Infrasonic crackle and supersonic jet noise from the eruption of Nabro Volcano, Eritrea

Abstract

The lowermost portion of an explosive volcanic eruption column is considered a momentum‐driven jet. Understanding volcanic jets is critical for determining eruption column dynamics and mitigating volcanic hazards; however, volcanic jets are inherently difficult to observe due to their violence and opacity. Infrasound from the 2011 eruption of Nabro Volcano, Eritrea has waveform features highly similar to the “crackle” phenomenon uniquely produced by man‐made supersonic jet engines and rockets and is characterized by repeated asymmetric compressions followed by weaker, gradual rarefactions. This infrasonic crackle indicates that infrasound source mechanisms in sustained volcanic eruptions are strikingly similar to jet noise sources from heated, supersonic jet engines and rockets, suggesting that volcanologists can utilize the modeling and physical understandings of man‐made jets to understand volcanic jets. The unique, distinctive infrasonic crackle from Nabro highlights the use of infrasound to remotely detect and characterize hazardous eruptions and its potential to determine volcanic jet parameters.

Investigating Spectral Distortion of Local Volcano Infrasound by Nonlinear Propagation at Sakurajima Volcano, Japan

“…Visual observations of wavefronts above erupting vents imply near‐source shock wave formation (Ishihara, ; Yokoo & Ishihara, ), but these waves do not necessarily indicate supersonic sources (Genco et al, ). Nonlinear propagation has been proposed as a possible explanation for asymmetric infrasound waveforms, which are commonly observed at volcanoes worldwide (e.g., Anderson et al, ; Fee et al, ; Marchetti et al, ; Matoza et al, ; Medici et al, ). However, this phenomenon can alternatively be explained with linear propagation and crater rim diffraction (Kim & Lees, ) or fluid flow at the source (Brogi et al, ).…”

“…Furthermore, while Equation was developed for analysis of acoustic signals in the audible frequency range, its basis in the Burgers equation dictates that it should be valid for any wave that steepens during propagation due to finite‐amplitude effects. Nonlinear steepening of infrasonic waves has previously been postulated at volcanoes (Fee et al, ; Lonzaga et al, ; Marchetti et al, ; Matoza et al, ; Morrissey & Chouet, ; Yokoo & Ishihara, ), so we consider the application of equation to Sakurajima infrasound appropriate.…”

Aeroacoustics of volcanic jets: Acoustic power estimation and jet velocity dependence

“…Recent work has suggested that eruptions involving volcanic jet flows generate a low‐frequency (infrasonic) form of the aeroacoustic jet noise produced by smaller scale man‐made jets [ Matoza et al , ; Fee et al , , , ]. Jet noise is the noise generated by a turbulent jet flow itself.…”

Researching the Earth—and a Few of Its Neighbors

“…The role of supersonic flow in volcanic eruptions has become more commonly incorporated into interpretations of volcanic events (e.g., Woods & Bower 1995, Lagmay et al 1999, Mitchell 2005, Fee et al 2013. Erosion surfaces, such as those at the Mount St. Helens lateral blast (Kieffer & Sturtevant 1988) or Lascar Volcano, Chile (Sparks et al 1997), are rarely exposed.…”