How do growlers and bergy bits form from larger icebergs?

Growlers and bergy bits form primarily through the mechanical and thermal erosion of larger icebergs as they drift in the open ocean.1

As an iceberg moves, ocean wave action creates a "wave cut" by eroding the berg's edges, both mechanically and through the transport of heat from ocean turbulence. This erosion can penetrate several meters into the iceberg, creating caves or undercuts. When the unsupported ice—specifically the snow and firn layers—above these cuts or within existing crevasses collapses, the resulting fragments break away from the main body.1

These smaller pieces are categorized by their size:
* Bergy bits: Larger blocks, typically the size of a small house.1
* Growlers: Smaller, floating blocks, typically the size of a grand piano.1

In addition to wave-driven collapse, icebergs may fragment due to structural instability, such as when a berg capsizes or shifts to a new position of stability, creating new surfaces that are then exposed to further erosion.1