IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A2_3E-O14

Room A1

Date/Time: July 24 12:15-12:30

Infrasonic Crackle from the 2011 Eruption of Nabro Volcano, Eritrea: Evidence forSupersonic Jet NoiseDavid Fee1 , Robin Matoza2 , Kent Gee3 , Tracianne Neilsen3 , Darcy Ogden2
1

Geophysical Institute, Alaska Volcano Observatory, University of Alaska Fairbanks, USA, 2 Institute ofGeophysics and Planetary Physics, Scripps Institution of Oceanography, USA, 3 Department of Physicsand Astronomy, Brigham Young University, USA
E-mail: dfee@gi.alaska.edu

An understanding of volcanic jets is critical to determining eruption column dynamics and mitigating volcanic
hazards. However, volcanic jets are inherently difficult to observe directly due to their violence, opacity, andcomplex multi-phase and multi-component flow features. Recent work has shown similarities between the soundproduced from explosive volcanic jets and man-made jet engines and rockets [Matoza et al., 2009]. We show that
infrasound generated by the eruption of Nabro Volcano, Eritrea has waveform features highly similar to waveforms
associated with the crackle phenomenon uniquely produced by supersonic jet engines and rockets. Crackle ischaracterized by repeated asymmetric pressure pulses with higher-amplitude compressions than rarefactions andcan be quantified by the skewness (a measure of the asymmetry of the waveform probability density function).
The infrasonic crackle from Nabro reported here strongly indicates that infrasound from some volcanic eruptions
is produced in similar ways to man-made jet noise from heated, supersonic jet engines and rockets. Noisesources and flow dynamics of jet engines and rockets are better characterized and understood than volcanic jets,suggesting volcanologists could utilize the modeling and physical understandings of man-made jets.
Nabro Volcano, Eritrea erupted explosively on 12 June 2011 and injected vast quantities of SO2 into the upper
troposphere and stratosphere, disrupted air traffic, and severely affected communities in this remote region.
Significant infrasound was recorded by two infrasound arrays: IS19 (Djibouti, 264 km) and IS32 (Kenya, 1708 km).
The IS19 infrasound array detected the eruption with high signal-to-noise and provides the most detailed eruption
chronology available, including eruption onset, duration, and changes in intensity. As seen in numerous otherstudies [Fee and Matoza, 2013], sustained low-frequency infrasound from Nabro is coincident with high-altitude
emissions. The unique, distinctive infrasonic crackle from Nabro highlights the potential to use infrasound todetermine some volcanic jet characteristics and parameters such as velocity, mass eruption rate, temperature,etc. Additionally, we reiterate the potential to use infrasound as a real-time, remote means to detect hazardous
emissions, particularly in remote and poorly monitored regions.

Fee, D. and Matoza, R.S., 2013.

An overview of volcano infrasound: From hawaiian to plinian, local toglobal. Journal of Volcanology and Geothermal Research, 249: 123-139, doi: 10.1016/j.jvolgeores.2012.09.002.

Matoza, R.S., Fee, D., Garces, M.A., Seiner, J.M., Ramon, P.A. and Hedlin, M.A.H., 2009.
noise from volcanic eruptions. Geophys. Res. Lett., 36(L08303) doi:10.1029/2008GL036486.

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Infrasonic jet