Ice needles: frost columns that grow up out of bare wet ground

Why this time of year

It needs saturated ground and air below freezing at once, so the shoulder of the season is the sweet spot: late autumn and early spring, when the soil is wet and unfrozen but the night drops below freezing. In deep midwinter the ground is often frozen solid and nothing can be drawn up.

How to notice it

1. Look at BARE ground rather than grass: a well-worn trail, a path edge, a scraped patch.
2. Go early. They crumble the moment they are stepped on and they go as soon as the sun reaches them.
3. Look at the TOP of a column for a cap of soil. That dirt was on the ground and the ice carried it up.
4. Look at the edge of the bare patch: the needles lift plants and small stones clear of the soil, which is how a bare patch grows itself bigger.

Sources

• northernwoodlands.orgNorthern Woodlands, northeastern US: needle ice forms when the soil is saturated but the air is below freezing, most often in late autumn and early spring; water travels up through the soil by capillary action toward the freezing point at or just below the surface, freezes and expands, and the ice is pushed up out of the soil forming long fragile columns; they appear as spiky threads in crunchy clusters, crumble readily when stepped on, and often carry a layer of dirt on top of each column lifted as the needle grew; found on bare ground such as well-worn hiking trails; causes turf exfoliation, where growing needles at the edge of a bare area lift plants up and away from the soil, producing more bare ground, and displace small rocks

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