The lake that breathes: winter ice, explained

On a still winter night, a frozen lake can make eerie sounds: booms, twangs and something like whale song. It sounds alive, and in a way it is. The ice is constantly expanding, contracting and cracking as the temperature changes.

Why lakes freeze from the top

Water is strange: it is heaviest just before it freezes, not when it is ice.

Most liquids get denser as they cool. Water does too, until about 4°C. Below that it starts to expand again. So in autumn, the coldest water sinks until the whole lake reaches about 4°C, and then the surface water cools further, floats, and freezes.

Why the ice sings

Ice expands and shrinks with temperature. As it does, it cracks, and the sound travels far through the sheet, bouncing and stretching into long, strange tones. Colder nights after warm days tend to be the noisiest.

Why fish survive

• The water at the bottom stays at around 4°C all winter.

• Ice acts as a lid, insulating the water below from the cold air.

• Fish slow down and need very little food or oxygen.

• Snow on the ice blocks light, which is why heavy-snow winters are harder for lake life.

Never walk on lake ice unless local authorities say it is safe. Ice that sings loudly is not necessarily thick.

How to enjoy it safely

If you want to hear a lake sing, you do not need to walk on it. Stand on the shore on a still, cold evening after a sunny day, and listen. The sounds carry a long way across the ice, and on a good night you will hear them within minutes.

Local guidance is the only reliable way to know whether ice is safe. Thickness varies across a single lake, especially near inflows, reeds and underwater springs, and ice that looks solid can be thin in places.

Bring a warm drink and a torch, and turn the torch off once you are settled. With your eyes adjusted and the lake booming softly in the dark, winter feels a lot less still than it looks.