Albuquerque Journal

N.M. Scientist Helps Crack 'Iceberg Arias'
By John Fleck, Journal Staff Writer

Scientists first heard the icebergs singing in 2001.
   
"Heard" is a bit of misnomer. The noise the Antarctic iceberg known as B15 was making was far too low to hear with the human ear.
   
But to a seismologist's instruments, the vibrations from B15 were music.
   
The prosaic scientific name for them is "iceberg harmonic tremors," but Doug MacAyeal has a more poetic name: "iceberg arias."
   
Rick Aster heard them, too.
   
MacAyeal, at the University of Chicago, is a glaciologist, an ice guy by training, usually more interested in questions like the effect of climate change on Antarctic icebergs.
   
Aster and Emile Okal are seismologists — Okal at Northwestern University in Illinois and Aster at New Mexico Tech in Socorro. The Earth's songs, vibrations bouncing this way and that around our lively planet as a result of earthquakes, are their stock in trade.
   
It took the marriage of earthquake and ice science to get to the bottom of the secret of the singing icebergs.
   
Seismologists' instruments are exquisitely sensitive, able to detect the vibrations of a truck driving by, or waves on the beach. The sound of the singing icebergs started as a mystery noise in seismic instruments Okal and his colleagues were running in French Polynesia.
   
Okal did a bit of triangulation, and puzzled over the fact that the noise seemed to be traveling through thousands of miles of ocean water, originating in icebergs along the Antarctic coast.
   
He wrote to Aster, who runs a seismic network of his own on an Antarctic volcano.
   
Aster looked at his data, and sure enough, he was picking up the strange noise, too — "these weird harmonic signals," Aster said.
   
B15 is an iceberg of legendary proportions that broke off of the Ross Ice Shelf in Antarctica in March 2000. It is the size of Massachusetts, Aster said by way of explanation, so large that when scientists land their airplanes on it, they have no idea they're on anything other than solid land.
   
Speeded up, the noise sounds like squeaking, groaning trombones, and the "songs" would last for hours at a time.
   
Once the scientists pinned down the iceberg as the source, MacAyeal scrounged up the necessary funding to install instruments on a piece of B15 and a neighboring iceberg known as C16 and figure out what makes the icebergs sing.
   
A team from New Mexico Tech, which specializes in operating seismic instruments in the harsh Antarctic conditions, flew in to dig "vaults" in the ice in which to place the seismic detectors. You could think of them as high-tech microphones, and for months at a time they would record the icebergs' songs.
   
Now, some seven years after first hearing the songs, the research team thinks it has figured out what makes them.
   
The key, MacAyeal said in an interview from his Chicago office, came when the scientists starting looking at the way the songs would periodically start and stop.
   
The scientists realized that the songs' starts and stops were connected to the icebergs' movements.
   
In much the same way that a violin bow creates an even, steady tone when it is drawn across the string, the icebergs were creating an even, steady tone when they ground against one another, or against the shore.
   
"It's the same process that makes a hinge squeak," Aster said. Except a lot lower in pitch and a lot louder — loud enough to pick up with seismic instruments thousands of miles away.
   
Call it, Aster said, "a mega-squeak."