AGU Press Releases and Images

December 2003

FOR IMMEDIATE RELEASE

Hawaiian Infrasound: A Mele of Fire, Wind, and Water

San Francisco - Some of the more interesting infrasonic signals routinely observed in Hawaii are associated with volcanic activity, severe weather, and ocean processes. "Infrasound extends our sense of hearing so that we can perceive objects that are much larger and farther away than normal," says Milton Garces, Director of the Infrasound Library at the School of Ocean and Earth Science and Technology, University of Hawaii. "With infrasound, we can "hear" storms out in the open sea, surf from distant coasts, and volcanoes erupting on remote islands."

An example of this is Kilauea volcano. It is one of the most active volcanoes in the world, and infrasonic observations from an expedition in November of 2002 strongly suggest that continuous infrasound in the 1-8 Hz frequency band may be generated from the lava tube system of Puu Oo and may correspond to pressure instabilities in the magma flow. The observed eruption signal corresponds to low-level effusive activity, and appears to only propagate for a few tens of kilometers.

In contrast, signals associated with severe weather in the ocean may propagate for thousands of kilometers. These infrasonic signals, known as microbaroms, are close relatives of microseisms and occupy the 0.1-0.6 Hz frequency band. Researchers believe that these signals are generated by the nonlinear interaction of ocean surface waves generated by storms, and show some observations from hurricanes Daniel and Jimena. When these waves hit the Hawaiian coastline, they can produce world class surf as well as substantial infrasonic energy.

Garces and colleagues suggest that surf infrasound can be generated by the collapse of the wave upon itself (barreling), impact against a cliff, or slamming against a shallow reef, as seen during the epic 2002-2003 Hawaiian winter. "Our observations in Hawaii demonstrate how infrasound can provide useful information of solid earth-ocean-atmosphere interactions," says Garces. "This can be integrated with other technologies to enhance our basic understanding of geophysical processes."

"The turn of the millennium marked the beginning of the Infrasound Renaissance," says Garces. "As our community builds momentum, we have been given a unique opportunity by the National Science Foundation to integrate infrasound with other methodologies in the geosciences. Infrasound can enhance seismic (touch), optical (sight), and chemical (smell and taste) analyses of atmospheric circulation, earthquakes, storms, eruptions, and swells. Geophysics has been deaf for far too long, and our infrasound community has the motivation and technology to turn silence into eloquence."

For more information, contact Milton Garces milton@isla.hawaii.edu (808) 327-6206 (808) 960-6393 (cell) www.isla.hawaii.edu

Director of Infrasound Laboratory, Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii

73-4460 Queen Kaahumanu Hwy., #119 Kailua-Kona, HI 96740-2638, USA

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Songs of the North Pacific: Ocean waves in the open ocean interact nonlinearly with each other and radiate continuous infrasonic vibrations known as microbaroms. This song of the sea propagates for thousands of kilometers and is recorded by station all over the globe.

(Image credit UH/ISLA)

Rumbling surf: When the ocean waves break against the coastline, they amplitude of the sound they generate scales with the wave height.

(Image credit UH/ISLA)

Babbling lava: Even a relatively quiet volcano like Kilauea generates infrasound associated with the flow of magma in the conduit that transports lava to the sea.

(Image credit UH/ISLA)

For more information, contact Tara Hicks.

Last Updated Wed December 3, 2003. Maintained by Tara Hicks.

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