When it’s this cold for this long, you start seeing holes in the dirt, with things lurking in their depths.
What’s in the holes? Pebbles.
This is what the soil is like underneath:
These crystals are called needle ice, and have lifted a layer of dirt right up. The overall structure is quite fragile and the swollen frozen ground will collapse when you step on it.
Either the pebbles warmed up in the sun faster than the surrounding frozen soil, and sank into it, or they were too heavy for the needle ice to lift. I’m not sure which explanation applies (maybe it’s both of them).
The depth of the frost heaves created by needle ice can be quite significant: here’s a chunk with three sections built on top of each other.
This makes cold-weather trail cycling quite interesting, I must say.
But someone likes all this frosty stuff!