Monday, December 19, 2005

Singing Berg

By now you've likely read about the singing iceberg B-09A (NOT pictured in the NOAA image above), but have you heard it? Now you can listen to an MP3 of the berg. Found near the Ekstroem ice shelf on Antarctica's South Atlantic coast by scientists from Germany's Alfred Wegener Institute, authors Müller, Schlindwein, Eckstaller, and Miller write in Science:
Sustained harmonic tremor signals were recorded by the seismographs of the German Neumayer Base seismological network in western Dronning Maud Land, Antarctica. These tremor episodes, lasting up to 16 hours, were recorded up to 820 kilometers from the source. Their spectra show narrow peaks with fundamental frequencies ranging from 0.5 to 6 hertz, more than 30 integer harmonic overtones, and frequency gliding, resembling volcanic tremor. Frequency-wave number analysis suggested a moving source, which was recognized as iceberg B-09A traveling along the coast of eastern Antarctica. The most probable tremor sources are fluid-flow-induced vibrations inside the iceberg's tunnel/crevasse systems.
Their press release notes:
Tracking the signal, the scientists found a 50 by 20 kilometer iceberg that had collided with an underwater peninsula and was slowly scraping around it. "Once the iceberg stuck fast on the seabed it was like a rock in a river," said scientist Vera Schlindwein. "The water pushes through its crevasses and tunnels at high pressure and the iceberg starts singing.
Since these frequencies are below range of the human ear, they have been sped to the point where they sound like busy bees.

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