Monotonic infrasound and Helmholtz resonance at Volcan Villarrica (Chile)

• Published in: Geophysical research letters Vol. 38; no. 6; pp. np - n/a
• Main Authors: Goto, A., Johnson, J. B.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.03.2011; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Cameras; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geophysics; Helmholtz resonance; Holes; Infrasound; Lakes; lava lake; Roofs; strombolian activity; Vents; Visual observation; Volcan Villarrica; Volcanoes; South America; Chile; vents; joints; Resonance frequency; Visual observation; Infrasound; aluminum; resonance; Diameter; lava lakes
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2011GL046858

Monotonic infrasound with stable peaked frequency of 0.77 Hz was recorded at Volcan Villarrica in January 2010. Similar monotonic infrasound had been previously reported at Villarrica (e.g., Ripepe et al. [2010]). Using joint infrasound and visual observations from a suspended camera we demonstrate that the likely source of infrasound is Helmholtz resonance produced from a cavity with volume 105 m3 that separates the active convecting lava lake from an overhanging spatter roof. Spatter roof dimension (65 m diameter) and vent diameter (10 m) in the roof are constrained from video observations. Assuming a cylindrical cavity we infer a cavity height of 31 m that is corroborated by video records of spatter drips. The drips take as long as 2.2 s to fall from the roof into the lake, corresponding to a height of more than 24 m, which is in good agreement with the observed resonance frequency.