Why Do Ice Cubes Crack When Dropped into a Drink?

An ice cube taken straight from the freezer often cracks with a sharp click when it lands in a warmer drink. The main cause is not trapped bubbles suddenly exploding, but thermal shock. The drink warms the surface first. Because heat takes time to travel inwards, the outer layer has already warmed and is trying to expand while the core remains colder and closer to its original size.

The connected layers of a solid cannot each change shape freely, so this mismatch creates stress inside the ice. Ice can deform slowly, but over a short time and at low temperature it behaves as a brittle material. When local tensile stress becomes too great near the tip of an existing microscopic flaw, the crack rapidly grows and produces the sound. Liquid entering the new crack then transfers more heat and promotes melting, but that follows the initial fracture rather than being its necessary cause.

A larger temperature difference and a larger cube make a strong gradient between surface and core more likely. A small cube, or one that has already warmed for a while at room temperature, will usually crack less dramatically. The mechanism is the same kind involved when thick glass breaks after sudden cooling: cold or heat alone is not the key; different parts of the object are trying to change size at different rates.

https://van.physics.illinois.edu/ask/listing/2679
https://openstax.org/books/physics/pages/11-2-thermal-expansion-of-solids-and-liquids