Frozen lake noises
What causes strange noises to come from a frozen lake? Why would the ice make pinging sounds when rocks are thrown onto it?
The cracking or popping you hear from the ice often occurs when there’s been a temperature change. Lake ice is dynamic. Like any solid, it expands and contracts with temperature changes. The ice cracks, and sometimes you hear it—anything from grinding to a thunder-like boom. A build-up of snow on the ice or fluctuating water levels may also cause the surface to split. The cracks don’t necessarily mean the ice is weakening, even if the sound is unnerving.
And the chirping and pinging when you chuck rocks at the frozen water? They’re different from the noises you’d generate by whipping rocks at, say, dirt, because underneath the ice the water isn’t solid. Ice vibrates up and down, similar to a drumhead or cymbal vibrating after being struck. Different ice produces different sounds: A high-pitched noise when your rock hits the lake likely means you have “clear” ice. This is the glassy, see-through ice that’s formed under cold, still, non-snowy conditions. “Snow” ice—the opaque ice that forms after snow falls on the surface of the lake, becomes saturated with water, and then freezes—produces a lower-frequency sound, because fine grains in the ice absorb some of the noise.