Acoustics of thin IceA tone is radiated when people are skating on thin, black ice. The phenomenon is well known to the experienced skater. In fact he estimates the thickness of the ice by listening to the tone.
I have measured the "ice frequency" at different thickness of the ice. My assistant, my little lightweight son, has hit the ice with an axe and I have recorded the sound with a microphone and a mini-disc at a safe place. The recordings were analyzed with a FFT-analyser in Time mode afterwards.
Walking on cold snow (sound file, 862 kB)