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COFFEE WITH WARREN: Twortle, twortle, twortle!

The phenomenon is technically referred to as acoustic dispersion
CT Warren Collage Nov 18

Twortle? What's that?

To find out, join me on a lakeside encounter my wife Mary Anna and I had some years ago with longtime coffee companion Angus McNee, of Ghost Lake Village at the time. He coined the onomatopoeic word to describe one of the most mysteriously musical sounds of winter. All it requires is a frozen pond or lake and a few stones to bounce across it.

Here's how Mary Anna described it in her diary for Nov. 12, 1998:

TWORTLE, TWORTLE, TWORTLE. We heard the strange sound distinctly as we walked toward the calm lake this late fall afternoon. It was one of those rare times when the wind was not blowing. We decided to savour the stillness and see how much ice had formed inside the lagoon and whether there was any ice on the rest of the lake.

Twortle, twortle. The sound continued as we drew closer. What kind of creature is making that noise, we wondered. Lately we had seen mud hens floating in groups in open water. But we'd never heard them make a sound like this. Nor was this the sound of geese. What could it be?

Looking around, we came upon Angus McNee standing on the rocky shore of the lagoon, skipping large stones across the fresh, smooth, snow-free ice – twortle, twortle, twortle.

"Come and listen to the sound these rocks make on the ice," Angus called. "They make this sound only at this time of year. The ice is still thin enough to vibrate with the bouncing of the rocks, but thick enough to hold them."

We listened in fascination to the reverberations as he continued to skip the stones, and soon found ourselves joining in.

"I call it 'twortling,'" Angus told us, "because you can hear the ice twortle as the rocks skip across it.”

AH, “TWORTLING,” what a perfect word for such a beautiful sound. The other day, I emailed Angus, living now in the Okanagan, and asked him if he remembered the occasion.

“How nice that you should recall our twortling on the lake,” the former mayor of Ghost Lake Village responded. “It had become a memory in my mind, when suddenly you reminisced that call of the pebbles as they spun across the thin ice.

“As you know, the ice is not very thick when the reverberation is produced and twortling can be heard. As the ice thickens, the twortling decreases and the stones simply skid along with little sound. The reward, when good conditions prevail, is that anyone can twortle, unlike skimming stones on water, which needs skill and a little luck.”

This memory lane journey into twortling land raised my curiosity about the science behind such a beautiful sound.

The phenomenon is technically referred to as “acoustic dispersion.” In twortling, it’s caused by an event, such as the sound of a stone bouncing across the ice and dividing into various frequencies as it echoes through layers of differing densities, ice versus water, and thus moving at different speeds.

By the way, twortling is first cousin to another kind of beautiful dispersion, optical dispersion: the rainbow! Happy twortling!

 © 2021 Warren Harbeck

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