They say swans sing before they die, but is it possible large, lumbering icebergs also screech a final tune?
German scientists have recently discovered that water running through the interior channels of Antarctica’s icebergs creates a shrill tune when they run aground that they found puzzling at first but now find fascinating. They published their findings in November 2005, telling the story of how they stumbled onto their discovery back in 2000.
"At first we had no explanation," says Christian Müller, a scientist with Fielax, a German company that teamed up with the Alfred Wegener Institute for Polar and Marine Research to study the phenomenon. "We thought it was technical problems with the sensors or data acquisition," he adds.
But the sounds were not the result of a technical glitch. Although inaudible to the human ear, the noises were measurable when played at higher speeds. Their tunes ranged from that of a humming beehive to the chaotic, shrill pulse of violins warming up for a performance.
The sounds are thought to come from water flowing within the iceberg’s network of crevasses and tunnels. The flow reaches a high enough pressure to produce sound when the iceberg grounds and water that normally helps push the iceberg begins to rush through it instead. That water current causes elastic vibrations similar to what occurs inside an organ pipe, according to scientists.
At first experts remarked that the sounds were eerily similar to those recorded during volcanic tremors.
"From a geological viewpoint, this was not impossible since the localization was in an old crustal rift system," says Müller from a research station in the Antarctic where he is prepared to record any iceberg harmonies within range. After further analysis they recognized the source of the sound was moving, cancelling out the possibility of the sound originating from the earth’s crust.
They found that not only was it moving, but the source of the harmonic currents covered an area 30 kilometres by 50 kilometres — an area twice the size of Toronto. The iceberg they stumbled upon was called B-09A and it quickly became clear that the team of researchers was onto something new.
Their most significant recording came on July 22, 2000 when researchers were treated to a 16-hour show. The sounds were triggered when a collision between the iceberg and the continental slope caused two brief earthquakes. Researchers heard a two-hour sequence of screeches, and then a one-hour intermission. But the iceberg was just warming up for a 13-hour grand finale harmonic tremor. Those tremors were detected 800 kilometres away with strengths comparable to volcanic tremors measured at Mount St. Helens.
Researchers continue to explore the phenomenon and how it can be useful in other fields. It seemed natural to apply the knowledge to volcanic tremors since it was initially thought to be the source of the music.
"The iceberg tremor recordings are strikingly similar to volcanic tremors," Müller says. Despite the fact that icebergs have much simpler structures than volcanoes, they are physically easier to work with. The similarities between volcanic and iceberg tremors include long durations and amplitudes, as well as common shifts in frequencies.
Müller and other scientists hope to exploit these similarities to help experts develop a better method for predicting volcano eruptions. Volcanic tremors often signal a looming eruption, so establishing a method for understanding and examining the tremors may very well allow experts to predict the eruptions more accurately and, most importantly, allow for earlier warnings to evacuate.
The research is still in its early stages, but Müller and his colleagues hope their continued work will not only lead to a more concrete understanding of icebergs, but also to a better feel for their red-hot polar opposites.