by Claire Pendergast
Last year, during our first winter and spring on Keoka, I was surprised when walking down by the shore to hear cracking and popping sounds and even something that sounded like singing or whale cries. I had never heard anything like this and was wondering why the frozen lake makes sounds. After a bit of research, I learned that lake ice is dynamic. When it moves it is forced to vibrate or crack. When that happens, a sound wave is generated. That sound then carries throughout the ice and into the water below and into the atmosphere above.
Lake ice expands and contracts with changes in temperature. Ice movements make the ice crack, which generates a noise that can sometimes sound like loud, booming thunder.
When there is no snow on the lake, a rock thrown onto the ice can generate an array of different sounds. There can be a pinging sound when the rock hits the ice. Where the ice is floating on water away from the shallow shoreline, a rock striking the ice will cause it to vibrate. This will additionally create movement in the water below, which will cause the ice to vibrate like a drumhead.
As vibrations, or sound waves, move through the ice, high frequencies will move faster than the low frequencies, changing the sound over time. If you are far away the sound waves will separate and the higher frequencies will reach your ears before the lower frequencies. The sound will change with the pitch, resulting in a pinging or chirping sound. The sound can also spread across the ice to the far shores and then bounce back to you like an echo. This most frequently happens on clear ice. Snow on the lake will insulate any of the sounds the lake ice will make.
Next time you are on Keoka during the winter listen for some magical lake sounds.