide a means to track bulk effusion rate. Our results indicate that infrasound offers a new way to characterize lava flow channel hydraulics and is a powerful tool for monitoring effusive eruptions when high-speed flows are possible.

Can Lava Flow Like Water? Assessing Applications of Critical Flow Theory to Channelized Basaltic Lava Flows

“…Measurements of wave trains in the active lava channel were made possible by regular channel monitoring with airborne remote sensing (Desmither et al, 2021;Dietterich et al, 2021;Lyons et al, 2021;Patrick et al, 2019). Airborne lidar captured elevation data from the lava-flow surface proximal to the vent between 8 and 12 July 2018 (USGS, 2018a, 2018b; available on OpenTopography).…”

“…Figure11. Downflow wave-train propagation during pulsing periods when flow velocity increased and decreased dramatically over minutes(Dietterich et al, 2021;Lyons et al, 2021;Patrick et al, 2019). (a) 12 July lidar hillshade of the proximal fissure 8 channel showing the widening reach past the channel bend and the extent of panels (b and c).…”

A look ahead to the next decade at US volcano observatories

“…a Kīlauea summit and East Rift Zone map with images of the summit caldera collapse (evacuated Hawaiian Volcano Observatory, HVO, in the foreground) and an unoccupied aircraft system (UAS) survey of the lava flows in Leilani Estates. b Integration of novel infrasound and UAS video analysis of magnitude, source location, and channel velocity of the main 2018 vent (fissure 8, Ahuʻailāʻau) capturing short-period changes in effusion rate (pulses) (redrafted after Lyons et al 2021 ). c Probabilistic lava flow forecasts in 2018 used DOWNFLOW (Favalli et al 2005 ) to model the likelihood of different flow routes from new vents (e.g., fissure 17; Neal et al 2019 ), building on the traditional use of steepest descent lines (Kauahikaua et al 2017 ) …”

“…The Kīlauea crisis response built upon this decade of progress, demonstrated by early detection and characterization of eruption precursors for forecasting (Neal et al 2019 ), syn-eruptive expansion of instrumentation (Shiro et al 2021 ), and multiparametric studies of volcanic plumbing system and eruption dynamics now resulting from these data (e.g., visual-infrasound lava channel dynamics, Fig. 2b ; Lyons et al 2021 ).…”

Fitting Jet Noise Similarity Spectra to Volcano Infrasound Data

“…The deployed Chaparral 60 UHP infrasound sensors have a flat response between 0.03 and 200 Hz at a 400 Hz sampling rate. Data from this infrasound array has been used to characterize cyclic effusion between July 14 and 21 (Patrick et al, 2019) and associated back-azimuth changes tracking the infrasonic source between the fountain location and the spillway during surges (Lyons et al, 2021). Here, we analyze 24 h of eruption data from June 16 to 17 and compare it to post-eruptive signal from August 5 to 6 shown in Figure 5.…”