frost columns; ice needles
Needle-like ice crystals that form in soil when the ground freezes, pushing up small columns of earth. A winter phenomenon often noticed in gardens or bare ground.
It was freezing this morning, and frost columns had formed in the garden.
When you step on frost columns, they make a crunchy sound.
Compound of 霜 (しも, frost) and 柱 (はしら, pillar), describing the pillar-like ice formations that rise from the ground.